CN110170652B - Variable area forming surface printing device and printing method thereof - Google Patents

Abstract

The invention discloses a variable area molding surface printing device and a printing method thereof. The device comprises a cooling system, a laser source, a diode laser array module, a collimating lens, a focusing lens, a workbench, a powder bed and a guide rail. In this device, an array of diode lasers is mounted on a substrate, all of which can cover the entire print area. When the metal powder of each layer is paved according to the set layer thickness, the laser beam projected by the laser source is started according to the preset printing path, the laser above the printing area is turned on, the laser above the non-printing area is turned off, and the next layer of metal powder is paved after the printing of the current layer is finished until the whole printing process is finished. Due to the fact that the device adopts the surface printing mode, compared with the line-by-line scanning printing of the traditional method, SLM printing efficiency can be greatly improved, and quality problems such as warping caused by too large scanning distance are solved.

Description

Variable area forming surface printing device and printing method thereof

Technical Field

The invention relates to a 3D printing technology, in particular to a surface printing device with variable region forming and a printing method thereof.

Background

The 3D printing technology has become an important technology indispensable in the current rapid prototyping means, and the Selective Laser Melting (SLM) technology was first proposed in 1995 by the germany froounhofer institute, and the working principle is similar to SLS. The SLM is to convert the energy of laser into heat energy to shape the metal powder, and the main difference is that SLS does not completely melt the metal powder during the manufacturing process, and SLM is shaped after the metal powder is heated to be completely melted during the manufacturing process. The SLM working process is that a printer controls laser to selectively irradiate the powder above the laid powder, and the metal powder is heated to be completely melted and then is molded. Then the piston makes the working table lower by one unit height, a new layer of powder is spread on the formed current layer, the equipment calls the data of the section of the new layer to carry out laser melting and is bonded with the section of the previous layer, and the process is circulated layer by layer until the whole object is formed. The entire process of SLM is performed in a process chamber protected with inert gas to avoid oxidation of the metal at high temperatures.

By the SLM printing principle it is known that: each final part is made by melting one layer after another, and each melted layer, the platform is lowered and new powder is spread over the layer and the process is repeated. The real forming principle is that laser irradiates energy with certain energy density to a powder layer, so that the powder in a scanned area reaches a molten state, the energy density received by the powder is related to a plurality of factors of the laser, such as scanning speed, scanning interval and scanning power, the energy of the laser forms a molten pool in a heat affected zone on the surface of the metal powder, and the molten pool affects the forming and welding effect of the surrounding powder. The laser can scan a melting area to be formed according to a certain rule and direction, the scanning area is divided into a strip shape, a chessboard shape and the like according to reasonable regression scanning paths of different materials, the internal stress of the part can be effectively released, and the internal defects can be reduced by planning each layer of scanning vectors to obtain the part with higher density and better mechanical property. However, a significant amount of material can be saved as compared to conventional subtractive manufacturing. SLM technical limitations: the molding speed is low, and a thinner processing layer thickness is required to improve the processing accuracy. The time taken to machine small volume parts is also long, and therefore difficult to apply to large scale manufacturing.

From the above analysis, it is known that the laser scanning pitch, scanning speed and laser power play a crucial role in the molding efficiency. If the printing efficiency is to be improved, the scanning surface interval can be increased, but the range of a molten pool is limited, and if the interval is too large, the overlapping rate of the cladding width is too small, and the surface quality of a formed part is seriously reduced; the scanning speed has a large influence on the density, the density is the highest when the scanning speed is 60mm/s, and the scanning speed is reduced along with the reduction of the scanning speed under different scanning intervals, but the scanning speed is reduced, so that the forming surface has serious spheroidization and rough and porous surface, and the scanning speed during the SLM forming of the powder is 60-90 mm/s; when the laser power is reduced, the density of the part is correspondingly reduced, the energy absorbed by the powder can be increased by increasing the laser power, the melting amount of powder particles is increased, the viscosity and the surface tension of the melt are reduced, the depth and the width of a molten pool are increased, the bonding force among the particles is increased, the forming quality and the density of the part are improved, under the same energy density, the energy is concentrated on the upper surface along with the increase of the diameter of a light spot, the powder below each layer cannot be well influenced by the laser molten pool to be effectively melted, and the quality of the part is directly influenced. The tensile strength in the direction perpendicular to the part is lowered, and cracks are more likely to occur.

Through examination of the prior art, papers and patents, the method for increasing the scan area pitch or increasing the laser scanning power in the prior art is essentially a line scanning mode, and is different from the line pitch size, the line scanning mode and the laser power size, but the scan area pitch, the laser power and the scan speed must be within a certain range, and the surface quality of the formed part is reduced after a certain threshold value is exceeded. Therefore, the SLM printing efficiency is improved by the conventional method and stays at a variable quantity level, and the method aims at improving the SLM progressive scanning mode and changing the scanning mode into area-surface printing, and aims to improve the SLM printing efficiency and improve the forming quality.

Disclosure of Invention

In order to overcome the defects in the background technology, the invention aims to provide a variable area forming surface printing device and a printing method thereof, and the printing device has the advantages of reasonable structural design, complete system, and capability of improving the SLM printing efficiency and improving the SLM forming quality.

The technical scheme adopted by the invention for solving the problems is as follows:

variable area forming surface printing device

The laser power generation device comprises a cooling system, a laser source, a diode laser array module, a collimating lens, a focusing lens, a workbench, a powder bed and a guide rail; the laser source is positioned in the cooling system, laser beams in the diode laser array module are projected into a powder bed of the workbench through the collimating lens and the focusing lens through optical fibers, a formed part is formed on the powder bed, and the bottom of the workbench can move on the guide rail.

The diode laser array module comprises a plurality of diode lasers which are arranged on a substrate in an array mode.

The area of a laser projection area projected by the diode laser array module is the same as the area of the minimum enclosing rectangle of the maximum cross-sectional outline of the CAD model.

The diode laser array module increases or decreases the number of lasers according to the minimum surrounding rectangular area of the maximum cross section outline of the CAD model, and the area of a laser projection area is not smaller than the rectangular area.

Secondly, a printing method of a variable area molding surface printing device, the printing method comprises the following steps:

step 1) inputting a CAD model to layer the model and determining outline data of each layer;

step 2) determining the mutual inclusion relation of each outline of each layer;

step 3) determining the specification and the number of the diode laser arrays;

step 4), determining a printing path of the diode laser array on the current layer;

step 5) determining the opening and closing state of the diode laser array according to the printing path and printing;

and 6) updating the next layer of profile data, judging whether the profiles of all layers are printed, if so, finishing, otherwise, continuously executing the steps 4) -5) until the printing finishing condition is met.

In the step 4), the specific step of determining the printing path of the diode laser array on the current layer is as follows:

step 4-1) extracting all contour curve sets C of the current layer;

step 4-2) assuming that the number of lasers in the X direction is m, the number of lasers in the Y direction is n, and the coordinates of the lasers in the jth row and ith column are (X)_i，y_j) Wherein j is more than or equal to 1 and less than or equal to m, and l is more than or equal to 1 and less than or equal to r;

step 4-3) for per (x)_i0) and perpendicular to X_iCalculating l_iThe intersection points with the curve set C are removed, the intersection points tangent to the curve set C are eliminated, and the intersection points are respectively marked as (x)_i，y₁)，(x_i，y₂)，...，(x_i，y_k)；

Step 4-4) judging the opening and closing state of the laser in the ith row according to the intersection point condition;

and 4-5) sequentially judging the opening and closing states of the 1,2, …, m lasers according to the step 4-3) and the step 4-4).

In the specific step of determining the open-close state of each laser in the current printing area, the open-close state of the laser in the ith column is judged according to the intersection point condition, and the specific judgment rule is as follows:

at the intersection point (x)_k，y₁) And intersection point (x)_k+1，y₁) All the lasers in the middle are started, wherein k is an odd number;

at the intersection point (x)_k，y₁) And intersection point (x)_k+1，y₁) The lasers in between are all off, where k is an even number.

The invention has the beneficial effects that:

compared with the line-by-line scanning printing of the traditional method, the SLM printing method has the advantages that the surface printing mode is adopted, the SLM printing efficiency can be greatly improved, and the quality problems of warping and the like caused by overlarge scanning distance are solved.

Drawings

Fig. 1 is a schematic structural view of the present invention.

Fig. 2 is a schematic perspective view of the present invention.

Fig. 3 is a schematic diagram of the switching of all lasers in the embodiment of the present invention.

Fig. 4 is a schematic of the laser turning on at each layer cross-sectional profile in an embodiment of the present invention.

Fig. 5 is a schematic diagram of the opening and closing of each laser in each row of lasers in the embodiment of the present invention.

Fig. 6 is a flowchart of a face printing method for variable area molding according to an embodiment of the present invention.

In the figure: 1. cooling system, 2, laser source, 3, diode laser array module, 4, collimating lens, 5, laser beam, 6, focusing lens, 7, workbench, 8, powder bed, 9, molded part, 9.1, molded part inner contour, 9.2, molded part outer contour, 10, guide rail, 11, optical fiber.

Detailed Description

The invention will be further described by way of example with reference to the accompanying drawings.

As shown in fig. 1 and 2, the present invention includes a cooling system 1, a laser source 2, a diode laser array module 3, a collimating lens 4, a focusing lens 6, a work table 7, a powder bed 8, and a guide rail 10; the laser source 2 is positioned in the cooling system 1, the laser beam 5 in the diode laser array module 3 is projected into the powder bed 8 of the worktable 7 through the collimating lens 4 and the focusing lens 6 by the optical fiber 11, the molded piece 9 is formed on the powder bed 8, and the bottom of the worktable 7 can move on the guide rail 9.

The diode laser array module 3 includes a plurality of diode lasers, and is arranged on the substrate in an array manner.

The area of the laser projection area projected by the diode laser array module 3 is the same as the area of the minimum enclosing rectangle of the maximum cross-sectional outline of the CAD model.

The diode laser array module 3 increases or decreases the number of lasers according to the minimum surrounding rectangular area of the maximum cross-sectional profile of the CAD model, and the area of a laser projection area is not smaller than the rectangular area.

Fig. 2 is a perspective view of the printing apparatus of the present invention, in which a laser source 2 is connected to a laser array module 3 through an optical fiber 11, and the projected laser projection area is the same as the minimum enclosed rectangular area of the maximum cross-sectional profile of the printing model, and these laser beams 5 can be turned on or off by using a single laser diode in parallel.

The following detailed description of the determination of the laser on/off state is given in conjunction with fig. 3-5:

in this embodiment, for convenience of illustration, each small circle in fig. 3-5 represents a laser, wherein the number of lasers is not the same as in fig. 2; in addition, in actual printing, the number of lasers is also set according to the size of the actual molded part, as described in claim 4.

As shown in fig. 3, the diode laser array module corresponds to the entire printing area, under which there are an inner profile 9.1 of the molded part and an outer profile 9.2 of the molded part, wherein the lasers outside the profile 9.2 of the molded part are all in the off state, the lasers between the inner profile 9.1 of the molded part and the outer profile 9.2 of the molded part are all in the on state, and the lasers within the inner profile 9.1 of the molded part are all in the off state. Wherein the lasers of the hollow circular part are all in a closed state, and the solid circular part indicates that the lasers are opened, namely, the area is an area to be printed

Model at each slice section, the corresponding lasers at the contour are shown in fig. 4, both in the on state and as the marking lasers for each column of lasers on and off.

As shown in fig. 5, given the X-coordinate of each column, the intersection of a straight line passing through the X-point and perpendicular to the X-axis with the inner profile 9.1 of the molded part and the outer profile 9.2 of the molded part, i.e. the marking lasers P1, P2, P3, P4, can be determined. If the lasers designated as P1, P2, P3 and P4 are the 1 st, 2 nd, 3 rd and 4 th lasers, respectively, according to the specific judgment rule of the on-off state of the ith row of lasers, all the lasers P1 to P2 are turned on, all the lasers P2 to P3 are turned off, and all the lasers P3 to P4 are turned on.

As shown in fig. 6, the printing method of the variable area forming surface printing apparatus of the present invention comprises the steps of:

step 1) layering a CAD three-dimensional model and determining profile data of each layer: generally, a given three-dimensional digital model is an STL file, a specified layering thickness is set for the STL file, and the model is layered according to the layering thickness to obtain profile data of each layer;

step 2) determining the inclusion relation of each layer of outline, thereby obtaining the data of the inner outline and the outer outline;

step 3) determining the area of a printing area according to the minimum bounding rectangle of the maximum section of the CAD model, and further determining the specification and the number of the laser arrays;

step 4) the printing path under surface printing actually divides the laser array period according to the profile data under the current section, ensures that each row of lasers corresponds to the whole printing area, and digitally marks all the lasers, thereby determining the marked lasers which are opened and closed in each row

Step 5) determining the opening and closing state of each laser in the current printing area: making a straight line of each row of lasers, wherein the straight line has intersection points with each contour curve inevitably in a printing area, the intersection points are marking lasers which are opened and closed in the row, further determining the opening and closing states of all the lasers in the row, and printing the current layer according to the determined opening and closing states of the lasers;

and 6) updating the next layer of profile data, judging whether the profiles of all the layers are printed, if so, finishing, otherwise, executing the steps 4) -5) and continuing printing until all the layers are printed.

In the step 4), the specific step of determining the printing path of the diode laser array on the current layer is as follows:

step 4-1) extracting all contour curve sets C of the current layer;

step 4-2) assuming that the number of lasers in the X direction is m, the number of lasers in the Y direction is n, and the coordinates of the lasers in the jth row and ith column are (X)_i，y_j) Wherein j is more than or equal to 1 and less than or equal to m, and i is more than or equal to 1 and less than or equal to r;

step 4-3) for per (x)_i0) and perpendicular to X_iCalculating l_iThe intersection points with the curve set C are removed, the intersection points tangent to the curve set C are eliminated, and the intersection points are respectively marked as (x)_i，y₁)，(x_i，y₂)，...，x_i，y_k)；

Step 4-4) judging the opening and closing state of the laser in the ith row according to the intersection point condition;

and in the step 4-5), the opening and closing states of the 1,2, …, m-column lasers are sequentially judged according to the step 4-3) and the step 4-4).

In the specific step of determining the open-close state of each laser in the current printing area, the open-close state of the laser in the ith column is judged according to the intersection point condition, and the specific judgment rule is as follows:

at the intersection point (x)_k，y₁) And intersection point (x)_k+1，y₁) All the lasers in the middle are started, wherein k is an odd number;

at the intersection point (x)_k，y₁) And intersection point (x)_k+1，y₁) The lasers in between are all off, where k is an even number.

Claims (1)

1. A printing method of a variable area forming surface printing device comprises a cooling system (1), a laser source (2), a diode laser array module (3), a collimating lens (4), a focusing lens (6), a workbench (7), a powder bed (8) and a guide rail (10); the laser source (2) is positioned in the cooling system (1), laser beams (5) in the diode laser array module (3) are projected into a powder bed (8) of the workbench (7) through a collimating lens (4) and a focusing lens (6) through an optical fiber (11), a formed part (9) is formed on the powder bed (8), and the bottom of the workbench (7) can move on a guide rail (10);

the diode laser array module (3) comprises a plurality of diode lasers which are arranged on a substrate in an array manner;

the area of a laser projection area projected by the diode laser array module (3) is the same as the minimum surrounding rectangular area of the maximum cross-sectional profile of the CAD model;

the diode laser array module (3) increases or decreases the number of lasers according to the minimum surrounding rectangular area of the maximum cross-sectional profile of the CAD model, so as to ensure that the area of a laser projection area is not smaller than the rectangular area;

the printing method of the device is characterized by comprising the following steps:

step 1) inputting a CAD model to layer the model and determining outline data of each layer;

step 2) determining the mutual inclusion relation of each outline of each layer;

step 3) determining the specification and the number of the diode laser arrays;

step 4) determining a printing path of the diode laser array on the current layer, specifically:

step 4-1) extracting all contour curve sets C of the current layer;

step 4-2) assuming that the number of lasers in the X direction is m, the number of lasers in the Y direction is n, and the coordinates of the lasers in the jth row and ith column are (X)_i，y_j) Wherein j is more than or equal to 1 and less than or equal to m, and i is more than or equal to 1 and less than or equal to n;

step 4-3) for per (x)_i0) and perpendicular to X_iCalculating l_iThe intersection points with the curve set C are removed, the intersection points tangent to the curve set C are eliminated, and the intersection points are respectively marked as (x)_i，y₁)，(x_i，y₂)，.. ，(x_i，y_k)；

Step 4-4) judging the opening and closing state of the laser in the ith row according to the intersection point condition;

the specific judgment rule is as follows:

at the intersection point (x)_i,y_k) And intersection point (x)_i,y_k+1) All the lasers in the middle are started, wherein k is an odd number;

at the intersection point (x)_i,y_k) And intersection point (x)_i,y_k+1) All lasers in between are off, where k is an even number;

step 4-5) is to sequentially judge the opening and closing states of the 1,2, …, m-line lasers according to the step 4-3) and the step 4-4);

step 5) determining the opening and closing state of the diode laser array according to the printing path and printing;

and 6) updating the next layer of profile data, judging whether the profiles of all layers are printed, if so, finishing, otherwise, continuously executing the steps 4) -5) until the printing finishing condition is met.

Images