CN114535618A

CN114535618A - Three-dimensional printing system

Info

Publication number: CN114535618A
Application number: CN202210179364.5A
Authority: CN
Inventors: 梁福鹏; 赵海鹏; 蔡艳
Original assignee: Nanjing Taitao Intelligent System Co ltd
Current assignee: Nanjing Taitao Intelligent System Co ltd
Priority date: 2021-12-07
Filing date: 2022-02-26
Publication date: 2022-05-27
Anticipated expiration: 2042-02-26
Also published as: CN217570879U; CN114535618B; CN217570880U; CN115319107A

Abstract

The invention relates to a three-dimensional printing system, in particular to a three-dimensional printing system which is more flexible than the existing laser coaxial wire feeding three-dimensional printing technology and has a non-contact forging function, and belongs to the technical field of material increase manufacturing. Compared with the existing coaxial wire feeding three-dimensional printing technology based on laser heating, the invention has a plurality of beneficial effects, such as: flexible heating strategies can be realized; supporting printing of finer structures; excessive heating of the molten raw material which is just deposited can be avoided; the metal crystal grains can be strongly modulated in the three-dimensional printing process, the stirring effect on a molten pool can be realized, the area where the molten raw materials are to be deposited can be preheated in advance, the thermal cracking can be inhibited, and parts with higher comprehensive performance can be obtained; the laser cleaning can be integrated in the three-dimensional printing process, so that the metal three-dimensional printing is realized on the premise of not using protective gas in the air; the method has extremely high fault-tolerant capability on the mechanical assembly precision of the laser path. The invention has outstanding substantive progress.

Description

Three-dimensional printing system

Technical Field

The invention relates to a three-dimensional printing system, in particular to a three-dimensional printing system which is more flexible than the existing laser coaxial wire feeding three-dimensional printing technology and has a non-contact forging function, and belongs to the technical field of additive manufacturing.

Background

Three-dimensional printing, also known as additive manufacturing, is a large category of advanced manufacturing techniques. Three-dimensional printing uses feedstock in a variety of forms, such as liquid, solid powder, granules, wire, rods, wires, etc., where the wire or wire feedstock is often less costly than powder feedstock, and easier to store, safer, and more environmentally friendly. In the existing three-dimensional printing technology which adopts laser as a heating source and adopts wires or silk materials as raw materials, two technical types of 'paraxial wire feeding' and 'coaxial wire feeding' exist. For example, the technical scheme disclosed in chinese patent application No. 2018800071130 is to use a "paraxial wire feeding" mode, in which a laser beam is perpendicular to a current forming surface, a wire is transported to the surface of a workpiece (also called a print body, which is an object formed after deposition of molten raw material) from outside a space surrounded by the laser beam, the wire and the surface of the workpiece are melted together with an area adjacent to the wire by the laser beam, the method does not need to consider the problem of shielding of the wire from the laser, and the optical path structure is simple, but problems such as directional defect in printing, difficulty in planning a printing path, complex programming of a multiaxial motion platform, low part surface quality, low printing efficiency, difficulty in printing a complex structure, and the like exist. A discussion of the directionality problem faced by Additive Manufacturing "side-axis feeding" is found in the paper entitled A Comprehensive Study of axial arrays for Additive Manufacturing in Additive Manufacturing Machine Tools (DOI: 10.1115/1.4049094). In order to solve the problems that wires shield laser beams and are heated and melted too early, the coaxial wire feeding mode generally expands the laser beams, shapes the laser beams into annular laser beams (hollow laser beams), allows the wires to pass through the centers of the annular laser beams, focuses the annular laser beams, and melts the wires near the laser beam focusing points. For example, the chinese patent applications with application numbers 2018103767579 and 2018104031543 disclose technical solutions that a "coaxial wire feeding" mode is adopted, no laser exists in an axial space of a laser beam (i.e., the center of the laser beam), the wire is conveyed to the surface of a workpiece along the center of the laser beam, the laser beam is focused on the surface of the workpiece and melts the wire and an area of the surface of the workpiece adjacent to the wire, the light path of the mode is complex, the difficulty of manufacturing the light path is greater than that of a side-axis wire feeding mode, however, because the wire is perpendicular to the surface of the workpiece on which the molten raw material is accumulating (also called depositing), the wire and the laser beam can be printed on the surface of the workpiece in any direction, so that the problem of directionality caused by the traditional paraxial wire feeding mode is solved, and the method also has the advantages that the printing path planning is simple, the required motion platform structure is simple, the program programming is simple, the surface quality of the part is higher, the complicated structure can be printed, and the like, and the method is not easy to obtain by means of paraxial wire feeding.

The existing metal three-dimensional printing technology based on a direct melting deposition mode, such as the technology based on arc heating and adopting a metal wire as a raw material, crystal grains generated after the material is solidified are not fine crystal grains, the growth of the crystal grains has directionality, and the mechanical property does not reach a forging level or the comprehensive performance is not high. For this reason, many techniques have emerged that integrate modulation of grain growth during three-dimensional printing. The modulation is various, for example, mechanical rolling or magnetic field application is performed on the region where the molten raw material is deposited before solidification to influence the grain growth process and suppress the growth of grains into coarse dendrites. For example, chinese patent application No. 2019108963185, mechanically crushes the area where the molten feedstock is deposited before it completely solidifies. The existing metal three-dimensional printing technology based on laser heating also has the same advantage that the grain growth has directionality, for example, dendritic or columnar crystal branches are seen in a metallographic microscopic image, and the material performance cannot reach the traditional forging level. The method as set forth in chinese patent application No. 2016101834688 is applicable to three-dimensional printing of metals with laser as the heating source: set up magnetic field in three-dimensional printing system, at the rapid solidification in-process that metal 3D printed, rapid solidification's solid/liquid interface department can produce the thermoelectric current, under the effect in magnetic field, thermoelectric current and magnetic field interact produce the thermoelectricity magnetic force that triggers the fuse-element flow, and the branch crystal tip produces the shearing after the effect of power, causes the branch crystal to break, forms a large amount of new crystal nucleuses. But the thermoelectric current generated at the solid/liquid interface is weak and unstable, the duration of the current is short, the generated electromagnetic action is weak, the viscosity of the metal melt is high, and the response to the acting force of high-speed change is slow, so that the modulation effect of the technology on crystal grains is not obvious, especially when the heat continuously accumulates on the printed part along with the continuous printing process, the basic temperature of the part is increased, the temperature gradient at the solid/liquid interface of a molten pool is reduced, the strength of the thermoelectric current is further reduced, and the interaction between the thermoelectric current and the magnetic field is further reduced; at the initial moment of generating the molten pool, the temperature difference at the solid/liquid interface reaches the peak value, but as the molten pool solidifies, the temperature difference between a zone where the molten pool is just solidified and a zone where the molten pool is not solidified is small, the thermal current generated at the solid/liquid interface is weaker, and the temperature difference inside the zone where the molten pool is not solidified is smaller, so that the thermal current is more difficult to generate; the grain is modulated by the interaction of the thermoelectric current generated at the solid/liquid interface and the external magnetic field, and the problem of uneven distribution of action strength exists in addition to insignificant action.

Disclosure of Invention

The inventor finds that: in the existing coaxial wire feeding mode, the relative position relationship between a laser beam and a wire is fixed, and the relative position relationship between a light spot and the wire or a molten raw material generated by the wire is fixed, so that the printing lacks flexibility, specifically, for example: in the three-dimensional metal printing process, a metal wire is heated and melted and deposited on a workpiece, the molten metal is heated by an annular light spot projected on the surface of the workpiece by a laser beam immediately after being deposited, the deposited molten metal is excessively heated, so that the flowability is increased, and the problems of low form controllability, rough surface appearance, low forming precision and the like are further caused by the increased flowability; excessive heating also causes problems such as increase in evaporation amount and increase in air holes; if heating of molten metal just deposited is avoided, the laser beam is required to be capable of quickly adjusting the position of a light spot on the periphery of the molten metal according to the change of a printing path, but the existing laser coaxial wire feeding three-dimensional printing technology does not have the flexibility. For another example: in the three-dimensional metal printing process, laser beams are projected on a workpiece, and annular light spots surrounding the periphery of molten metal heat an area which is not on a printing path, so that a molten pool is large, a heat affected zone is large, and when finer structures such as thin-wall structures and the like and structures with slow heat dissipation are printed, the structures are easily damaged or deformed by overheating; the ideal heating mode is to heat the front part of the printing path, and the width of the molten pool is basically consistent with the width of the thin-wall structure, which also needs the laser beam to be capable of quickly adjusting the spot position according to the change of the printing path, and the existing laser coaxial wire feeding three-dimensional printing technology does not have such flexibility.

In view of the shortcomings of the prior art, the present invention provides a three-dimensional printing system capable of flexibly laser-scanning and heating a deposition area of molten material in a three-dimensional printing process using a wire or a rod as a raw material, which is different from the existing coaxial wire feeding three-dimensional printing system based on laser heating.

It is another object of the present invention to provide a three-dimensional printing system that applies strong electromagnetic action to the molten zone prior to solidification during three-dimensional forming to achieve strong modulation of the solidifying tissue to achieve high performance parts.

In order to achieve the above purpose, the invention adopts the technical scheme that: a three-dimensional printing system is provided with a motion platform, a laser, a light path, a solid raw material conveying mechanism, a solid raw material guiding mechanism, a control circuit and a power supply; wherein: the control circuit controls the movement of the motion platform, and the movement of the motion platform determines the deposition position of a molten raw material formed after the solid raw material is molten in the forming area; the control circuit controls the solid raw material conveying mechanism to move the solid raw material to the forming area through the solid raw material guide mechanism, the front end of the solid raw material is melted in the forming area to form a molten raw material, and the molten raw material is deposited in the forming area to form a printing body; the control circuit controls the working state of the laser, and laser generated by the laser forms a laser beam through a light path and is transmitted to the forming area; the power supply supplies electric energy to all electric components of the three-dimensional printing system; the forming area refers to a space used by the three-dimensional printing system when printing the parts, and the parts are formed in the space;

the method is characterized in that:

the laser beam is projected to the printing body from the space around the solid raw material;

the optical path comprises a laser beam moving mechanism, the laser beam moving mechanism controls the laser beam to scan and heat the edge and/or the periphery of the area on the printing body where the molten raw material is deposited (the scanning and heating are not limited to generating a molten pool at the edge and/or the periphery of the area on the printing body where the molten raw material is deposited, and for example, the temperature of the edge and/or the periphery of the area on the printing body where the molten raw material is deposited can be only increased to be close to the melting point); (Explanation: edge scan heating of the area on the print body where the molten raw material is being deposited by the laser beam, i.e., the spot of the laser beam moves around the edge of the area on the print body where the molten raw material is being deposited, and heat is conducted by the molten raw material being deposited to the edge of the area on the print body where the molten raw material is being deposited to achieve indirect scan heating, although the laser directly heats the periphery of the area on the print body where the molten raw material is being deposited, which is also conducted by thermal conduction to the edge of the area on the print body where the molten raw material is being deposited, and actually indirectly heats the edge of the area on the print body where the molten raw material is being deposited; edge scan heating of the area on the print body where the molten raw material is being deposited by the laser beam, i.e., the spot of the laser beam moves around the area on the print body where the molten raw material is being deposited).

The laser beam moves relative to the print body in a scanning heating zone on the print body while scanning and heating the edge and/or periphery of the region on the print body where molten feedstock is being deposited;

the number of the laser beams which pass through the laser beam moving mechanism and can be projected is at least two, and each laser beam can be independently controlled; the number of laser beams projected at the same time can be controlled (for example, one beam, zero beam, two beams or multiple beams); the number of the lasers is at least one;

applying current between the solid raw material and the printing body to generate resistance heating effect, and generating molten raw material between the solid raw material and the printing body only under the effect of resistance heating; or applying current between the solid raw material and the printing body to generate resistance heating effect, and generating molten raw material between the solid raw material and the printing body under the combined action of resistance heating and laser beam heating; alternatively, the molten raw material is generated between the solid raw material and the print body only by the heating action of the laser beam; (wherein the need for laser power can be reduced, especially in the case of a high melting rate of the solid material, i.e. a high thermal energy requirement, for example, a melting rate of 300 kg/hr using a 304 stainless steel wire with a diameter of 6mm, by using a solid material with a melting rate of 300 kg/hr), by using a solution in which molten material is produced between the solid material and the print body under the combined action of resistive heating and the laser beam heating, so that the need for laser power can be greatly reduced, and the equipment cost and the electric energy cost can be greatly reduced, because the energy conversion efficiency of lasers is generally low, such as fiber lasers, the conversion efficiency generally does not exceed 40%, such as 100 watts of electric energy input, and only lasers with a power output of not more than 40 watts.)

The region where the molten raw material is being deposited refers to a region on the print body which is in contact with the molten raw material being deposited (generated) (the region in contact with the molten raw material already deposited does not belong to the region where the molten raw material is being deposited); (the area where the molten material is being deposited is in contact with the molten material being deposited, resulting in the area being covered by the molten material being deposited, the laser cannot directly heat the area on the surface of the print body covered by the molten material, requiring heat to be transferred to the area where the molten material is being deposited by heating the molten material being deposited, and then by conducting heat through the molten material being deposited;)

The edge of the area where the molten raw material is deposited refers to the edge of the area, which is in contact with the deposited raw material, on the printing body;

the periphery of the region where the molten raw material is being deposited means a region on the print body adjacent to or continuous with the region where the molten raw material is being deposited.

(for explanation: molten feedstock being deposited is understood to mean molten feedstock that has contacted the print, the space between the solid feedstock and the print.)

Optionally:

the laser beam moving mechanism controls the laser beam to scan and heat the edge and/or the periphery of the area where the molten raw material is deposited on the printing body so as to generate a molten pool; the range of the scanning heating area of the laser beam is controllable; (to explain: for example, the scanning width, e.g., the spot always being located in front of the deposition path of the molten raw material being deposited;)

When the number of the laser beams projected through the laser beam moving mechanism is two or more than two, the power of each laser beam can be independently controlled;

when the number of laser beams projected through the laser beam moving mechanism is two or more, the scanning parameters of each laser beam can be independently controlled. The scanning parameters may be the shape of the scanning area, the area of the scanning area, the scanning speed, the average power density of the laser spot in the scanning area, the dwell time of the laser spot at certain positions during the scanning process, the curve shape of the scanning path, and the like.

The heating energy to produce the molten bath may be independent of the heating energy to produce the molten feedstock.

Optionally:

depositing the molten feedstock on a substrate while printing a first layer of the printed body; the substrate is a structure (such as a metal plate) for supporting the printing body;

during the forming of the first layer of the printed body, the laser beam heats the front end of the solid raw material in the first layer partial area of the printed body and does not generate a molten pool on the substrate contacted by the area of the first layer, and the laser beam heats the front end of the solid raw material and heats the substrate in the first layer partial area of the printed body and generates a molten pool on the substrate contacted by the area of the first layer. Thus, the printed body can be firmly attached to the substrate, and the printed body can be easily separated from the substrate after printing is completed.

Optionally:

in the forming process of the first layer of the printing body, the laser beam heats the front end of the solid raw material, and a molten pool is not generated on the substrate. In this way, the print body can be easily separated from the substrate after printing is completed.

Optionally:

the optical path mainly comprises an optical cable, a collimation component, a reflection component, a laser beam moving mechanism and a focusing component, wherein the laser beam moving mechanism, the reflection component and the focusing component are arranged relatively independently, and a laser is connected with the optical path through the optical cable.

Optionally:

the optical path mainly comprises an optical cable, a collimating component, a reflecting component and a focusing component, wherein a part of components or all components which can move in the reflecting component and/or the focusing component form the laser beam moving mechanism, and the laser is connected with the optical path through the optical cable. The focusing component is a field lens type focusing lens or a non-field lens type focusing lens.

Optionally:

the laser is directly connected with the light path without being connected through an optical cable. The focusing component is a field lens type focusing lens or a non-field lens type focusing lens.

Optionally:

the laser is directly connected with the optical path and is not connected with the optical path through an optical cable. The focusing component is a field lens type focusing lens or a non-field lens type focusing lens.

Optionally:

the laser is directly connected with the optical path without being connected through an optical cable. The focusing component is a field lens type focusing lens or a non-field lens type focusing lens.

Optionally:

the optical path mainly comprises an optical cable, a reflecting component and a laser beam moving mechanism, and the laser is connected with the optical path through the optical cable.

Optionally:

the optical path mainly comprises a reflection component and a laser beam moving mechanism, and the laser is directly connected with the optical path and is not connected with the optical path through an optical cable.

Optionally:

the optical path mainly comprises a laser beam moving mechanism, and the laser is directly connected with the optical path and is not connected through an optical cable.

It should be noted that the optical path may or may not include a collimating component, a reflecting component and a focusing component, for example, when the laser beam is focused or is a parallel beam with high power density before entering the optical path, there is no need to provide a focusing component in the optical path for focusing, etc.

Optionally:

the optical component of the laser beam moving mechanism comprises a galvanometer. The method comprises the following steps of (1) adopting a galvanometer in the prior art, wherein the galvanometer in the prior art is divided into a two-dimensional galvanometer and a three-dimensional galvanometer: the optical component of the two-dimensional galvanometer consists of two rotatable reflectors, and the two reflectors respectively control the light beams to move in the X-axis direction and the Y-axis direction in a plane; the three-dimensional galvanometer is formed by adding a group of electric focusing lenses on the basis of the two-dimensional galvanometer, and the electric focusing lenses control the position of a light beam focusing point in the Z-axis direction, so that the position of a focus in a three-dimensional space represented by XYZ three axes is realized.

Optionally:

the optical component of the laser beam moving mechanism mainly comprises a reflecting mirror and/or a lens, and the laser beam is moved by moving the reflecting mirror and/or the lens. For example: the laser beam moving mechanism is combined by two movable lenses, and the two lenses respectively control the light beams to move in the X-axis direction and the Y-axis direction in a plane. For another example: only one lens is used, and the lens is driven by a mechanical mechanism to move in the X-axis and Y-axis directions in a plane.

Optionally:

the optical component of the laser beam moving mechanism mainly comprises a reflector and/or a lens, and the laser beam is moved by rotating the reflector and/or the lens.

Optionally:

using two laser beams, wherein one laser beam is used for heating a region of the surface of the printing body, which is positioned in front of the printing path and adjacent to or connected with the molten raw material, with higher power so as to generate a molten pool; the other laser beam is used only for heating the surface of the print body and the just deposited molten raw material with a low power, and thus is insufficient for heating and vaporizing or partially vaporizing the just deposited molten raw material.

Optionally:

two laser beams are used, wherein one laser beam is used for heating a region of the surface of the printing body, which is positioned in front of the printing path and adjacent to or connected with the molten raw material, and heating one side of the front end of the solid raw material, which faces the front side of the printing path, and the other laser beam is used for heating the other side of the solid raw material and not heating the surface of the printing body and the molten raw material which is just deposited. (where "molten material just deposited" means that the molten material after contacting the print body leaves the space between the solid material and the print body, and the molten material after contacting the print body is no longer connected between the solid material and the print body, and the molten material is already on the print body but is still molten), driven by the motion stage of the three-dimensional printing system

Optionally:

the laser beam is at least two in number, the light spot of a part of the laser beam falls on the front end of the solid raw material, and the light spot of a part of the laser beam falls on the area of the surface of the printing body adjacent to or connected with the accumulated molten raw material.

Optionally:

the optical component of the laser beam moving mechanism is a lens, and the lens is driven by a moving part to move in the radial plane direction vertical to the optical axis of the lens, so that the laser beam is moved.

Optionally:

the optical component of the laser beam moving mechanism is composed of a reflecting mirror, and the laser beam is moved by rotating the reflecting mirror.

Optionally:

the optical component of the laser beam moving mechanism is composed of a reflector, the movement of the laser beam is realized by rotating the reflector, and the reflector and the lens are arranged in the same shell.

Optionally:

arranging a magnetic field generating device in the space around the solid raw material, wherein the magnetic field generated by the magnetic field generating device at least covers the area on the printing body where the molten raw material is deposited; applying a current between the solid feedstock and the print body, the current flowing through a molten feedstock produced upon melting of the solid feedstock and a region of the print body where the molten feedstock is being deposited.

Optionally:

the magnetic field generating device, the solid raw material guiding mechanism and the laser beam moving mechanism are connected into a whole through mechanical structures and can move integrally under the driving of the motion platform.

Optionally:

the magnetic field generated by the magnetic field generating device is a static magnetic field or an alternating magnetic field or a rotating magnetic field or a pulse magnetic field;

the current applied between the solid feedstock and the print is either direct current or alternating current.

Optionally:

the magnetic field generating device comprises a pair of electromagnets or a pair of permanent magnets to generate a static magnetic field, alternating current is conducted between the solid raw material and the printing body, and magnetic vibration is generated in an area on the printing body which is not solidified.

An electromagnet is an assembly that generates a magnetic field when energized, and is primarily composed of a magnetizer, which may be a common silicon steel, ferrite, or the like, and a coil, or simply a coil.

Optionally:

the magnetic field generating device comprises at least two pairs of electromagnets, and multi-phase alternating current is supplied to the electromagnets, and the number of the alternating current is the same as the number of the pairs of the electromagnets so as to generate a rotating magnetic field; and D, passing direct current or alternating current between the solid raw material and the printing body.

Optionally:

the magnetic field generating device comprises a hollow electromagnet or a hollow permanent magnet arranged in the space around the solid raw material, and the solid raw material passes through the central area of the hollow electromagnet or the hollow permanent magnet.

Optionally:

the solid raw material adopts a wire or a bar;

arranging a straightening device, and straightening the wire or the bar by the straightening device before the wire or the bar is heated;

the straightening device is connected with the solid raw material conveying mechanism or the solid raw material guiding mechanism.

(for example, a "wire rod" means a form having a large aspect ratio, for example, an aspect ratio of >10:1, and specific examples thereof include an electric wire, a metal wire, a kite wire, a metal wire, a spiral spring, a steel bar, a wooden bar, a railway line, a crude oil line, a horizon line, etc.)

Optionally:

the straightening device is connected with the solid raw material conveying mechanism through a pipeline, or the straightening device is connected with the solid raw material guiding mechanism through a pipeline, and the solid raw material enters the solid raw material conveying mechanism or the solid raw material guiding mechanism from the straightening device through a pipeline; or the straightening device and the solid raw material conveying mechanism are directly arranged together without adopting pipeline connection, namely the straightening device and the solid raw material conveying mechanism are directly arranged together or the straightening device and the solid raw material guiding mechanism are directly arranged together.

Optionally:

a solid member contactable with the printing body is disposed in a space around the solid raw material, and the molten raw material is contacted with the solid member after the printing body is deposited.

Optionally:

a solid part which can be contacted with the printing body is arranged in the space around the solid raw material, the molten raw material is contacted with the solid part after being deposited on the printing body, and the position between the solid part and the solid raw material guiding mechanism is relatively fixed; under the drive of the motion platform, the solid part and the whole body formed by the solid raw material guide mechanism move relatively to the printing body.

Optionally:

the solid component which can contact with the printing body is internally provided with a passage for circulating cooling liquid.

Optionally:

the solid part which can contact with the printing body is annular and can rotate by taking the solid raw material as an axis.

Optionally:

the solid part which can be contacted with the printing body is in a block shape.

Optionally:

the motion platform is a multi-axis motion platform based on Cartesian three-dimensional coordinates, or a three-dimensional motion platform based on polar coordinates, or a multi-axis mechanical arm.

Optionally:

the molding area is a space arranged in the three-dimensional printing system.

Optionally:

the forming area is an operation space arranged outside the three-dimensional printing system.

Optionally:

in the three-dimensional printing process, the whole printing body is soaked in the cooling liquid, and the current forming layer is always positioned above the liquid level of the cooling liquid.

Optionally:

in the three-dimensional printing process, a low-temperature gas is blown to the region where the molten raw material has been deposited.

Optionally:

in the three-dimensional printing process, liquid is ejected to the area where the molten raw material has been deposited.

Optionally:

during three-dimensional printing, a shielding gas is ejected to the area being formed.

Optionally:

the laser beam can scan heat the edge and/or peripheral annular region or a portion of the annular region of the area where molten raw material is being deposited, i.e., the laser beam can scan heat the edge and/or peripheral 360 ° or less of the area where molten raw material is being deposited centered on the area where molten raw material is being deposited. The shape of the annular region is not limited, and may be a circular ring region, a square ring region, an annular region of inside and outside circles, or the like.

Optionally:

when the solid raw material is a metal material, heating a region of the surface of the printing body, which is located in front of the printing path and adjacent to or connected with the molten raw material, by using a laser beam, wherein the molten raw material which is just deposited is not heated by the laser beam; meanwhile, current is applied between the solid raw material and the printing body, a magnetic field is applied to the area where the molten raw material is deposited and the area where the molten raw material is not solidified on the printing body, the molten raw material is generated between the solid raw material and the printing body only under the action of resistance heating or under the combined action of resistance heating and laser beam heating, and electromagnetic force generated by the interaction of the current flowing through the area where the molten raw material is deposited and the area where the molten raw material is not solidified on the printing body is acted on the area where the molten raw material is deposited and the area where the magnetic field is not solidified, so that metal crystal grains can be broken to obtain fine crystal grains, and the broken crystal grains in the metal material are retained because the molten raw material which is just deposited is not heated secondarily by the laser beam, which has more advantages than the existing coaxial three-dimensional wire feeding printing technology based on laser heating, and the reason is that: the existing coaxial wire feeding three-dimensional printing technology based on laser heating uses annular light spots for heating, molten raw materials which are just deposited can be heated for the second time, the molten raw materials which are just deposited are melted again at high temperature, so that metal crystal grains can grow again, and the quality of a printed body is reduced.

Optionally:

the magnetic field is generated by a magnet, the magnet is provided with an air gap, and the air gap magnetic field generated by the air gap acts on the deposited melting raw material and the unsolidified area on the printing body; the magnet is an electromagnet and/or a permanent magnet.

Optionally:

when the number of laser beams projected onto the printing body at the same time is two or more, the spot scanning area where the laser beams are projected onto the printing body may constitute a composite scanning area which may surround an area on the printing body where the molten raw material is being deposited.

Optionally:

the laser beam projected on the print body may be scanned in one dimension or two dimensions or three dimensions. (for one-dimensional scanning and two-dimensional scanning, the two-dimensional galvanometer can be adopted, for three-dimensional scanning, the three-dimensional galvanometer can be adopted, the three-dimensional galvanometer (the optical component comprises a two-surface rotatable reflecting mirror and a group of electric focusing lenses), the two reflecting mirrors respectively control the light beams to move in the X-axis direction and the Y-axis direction in a plane, the electric focusing lenses control the position of a light beam focusing point in the Z-axis direction, so that the position of the focus in a three-dimensional space represented by three X, Y and Z axes can be realized, and the focus of the light beams can be scanned in the three-dimensional space.)

Optionally:

at least two laser beams are projected, wherein one part of the laser beams scan and heat the edge and/or periphery of the region on the printing body where the molten raw material is deposited to generate a molten pool, and the other part of the laser beams modify the shape of the surface of the printing body on which the molding is printed (for example, laser cutting, laser engraving and laser cleaning (for example, cleaning an oxide film) of the region of the printing body where the molten raw material is not currently deposited so as to obtain better surface quality and adjust the structure of the partial region of the printing body (for example, modifying the wall thickness)).

Optionally:

the laser beam moving mechanism controls the laser beam to heat the edge of the deposited molten raw material, so that heat is conducted to the edge of the area of the printing body where the molten raw material is deposited through the deposited molten raw material, and edge scanning heating of the area of the printing body where the molten raw material is deposited is achieved. (to explain that the area where the molten raw material is being deposited contacts the molten raw material being deposited, causing the area to be covered by the molten raw material being deposited, the laser cannot directly heat the area on the surface of the print body covered by the molten raw material, and it is necessary to heat the molten raw material being deposited, and then conduct heat to the edge of the area where the molten raw material is being deposited through the molten raw material being deposited, i.e., the laser beam indirectly heats the edge of the area where the molten raw material is being deposited; of course, the laser directly heats the periphery of the area where the molten raw material is being deposited adjacent to or connected to the edge of the area where the molten raw material is being deposited, and the heat of the periphery is also conducted to the edge of the area where the molten raw material is being deposited by means of heat conduction, and actually indirectly heats the edge of the area where the molten raw material is being deposited.)

Optionally:

the laser beam moving mechanism controls the edge and/or periphery scanning heating of the laser beam on the printing body in the area where the molten raw material is deposited, and the scanning parameters can be dynamically adjusted. That is, the parameters of the laser scanning heating are not fixed throughout the process of printing a part (print body). While printing different areas of a part, parameters such as the width of the scan area, the degree of overlap of the scan area with the area of the print body where molten material is being deposited, the scan line density within the scan area, power, etc. can be dynamically adjusted, for example: when a part is printed, the part needs to be constructed on a bottom plate (a support plate/a substrate), because the first layer is tightly connected with the bottom plate, the heat dissipation condition is good, the maximum heating power and the larger scanning range are needed when the first layer is printed, the heat dissipation condition becomes worse along with the higher printing height, and the scanning parameters can be adjusted according to the requirement; for another example, when printing a thin-walled structure, the scanning range and heating power are smaller than those of a thick-walled structure; as another example, the scanning parameters required when printing edge structures with sharp corners are not the same as those for printing non-edge locations. Printing of various complex parts can be better supported by dynamically adjusting scanning parameters.

Optionally:

the laser beam moving mechanism controls the laser beam to scan and heat the edge and/or periphery of the area where the molten raw material is being deposited, and simultaneously heats the raw material being deposited.

Optionally:

the laser beam moving mechanism controls the laser beam to scan and heat the edge and/or the periphery of the area where the molten raw material is deposited, and the scanning heating area of the laser beam is the area where the molten raw material is to be deposited. (that is, the scanning heating zone is located in front of the deposition path of the molten raw material, which is the area where the molten raw material is about to be/is deposited soon.)

Optionally:

the scanning heating area is an area where a light spot of the laser beam on the printing body is located, and the light spot is always located in front of a deposition path of the molten raw material which is being deposited.

Optionally:

the optical path also comprises a non-scanning laser beam projecting mechanism, and the laser beam projected by the non-scanning laser beam projecting mechanism heats the area on the printing body where the molten raw material is deposited in a non-scanning manner, namely the position relation between a light spot generated by the projected laser beam on the printing body and the projection of the outlet of the solid raw material guiding mechanism on the surface of the printing body is relatively fixed. (explanation: the non-scanning laser beam projecting means is understood to mean that the laser beam projected by the projecting means cannot be heated in a scanning manner; conversely, the positional relationship between the spot of the scanning laser beam on the surface of the printing body and the projection of the outlet of the solid raw material guide means on the surface of the printing body is relatively variable.)

Optionally:

the laser beam projected by the non-scanning laser beam projection mechanism in the light path is a hollow laser beam, an annular light spot is formed on the surface of the printing body, and the molten raw material which is being deposited is surrounded by the annular light spot on the surface of the printing body.

Optionally:

the non-scanning laser beam projection mechanism is arranged in the light path, the number of the projected laser beams is at least three, at least three light spots are formed on the surface of the printing body, and the light spots surround the deposited melting raw materials on the surface of the printing body.

Optionally:

the control circuit monitors the state of the light spot of the laser beam on the surface of the printing body through the sensing circuit, and controls the laser beam moving mechanism in real time to ensure that the laser beam is scanned and heated at the edge and/or periphery of the area of the printing body where the molten raw material is deposited. For example: the control circuit acquires the image of the light spot through the high-speed infrared camera, calculates the position relation between the light spot and the area on the printing body where the melting raw material is deposited and the melting raw material being deposited, and corrects the position relation in real time when the light spot deviates from a preset range, so as to ensure that the laser beam scans and heats the edge and/or the periphery of the area on the printing body where the melting raw material is deposited.

The invention has the following main beneficial effects:

(1) compared with the existing coaxial wire feeding three-dimensional printing technology based on laser heating, the coaxial wire feeding three-dimensional printing method has the advantages of a coaxial wire feeding mode through laser scanning heating, namely: the device can deposit/accumulate the melting raw material in any direction on a forming plane, and has the advantages that the device is simple in printing path planning, simple in structure of a required moving platform, capable of meeting the requirements of an XYZ three-axis moving platform, simple in programming of a machine system program, higher in surface quality of parts generated by printing, capable of printing complex structures and the like, and is not easy to obtain by means of paraxial wire feeding.

(2) Compared with the existing coaxial wire feeding three-dimensional printing technology based on laser heating, the invention can realize a flexible heating strategy by regulating and controlling the scanning position of the laser beam facula through the laser beam moving mechanism in the three-dimensional printing process, such as: two laser beams are used, wherein one laser beam is responsible for heating a region, adjacent to or connected with the molten raw material, of the surface of the printing body in front of the printing path at a higher power, and the other laser beam is only used for heating the surface of the printing body and the molten raw material just deposited at a low power so as to obtain a smoother surface and avoid serious problems caused by overheating due to the higher-power heating of the molten raw material just deposited, such as obvious gasification; for another example: and calculating a scanning strategy corresponding to the minimum stress according to the characteristics of the area and the peripheral structure of the melting raw material being accumulated, and dynamically adjusting the scanning range and the scanning path of the light spot.

(3) Compared with the existing coaxial wire feeding three-dimensional printing technology based on laser heating, the invention can adopt a laser scanning heating strategy of only heating the area, which is positioned in front of the printing path and is adjacent to or connected with the molten raw material, on the surface of the printing body when the thin-wall structure is printed, thereby reducing the thermal influence range of laser, avoiding overheating and deformation of the thin-wall structure; the invention has more advantages when printing thin-wall structures and is more suitable for printing complex fine structures.

(4) Compared with the existing coaxial wire feeding three-dimensional printing technology based on laser heating, the coaxial wire feeding three-dimensional printing technology based on laser heating can also perform laser irradiation heating on the area of the surface of a workpiece where the molten raw material is to be deposited (accumulated), but not heat the molten raw material which is just deposited, so that the molten raw material which is just deposited is prevented from being overheated (the overheating can cause higher fluidity or gasification), higher molding precision can be obtained, and the micro air holes in the part material are fewer and the density is higher, so that the coaxial wire feeding three-dimensional printing technology based on laser heating has greater significance for the application of additive manufacturing; thus, the present invention may be used for higher precision welding or additive manufacturing.

(5) Compared with the existing coaxial wire feeding three-dimensional printing technology based on laser heating, the coaxial wire feeding three-dimensional printing method based on laser heating adopts the laser beam moving mechanism to control laser dynamic scanning, the projection position of the laser beam is dynamically adjustable, and the coaxial wire feeding three-dimensional printing method based on laser heating has extremely high fault-tolerant capability on mechanical assembly precision among the optical path mechanical structure, the solid raw material and the solid raw material guiding mechanism.

(6) The electromagnetic force is used for modulating grain growth, the magnetic field always covers the area where the molten raw material is accumulating/deposited and the time period before the deposited molten raw material is solidified, the current always flows on the electric path of the area where the molten raw material is accumulating on the linear solid raw material-molten raw material-printing body, and the area where the molten raw material is accumulating on the linear solid raw material-printing body is small in the radial section perpendicular to the axis of the linear solid raw material, so that high current density can be realized, the area which is not solidified on the printing body is always subjected to strong electromagnetic vibration or strong electromagnetic stirring action, and the strong inhibition capability of the grain growth of the area which is not solidified in the three-dimensional printing process can be obtained when a metal material, particularly an alloy material is printed. The present invention may employ such heating strategies: the method comprises the steps of heating the surface of a workpiece by adopting low-power laser, namely, generating a shallow molten pool (for example, 50 microns deep) in an area where a molten raw material is to be deposited, wherein the width of the molten pool is the same as the line width of the deposited molten raw material, the deposited molten raw material is not heated secondarily by the laser, and the molten raw material is obtained by adopting a resistance heating mode, so that fine grains obtained by modulation can be reserved.

(7) Compared with the existing coaxial wire feeding three-dimensional printing system based on laser heating, the invention adopts a laser scanning mode to generate a molten pool on a printing body (workpiece), and the scanning heating mode generates a stirring effect on the molten pool, thereby generating beneficial effects on the performance of parts finally obtained by three-dimensional printing, such as reducing micro-pores.

(8) Compared with the existing coaxial wire feeding three-dimensional printing system based on laser heating, the coaxial wire feeding three-dimensional printing system based on laser scanning heating adopts a laser scanning mode to heat the printing body (workpiece), can preheat the area to be deposited with the molten raw material in advance, reduces the temperature gradient between the area to be deposited with the molten raw material and other areas of the printing body (workpiece), can inhibit the generation of thermal cracks, and improves the material performance (mainly mechanical performance, such as fatigue resistance) of the three-dimensional printing part. The existing metal three-dimensional printing technology, especially Selective Laser Melting (SLM) and Direct Energy Deposition (DED) (existing coaxial wire feeding and paraxial wire feeding three-dimensional printing based on Laser heating, paraxial wire feeding three-dimensional printing based on arc heating, coaxial powder feeding and paraxial powder feeding three-dimensional printing based on Laser heating, and also belong to the DED technology), generally has the problem of low fatigue resistance of parts, and is a huge obstacle for restricting the application of the existing metal three-dimensional printing technology in industrial production.

(9) Because the heating mode of the existing laser coaxial wire feeding is the same as the heat conduction mode of laser welding (the forming foundation of the existing laser coaxial wire feeding metal three-dimensional printing is essentially laser welding), namely: the laser spot power density range is the same as that of the traditional heat conduction type laser welding, the spot power density value cannot be obviously gasified, otherwise, the three-dimensional printing process is seriously damaged, and therefore, the spot power density cannot be improved to realize the laser cleaning function. The invention adopts a scanning heating mode, can quickly disperse heat on a larger area, and can diffuse the heat without depending on a heat conduction mode, so that a laser beam with higher power density can be used, a molten pool is generated by heating, laser cleaning is synchronously realized, substances harmful to three-dimensional forming on the surface layers of the molten pool and a molten raw material are removed (such as an oxide film is removed), the molten raw material is generated by combining resistance heating and other modes, and the toxic action of air on the three-dimensional forming process can be resisted. Therefore, the invention can realize three-dimensional printing without using protective gas in the air, has lower cost and can print metal components in open environment. Laser ablation, also known as Laser ablation or photoablation, is a process in which a solid (or sometimes liquid) surface is removed by irradiation with a Laser beam, which heats and evaporates or sublimes as the surface material is absorbed by the Laser energy. Generally, laser cleaning refers to the use of a pulsed laser to remove a thin layer of material from the surface of an object without damaging the underlying structure of the object. In rare cases, the continuous laser ablation can be used for removing the thin material on the surface of the object, but the energy of the continuous laser is too high, so that the thermal effect is very serious, for example, the remelting can be generated on the surface of solid metal, namely, a molten pool (thin molten pool) is generated while the metal is ablated. The present invention can utilize continuous laser as the laser cleaning heat source to produce the molten pool characteristic.

In summary, compared with the existing coaxial wire feeding three-dimensional printing technology based on laser heating, the invention has the beneficial effects that: flexible heating strategies can be realized; printing of finer structures can be achieved; the excessive heating of the melting area can be avoided, and the micro air holes in the part material are fewer and the density is higher; the crystal grains can be strongly modulated in the three-dimensional printing process, and parts with higher comprehensive performance are obtained; the mechanical assembly precision between the mechanical structure of the optical path and the solid raw material guide mechanism has extremely high fault-tolerant capability; the stirring effect is generated on the molten pool, and the performance of the part finally obtained by three-dimensional printing is improved; the region where the molten raw material is to be deposited can be preheated in advance, the temperature gradient between the region where the molten raw material is being deposited and other regions of the print body (workpiece) can be reduced, and the generation of thermal cracks can be suppressed; the laser cleaning function can be synchronously integrated in the three-dimensional printing process, the metal three-dimensional printing is realized on the premise of not using protective gas in the air, the cost is lower, and large metal components can be printed in an open environment. The invention has outstanding substantive progress.

Drawings

FIG. 1 is a three-dimensional perspective view illustrating the composition of a first embodiment of a three-dimensional printing system of the present invention;

FIG. 2 is a schematic diagram illustrating the principles of a first embodiment of a three-dimensional printing system of the present invention;

FIG. 3 is a schematic diagram illustrating a laser beam scanning area of a first embodiment of a three-dimensional printing system according to the present invention;

FIG. 4 is a three-dimensional perspective view illustrating the composition of a second embodiment of a three-dimensional printing system according to the present invention;

FIG. 5 is a bottom view of FIG. 4;

FIG. 6 is a schematic diagram illustrating the composition of a third embodiment of a three-dimensional printing system according to the present invention;

FIG. 7 is a three-dimensional perspective view illustrating the composition of a fourth embodiment of a three-dimensional printing system of the present invention;

FIG. 8 is a schematic view for explaining a laser beam moving mechanism using a single-chip lens;

FIG. 9 is a schematic view for explaining a laser beam moving mechanism using two lenses;

FIGS. 10-14 are schematic diagrams illustrating the laser scanning strategy of the present invention;

FIG. 15 is a microphotograph for illustrating that ultra-fine grains can be obtained when the metallic material is printed according to the present invention;

FIGS. 16-21 are schematic diagrams illustrating the laser scanning strategy of the present invention;

wherein the reference numbers: 1-a first vibrating mirror, 2-a second vibrating mirror, 3-a first laser beam, 4-a second laser beam, 5-a first solid raw material guiding mechanism, 6-a first linear solid raw material, 7-a first magnetic field generating device, 8-a first substrate, 9-a first resistance heating power supply, 10-a first printing body, 11-a first molten pool, 12-a first focusing mirror, 13-a second focusing mirror, 14-a region where a molten raw material is being deposited, 15-a region where the first laser beam is scanned, and 16-a region where the second laser beam is scanned;

20-a second laser beam moving mechanism array, 21-a third laser beam, 22-a fourth laser beam, 23-a fifth laser beam, 24-a sixth laser beam, 25-a second solid raw material guiding mechanism, 26-a second linear solid raw material, 27-a second magnetic field generating device;

30-a third laser beam moving mechanism array, 31-a seventh laser beam, 32-an eighth laser beam, 35-a third solid raw material guiding mechanism, 36-a third linear solid raw material, 37-a third magnetic field generating device;

40-laser beam moving mechanism array four, 41-laser beam nine, 42-laser beam ten, 45-solid raw material guiding mechanism four, 46-linear solid raw material four, 47-magnetic field generating device four;

50-lens I, 51-lens support, 52-neodymium iron boron magnet array, 53-spring array, 54-electromagnet array and 55-shell;

60-concave lens, 61-convex lens, 62-laser beam eleven;

a first 63-Y axis moving direction, a second 64-Y axis moving direction, a first 65-X axis moving direction and a second 66-X axis moving direction;

67-the region scanned by laser beam one, 68-the region scanned by laser beam two, 681-the lower scan density region of the region scanned by laser beam two, 682-the higher scan density region of the region scanned by laser beam two, 69-the overlap region of the region scanned by laser beam two and the region where molten feedstock is being deposited; 71-melting raw material being deposited, 72-spot of laser beam projected on printing body, 73-printing raw material having completed deposition;

arrow D1-accumulation direction of molten raw material on the molding surface, arrow D2-advancing direction of solid raw material toward the print body, arrow D3-scanning direction of laser beam one, arrow D4-scanning direction of laser beam two;

arrow D11-raw material deposition track advancing direction one, arrow D12-raw material deposition track advancing direction two, arrow D13-raw material deposition track advancing direction three;

arrow D151-raw material deposition trajectory advancing direction four, arrow D152-raw material deposition trajectory advancing direction five, and arrow D153-raw material deposition trajectory advancing direction six.

Detailed Description

The following describes the present invention in detail by way of preferred embodiments thereof with reference to the accompanying drawings.

In the description of all the specific embodiments of the present invention, the terms "upper", "lower", "left", "right", and the like are used in the orientation or positional relationship shown in the drawings for convenience of description and simplicity of operation, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated.

The principle of the first embodiment of the three-dimensional printing system of the present invention as shown in fig. 1 to 3 is as follows: a motion platform (not shown in the drawing), a laser (not shown in the drawing), an optical path, a solid raw material conveying mechanism (not shown in the drawing), a solid raw material guiding mechanism (namely, a solid raw material guiding mechanism one 5), a control circuit (not shown in the drawing) and a power supply are arranged; wherein: the control circuit controls the movement of the motion platform, and the movement of the motion platform determines the deposition position of a molten raw material formed after the solid raw material is molten in the forming area; the control circuit controls the solid raw material conveying mechanism to move the solid raw material (namely the linear solid raw material I6) to the forming area through the solid raw material guide mechanism, the front end of the solid raw material is melted in the forming area to form a molten raw material, and the molten raw material is deposited in the forming area to form a printing body (namely the printing body I10); the control circuit controls the working state of the laser, and laser generated by the laser forms a laser beam through a light path and is transmitted to the forming area; the power supply supplies electric energy to all electric components of the three-dimensional printing system; the forming area refers to a space used by the three-dimensional printing system when printing the part, and the part is formed in the space;

the key point is that:

the laser beams (namely the laser beam I3 and the laser beam II 4) are projected onto the printing body from the space around the solid raw material (namely the linear solid raw material I6);

the optical path comprises a laser beam moving mechanism (namely a laser beam moving mechanism array consisting of a first galvanometer 1 and a second galvanometer 2), the laser beam moving mechanism controls a laser beam to scan and heat the periphery of a region where the molten raw material is deposited on a printing body (namely the printing body I10) so as to generate a molten pool (namely the laser beam scans and heats the periphery of the region where the molten raw material is in contact with the molten raw material being deposited on the printing body), namely a light spot formed by the laser beam projected on the printing body moves on the periphery of the region where the molten raw material is deposited on the printing body; the laser beam moves relative to the printing body in a scanning heating area on the printing body while scanning and heating the edge and/or the periphery of the area on the printing body where the molten raw material is deposited, namely the scanning heating area moves relative to the printing body together with the solid raw material guiding mechanism (namely the solid raw material guiding mechanism-5) (the printing body is taken as a reference object); the range of the scanning heating area of the laser beam is controllable; for example, the area 15 scanned by the first laser beam and the area 16 scanned by the second laser beam belong to the scanning heating area of the laser beam;

the number of the laser beams projected by the laser beam moving mechanism is two, and each laser beam can be independently controlled (such as laser intensity, the position projected by the laser beam and whether the laser beam is on or not); the number of laser beams projected at the same time is controllable (e.g., one, zero, or two); the number of the lasers is two;

applying current between the solid raw material and the printing body to generate resistance heating effect, and generating molten raw material between the solid raw material and the printing body only under the resistance heating effect;

in this example, the heating energy for generating the molten pool was laser, and the heating energy for generating the molten raw material was resistance heat, which were independent of each other. The use of resistance heating to produce molten material enables higher forming rates (resistance heat is a bulk heat source, heating occurs synchronously inside and outside, laser is a surface heat source, heat is conducted from outside to inside, and time is required for the heat conduction process), and in addition, resistance heating can be used in conjunction with a magnetic field to produce strong electromagnetic force to modulate the grains of the printed body and make the device more compact (see details below).

The molten raw material being deposited can be understood as: molten raw material that has contacted the print body, a space between the solid raw material and the print body.

The optical path mainly comprises an optical cable, a collimating component, a reflecting mirror, a laser beam moving mechanism and a focusing mirror. The laser beam moving mechanism adopts a two-dimensional vibrating mirror (namely a vibrating mirror 1 and a vibrating mirror 2), and a focusing mirror is arranged at the outlet of the vibrating mirror: in fig. 3, the first focusing lens 12 is disposed at the exit of the first galvanometer 1, the second focusing lens 13 is disposed at the exit of the second galvanometer 2, and both the first focusing lens 12 and the second focusing lens 13 may use field lenses or non-field lenses (i.e., conventional focusing lenses, such as those used in laser cutting machines). Laser is emitted from a laser, is transmitted to a vibrating mirror through an optical cable (the transmitting end of the optical cable adopts a QBH joint), a collimating mirror and a reflecting mirror, and then is focused through a focusing mirror. The reflecting mirror inside the galvanometer controls the incident position of the laser beam on the focusing mirror, so that the irradiation position of the focused laser beam is controlled. The galvanometers in the prior art are divided into two-dimensional galvanometers and three-dimensional galvanometers: the optical component of the two-dimensional galvanometer consists of two rotatable reflectors, and the two reflectors respectively control the light beams to move in the X-axis direction and the Y-axis direction in a plane; the three-dimensional galvanometer is formed by adding a group of electric focusing lenses on the basis of a two-dimensional galvanometer, and the electric focusing lenses control the position of a light beam focusing point in the Z-axis direction, so that the position adjustment of a focus in a three-dimensional space represented by three X, Y and Z axes is realized (namely, the three-dimensional scanning of a laser beam is realized). If a three-dimensional galvanometer is used, the optical components of the laser beam moving mechanism are composed of a mirror and a lens.

The solid raw material adopts a wire (namely a linear solid raw material I6); -providing straightening means (not shown in the drawings) through which the wire or rod is straightened before being heated; the straightening device is directly connected with the solid raw material conveying mechanism (not shown in the attached drawing).

In the first embodiment, the front end of the linear solid raw material 6 is melted to generate the molten raw material, and the area of the surface of the print body 10 that is in contact with the melted front end of the linear solid raw material 6 is the area where the molten raw material is being deposited.

And a magnetic field generating device (a first magnetic field generating device 7) is arranged in the space around the solid raw material and consists of a pair of electromagnets, and the electromagnets are electrified with direct current to generate a static magnetic field. Each group of electromagnets consists of silicon steel and coils. The upper ends of the two groups of electromagnets are connected through silicon steel, and the lower ends of the two groups of electromagnets are symmetrically distributed on the outer side of the lower end of the first solid raw material guide mechanism 5. The gap between the lower ends of the two groups of electromagnets is the air gap of the first magnetic field generating device 7, magnetic lines of force are dispersed to the surrounding space when passing through the air gap, and the action range of the air gap magnetic field covers the area where the printing body is accumulating the molten raw materials and the surrounding area. After being output from the solid raw material guide mechanism one 5, the solid raw material passes through an air gap between the lower ends of the two groups of electromagnets and reaches the upper surface of the printing body. In this embodiment, the solid raw material guiding means one 5 is substantially located in a space between the magnetic field generating means one 7 and the linear solid raw material one 6.

In the embodiment, the magnetic field generated by the magnetic field generating device covers the area where the molten raw material is deposited and the peripheral area of the area, which takes the molten raw material being deposited as the center and is in the range of more than 40mm by 40 mm; an alternating current is applied between the solid raw material and the print body, and the current flows through a molten raw material generated after the solid raw material is melted and a region on the print body where the molten raw material is being deposited.

The magnetic field generating device, the solid raw material guiding mechanism and the laser beam moving mechanism are mutually connected through a mechanical structure, are integrally combined into a printing head and can integrally move under the driving of the motion platform.

FIG. 2 is a schematic view obtained by cutting along a plane passing through the axis of the linear solid raw material I6 and the optical axes of the focusing lenses at the outlets of the two vibrating lenses at the same time. The first galvanometer 1 moves the first laser beam 3, the second galvanometer 2 moves the second laser beam 4, and the linear solid raw material 6 reaches the forming area through the guidance of the solid raw material guiding mechanism 5; arranging a first magnetic field generating device 7 in the space around the linear solid raw material 6, wherein a first solid raw material guiding mechanism 5 is arranged between the linear solid raw material 6 and the first magnetic field generating device 7; the first magnetic field generating device 7 is an electromagnet and consists of silicon steel and a coil; an air gap of the silicon steel of the field generating device I7 is positioned below an outlet of the solid raw material guiding mechanism I5; the linear solid raw material I6 and the substrate I8 are respectively connected to two output electrodes of a resistance heating power supply I9, the high-power high-frequency alternating current output by the resistance heating power supply I9 heats and melts the area of the linear solid raw material I6, which is contacted with a molten pool I11 on a printing body I10, so as to obtain molten raw material, and the molten raw material is synchronously deposited (i.e. accumulated) on the molten pool I11 while being generated; the first substrate 8 is fixed on the motion stage, and the molten material is deposited directly on the first substrate 8 while the first layer of the first print 10 is being formed. In this embodiment, the first linear solid material 6 is 304 stainless steel wire with a wire diameter of 1mm, and the first substrate 8 is 304 stainless steel plate. The spot of the laser beam always falls in front of the area where the molten raw material is being deposited, i.e., the area adjacent to or contiguous with the area where the molten raw material is being deposited in the advancing direction of the printing path, as indicated by arrow D1 in fig. 2, which is the advancing direction of the deposition path of the molten raw material, the scanning area for the laser beam two 4 is now located in the direction indicated by arrow D1, the laser beam two 4 is activated, the scanning area for the laser beam one 3 is not located in the direction indicated by arrow D1, and the laser beam one 3 is deactivated. The linear solid raw material one 6 is advanced to the printing body one 10 in the direction shown by an arrow D2, and the raw material is continuously replenished; the direction indicated by the arrow D2 is substantially perpendicular to the area of the surface of the print body 10 where the molten raw material is currently deposited. Since the linear solid raw material-6 and the print body-10 are relatively moved in the direction indicated by the arrow D1 (for example, at a moving speed of 50mm/s) and a certain time interval is required for the molten metal to change from the molten state to the solidified state, the molten pool-11 generated by heating the laser beam on the print body-10 can be kept in the molten state when it becomes the current accumulation region. Whether a molten pool I11 generated by heating the laser beam on the printing body I10 can still keep a molten state when the molten pool becomes a current accumulation area or not depends on the area of a light spot generated by projecting the laser beam, the power density of the light spot and the relative movement rate of the linear solid raw material I6 and the printing body I10 in the direction shown by an arrow D1 on the premise that the heat dissipation condition and the thermal conductivity of the material are not changed, and specific control parameters are empirical values in the embodiment and are obtained through a plurality of tests. When the linear solid raw material 6 is positioned above the molten pool 11, the resistance heat generated by the high-power high-frequency alternating current output by the resistance heating power supply 9 melts the part of the front end of the linear solid raw material 6 connected (contacted) with the molten pool 11, and simultaneously heats the molten pool 11, and the molten raw material is synchronously deposited on the molten pool 11 while generating the molten raw material. The higher the temperature and the higher the resistivity of common metal materials are, the smaller the cross section area and the larger the resistance are under the premise of unchanged length, because the temperature of the interface between the front end of the linear solid raw material I6 and the molten pool I11 is high (can reach the melting point) and the area is small (is close to the radial cross section area of the solid raw material), the interface between the front end of the linear solid raw material I6 and the molten pool I11 is the region with the maximum resistance in a resistance heating series circuit formed by the linear solid raw material I6 and the printing body I10, the occurrence point of the molten raw material is clamped at the interface, and the heat generated by the resistance heating mode is synchronously generated inside and outside (not conducted by the outside), so that the front end of the linear solid raw material I6 still has certain rigidity at the interface. The movement of the linear solid raw material-6 in the directions of the arrow D1 and the arrow D2 generates mechanical force on the molten pool-11, which can produce a number of beneficial effects, such as: stirring the molten pool to generate the functions of driving micro bubbles in the molten pool and inhibiting hot cracks; if the bath is not adequately protected by the shielding gas (e.g., the forming zone used in three-dimensional printing systems is open, and the inert shielding gas is at a lower concentration at some point above the bath), the oxide film produced may also be broken and thus resist oxidation. When the printing material used is a material such as an aluminum alloy which can rapidly form an oxide film at a high temperature and prevent further oxidation, the present invention can perform three-dimensional printing directly in the atmospheric environment without using a protective gas. The existing laser coaxial wire feeding three-dimensional printing technology is different from the invention in that the front end of a wire (wire rod) is heated by external heating energy, heat is conducted from outside to inside, the front end of the wire is heated and melted, the interface between the front end of a linear solid raw material I6 and a molten pool I11 and a molten raw material generation point do not exist, the front end of the wire is heated and melted by laser and has fluidity, and the interface between the front end of the linear solid raw material I6 and the molten pool I11 cannot be obtained, so that the solid raw material cannot generate mechanical force on the molten pool, the volume of the molten raw material is large, and the wire width smaller than the diameter of the wire (wire rod) is difficult to print.

In this embodiment, the magnetic induction intensity of the air gap magnetic field of the first magnetic field generating device 7 in the space between the lower end of the first solid raw material guiding mechanism 5 and the first printing body 10 is about 5000Gs (gauss), the moving speed in the directions indicated by the arrow D1 and the arrow D2 is 80mm/s, the laser power is adjustable between 500W and 2000W, the laser wavelength is 1064nm, the spot diameter is about 1.0mm, the average current of resistance heating is more than 300A (ampere), the current frequency is 5kHz, the magnetic field intensity and the current density flowing through the melt are high. Under the combined action of a strong static magnetic field and a strong alternating current, strong electromagnetic force vibration is generated in an unsolidified area on the printing body I10 (on the premise that the viscosity of a melt is not changed, the stronger the electromagnetic force is, the higher the response rate of the melt to the vibration is), the end part of a dendritic crystal is subjected to strong shearing, the dendritic crystal is rapidly broken, a large number of new crystal nuclei are formed, the vibration (flowing) of the melt in a molten pool effectively slows down the temperature gradient of the front edge of a solid/liquid interface, and thermal cracking is inhibited. The specific embodiment can obtain fine equiaxed grains, the structure becomes uniform and compact, and the structure control of the metal 3D printing part is further realized.

As shown in fig. 3: the first laser beam 3 and the second laser beam 4 are respectively divided into areas of 180 degrees around the area 14 where the molten raw materials are deposited, namely: a region 15 scanned by the first laser beam and a region 16 scanned by the second laser beam; the galvanometer I1 moves the laser beam I3 to be focused by the focusing lens I12, and the light spot moves in the area 15 scanned by the laser beam I in the direction indicated by a double-headed arrow D3; the second galvanometer 2 moves the second laser beam 4 to be focused by the second focusing lens 13, and the light spot moves in the area 16 scanned by the second laser beam in the direction indicated by the double-headed arrow D4. Both the area 15 scanned by the first laser beam and the area 16 scanned by the second laser beam belong to the scanning heating area, and both the area 15 scanned by the first laser beam and the area 16 scanned by the second laser beam are controllable in area and shape.

Of course, the optical path can be the case: the device mainly comprises an optical cable, a collimation component, a reflection component and a focusing component; some or all of the reflecting and/or focusing elements may be movable, e.g., controlled by a motor, and may also function as a laser beam moving mechanism. For example: the optical component of the laser beam moving mechanism is a focusing mirror, and the focusing mirror is driven by a moving component to move in the direction of a radial plane vertical to the optical axis of the focusing mirror, so that the movement of the laser beam is realized.

In this embodiment, the magnetic field generating device may also adopt a permanent magnet (such as an ndfeb magnet) and a magnetizer (such as silicon steel), and the permanent magnet and the magnetizer are fixed together by a material with very low magnetic permeability (such as aluminum) to form a composite permanent magnet. The two ends of the composite permanent magnet for generating the air gap are symmetrically arranged in the space outside the lower part of the solid raw material guiding mechanism I5, and the magnetic lines of force diverge in the air gap and cover the space between the lower end of the solid raw material guiding mechanism I5 and the printing body I10 and the surrounding area thereof.

In this embodiment, the laser uses a fiber laser with a laser wavelength of 1064nm, and the control circuit monitors the state of the spot of the laser beam on the surface of the printing body through the sensing circuit and controls the laser beam moving mechanism in real time to ensure that the laser beam scans and heats the edge and/or periphery of the area of the printing body where the molten raw material is being deposited. For example: the control circuit acquires the image of the light spot through the high-speed infrared camera, calculates the position relation between the light spot and the area on the printing body where the melting raw material is deposited and the melting raw material being deposited, and corrects the position relation in real time when the light spot deviates from a preset range, so as to ensure that the laser beam scans and heats the edge and/or the periphery of the area on the printing body where the melting raw material is deposited.

This first embodiment prints on a metal substrate a first layer of a metal part, i.e. a first layer of a workpiece, for example on a stainless steel plate or a metal plate that can be welded to a stainless steel material.

The principle of the second embodiment of the present invention as shown in fig. 4 and 5 is mainly different from the first embodiment of the present invention as shown in fig. 1 to 3 in that: the laser beam moving mechanism (namely the laser beam moving mechanism array two 20) adopts 4 two-dimensional galvanometers, at most 4 laser beams (namely a laser beam three 21, a laser beam four 22, a laser beam five 23 and a laser beam six 24) are generated, the magnetic field generating device two 27 is composed of two pairs of electromagnets, and the magnetic conductive materials of the electromagnets adopt ferrite cores. And an air gap of the second magnetic field generating device 27 is arranged at the lower end outlet of the second solid raw material guiding mechanism 25. Two-phase alternating current is supplied to the second magnetic field generator 27, a rotating magnetic field having the second linear solid raw material 26 as a rotation axis is generated in a space around the lower end of the outlet of the second solid raw material guide mechanism 25 and the front end of the second linear solid raw material 26, the rotation frequency of the magnetic field is 500Hz, and direct current is applied between the second linear solid raw material 26 and a printing body (not shown in the drawing), and 4 lasers are used.

The principle of the third embodiment of the present invention as shown in fig. 6 is mainly different from the first embodiment of the present invention as shown in fig. 1 to 3 in that: using 1 laser (not shown in the drawing), introducing the laser into different vibrating mirrors of the laser beam moving mechanism (i.e. laser beam moving mechanism array three 30) through the optical path switcher respectively, wherein the laser beam seven 31 and the laser beam eight 32 come from the same laser; the third magnetic field generating device 37 is a hollow electromagnet, and the third solid raw material guiding mechanism 35 penetrates through the center of the third magnetic field generating device 37. The linear solid raw material three 36 passes through the center of the solid raw material guide means three 35. The magnetic field generating device three 37 is also substantially located in the space around the linear solid raw material three 36, and the solid raw material guiding mechanism three 35 is located in the space between the magnetic field generating device three 37 and the linear solid raw material three 36. The third magnetic field generator 37 is composed of a hollow ferrite and a coil, a direct current is supplied to the third magnetic field generator 37, a divergent static magnetic field is generated in the space around the lower end of the outlet of the third solid raw material guide mechanism 35 and the front end of the third linear solid raw material 36, and a strong alternating current having a frequency of 5kHz is applied between the third linear solid raw material 36 and a printing body (not shown in the figure).

In this embodiment, the optical path mainly includes an optical cable, a collimating component, an optical path switcher, a reflecting mirror, a laser beam moving mechanism, and a focusing mirror. As in the first embodiment, the laser beam moving mechanism employs a galvanometer, and a focusing mirror (not shown in the drawings) is provided at the exit of the galvanometer. Laser emits from the laser, transmits beam expanding lens and collimating mirror through the optical cable, by the trend of the light beam of light path switch control after the collimation, and what shakes mirror is controlled by the light path switch that the laser beam got into promptly. In this embodiment, the core component of the optical path switch is a 45-degree mirror controlled by a motor, and the working principle thereof is as follows: when the reflector completely cuts off the laser beam (namely the laser beam is totally reflected), the laser beam totally enters the first vibrating mirror; when the laser beam is not shielded (i.e. not reflected) by the reflector, the laser beam completely enters the second vibrating mirror; the reflecting mirror can also partially shield the laser beam, one part of the laser beam enters the first vibrating mirror, and the rest part of the laser beam enters the second vibrating mirror; the proportion of the laser beams entering the two vibrating mirrors is distributed by controlling the proportion of the laser beams reflected by the reflecting mirrors.

The principle of the fourth embodiment of the present invention as shown in fig. 7 is mainly different from the third embodiment of the present invention as shown in fig. 6 in that: the optical components of the laser beam moving mechanism (i.e., the laser beam moving mechanism array four 40) are constituted by lenses, and no galvanometers are used. Using 1 laser (not shown in the drawing), the laser light is introduced into two laser beam moving mechanisms through optical path switchers, respectively, to generate laser beams nine 41 and ten 42, respectively. The magnetic field generating device IV 47 is also a hollow electromagnet, which is composed of a hollow ferrite and a coil, and a pulse direct current with the frequency of 5kHz is passed through the magnetic field generating device IV 47, so that a divergent pulse magnetic field is generated in the space around the lower end of the outlet of the solid raw material guiding mechanism IV 45 and the front end of the linear solid raw material IV 46. Direct current is applied between the linear solid raw material four 46 and a print body (not shown in the drawings).

The laser beam moving mechanism used in the fourth embodiment can be implemented in two ways, as shown in fig. 8 and 9.

Mode shown in fig. 8: only one lens (namely, a lens I50) is used, a neodymium iron boron magnet array 52 (symmetrically distributed at four positions, namely, the upper position, the lower position, the left position and the right position) is arranged on a lens support 51, the lens support 51 is hung on a shell 55 through a spring array 53, and an electromagnet array 54 (the position corresponds to the neodymium iron boron magnet array 52) is arranged on the shell 55; lens one 50 is moved by energizing different electromagnets in electromagnet array 54 with direct current to synthesize a vector electromagnetic force directed in any direction in the radial plane of lens one 50, thereby moving the laser beam through lens one 50.

Mode shown in fig. 9: two lenses, i.e., a concave lens 60 and a convex lens 61, are used, the concave lens 60 is driven by a motor or an electromagnet to move in an X-axis moving direction one 65 or an X-axis moving direction two 66, and the convex lens 61 is driven to move in a Y-axis moving direction one 63 or a Y-axis moving direction two 64, so that the laser beam eleven 62 is controllably moved while passing through the concave lens 60 and the convex lens 61.

A fifth embodiment of the invention (without the attached figures): the apparatus composition is completely identical to that of the first embodiment of the invention, with the difference that the scanning strategy of the laser beam is: the light spot falls on the area of the surface of the printing body, which is positioned in front of the printing path and adjacent to or connected with the molten raw material, and on the side, facing the front of the printing path, of the front end of the solid raw material, most of energy (for example, about 95% of energy) of the light spot is distributed on the area of the surface of the printing body, which is positioned in front of the printing path and adjacent to or connected with the molten raw material, and a small part of energy (for example, about 5% of energy) of the light spot falls on the lower end edge of the side, facing the front of the printing path, of the front end of the solid raw material; applying current between the solid raw material and the printing body to generate resistance heating action, generating molten raw material between the solid raw material and the printing body under the combined action of resistance heating and laser heating, and melting the solid raw material mainly by the action of resistance heat to generate the molten raw material.

Sixth embodiment of the invention (not shown in the drawings) on the basis of the first embodiment of the invention, the magnetic field generating device and the components related to resistance heating are removed, and the solid raw material is melted completely by means of laser to obtain the molten raw material. Scanning strategy of the laser beam: the light spot falls on the surface of the printing body in a region adjacent to or connected with the molten raw material in front of the printing path and on the side of the front end of the solid raw material facing the front of the printing path, most energy (for example, about 80% of energy) of the light spot is distributed on the surface of the printing body in front of the printing path in the region adjacent to or connected with the molten raw material, a small part of energy (for example, about 20% of energy) of the light spot falls on the lower edge of the front end of the solid raw material facing the front side of the printing path, the printing speed is reduced, the front end of the solid raw material is fully melted, and the region of the surface of the printing body adjacent to or connected with the molten raw material in front of the printing path is fully melted to form a deeper molten pool (for example, the depth is 300 microns); part of parameters: the solid raw material is 304 stainless steel wire with the wire diameter of 1mm, the laser power is 1000 watts, the printing speed is 20mm/s, and the progressive speed of the solid raw material is also 20 mm/s.

The present invention is not limited to the motion platform. The motion platform can be a multi-axis motion platform based on Cartesian three-dimensional coordinates, or a three-dimensional motion platform based on polar coordinates, or a multi-axis mechanical arm. The solid raw material guiding mechanism can be immovable, and the moving platform drives the substrate to move in three dimensions, namely the printing body to move in three dimensions.

The forming zone is not limited by the present invention. The forming zone may be a space disposed within the three-dimensional printing system, having a housing. The forming area may also be a working space disposed outside the three-dimensional printing system, for example, a six-axis robot is used as a motion platform to print on a metal substrate in an atmospheric environment, and the forming area is an open space based on the metal substrate.

There are other preferred embodiments of the present invention. For example: the number of the laser beams is two, one laser beam falls on the area where the molten raw material is deposited in the advancing direction of the printing path and is heated with larger power and used for generating a molten pool, and the other laser beam falls on the molten raw material which is just deposited and has insufficient facula power density to heat and gasify or locally gasify the molten raw material which is just deposited, so that the surface of the molten raw material which is just deposited is smoother.

For another example: a small semiconductor laser is selected and directly connected with a collimating mirror and a vibrating mirror instead of using a fiber laser, so that the volume of the equipment is reduced;

for another example: the straightening device is connected with the solid raw material conveying mechanism, or the straightening device is connected with the solid raw material guiding mechanism through a pipeline, and the solid raw material enters the solid raw material conveying mechanism or the solid raw material guiding mechanism from the straightening device through the pipeline.

For another example: a solid member contactable with the printing body is disposed in a space around the solid raw material, and the molten raw material is contacted with the solid member after the printing body is deposited. The surface finishing and extruding device is used for performing surface finishing and extruding on the deposited molten raw material before the molten raw material is solidified, obtaining a smoother surface and further enhancing the modulation effect on crystal grains through mechanical force, and also can accelerate the temperature reduction of the deposited molten raw material, lower the temperature of a printing body and reduce thermal deformation. The solid component and the solid raw material guiding mechanism are relatively fixed in position; under the drive of the motion platform, the solid part and the solid raw material guide mechanism integrally move relative to the printing body. The solid component which can contact with the printing body is internally provided with a passage for circulating cooling liquid. The solid component capable of contacting with the printing body is annular and can rotate by taking the solid raw material as an axis. Alternatively, the solid member contactable with the printing body is in a block shape or an annular shape, and is not rotatable about the solid material as an axis.

For another example: in the three-dimensional printing process, the whole printing body is soaked in the cooling liquid, and the current forming layer is always located above the liquid level of the cooling liquid, for example, the current forming layer is located 5mm above the liquid level of the cooling liquid. The temperature of the printing body is accelerated, which has great benefits for printing thin-wall structures and supports high-speed printing.

For another example: in the three-dimensional printing process, a low-temperature gas is blown to the region where the molten raw material has been deposited. The temperature of the printing body is accelerated, which has great benefits for printing thin-wall structures and supports high-speed printing.

For another example: in the three-dimensional printing process, liquid is ejected to the area where the molten raw material has been deposited. For example, deionized water is sprayed when printing 316L stainless steel parts.

For another example: during three-dimensional printing, a shielding gas is ejected to the area being formed. For example, when printing titanium alloy, high-purity argon gas is sprayed to protect the molten pool.

For another example: a rod-shaped solid raw material is used. "rod-like" generally means a form having a small "aspect ratio", for example, an aspect ratio of 10:1 or less, and specifically includes: glass rods, carbon rods, wood rods, corynebacteria, and the like. "linear" generally refers to a form having a large "aspect ratio", for example, an aspect ratio >10:1, as specific examples: electrical wiring, metal wiring, kite wiring, wire, spring, steel bar, wood bar, railway wiring, crude oil piping, horizon wiring, and the like.

For another example: at least two laser beams are projected, wherein one part of the laser beams scan and heat the edge and/or periphery of the region on the printing body where the molten raw material is deposited to generate a molten pool, and the other part of the laser beams modify the shape of the surface of the printing body on which the molding is printed (for example, laser cutting, laser engraving and laser cleaning (for example, cleaning an oxide film) of the region of the printing body where the molten raw material is not currently deposited so as to obtain better surface quality and adjust the structure of the partial region of the printing body (for example, modifying the wall thickness)).

For another example: the laser beam moving mechanism controls the laser beam to heat the edge of the deposited molten raw material, so that heat is conducted to the edge of the area of the printing body where the molten raw material is deposited through the deposited molten raw material, and edge scanning heating of the area of the printing body where the molten raw material is deposited is achieved. (to explain that the area where the molten raw material is being deposited contacts the molten raw material being deposited, causing the area to be covered by the molten raw material being deposited, the laser cannot directly heat the area on the surface of the print body covered by the molten raw material, the laser heats the molten raw material being deposited, and then conducts heat to the edge of the area where the molten raw material is being deposited through the molten raw material being deposited, i.e., the laser beam indirectly heats the edge of the area where the molten raw material is being deposited; of course, the laser directly heats the periphery of the area where the molten raw material is being deposited adjacent to or continuous with the edge of the area where the molten raw material is being deposited, and the heat of the periphery is also conducted to the edge of the area where the molten raw material is being deposited by means of heat conduction, and actually indirectly heats the edge of the area where the molten raw material is being deposited.)

For another example: the laser beam moving mechanism controls the edge and/or periphery scanning heating of the laser beam on the printing body in the area where the molten raw material is deposited, and the scanning parameters can be dynamically adjusted. That is, the parameters of the laser scanning heating are not fixed throughout the process of printing a part (print body). When printing different areas of a part, the width of the scan area, the degree of overlap of the scan area with the area of the print body where molten material is being deposited, the scan line density within the scan area, the power, etc. can be dynamically adjusted, for example: when a part is printed, the part needs to be constructed on a bottom plate (supporting plate), because the first layer is tightly connected with the bottom plate, the heat dissipation condition is good, the maximum heating power and the larger scanning range are needed when the first layer is printed, the heat dissipation condition becomes worse along with the higher printing height, and the scanning parameters can be adjusted as required; for another example, when printing a thin-walled structure, the scanning range and heating power are smaller than those of a thick-walled structure; as another example, the scanning parameters required when printing edge structures with sharp corners are not the same as those for printing non-edge locations. And large printing of various complex parts can be better supported by dynamically adjusting scanning parameters.

For another example: the laser beam moving mechanism controls the laser beam to scan and heat the edge and/or periphery of the area where the molten raw material is being deposited, and simultaneously heats the raw material being deposited.

For another example: the optical path also comprises a non-scanning laser beam projection mechanism, and the laser beam projected by the non-scanning laser beam projection mechanism performs non-scanning heating on the area of the printing body where the molten raw material is deposited, namely the position relation between the light spot generated on the printing body by the projected laser beam and the projection of the outlet of the solid raw material guide mechanism on the surface of the printing body is relatively fixed. (explain: the non-scanning laser beam projection mechanism can be understood as that the laser beam projected by said projection mechanism can not be scan-type heated.) the non-scanning laser beam projection mechanism contained in the described optical path can be used for projecting hollow laser beam, and can form ring-shaped light spot on the surface of printing body, and the ring-shaped light spot can be used for enclosing the molten raw material being deposited on the surface of printing body. A non-scanned hollow laser beam in cooperation with a scanned laser beam may enable more flexible heating strategies, such as: the non-scanning hollow laser beam heats the edge and/or the periphery of the area where the molten raw material is deposited at a lower power density in a range of 360 degrees, the scanning laser beam heats the specific area of the edge and/or the periphery of the area where the molten raw material is deposited, and the energy of the scanning laser beam and the specific area is superposed to reduce the requirement of the three-dimensional printing process on the scanning speed of the laser beam; another example is: the non-scanning hollow laser beam adopts laser with 532nm wavelength, the scanning laser beam adopts laser with 1064nm wavelength, the cost of 1064nm laser is obviously lower than that of 532nm laser, the reflectivity of aluminum and copper to the 532nm laser is lower, and the reflectivity of aluminum and copper to the 1064nm laser is higher (especially, the reflectivity of pure copper to the 1064nm laser is very high, even reaches 95%), but when the temperature of aluminum and copper is increased, the reflectivity of 1064nm and 532nm lasers is reduced, the hollow laser beam with the wavelength of 532nm preheats the edge and/or the peripheral 360-degree range of the area in which the molten raw material is deposited with lower power density, and the scanning laser beam with the wavelength of 1064nm heats the edge and/or the peripheral specific area of the area in which the molten raw material is deposited with high power, so that the three-dimensional printing process of aluminum and copper materials can be flexibly and quickly heated.

For another example: the non-scanning laser beam projection mechanism is arranged in the light path, the number of the projected laser beams is at least three, at least three light spots are formed on the surface of the printing body, and the light spots surround the deposited melting raw materials on the surface of the printing body. The non-scanned multiple laser beams cooperate with the scanned laser beams to provide a more flexible heating strategy than embodiments that use only the scanned laser beams.

In the invention, when the number of the laser beams projected by the laser beam moving mechanism is two or more than two, the power of each laser beam can be independently controlled; when the number of laser beams projected through the laser beam moving mechanism is two or more, the scanning parameters of each laser beam can be independently controlled. Taking the first embodiment of the present invention as an example, the shape, area, scanning rate, average power density of the laser spot in the scanning area, dwell time of the laser spot at certain positions during the scanning process, curve shape of the scanning path, overlap degree between the scanning area and the area where the molten raw material is being deposited, and other scanning parameters are adjusted, as shown in fig. 10 to 13.

In fig. 10, the curved shapes of the scanning paths of the first laser beam 3 and the second laser beam 4 are shown by lines in the figure, the region 14 where the molten raw material is being deposited is connected with, but does not overlap, both the first laser beam-scanned region 67 and the second laser beam-scanned region 68 are curved as a whole, neither the first laser beam-scanned region 67 nor the second laser beam-scanned region 68 occupies a range of 180 °, and the combined annular shape of the first laser beam-scanned region 67 and the second laser beam-scanned region 68 is not a complete circle and does not occupy a peripheral 360 ° region centered on the region 14 where the molten raw material is being deposited. (the front end of the linear solid raw material was melted to produce a molten raw material, and the region of the surface of the print body that was in contact with the melted front end of the linear solid raw material was the region where the molten raw material was being deposited.)

In fig. 11, the curved shapes of the scanning paths of the first laser beam 3 and the second laser beam 4 are shown by lines in the figure, the first laser beam scanned region 67 is not continuous and square, the second laser beam scanned region 68 is triangular as a whole, and the shape of the first laser beam scanned region 67 and the second laser beam scanned region 68 is not directly continuous with, but adjacent to, the region 14 where the molten raw material is being deposited, and does not occupy a peripheral 360 ° region centered on the region 14 where the molten raw material is being deposited.

In fig. 12, the curved shapes of the scanning paths of the first laser beam 3 and the second laser beam 4 are shown as lines in the figure, the scanning density of the lower scanning density region 681 of the region scanned by the second laser beam is lower than that of the higher scanning density region 682 of the region scanned by the second laser beam, and on the premise that the power of the second laser beam 4 is kept constant, the power densities of the lower scanning density region 681 of the region scanned by the second laser beam and the higher scanning density region 682 of the region scanned by the second laser beam are different, so that a special thermal field is formed, the shape of a molten pool formed by heating the second laser beam 4 in the first printing body 10 and the thermal field of the molten pool are affected, and the three-dimensional printing process and the properties of the finally obtained part material are affected. The area 67 scanned by the first laser beam and the lower scan density region 681 scanned by the second laser beam, and the higher scan density region 682 scanned by the second laser beam are not directly connected to the area 14 where the molten raw material is being deposited, but occupy a peripheral 360 ° region centered on the area 14 where the molten raw material is being deposited. The first laser beam 3 uses lower power and is only used for heating the surface of the printing body and the just deposited molten raw material with lower power, so that a 'heat preservation effect' is generated in the area 67 scanned by the first laser beam, and the just deposited molten raw material is not heated to be gasified or partially gasified, thereby avoiding serious problems caused by excessive heating, such as obvious gasification, of the just deposited molten raw material on the premise of obtaining a smoother surface.

In fig. 13, the curved shape of the scanning path of the second laser beam 4 is shown by the line in the figure, and the area 68 scanned by the second laser beam is triangular as a whole, and the first laser beam 3 is not generated by the three-dimensional printing system of the embodiment at the present moment. There is an overlapping area between the area 68 scanned by the laser beam and the area 14 where the molten raw material is being deposited, i.e. the overlapping area 69 between the area scanned by the laser beam and the area where the molten raw material is being deposited, i.e. the overlapping area 69 is the edge of the area where the molten raw material is being deposited, i.e. when the laser beam is simultaneously scanning and heating the edge and the periphery of the area on the print body where the molten raw material is being deposited. The laser beam heats the edge of the depositing molten raw material, thereby transferring heat through the depositing molten raw material to the edge of the region of the printing body where the molten raw material is being deposited, thereby achieving indirect edge scanning heating of the region of the printing body where the molten raw material is being deposited. The second laser beam 4 heats the linear first solid raw material 6 through an overlapping area 69 between a scanning area of the second laser beam and an area where the molten raw material is being deposited, and the intensity of the heating depends mainly on the area of the overlapping area. When the advancing direction of the deposition path of the molten raw material for three-dimensional printing is located in the positive direction of the area 68 for two scans of the laser beam (i.e. the direction indicated by the arrow D1), the molten raw material just after deposition is not heated again by the laser, so as to avoid serious problems caused by excessive heating, such as reduced shape controllability and reduced forming precision due to too high fluidity of the molten raw material just after deposition, and material composition changes caused by significant vaporization (different boiling points of different components in the alloy material are not consistent, so that the components with lower boiling points are more vaporized, for example, aluminum of the TiAl6V4 titanium alloy is more easily vaporized than titanium), and micro pores are generated in the material (the micro pores can cause reduced performance of the finally obtained parts).

In fig. 14, the curved shape of the scanning path of the laser beam two 4 is shown by the lines in the figure, and the area 68 scanned by the laser beam two is distributed along the deposition path of the molten raw material on the surface of the print body and is an area which is continuous with the area 14 where the molten raw material is being deposited but where the molten raw material is not yet deposited (i.e., an area where the molten raw material is to be deposited). The raw material deposition trajectory advancing direction one D11, the raw material deposition trajectory advancing direction two D12, and the raw material deposition trajectory advancing direction three D13 represent advancing vectors of three raw material deposition paths having a total length of about 3.5 times the diameter of the region 14 where the molten raw material is being deposited, and the lengths can be set in the laser scanning parameters. There is an overlapping area between the area 68 scanned by the laser beam and the area 14 where the molten raw material is being deposited, i.e. the overlapping area 69 between the area scanned by the laser beam and the area where the molten raw material is being deposited, i.e. the overlapping area 69 is the edge of the area where the molten raw material is being deposited, i.e. when the laser beam is simultaneously scanning and heating the edge and the periphery of the area on the print body where the molten raw material is being deposited. The laser beam heats the edge of the depositing molten raw material, thereby transferring heat through the depositing molten raw material to the edge of the region of the printing body where the molten raw material is being deposited, thereby achieving indirect edge scanning heating of the region of the printing body where the molten raw material is being deposited. The leading end of the linear solid raw material is melted to produce a molten raw material being deposited, the region on the surface of the print body that is in contact with the melted leading end of the linear solid raw material is the region where the molten raw material is being deposited, and the region where the molten raw material is being deposited is surrounded (180 ° surrounded/half surrounded) by the region 68 where the laser beam is scanned twice. The overlap 69 of the area scanned by the second laser beam and the area where the molten material is being deposited is actually occupied by the molten material being deposited, and the heating effect of the second laser beam in the overlap is conducted to the overlap by heating the molten material being deposited, which is indirect heating. The scanning pattern of the laser beam two-scan region 68 can preheat the region where the molten raw material is to be deposited in advance, reduce the temperature gradient between the region where the molten raw material is being deposited and other regions of the print body, inhibit the generation of thermal cracks, and improve the material properties (mainly mechanical properties, such as fatigue resistance of metal parts) of the three-dimensional printed part or welded part. The existing metal three-dimensional printing technology, especially Selective Laser Melting (SLM) and Direct Energy Deposition (DED) (existing coaxial wire feeding and paraxial wire feeding three-dimensional printing system based on Laser heating, paraxial wire feeding three-dimensional printing system based on arc heating, and coaxial powder feeding and paraxial powder feeding three-dimensional printing system based on Laser heating, also belong to the DED technology), generally has the problem of low fatigue resistance of parts, which is a great obstacle for restricting the application of the existing metal three-dimensional printing technology in industrial production.

It can be seen that fig. 10 is a view showing the scanning heating of the laser beam at the periphery of the area on the print body where the molten raw material is being deposited, specifically, the scanning heating of the laser beam at the area on the print body which is continuous with the area where the molten raw material is being deposited. Fig. 11 and 12 are views illustrating the scanning heating of the laser beam at the periphery of the area on the print body where the molten raw material is being deposited, and in particular, the scanning heating of the laser beam at the area on the print body adjacent to the area where the molten raw material is being deposited. Fig. 13 and 14 show the scanning heating of the laser beam on both the edge and the periphery of the area on the print body where the molten raw material is being deposited. Of course, in other scanning heating methods, only the edge of the region where the molten raw material is being deposited on the print body may be scanned and heated.

As shown in fig. 10 to 14, in the scanning heating mode, during the process of generating the molten pool by scanning and heating the surface of the printing body by the laser, the scanning heating mode generates a "stirring" effect on the molten pool, and has a beneficial effect on the performance of the finally obtained part by three-dimensional printing, such as reducing micro-pores.

The laser scanning strategy of the invention is flexible, can obtain a great deal of beneficial effects, and can obtain high-performance three-dimensional printing parts. For example: when the solid raw material is a metal material, the laser beam only heats a region of the surface of the printing body, which is located in front of the printing path and adjacent to or connected with a region where the molten raw material is being deposited, and the laser beam does not heat the molten raw material which is just deposited; simultaneously, applying an electric current between the solid raw material and the print body and a magnetic field in a region where the molten raw material is being deposited and the print body is not yet solidified, and generating the molten raw material between the solid raw material and the print body only under the action of resistance heating or under the combined action of resistance heating and laser heating; melting solid metal completely or mainly by resistance heating requires high current density to melt the solid metal instantaneously (e.g. 304 stainless steel wire with 1mm wire diameter is melted at a rate of 40mm/s, average equivalent current intensity is more than 150A (depending on material type, heat source composition ratio, melting rate, heat dissipation rate and other factors), and about 1.9 x 10 is formed in the area where the molten raw material is being deposited⁸A/m²Superstrong current density of); the strong electromagnetic force generated by the interaction of the strong current flowing through the deposited melting raw material and the unset area on the printing body and the magnetic field acts on the unset area on the deposited melting raw material and the printing body, so that the metal crystal grains can be broken to obtain fine crystal grains, and particularly when the generated electromagnetic force is of an oscillation type or a rotation type, the remarkable shearing action is generated on the crystal grains, and the ultrafine crystal grains are easy to obtain, which is difficult to obtain by the traditional forging technology; since the molten raw material just after deposition is not heated by the laser beam and the print body is chargedThe split flow of the flow and the heat dissipation of the molten raw material just finished deposition lead to the rapid cooling of the molten raw material just finished deposition, and the broken crystal grains inside the metal material can be retained, so that the coaxial wire feeding three-dimensional printing technology based on laser heating has more advantages than the existing coaxial wire feeding three-dimensional printing technology based on laser heating, because: the existing coaxial wire feeding three-dimensional printing technology based on laser heating uses annular light spot heating, secondary heating can be carried out on the molten raw material which just completes deposition, the molten raw material which just completes deposition is melted again at high temperature, so that metal grains can grow again, thick grains or longer columnar grains are formed, and the quality of a printing body is reduced. As shown in photomicrographs a and B of fig. 15 (golden photograph), where the material corresponding to photograph B was printed using the technique of the present invention, and photomicrograph a of fig. 15 (golden photograph), which is a comparison chart, the material corresponding to photograph a is a 304 stainless rolled steel sheet available from the market. The scale markings at the bottom right of both micrograph a and micrograph B are 50 microns and the microscope magnification is 200X. It can be seen from the photograph B that the metal grains of the printed body obtained by printing using the technique of the present invention are very fine and belong to ultra-fine grains. The existing laser coaxial wire feeding three-dimensional printing technology melts linear solid raw materials through laser and heats and melts the area and the peripheral area of the surface of a printing body where the molten raw materials are deposited to generate a molten pool, and high-density current cannot be applied between the solid raw materials and the printing body (because the molten metal has high temperature and high resistivity, when the high-density current is passed through, the resistance heating action can instantly gasify the molten metal being deposited to cause the deposition process of the molten metal to become uncontrollable), so that the existing laser coaxial wire feeding three-dimensional printing technology cannot apply strong electromagnetic force on the area and the peripheral area where the molten raw materials are deposited through the interaction of a magnetic field and current, and is difficult to obtain ultrafine grains through the action of the electromagnetic force.

As another example, an alternative laser scanning strategy of the present invention is illustrated, as shown in fig. 16-21, to print one layer (top view) of the structure shown in fig. 21: the spot 72 projected by the laser beam on the printing body first irradiates the area where the molten raw material is to be deposited and generates a molten pool, the molten raw material is rapidly deposited on the molten pool just generated (the cooling of the molten pool requires time, the molten pool is still in a liquid state when the molten raw material is deposited by rapid movement in this example), so that the printing process is started, and then the spot 72 projected by the laser beam on the printing body is positioned in front of the molten raw material 71 just deposited on the molten raw material deposition path shown by an arrow D151 (the advancing direction of the raw material deposition track is four), the molten raw material 71 just deposited is rapidly moved in the direction shown by the arrow D151 together with the spot 72 projected by the laser beam, the solid printing raw material is synchronously moved to the surface of the printing body by the guidance of the solid raw material guiding mechanism and is resistively heated to melt and replenish the molten raw material just deposited, and the printing raw material 73 which has completed deposition is positioned in the opposite direction shown by the arrow D151, the printing material 73, which has completed deposition, forms a print body, as shown in fig. 16; the direction of deposition of the molten raw material is changed as shown by an arrow D152 (a raw material deposition trajectory advancing direction five) in fig. 17, the position of the spot 72 projected by the laser beam on the print body is rapidly switched to the front of the molten raw material 71 being deposited on the molten raw material deposition path shown by the arrow D152 (the whole switching process is in the order of 1 millisecond), and the molten raw material 71 being deposited is rapidly moved in the direction shown by the arrow D152 together with the spot 72 projected by the laser beam on the print body as shown in fig. 18; the direction of deposition of the molten raw material is changed as shown by an arrow D153 (a raw material deposition trajectory advancing direction six) in fig. 19, the position of the spot 72 projected by the laser beam on the print body is rapidly switched to the front of the molten raw material 71 being deposited on the molten raw material deposition path shown by the arrow D153, and the molten raw material 71 being deposited is rapidly moved in the direction shown by the arrow D153 together with the spot 72 projected by the laser beam on the print body as shown in fig. 20; finally, one layer of the structure shown in fig. 21 is obtained. The laser scanning strategies shown in fig. 16 to 21 are: the laser beam carries out scanning heating on the edge and the periphery of the area on the printing body, on which the molten raw material is deposited, around the area, on which the molten raw material is deposited, wherein the laser beam scanning heating area is the area, on which the molten raw material is to be deposited; the spot 72 projected by the laser beam onto the print body is always located in front of the deposition path of the molten raw material 71 being deposited, and only when the direction of the deposition path of the molten raw material changes, the spot 72 projected by the laser beam onto the print body is switched in position with respect to the molten raw material 71 being deposited; the scanning heating zone of the laser beam is moved relative to the print body while the laser beam is scanning heating the edges and periphery of the area on the print body where molten feedstock is being deposited. The impact of this scanning heating strategy on the three-dimensional printing process is: the requirement on laser power is reduced, the thermal action range is reduced, secondary laser heating is not performed on the molten raw material which is just deposited, and fine grains obtained after magnetic stirring/magnetic vibration modulation can be reserved.

If the invention adopts the mode that the molten raw material is generated between the solid raw material and the printing body only under the action of resistance heating or under the combined action of resistance heating and laser beam heating, the three-dimensional printing can be realized by only needing lower laser power and heating the area of the surface of the printing body, which is positioned in front of the printing path and is adjacent to or connected with the area where the molten raw material is deposited, to obtain a very thin molten pool, so that the appearance of the material which is formed previously and the internal microstructure (such as grain size) of the material are not damaged, and the stress and the thermal deformation are smaller. In addition, because the raw material is melted to obtain at least the heat provided by the resistance heating mode, the solid raw material is heated by the resistance heating mode from inside to outside simultaneously (the resistance heating belongs to a volume heat source), and the solid raw material is heated by the laser beam from outside to inside (the laser belongs to a surface heat source), the front end of the solid raw material is synchronously heated from inside to outside, and high-speed printing can be realized; in the prior art, only laser beam heating is used, the laser needs larger power and longer heating time, a deeper molten pool is generated, the appearance of the formed material and the internal microstructure of the material are damaged, the surface of the part is rough, and the grains in the material are coarse or long columnar crystals are formed; in the prior art, the heat is conducted from outside to inside by laser irradiation, so that a long time is required (compared with the invention) to fully melt the solid raw material and the surface of a printing body, and the prior art cannot be used for high-speed printing, and particularly, the high-speed printing of large parts is difficult to perform by using a thicker metal wire as the solid raw material (for example, a metal wire with the wire diameter of 6 mm).

The invention can obtain the molten raw material in a resistance heating mode, the front end of the solid raw material, which is in contact with the printing body, synchronously heats inside and outside (belonging to a volume heat source), heat energy is not transferred from the outside, the limitation of the heat conduction rate of the material does not exist, the surface of the laser heating printing body only needs to generate a very shallow molten pool (for example, a molten pool with the depth of 50 microns), a thick and large metal wire or bar can be used as the solid raw material, for example, a titanium wire with the diameter of 8mm can realize ultrahigh deposition rate, and for example, a 304 stainless steel wire with the wire diameter of 6mm can be used for printing at the moving rate of 400mm/s, the deposition rate can exceed 300 kg/h, and the invention has great value for printing large metal parts (for example, a large metal container of a nuclear power station). However, in the conventional technique, for example, a laser is used as a heat source (the laser is a surface heat source), and high-speed printing cannot be performed using a thick metal wire as a raw material due to a heat conduction model such as "heat energy is conducted from the outside into the material".

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the scope of the present invention, which is intended to be covered by the appended claims and equivalents thereof.

Claims

1. A three-dimensional printing system is provided with a motion platform, a laser, a light path, a solid raw material conveying mechanism, a solid raw material guiding mechanism, a control circuit and a power supply; wherein: the control circuit controls the movement of the motion platform, and the movement of the motion platform determines the deposition position of a molten raw material formed after the solid raw material is molten in the forming area; the control circuit controls the solid raw material conveying mechanism to move the solid raw material to the forming area through the solid raw material guide mechanism, the front end of the solid raw material is melted in the forming area to form a molten raw material, and the molten raw material is deposited in the forming area to form a printing body; the control circuit controls the working state of the laser, and laser generated by the laser forms a laser beam through a light path and is transmitted to the forming area; the power supply supplies electric energy to all electric components of the three-dimensional printing system; the forming area is a space used by the three-dimensional printing system when printing the part, and the part is formed in the space;

the method is characterized in that:

the laser beam is projected onto a printing body from the space around the solid raw material;

the optical path comprises a laser beam moving mechanism, and the laser beam moving mechanism controls the laser beam to scan and heat the edge and/or the periphery of the area on the printing body where the molten raw material is deposited; the laser beam moves relative to the print body in a scanning heating zone on the print body while scanning and heating the edge and/or periphery of the region on the print body where molten feedstock is being deposited;

the number of the laser beams which pass through the laser beam moving mechanism and can be projected is at least two; each laser beam can be controlled independently; the quantity of the laser beams projected in the same time is controllable; the number of the lasers is at least one;

applying current between the solid raw material and the printing body to generate resistance heating effect, and generating molten raw material between the solid raw material and the printing body only under the effect of resistance heating; or applying current between the solid raw material and the printing body to generate resistance heating effect, and generating molten raw material between the solid raw material and the printing body under the combined action of resistance heating and laser beam heating; or, generating molten raw material between the solid raw material and the printing body only under the heating action of the laser beam;

the area where the molten raw material is deposited refers to an area on the printing body, which is in contact with the molten raw material being deposited;

2. The three-dimensional printing system of claim 1, wherein:

the laser beam moving mechanism controls the laser beam to scan and heat the edge and/or the periphery of the area where the molten raw material is deposited on the printing body so as to generate a molten pool; the range of the scanning heating area of the laser beam is controllable;

when the number of laser beams projected through the laser beam moving mechanism is two or more, the scanning parameters of each laser beam can be independently controlled.

3. The three-dimensional printing system of claim 2, wherein:

the optical path mainly comprises an optical cable, a collimation component, a reflection component, a laser beam moving mechanism and a focusing component, wherein the laser beam moving mechanism, the reflection component and the focusing component are arranged relatively independently, and a laser is connected with the optical path through the optical cable; or the optical path mainly comprises an optical cable, a collimating component, a reflecting component and a focusing component, wherein a part of components or all components which can move in the reflecting component and/or the focusing component form the laser beam moving mechanism, and the laser is connected with the optical path through the optical cable; or the optical path mainly comprises a collimation component, a reflection component, a laser beam moving mechanism and a focusing component, and the laser is directly connected with the optical path and is not connected with the optical path through an optical cable; or the optical path mainly comprises a collimation component, a laser beam moving mechanism and a focusing component, and the laser is directly connected with the optical path and is not connected with the optical path through an optical cable; or the optical path mainly comprises a reflecting component, a laser beam moving mechanism and a focusing component, and the laser is directly connected with the optical path and is not connected with the optical path through an optical cable; or the optical path mainly comprises a laser beam moving mechanism and a focusing component, and the laser is directly connected with the optical path and is not connected with the optical path through an optical cable; the focusing component is a field lens type focusing lens or a non-field lens type focusing lens.

Or the optical path mainly comprises an optical cable, a reflecting component and a laser beam moving mechanism, and the laser is connected with the optical path through the optical cable; or the optical path mainly comprises a reflecting component and a laser beam moving mechanism, and the laser is directly connected with the optical path and is not connected with the optical path through an optical cable; or the optical path mainly comprises a laser beam moving mechanism, and the laser is directly connected with the optical path and is not connected with the optical path through an optical cable.

4. The three-dimensional printing system of claim 2, wherein:

the optical component of the laser beam moving mechanism comprises a galvanometer;

or the optical component of the laser beam moving mechanism mainly comprises a reflecting mirror and/or a lens, and the laser beam is moved by moving the reflecting mirror and/or the lens;

alternatively, the optical component of the laser beam moving mechanism is mainly composed of a mirror and/or a lens, and the laser beam is moved by rotating the mirror and/or the lens.

5. The three-dimensional printing system of claim 1, wherein:

arranging a magnetic field generating device in the space around the solid raw material, wherein the magnetic field generated by the magnetic field generating device at least covers the area on the printing body where the molten raw material is deposited; applying a current between the solid raw material and the print body, the current flowing through a molten raw material produced after the solid raw material is melted and a region on the print body where the molten raw material is being deposited;

the magnetic field generated by the magnetic field generating device is a static magnetic field or an alternating magnetic field or a rotating magnetic field;

6. The three-dimensional printing system of claim 5, wherein:

7. The three-dimensional printing system of claim 5, wherein:

the magnetic field generating device comprises a pair of electromagnets or a pair of permanent magnets to generate a static magnetic field, alternating current is conducted between the solid raw material and the printing body, and magnetic vibration is generated in an unsolidified area on the printing body;

or the magnetic field generating device comprises at least two pairs of electromagnets, and multi-phase alternating current is supplied, and the number of the alternating current is the same as the number of the pairs of the electromagnets so as to generate a rotating magnetic field; direct current or alternating current is conducted between the solid raw material and the printing body;

or the magnetic field generating device comprises a hollow electromagnet or a hollow permanent magnet arranged in the space around the solid raw material, and the solid raw material passes through the central area of the hollow electromagnet or the hollow permanent magnet;

the electromagnet is an assembly which generates a magnetic field after being electrified and mainly consists of a magnetizer and a coil or is only a coil.

8. The three-dimensional printing system of claim 1, wherein:

the solid raw material adopts a wire or a bar;

arranging a straightening device, and straightening the wire or the rod by the straightening device before the wire or the rod is heated; the straightening device is connected with the solid raw material conveying mechanism or the solid raw material guiding mechanism;

9. The three-dimensional printing system of claim 1, wherein:

10. The three-dimensional printing system of claim 9, wherein:

11. The three-dimensional printing system of claim 1, wherein:

the molding area is a space arranged in the three-dimensional printing system; or the molding area is a working space arranged outside the three-dimensional printing system;

in the three-dimensional printing process, the whole printing body is soaked in cooling liquid, and the current forming layer is always positioned above the liquid level of the cooling liquid; or blowing low-temperature gas to the area where the molten raw material is deposited in the three-dimensional printing process; alternatively, in the three-dimensional printing process, the liquid is ejected to the area where the molten raw material has been deposited;

12. The three-dimensional printing system according to any one of claims 1 to 11, wherein: the laser beam can scan heat the edge of the area where molten feedstock material is being deposited and/or the peripheral annular region or a portion of the annular region.

13. The three-dimensional printing system of claim 1, wherein: two laser beams are used, one for higher power heating of the area of the print surface in front of the print path adjacent to or in contact with the molten material and the other for lower power heating only of the print surface and the just deposited molten material.

14. The three-dimensional printing system of claim 1, wherein: when the solid raw material is a metal material, heating a region of the surface of the printing body, which is located in front of the printing path and is connected with or adjacent to the molten raw material, by using a laser beam, wherein the molten raw material which is just deposited is not heated by the laser beam; at the same time, current is applied between the solid raw material and the print body and a magnetic field is applied to the region where the molten raw material is being deposited and the region where the molten raw material is not yet solidified on the print body, the molten raw material is generated between the solid raw material and the print body only by the action of resistance heating or by the combined action of resistance heating and laser beam heating, and electromagnetic force generated by the interaction of the current flowing through the region where the molten raw material is being deposited and the region where the molten raw material is not yet solidified on the print body acts on the region where the molten raw material is being deposited and the region where the magnetic field is not yet solidified.

15. The three-dimensional printing system of claim 14, wherein:

16. The three-dimensional printing system of claim 1, wherein:

17. The three-dimensional printing system of claim 1, wherein:

the laser beam projected on the print body may be scanned in one dimension or in two dimensions or in three dimensions.

18. The three-dimensional printing system of claim 1, wherein:

at least two laser beams are projected, wherein one part of the laser beams scans and heats the edge and/or periphery of the area on the printing body where the molten raw material is deposited to generate a molten pool, and the other part of the laser beams trims the shape of the surface of the printing body on which the molding is printed.

19. The three-dimensional printing system of claim 1, wherein:

the laser beam moving mechanism controls the laser beam to heat the edge of the deposited molten raw material, so that heat is conducted to the edge of the area of the printing body where the molten raw material is deposited through the deposited molten raw material, and edge scanning heating of the area of the printing body where the molten raw material is deposited is achieved.

20. The three-dimensional printing system of claim 1, wherein:

the laser beam moving mechanism controls the edge and/or periphery scanning heating of the laser beam on the printing body in the area where the molten raw material is deposited, and the scanning parameters can be dynamically adjusted.

21. The three-dimensional printing system of claim 1, wherein:

22. The three-dimensional printing system of claim 1, wherein:

the laser beam moving mechanism controls the laser beam to scan and heat the edge and/or the periphery of the area where the molten raw material is deposited, and the scanning heating area of the laser beam is the area where the molten raw material is to be deposited.

23. The three-dimensional printing system of claim 1, wherein:

24. The three-dimensional printing system of claim 1, wherein:

the optical path also comprises a non-scanning laser beam projection mechanism, and the laser beam projected by the non-scanning laser beam projection mechanism performs non-scanning heating on the area of the printing body where the molten raw material is deposited, namely the position relation between the light spot generated on the printing body by the projected laser beam and the projection of the outlet of the solid raw material guide mechanism on the surface of the printing body is relatively fixed.

25. The three-dimensional printing system of claim 1, wherein:

the control circuit monitors the state of the light spot of the laser beam on the surface of the printing body through the sensing circuit, and controls the laser beam moving mechanism in real time to ensure that the laser beam is scanned and heated at the edge and/or periphery of the area of the printing body where the molten raw material is deposited.