CN114131045B

CN114131045B - 3D printing method and system for hole structure

Info

Publication number: CN114131045B
Application number: CN202111392461.4A
Authority: CN
Inventors: 金学军; 刘延卿; 刘仕龙
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2021-11-23
Filing date: 2021-11-23
Publication date: 2022-12-30
Anticipated expiration: 2041-11-23
Also published as: CN114131045A

Abstract

The application discloses a 3D printing method of a hole structure, which comprises the steps of utilizing a selective laser melting method to perform scanning and printing layer by layer, wherein when each layer is scanned and printed, scanning and printing at least one circle around the edge of the layer to form a closed area, and then printing the inside of the closed area; when the inside of the closed area is printed, at least one circle of the edge of the hole inside the closed area is printed, and then the rest positions are printed. The product obtained by the method can greatly improve the energy absorption performance of the structure by only changing the process method during printing on the basis of not changing the original design and parameters.

Description

3D printing method and system for hole structure

Technical Field

The application relates to the field of material manufacturing, in particular to a method for preparing a hole structure material by selective laser melting.

Background

Selective Laser Melting (SLM) is one of the main techniques in additive manufacturing of metallic materials. The technical method uses laser as an energy source, and scans layer by layer on a metal powder bed according to a path after three-dimensional model CAD slicing, so that metal powder on the scanning path is melted and solidified to finally obtain a part designed by a model.

With the recent trend of light weight of automobiles, the part of the automobile interlayer for anti-collision protection is gradually replaced by a hole structure prepared by 3D printing. Although these pore structures may function, their energy absorption properties are yet to be improved.

Disclosure of Invention

The embodiment of the application provides a 3D printing method for a hole structure, and aims to at least solve the problem that the energy absorption and energy absorption of the existing hole structure formed by 3D printing still need to be improved.

According to one aspect of the application, a 3D printing method of a hole structure is provided, scanning and printing layer by layer is carried out by utilizing a laser selective melting method, when each layer is scanned and printed, scanning and printing are carried out for at least one circle around the edge of the layer to form a closed area, and then the inside of the closed area is printed; when the inside of the closed area is printed, at least one circle of the edge of the hole inside the closed area is printed, and then the rest positions are printed.

Further, the scanning speed when the layer is firstly scanned and printed around the edge of the layer is lower than the scanning speed when the inside of the closed area is printed.

Further, the scanning speed of the layer around the edge of the layer is 1700mm/s-2000mm/s, and the scanning speed of the closed area inside the layer is 2000mm/s-2700mm/s.

Further, the laser power when the layer is scanned around the edge of the layer for printing is larger than that when the laser power is printed inside the closed area.

Furthermore, the laser power during scanning and printing around the edge of the layer is 300W-340W, and the laser power during printing inside the closed area is 230W-300W.

Further, said first scanning at least one revolution around the edge of the layer comprises: the printing was done around the edge of the layer in an outside-in order for 3 weeks.

Further, the printing at least one circle around the edge of the layer in the order from outside to inside includes printing for 2 or more circles with a degree of overlap of 20% to 30% between each circle and an adjacent circle in the width direction of the printing path.

Further, when the inside of the closed area is printed, taking an end point when scanning and printing are performed around the edge of the layer as a starting point, and calculating the hole with the shortest distance from each point of the edge of each hole in the current closed area to the starting point as the initial printing hole of the closed area.

Further, when the inside of the closed area is printed, the end point surrounding the hole which is printed before is taken as a starting point, and the hole with the shortest distance from each point of the edge of each unprinted hole in the current closed area to the starting point is calculated as the next hole to be printed.

According to another aspect of the present application, there is provided a 3D printing system of a hole structure, comprising an optical path unit, a mechanical unit, a control unit and a protective gas sealing unit, and software for implementing printing according to the method of the first aspect.

The invention provides a 3D printing method and a system of a hole structure, which utilize a laser selective melting method to perform scanning and printing layer by layer, when each layer is scanned and printed, the layer is scanned and printed for at least one circle around the edge of the layer to form a closed area, and then the inside of the closed area is printed; when the inside of the closed area is printed, at least one circle of the edge of the hole inside the closed area is printed, and then the rest positions are printed. The product obtained by the method can greatly improve the energy absorption performance of the structure by only changing the process method during printing on the basis of not changing the original design and parameters.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, are included to provide a further understanding of the application, and the description of the exemplary embodiments of the application are intended to be illustrative of the application and are not intended to limit the application. In the drawings:

fig. 1 is a schematic flow chart of a 3D printing method according to an embodiment of the present application;

fig. 2 is a diagram showing the relationship between deformation and load obtained by performing a quasi-static compression test on a product obtained by printing different numbers of turns on the edge of each layer according to an embodiment of the present application.

Detailed Description

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments with reference to the attached drawings.

It should be noted that the steps illustrated in the flowcharts of the figures may be performed in a computer system such as a set of computer-executable instructions and that, although a logical order is illustrated in the flowcharts, in some cases, the steps illustrated or described may be performed in an order different than here.

As shown in fig. 1, an embodiment of the present invention provides a 3D printing method of a hole structure, including the following steps:

s102, scanning and printing layer by using a selective laser melting method, wherein when each layer is scanned and printed, scanning and printing at least one circle around the edge of the layer to form a closed area, and then printing the inside of the closed area;

s104, when printing is carried out on the inside of the closed area, firstly, at least one circle of printing is carried out around the edge of a hole in the closed area;

s106, printing the rest positions.

In accordance with conventional methods, the internal path is scanned 67 ° for each rotation relative to the previous layer. The above process also involves the preparation of the material and the use of software for printing, and therefore, at least a typical preparation process like the following is included:

s002: selecting and drying 17-4PH stainless steel powder as a raw material, wherein the drying temperature is 70 ℃, and the drying time is 3 hours;

s004: importing a three-dimensional model of a hole structure to be formed into 3D printing processing software in an STL format, and adding necessary support for a more complex model; slicing the model to obtain two-dimensional section data information, and importing the two-dimensional section data information into 3D printing equipment;

s006: and 3D printing and forming according to a preset scanning strategy and process parameters.

The metal powder 17-4PH stainless steel provided in certain preferred embodiments comprises the following chemical components in percentage by mass: c is less than or equal to 0.07 percent; mn is less than or equal to 1.00 percent; si is less than or equal to 1.00 percent; 15.5 to 17.5 percent of Cr; 3.0 to 5.0 percent of Ni; p is less than or equal to 0.04 percent; s is less than or equal to 0.03 percent; 3.0 to 5.0 percent of Cu; 0.15 to 0.45 percent of Nb and Ta; the balance being Fe. The 17-4PH stainless steel powder is spherical powder, the weight percentage of the grain diameter less than or equal to 60 mu m is not less than 95 percent, and the weight percentage of the grain diameter more than 60 mu m is less than 5 percent; the 17-4PH stainless steel powder had a minimum particle size of 15 μm and a maximum particle size of 75 μm, and an average particle size of 50 μm.

The method changes the printing process of the traditional selective laser melting method, distinguishes the edge of each layer from the inside, and prints the edge to form a closed area, so that the materials on the edge of each layer are higher in the degree of connection, stronger in structure and more compact in energy transfer; correspondingly, the hole edge and the rest part are also distinguished in the closed area, and the edge part limited to the hole is printed, so that the materials on the hole edge in the closed area are higher in connection degree, the hole structure is more stable, and the energy transfer is tighter. No matter the edge of the hole in the inner closed area of the edge sea of each layer, the microstructure obtained in the scanning process is isometric crystal with smaller size relative to the inner scanning structure, the integral strength and toughness of the sample can be improved, and the integral energy absorption performance of the product obtained by the method provided by the embodiment is obviously superior to that of the traditional method. Compared with the prior art, when the hole structure is printed by the process, the proportion of fine grains in the structure of the finally-formed part is relatively high due to the fact that the surface of the hole structure is large, and therefore the strength and the toughness of the part are integrally improved, the metal hole structure printed by the technical scheme is used for anti-collision protection, the original part design and size are not changed, the process is improved through 3D printing, and the performance of the metal hole structure in the aspect of energy absorption can be remarkably improved.

In the implementation process of the method, because the scanning position is located at the periphery during edge scanning, each non-intersected scanning area of the layer is not subjected to path scanning, the heat dissipation condition is better, the molten metal on the laser scanning path can be quickly cooled, and heat is accumulated to assist metal powder in melting due to relatively insufficient heat dissipation during internal scanning.

Therefore, in the scanning process, the outer area has more heat dissipation than when the inside of the closed area is scanned, and in order to effectively melt the material, an effective method is to reduce the scanning speed and give more melting time, so that the scanning speed when scanning and printing around the edge of the layer is lower than the scanning speed when printing inside the closed area. Preferably, the scanning speed when the layer is firstly scanned and printed around the edge of the layer is 1700mm/s-2000mm/s, and the scanning speed when the closed area is internally printed is 2000mm/s-2700mm/s.

Also for reasons of material melting which is affected by too rapid heat dissipation, it is also useful to increase the laser power, which is greater when printing around the edge of the layer than when printing inside the enclosed area, by applying more power to make the material more easily melt. Preferably, the laser power for printing by scanning around the edge of the layer is 300W-340W, and the laser power for printing inside the closed area is 230W-300W.

In certain preferred embodiments, the number of passes of the initial pass around the edge of the layer needs to be controlled within a reasonable range so that the printing occurs in an outside-in sequence for 3 passes around the edge of the layer, in order to integrate the material absorbency properties with the time-consuming and performance-enhancing limitations of excessive number of passes of edge printing.

As shown in fig. 2, the graph shows the relationship between deformation and load obtained by performing the quasi-static compression test on the product obtained by printing the edge on each layer at different numbers of turns, wherein 3 curves are shown in the graph, and the curves are respectively the relationship between printing for 3 turns, 1 turn and no edge printing from top to bottom. By comparison, the samples without edge path scan and with 1-perimeter edge path scan have about a 50% increase in yield load and about a 25% increase in energy absorption performance over the former in the quasi-static compression test. Wherein the energy absorption properties are obtained by integrating the area under the curve and between the abscissa axis.

Meanwhile, as can be seen from the figure, the curves printed for 3 weeks and 1 week both have significantly more energy absorption effect than the curves printed for no, and the curves printed for 3 weeks have stronger energy absorption effect than the curves printed for 1 week, but the increase is not significant, and particularly after the displacement is greater than or equal to 12mm, the two curves almost coincide, which shows that the energy absorption effect is equivalent to the energy absorption effect thereafter. But when the displacement is between 2mm and 12mm, the energy absorption effect is still slightly better than that of printing for 1 week when the printing is carried out for 3 weeks, and the number of printing weeks can be reasonably selected according to the use requirement.

During the scanning process, the scanning distance and the layer thickness can be kept the same between the inner part and the outer part, for example, the scanning distance is 0.08-0.12mm, and the layer thickness is 0.02-0.04mm. But also provides a preferred embodiment, in order to further strengthen the material strength of the periphery, the printing at least one circle around the edge of the layer from outside to inside comprises printing for 2 or more circles, and the overlap ratio between each circle and the adjacent circle in the width direction of the printing path is 20-30%. Through the coincidence in the width direction for the circle layer of edge is better in the hookability in the interior outside direction, can provide stronger support when impacting to the material inside.

Therefore, in some embodiments, when the inside of the closed area is printed, the end point when the inside of the closed area is scanned and printed around the edge of the layer is taken as the starting point, and the hole with the shortest distance from each point of the edge of each hole in the closed area to the starting point is calculated as the initial printing hole of the closed area. By the method, unnecessary laser head idle time is reduced, and scanning efficiency can be improved.

Similarly, the path planning between the holes inside also affects the scanning efficiency, and in the above embodiment, when the inside of the closed area is printed, the hole with the shortest distance from each point of the edge of the unprinted hole inside the current closed area to the starting point is calculated as the next hole to be printed, with the ending point of the hole around the previous printed hole as the starting point.

The embodiment of the invention also provides a 3D printing system of a hole structure, which adopts the scanning strategy on the basis of a traditional selective laser melting device (SLM), so that the system comprises a light path unit, a mechanical unit, a control unit, a protective gas sealing unit and software, wherein the software is used for realizing printing according to the scanning strategy method.

The optical path unit mainly comprises an optical fiber laser, a beam expanding lens, a reflecting mirror, a scanning galvanometer, a focusing lens and the like. The laser is the most core component in the laser selective melting device and directly determines the forming quality of the whole device. Because the quality of laser beams is good, the laser beams can be gathered into superfine beams, and the output wavelength of the laser beams is short, the fiber laser has very obvious advantages in selective laser melting and rapid forming of precise metal parts. The beam expander is an optical component essential for adjusting the quality of the light beam, and the beam expander is adopted in a light path to enlarge the diameter of the light beam, reduce the divergence angle of the light beam and reduce energy loss. The scanning galvanometer is driven by a motor and is controlled by a computer, so that laser spots can be accurately positioned at any position of a processing surface. In order to overcome the distortion of the scanning galvanometer unit, a special flat field scanning lens is needed, so that the focusing light spot obtains consistent focusing characteristics in a scanning range.

The mechanical unit mainly comprises a powder spreading device, a forming cylinder, a powder cylinder, forming chamber sealing equipment and the like. The powder spreading quality is a key factor influencing the SLM forming quality, and two types of powder spreading devices, namely a powder spreading brush and a powder spreading roller, are mainly arranged in the SLM equipment at present. The forming cylinder and the powder cylinder are controlled by a motor, and the forming precision of the SLM is also determined by the control precision of the motor.

The control system consists of a computer and a plurality of control cards, and the laser beam scanning control is that the computer sends a control signal to the scanning galvanometer through the control cards to control the X/Y scanning galvanometer to move so as to realize laser scanning. The equipment control system completes the machining operation of the parts. The method mainly comprises the following functions: (1) System initialization, state information processing, fault diagnosis and man-machine interaction functions; (2) Various controls are carried out on the motor system, and motion control of the forming piston, the powder supply piston and the powder spreading roller is provided; (3) Controlling the scanning galvanometer, and setting the movement speed, the scanning delay and the like of the scanning galvanometer; (4) Setting various parameters of automatic molding equipment, such as adjusting laser power, ascending and descending parameters of a molding cylinder and a powder spreading cylinder, and the like; (5) Provides the coordination control of five motors of the molding equipment to finish the processing operation of parts.

According to yet another aspect of the application, a processor is provided for executing software for performing the 3D printing method. According to the requirements of SLM technology, professional software involved in the SLM technology mainly comprises three types: slicing software, scan path generation software, and device control software. The slicing processing implemented by the slicing software is one of key contents of the rapid prototyping software, and the function of the slicing software is to convert a three-dimensional CAD model of a part into a two-dimensional slicing model to obtain layer-by-layer section contour data. In the SLM process, the most basic operation is to control the laser to scan. Since the cross-sectional information obtained by layering is contour data, it is necessary to perform internal filling. The function of the scan path generation software is to generate a fill scan path from the profile data. The master control software mainly controls the forming process, displays the processing state and further realizes human-computer interaction.

According to yet another aspect of the present application, there is provided a memory for storing software for performing the 3D printing method.

It should be noted that the 3D printing performed by the software is the same as the 3D printing described above, and is not described herein again.

In this embodiment, an electronic device is provided, comprising a memory in which a computer program is stored and a processor configured to run the computer program to perform the method in the above embodiments.

These computer programs may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks, and corresponding steps may be implemented by different modules.

The programs described above may be run on a processor or stored in memory (or referred to as computer-readable media), which includes both non-transitory and non-transitory, removable and non-removable media, that enable storage of information by any method or technology. The information may be computer readable instructions, data structures, modules of a program, or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static Random Access Memory (SRAM), dynamic Random Access Memory (DRAM), other types of Random Access Memory (RAM), read Only Memory (ROM), electrically Erasable Programmable Read Only Memory (EEPROM), flash memory or other memory technology, compact disc read only memory (CD-ROM), digital Versatile Discs (DVD) or other optical storage, magnetic cassettes, magnetic tape magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information that can be accessed by a computing device. As defined herein, a computer readable medium does not include a transitory computer readable medium such as a modulated data signal and a carrier wave.

The above are merely examples of the present application and are not intended to limit the present application. Various modifications and changes may occur to those skilled in the art to which the present application pertains. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A3D printing method of a hole structure is used for anti-collision protection, and is characterized in that: scanning and printing layer by using a laser selective melting method, wherein when each layer is scanned and printed, a closed area is formed by scanning and printing more than or equal to 2 circles around the edge of the layer from outside to inside, and the contact ratio between each circle and the adjacent circle in the width direction of a printing path is 20% -30%; then printing the inside of the closed area; when printing the inside of the closed area, firstly printing at least one circle around the edge of the hole inside the closed area, and then printing the rest positions;

wherein, the first and the second end of the pipe are connected with each other,

the scanning speed when scanning and printing around the edge of the layer is lower than the scanning speed when printing inside the closed area; the laser power during scanning and printing around the edge of the layer is larger than that during printing inside the closed area;

when the inside of the closed area is printed, taking an end point when scanning and printing are carried out around the edge of the layer as a starting point, and calculating a hole with the shortest distance from each point of the edge of each hole in the current closed area to the starting point as a starting printing hole of the closed area; and taking the end point of the hole which is printed around the previous hole as a starting point, and calculating the hole with the shortest distance from each point of the edge of each unprinted hole in the current closed area to the starting point as the next hole to be printed.

2. The method of claim 1, wherein: the scanning speed of the first scanning printing around the edge of the layer is 1700mm/s-2000mm/s, and the scanning speed of the inner part of the closed area is 2000mm/s-2700mm/s.

3. The method of claim 1, wherein: the laser power during scanning and printing around the edge of the layer is 300W-340W, and the laser power during printing inside the closed area is 230W-300W.

4. The method of claim 1, wherein: the first scanning at least one circle around the edge of the layer comprises: the printing was done around the edge of the layer in an outside-in order for 3 weeks.

5. The utility model provides a 3D printing system of hole structure which characterized in that: the device comprises an optical path unit, a mechanical unit, a control unit, a protective air sealing unit and software, wherein the software is used for realizing printing according to the method of any one of claims 1 to 4.