System and method for variable-speed laser forming of continuous gradient materials

Abstract

The invention relates to the technical field of selective laser melting additive manufacturing, and provides a system and method for variable-speed laser forming of a continuous gradient material, and the system comprises a powder laying module used for laying a gradient powder layer on a workbench; the laser module is used for emitting laser with different scanning speeds to the gradient powder layer on the workbench according to areas; and the control module is used for dividing the powder bed into a plurality of rows and a plurality of columns of characteristic rectangles, selecting the characteristic rectangles in the two-dimensional outline of the printed part slice as to-be-printed characteristic rectangles, assigning printing parameters of each to-be-printed characteristic rectangle, arranging the printing direction and sequence of the to-be-printed characteristic rectangles, and controlling the laser module and the powder spreading module. The method uses the system. Compared with existing equipment, laser scanning parameters can be dynamically adjusted to be matched with powder bed material characteristics, the excellent metallurgy densification effect is achieved, and the defects in the prior art are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of laser selective melting additive manufacturing, and in particular to a system and method for variable speed laser forming continuous gradient materials. Background Art

[0002] With the development of science and technology and the progress of society, people's requirements for the performance of materials are increasing day by day. Traditional single materials or ordinary composite materials can no longer meet these needs. Continuous gradient materials are a new type of composite materials whose composition and structure change continuously in a gradient manner inside the material. This material is composed of two or more materials with different properties. There is no obvious interface between them. Seamless connection is achieved through the gradual transition of components. This continuously changing structure enables the material to better exert the characteristics of various materials while avoiding the risk of damage caused by interface problems. This characteristic of continuous gradient materials enables it to show broad application prospects in many fields such as nuclear energy, electronics, optics, chemistry, electromagnetism, biomedicine, etc. It currently has high use value and broad application prospects in many fields such as aerospace, biomedicine, energy engineering, mechanical engineering, electromagnetism and nuclear engineering. At the same time, the preparation of gradient materials is also an international cutting-edge technology.

[0003] Additive manufacturing, as an emerging manufacturing method, is used to prepare continuous gradient materials due to its unique advantages of point-by-point and layer-by-layer construction. Among them, selective laser melting technology is widely used due to its high precision and excellent performance.

[0004] At present, the method of preparing continuous gradient materials by selective laser melting technology is to use a single laser parameter to scan the gradient powder bed. However, in practice, it is found that in the gradient powder layer, the physical properties of the material such as melting point, density, laser absorptivity, etc. change with the composition, and the corresponding laser processing parameters and scanning process also change accordingly. Therefore, the traditional single laser parameter scanning process cannot achieve metallurgical densification of a specific gradient powder layer. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide a system and method for variable speed laser forming of continuous gradient materials, which can be used for forming continuous gradient materials in different selected area laser melting equipment, adjusting the laser scanning speed according to the physical properties of different powders in the gradient layering, and realizing the metallurgical densification of the gradient powder layer.

[0006] The present invention adopts the following technical solution:

[0007] In one aspect, the present invention provides a system for variable speed laser forming continuous gradient materials, including a powder spreading module, a laser module, a control module and a workbench:

[0008] The powder laying module is used to lay a gradient powder layer on the workbench, and the area where the gradient powder layer is located is the powder bed;

[0009] The laser module is used to emit lasers with different scanning speeds to the gradient powder layer on the workbench according to regions;

[0010] The control module is used to divide the powder bed into a plurality of rows and columns of feature rectangles, select the feature rectangles within the two-dimensional contour of the printed part slice as the feature rectangles to be printed, assign printing parameters to each feature rectangle to be printed, arrange the printing direction and order of the feature rectangles to be printed, and control the laser module and the powder spreading module;

[0011] The control module is respectively controlled and connected with the powder spreading module and the laser module.

[0012] According to any possible implementation described above, there is further provided an implementation, wherein the control module includes a powder bed segmentation unit, a feature rectangle selection unit, a parameter setting unit, and a path planning unit;

[0013] The powder bed segmentation unit is used to segment the entire powder bed into characteristic rectangles that are closely arranged in multiple rows and columns;

[0014] The feature rectangle selection unit selects the feature rectangle located inside the slice two-dimensional contour as the feature rectangle to be printed according to the slice analysis of the printed part, and deletes other feature rectangles located outside the slice two-dimensional contour;

[0015] The parameter setting unit sets the laser scanning speed according to the composition characteristics of the powder layer of each feature rectangle to be printed;

[0016] The path planning unit is used to arrange the laser scanning sequence of the feature rectangles to realize the planning of the scanning path;

[0017] The powder bed segmentation unit, the feature rectangle selection unit, the parameter setting unit, and the path planning unit are all integrated into a controller or a computer.

[0018] As any possible implementation described above, there is further provided an implementation, wherein the width of the characteristic rectangle is equal to the laser scanning interval, and the laser performs only a single scan on each characteristic rectangle.

[0019] Any possible implementation as described above further provides an implementation, wherein the length of the characteristic rectangle is determined through experiments according to the composition characteristics and gradient distribution of the gradient powder layer, and the laser scanning speed is finely adjusted by adjusting the length of the characteristic rectangle.

[0020] As any possible implementation described above, there is further provided an implementation, wherein the control module further includes a user input interface for inputting powder composition information and adjusting laser scanning parameters.

[0021] On the other hand, the present invention also provides a method for variable speed laser forming continuous gradient material, the method using the above system, the method comprising:

[0022] S1. Slicing of parts to be printed: Slice and analyze the parts to be printed to generate a two-dimensional profile of the slices;

[0023] S2, powder bed segmentation: the entire powder bed is divided into multiple rectangular areas with multiple rows and columns, each rectangular area is a feature rectangle and corresponds to a specific position of the powder bed;

[0024] S3, feature rectangle selection: according to the two-dimensional contour of the slice, the feature rectangle located inside the two-dimensional contour is selected as the feature rectangle to be printed, and the feature rectangle outside the two-dimensional contour is deleted;

[0025] S4, parameter setting and allocation: assigning laser scanning parameters to each feature rectangle to be printed according to the gradient material composition;

[0026] S5, printing sequence optimization: set the printing sequence for each feature rectangle to be printed, so that the laser scanning path is as continuous as possible and changes continuously along the powder bed gradient direction;

[0027] S6. Gradient powder laying: The scraper scrapes the gradient powder into the designated position of the workbench to complete the gradient layered laying;

[0028] S7, laser melting forming: turn on the laser module, scan the feature rectangle to be printed according to the set scanning path and laser scanning parameters, and realize the melting forming of the continuous gradient material of this layer;

[0029] S8. Repeat steps S3-S7 until the part printing is completed.

[0030] Any possible implementation as described above further provides an implementation method, firstly establishing a "gradient material-laser scanning parameter" database, determining the corresponding laser scanning parameters through experiments according to the composition and proportion of different gradient materials, and storing them in the database, and in step S4, the control module directly reads the laser scanning parameters from the database according to the composition and proportion of the gradient material.

[0031] Any possible implementation as described above further provides an implementation, in which in step S4, the scanning speed of the components at both ends of the gradient material is manually input through the user input interface of the control module, and the parameter setting unit automatically allocates laser scanning parameters for each feature rectangle to be printed using a linear interpolation method.

[0032] Any possible implementation as described above further provides an implementation, in which when two adjacent layers are printed, the laser scanning direction is rotated to change the acute angle θ formed by the long side of the characteristic rectangle and the straight line where the powder gradient direction is located, thereby reducing the residual stress generated by printing.

[0033] As any possible implementation described above, there is further provided an implementation, in which the acute angle θ formed by the long side of the characteristic rectangle and the straight line where the powder gradient direction is located is 0°-90°.

[0034] The beneficial effects of the present invention are:

[0035] By precisely controlling the laser scanning speed and path, combined with the computer system's intelligent segmentation of the powder bed and the assignment of printing parameters to the characteristic rectangles, the laser scanning speed can be continuously changed during the printing process, thereby achieving the best match between laser energy and powder properties, more efficiently constructing continuous gradient materials, and ultimately achieving the densification of continuous gradient materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The figure shows a schematic diagram of the working principle of the present invention for realizing laser speed change.

[0037] Figure 2 Shown is a schematic diagram of powder bed segmentation and scanning path of Example 1.

[0038] Figure 3 Shown is a schematic diagram of selecting feature rectangles to be printed in Example 1.

[0039] Figure 4 Shown is a schematic diagram of the characteristic rectangular arrangement of Example 2.

[0040] Figure 5 Shown is a schematic diagram of powder bed segmentation and scanning path of Example 2.

[0041] Figure 6 The figure shows a schematic diagram of selecting a feature rectangle to be printed in Example 2.

[0042] Figure 7 The figure shows a comparative example of a prior art part formed using a single laser scanning parameter.

[0043] Figure 8 The figure shows a physical picture of Example 3, in which a complex part is formed using the system and method of the present invention for variable speed laser forming of continuous gradient materials.

[0044] In the figure: 1. Initial velocity of single-channel variable-speed laser; 2. Feature rectangle; 3. Parallel gradient direction; 4. Workbench; 5. Powder bed; 6. Final velocity of single-channel variable-speed laser; 7. Laser module; 8. Scanning path; 9. Two-dimensional contour; 10. Angle between laser scanning direction and gradient direction. DETAILED DESCRIPTION

[0045] The specific embodiments of the present invention will be described in detail below in conjunction with specific drawings. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered isolated, and they can be combined with each other to achieve better technical effects.

[0046] The embodiment of the present invention provides a system for variable speed laser forming continuous gradient materials, including a powder spreading module, a laser module 7, a control module and a workbench 4:

[0047] The powder laying module is used to lay a gradient powder layer on the workbench 4, and the area where the gradient powder layer is located is the powder bed;

[0048] The laser module 7 is used to emit lasers with different scanning speeds to the gradient powder layer on the workbench 4 according to regions;

[0049] The control module is used to divide the powder bed into a plurality of rows and columns of feature rectangles 2, select the feature rectangles 2 within the two-dimensional outline 9 of the printed part slice as the feature rectangles to be printed, assign printing parameters to each feature rectangle 2 to be printed, arrange the printing direction and order of the feature rectangles 2 to be printed, and control the laser module 7 and the powder spreading module;

[0050] The control module is controlled and connected with the powder spreading module and the laser module 7 respectively.

[0051] In a specific embodiment, the control module includes a powder bed segmentation unit, a feature rectangle selection unit, a parameter setting unit, and a path planning unit;

[0052] The powder bed segmentation unit is used to segment the entire powder bed into characteristic rectangles 2 that are closely arranged in multiple rows and columns;

[0053] The feature rectangle selection unit selects the feature rectangle 2 located inside the slice two-dimensional contour 9 as the feature rectangle to be printed according to the slice analysis of the printed part, and deletes other feature rectangles 2 located outside the slice two-dimensional contour;

[0054] The parameter setting unit sets the laser scanning speed according to the composition characteristics of the powder layer of each feature rectangle 2 to be printed;

[0055] The path planning unit is used to arrange the laser scanning sequence of the feature rectangle 2 to realize the planning of the scanning path;

[0056] The powder bed segmentation unit, the feature rectangle selection unit, the parameter setting unit, and the path planning unit are all integrated into a controller or a computer.

[0057] In a specific embodiment, the width of the characteristic rectangle 2 is equal to the laser scanning interval, and the laser performs only a single-pass scanning on each characteristic rectangle 2 .

[0058] In a specific embodiment, the length of the characteristic rectangle 2 can be experimentally determined in a numerical range according to the composition characteristics and gradient distribution of the gradient powder layer; and fine adjustment of the laser scanning speed can be achieved by adjusting the length of the characteristic rectangle 2 .

[0059] In a specific embodiment, the control module further includes a user input interface for inputting powder composition information and adjusting laser scanning parameters.

[0060] An embodiment of the present invention provides a method for variable speed laser forming of a continuous gradient material, the method using the above system, and the method comprising:

[0061] S1, slicing the parts to be printed: slicing and analyzing the parts to be printed, and generating a two-dimensional contour of the slices 9;

[0062] S2, powder bed segmentation: the entire powder bed is divided into a plurality of rectangular areas with multiple rows and columns, each rectangular area is a feature rectangle 2 and corresponds to a specific position of the powder bed;

[0063] S3, feature rectangle 2 selection: according to the sliced ​​two-dimensional contour 9, the feature rectangle 2 located inside the two-dimensional contour 9 is selected as the feature rectangle to be printed, and the feature rectangle 2 outside the two-dimensional contour 9 is deleted;

[0064] S4, parameter setting and allocation: assigning laser scanning parameters to each feature rectangle 2 to be printed according to the gradient material composition;

[0065] S5, printing sequence optimization: setting the printing sequence for each feature rectangle 2 to be printed, so that the laser scanning path 8 is as continuous as possible and changes continuously along the powder bed gradient direction;

[0066] S6, gradient powder laying: the scraper scrapes the gradient powder into the specified position of the workbench 4 to complete the gradient layered laying;

[0067] S7, laser melting forming: turn on the laser module 7, scan the feature rectangle 2 to be printed according to the set scanning path 8 and laser scanning parameters, and realize the melting forming of the continuous gradient material of this layer;

[0068] S8. Repeat steps S3-S7 until the part printing is completed.

[0069] In a specific embodiment, a "gradient material-laser scanning parameter" database can be first established, and the corresponding laser scanning parameters can be determined through experiments according to the composition and proportion of different gradient materials, and stored in the database. In step S4, the control module reads the laser scanning parameters directly from the database according to the composition and proportion of the gradient material.

[0070] In a specific embodiment, in step S4, the scanning speeds (initial speed 1 and final speed 6) of the components at both ends of the gradient material are manually input through the user input interface of the control module, and the parameter setting unit automatically assigns laser scanning parameters to each feature rectangle 2 to be printed using a linear interpolation method.

[0071] In a specific embodiment, when two adjacent layers are printed, the laser scanning direction is rotated to change the acute angle θ formed by the long side of the characteristic rectangle and the straight line where the powder gradient direction is located, thereby reducing the residual stress generated by printing.

[0072] In a specific embodiment, the acute angle θ formed by the long side of the characteristic rectangle and the straight line where the powder gradient direction is located is in a range of 0°-90°.

[0073] Technical principle of the present invention:

[0074] Melting point difference is an important factor affecting the printing of gradient materials, and it is more advantageous in printing gradient materials with large melting point differences (such as Cu and Fe). Powders with high melting points require higher energy input, greater laser power and / or lower scanning speeds; powders with low melting points require lower energy input, smaller laser power and / or higher scanning speeds. In a gradient powder layer, powders at different composition positions require different energy inputs, and a gradually faster laser scanning speed is required from the low melting point end to the high melting point end.

[0075] In addition to the difference in melting point, the material's absorption efficiency of the laser will also affect the printing effect. The powder's absorption rate of the laser directly affects the energy absorbed by the powder. If the laser absorption rate is too low, most of the energy will be reflected. Even if the laser input energy meets the powder melting requirements, the powder cannot be effectively melted. Therefore, for materials with large differences in laser absorption rates (Cu has a very low laser absorption rate), even if the melting point difference is not large, different energy inputs are required, and variable speed scanning can achieve gradually changing energy input on the gradient powder layer.

[0076] In actual practice, if the laser power is adjusted, frequent rapid changes in laser power will have an adverse effect on the life of the laser. The laser needs time to stabilize the output during the power change process. Frequent rapid changes will cause the internal components of the laser to overheat or be damaged, shortening the service life of the laser. When the number of characteristic rectangles in the gradient direction of this application is large, the laser will have to change the power quickly all the time, which will have some negative effects on the laser. Therefore, under current technical conditions, it is not recommended to regulate the power. However, it does not rule out the possibility of directly regulating the laser power when the technology is iteratively advanced.

[0077] like Figure 1 As shown, the control module cuts the powder bed of a certain width in the gradient direction 3 into n feature rectangles 2. The width of the powder bed and the width of the feature rectangle 2 jointly determine the value of n, and the width of the feature rectangle 2 is the laser scanning spacing. For each feature rectangle 2, the laser scanning path 8 scans along the longer side, and each feature rectangle 2 is only scanned once. The initial speed 1 and the final speed 6 are input, and the control module assigns the value of the laser scanning speed to each feature rectangle in between according to the value of n, so that the laser scanning speed changes continuously from the initial speed 1 to the final speed 6. Next, the control module adjusts the scanning direction and printing order of each feature rectangle 2 to realize continuous scanning of the laser and planning of the scanning path, and finally realizes controllable variable speed scanning of the laser in the gradient direction of the powder bed.

[0078] Example 1

[0079] The length of the powder bed 5 is a, the width is b, the side parallel to the gradient direction 3 is the length of the powder bed 5, and the side perpendicular to the gradient direction 3 of the powder bed is the width of the powder bed 5; the length of the longer side of the characteristic rectangle 2 is n, and the length of the shorter side of the characteristic rectangle 2 is m; the laser scanning direction is parallel to the longer side of the characteristic rectangle 2; the longer side of the characteristic rectangle 2 is parallel to the gradient direction 3.

[0080] like Figure 2 As shown, the control module divides the powder bed 5 into a number of closely arranged feature rectangles 2. In each row parallel to the gradient direction 3, the number of feature rectangles is In each column perpendicular to the gradient direction, the number of feature rectangles is like Figure 1 As shown, for each row of feature rectangles parallel to the gradient direction 3, the input initial velocity 1-1 is v1, and the input final velocity 6-1 is v D , then the scanning speed of the xth feature rectangle in the gradient direction 3 will be set to v x , v x It can be determined by the relationship (1):

[0081]

[0082] Next, the control module adjusts the scanning direction and scanning order of the feature rectangle 2 to achieve continuous scanning of the laser and planning of the scanning path 8-1. Figure 3 As shown, the control module retains the feature rectangle 2 located inside the two-dimensional contour and deletes the feature rectangle 2 located outside the two-dimensional contour according to the two-dimensional contour information 9-1 of the model.

[0083] Preferably, the length m of the short side of the characteristic rectangle 2 can be changed, and the value of m is the scanning spacing in the printing parameters.

[0084] Preferably, the length n of the long side of the characteristic rectangle 2 can be changed. Different n values ​​can be set according to different powder properties to change the fineness of the laser scanning speed change. The smaller the n value, the smoother the laser scanning speed change.

[0085] Preferably, in addition to simple linear changes, in certain application scenarios, the laser scanning speed may be adjusted using other nonlinear change functions according to the specific physical properties of the powder to further improve the molding effect.

[0086] Example 2

[0087] In the actual additive manufacturing process, in order to reduce the stress generated by printing, it is usually necessary to rotate the laser scanning direction after each layer is printed. At this time, an acute angle 10 with an angle of θ is formed between the long side of the feature rectangle 2 and the straight line where the gradient direction is located, as shown in Figure 4 At this time, Figure 5 As shown, the characteristic rectangles will be closely arranged to cover a parallelogram, a pair of parallel sides of the parallelogram are parallel to the gradient direction and coincide with a pair of parallel sides of the powder bed 5, and the length of the parallelogram parallel to the gradient direction is the minimum value that satisfies the above conditions. Several rows and columns of characteristic rectangles are closely arranged to cover the parallelogram, from left to right, they are the 1st column, the 2nd column, the 3rd column... the xth column, and from bottom to top, they are the 1st row, the 2nd row, the 3rd row... the yth row. The speed of the xth row and the yth row will be set to v xy ,v xy It can be determined by equation (2):

[0088]

[0089] Where a is the length of the side of the powder bed 5 parallel to the gradient direction 3, b is the length of the side of the powder bed 5 perpendicular to the gradient direction 3; n is the length of the longer side of the characteristic rectangle 2, m is the length of the shorter side of the characteristic rectangle 2; v s and v eare the optimal scanning speeds for the powders at both ends of the gradient powder bed. After assigning parameter values ​​to each feature rectangle, the control module adjusts the scanning direction and scanning order of the feature rectangle 2 to achieve continuous scanning of the laser and planning of the scanning path 8-2. Figure 6 As shown, the control module retains the feature rectangle 2 located inside the two-dimensional contour and deletes the feature rectangle 2 located outside the two-dimensional contour according to the two-dimensional contour information 9-2 of the model.

[0090] Example 3

[0091] When printing a gradient material with two ends of Cu10Sn and SS316, the system and method of the present invention are used to input the optimal process parameters of the Cu10Sn end and the optimal process parameters of SS316, respectively. The process parameters include the laser scanning speed. By inputting different laser energy densities to different powder bed areas, complex parts are formed, such as Figure 8 As shown, the prepared parts have a dense structure and high strength.

[0092] Comparative Example

[0093] When printing a gradient material with components of Cu10Sn and SS316 at both ends, using the single laser scanning parameters of the existing technology, no matter whether the gradient material is printed using the single optimal process parameters of Cu10Sn or the single optimal process parameters of SS316, the gradient component cannot be formed. Figure 7 As shown in the figure, it can be seen that when forming this type of gradient material parts, the forming quality is poor and cracking and warping occur.

[0094] contrast Figure 8 and Figure 7 It can be seen that the present invention has significant advantages when forming gradient materials such as those with large differences in melting points of materials at both ends of the gradient or large differences in laser absorption rates: high molding quality, high strength, and the ability to mold complex parts.

[0095] The present invention uses modeling and control modules to assign printing parameters of characteristic rectangles and select characteristic rectangles, so that the laser scanning speed changes continuously in the composition gradient direction of the powder bed, so that the laser energy density adapts to the physical properties of the powder layer, and realizes the complete densification and alloying process control of the gradient powder layer. Compared with existing equipment, the present invention can dynamically adjust the laser scanning parameters to match the material properties of the powder bed, achieve excellent metallurgical densification effects, and fill the deficiencies of the existing technology.

[0096] Although several embodiments of the present invention have been given herein, those skilled in the art should understand that the embodiments of the present invention may be modified without departing from the spirit of the present invention. The above embodiments are merely exemplary and should not be used as a limitation on the scope of the present invention.

Claims

1. A system for variable speed laser forming of continuous gradient materials, characterized in that: The system includes a powder spreading module, a laser module, a control module and a workbench: The powder laying module is used to lay a gradient powder layer on the workbench, and the area where the gradient powder layer is located is the powder bed; The laser module is used to emit lasers with different scanning speeds to the gradient powder layer on the workbench according to regions; The control module is used to divide the powder bed into a plurality of rows and columns of feature rectangles, select the feature rectangles within the two-dimensional contour of the printed part slice as the feature rectangles to be printed, assign printing parameters to each feature rectangle to be printed, arrange the printing direction and order of the feature rectangles to be printed, and control the laser module and the powder spreading module; The control module is respectively connected to the powder spreading module and the laser module by signals.

2. The system for variable speed laser forming continuous gradient materials according to claim 1, characterized in that: The control module includes a powder bed segmentation unit, a feature rectangle selection unit, a parameter setting unit, and a path planning unit; The powder bed segmentation unit is used to segment the entire powder bed into characteristic rectangles that are closely arranged in multiple rows and columns; The feature rectangle selection unit selects the feature rectangle located inside the slice two-dimensional contour as the feature rectangle to be printed according to the slice analysis of the printed part, and deletes other feature rectangles located outside the slice two-dimensional contour; The parameter setting unit sets the laser scanning speed and the laser power according to the composition characteristics of the powder layer of each feature rectangle to be printed; The path planning unit is used to arrange the laser scanning sequence of the feature rectangles to realize the planning of the scanning path; The powder bed segmentation unit, the feature rectangle selection unit, the parameter setting unit, and the path planning unit are all integrated into a controller or a computer.

3. The system for variable speed laser forming continuous gradient materials according to claim 1, characterized in that: The width of the characteristic rectangle is equal to the laser scanning interval, and the laser performs only one single-pass scanning on each characteristic rectangle.

4. The system for variable speed laser forming continuous gradient materials according to claim 1, characterized in that: The length of the characteristic rectangle is determined in a numerical range through experiments according to the composition characteristics and gradient distribution of the gradient powder layer; and fine adjustment of the laser scanning speed is achieved by adjusting the length of the characteristic rectangle.

5. The system for variable speed laser forming continuous gradient materials according to claim 1, characterized in that: The control module also includes a user input interface for inputting powder composition information and adjusting laser scanning parameters.

6. A method for variable speed laser forming of continuous gradient materials, characterized in that: The method uses the system according to any one of claims 1 to 5, and the method comprises: S1. Slicing of parts to be printed: Slice and analyze the parts to be printed to generate a two-dimensional profile of the slices; S2, powder bed segmentation: the entire powder bed is divided into multiple rectangular areas with multiple rows and columns, each rectangular area is a feature rectangle and corresponds to a specific position of the powder bed; S3, feature rectangle selection: according to the two-dimensional contour of the slice, the feature rectangle located inside the two-dimensional contour is selected as the feature rectangle to be printed, and the feature rectangle outside the two-dimensional contour is deleted; S4, parameter setting and allocation: assigning laser scanning parameters to each feature rectangle to be printed according to the gradient material composition; S5, printing sequence optimization: set the printing sequence for each feature rectangle to be printed, so that the laser scanning path is as continuous as possible and changes continuously along the powder bed gradient direction; S6. Gradient powder laying: The scraper scrapes the gradient powder into the designated position of the workbench to complete the gradient layered laying; S7, laser melting forming: turn on the laser module, scan the feature rectangle to be printed according to the set scanning path and laser scanning parameters, and realize the melting forming of the continuous gradient material of this layer; S8. Repeat steps S3-S7 until the part printing is completed.

7. The method for variable speed laser forming continuous gradient material according to claim 6, characterized in that: First, a "gradient material-laser scanning parameter" database is established. According to the composition and proportion of different gradient materials, the corresponding laser scanning parameters are determined through experiments and stored in the database. In step S4, the control module directly reads the laser scanning parameters from the database according to the composition and proportion of the gradient material.

8. The method for variable speed laser forming continuous gradient material according to claim 6, characterized in that: In step S4, the scanning speed of the components at both ends of the gradient material is manually input through the user input interface of the control module, and the parameter setting unit automatically allocates laser scanning parameters to each feature rectangle to be printed using a linear interpolation method.

9. The method for variable speed laser forming continuous gradient material according to claim 6, characterized in that: When printing two adjacent layers, the laser scanning direction is rotated to change the acute angle θ formed by the long side of the characteristic rectangle and the straight line where the powder gradient direction is located, thereby reducing the residual stress generated by printing.

10. The method for forming a continuous gradient material by variable speed laser according to claim 6, characterized in that: The acute angle θ formed by the long side of the characteristic rectangle and the straight line where the powder gradient direction is located is 0°-90°.

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