Pre-part shape control process for selective laser melting forming of large-size additive part

Abstract

The invention discloses a pre-part shape control process for selective laser melting forming of a large-size additive workpiece. The pre-part shape control process comprises the steps that S1, an appropriate material is selected; s2, model processing, wherein the size specification of the pre-part can be set to be a projection area of the pre-part on the bottom face when the part is printed and formed, and the thickness of the pre-part is set to be 1-20 mm; drawing a pre-part model in CAD software, converting the pre-part model into an STL format, and then importing the pre-part model into Magics software; s3, setting a laser scanning strategy; s4, heat treatment; s5, carrying out linear cutting on the pre-part and the substrate; s6, carrying out destressing heat treatment; s7, the part body and the pre-part are linearly cut, and a high-quality and high-precision near-net forming large-size 3D printed part can be prepared through a pre-part shape control technology; by adding pre-part sintering forming, the effect of buffering stress deformation is achieved, and meanwhile the part cracking phenomenon caused by uneven stress deformation can be reduced. And an optimized process scheme for selective laser melting forming, shape control and cracking prevention of the 3D printing component is provided for aerospace key parts.

Description

Technical Field

[0001] The invention belongs to the technical field of aerospace parts, and in particular relates to a pre-part shape-control process for laser selective melting of large-size additive parts. Background Art

[0002] With the rapid development of aerospace military equipment, higher requirements are placed on the development of new materials and new processes. Laser selective melting technology is the most widely used processing technology in the field of 3D printing. This technology does not require the use of other auxiliary equipment and can be directly formed only through laser selective melting equipment. It solves the problems of traditional preparation processes, low yield, long production cycle, and cumbersome processes.

[0003] In recent years, the size of parts formed by 3D printing has become larger and larger, and the difficulty of forming and controlling the shape has also increased significantly. In particular, if the shape control of large-sized thin-walled parts of meter-level is not appropriate, it will cause serious product deviations and eventually lead to scrapping. In the process of laser selective melting, the substrate serves as the forming base, and the parts, supports and auxiliary forming structures are all grown layer by layer from the substrate plane. Due to the printing process, a high-energy laser beam is generated to selectively melt the metal powder and form it. The temperature of the molten metal powder reaches thousands of degrees Celsius. The whole part is printed layer by layer and finally the preparation of the entire part is completed. At this time, the temperature inside the forming chamber is high, and the formed parts and powder in the chamber reach hundreds of degrees Celsius. After the forming is completed, the temperature inside the forming chamber gradually drops to room temperature, and the parts will also shrink. Because the parts grow directly on the substrate, or the parts grow on the substrate through support, the lower part of the part close to the substrate is subject to the fixed constraint of the substrate and cannot shrink, while the upper part away from the substrate can shrink freely, resulting in different shrinkage rates at the upper and lower ends of the part, and the final part size deviation is inconsistent, which is very likely to cause the part size deviation to exceed the tolerance. At the same time, due to uneven stress deformation, the risk of part cracking is increased.

[0004] In order to solve the above problems, the present invention belongs to a brand-new process scheme, which is to introduce the design of "pre-part" between the formed part and the substrate. The "real part" is stacked on top of the "pre-part" through support. When the printing is completed and the cooling stage is staged, the pre-part shrinks, but due to the constraint of the substrate, the pre-part will not shrink completely into place. The "real part" further shrinks on the basis of the pre-part, infinitely approaching the theoretical size of the part, thereby achieving the purpose of shape control. Summary of the invention

[0005] The object of the present invention is to provide a pre-part shape control process for laser selective melting forming of large-sized additive parts to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions: A pre-part shape control process for selective laser melting forming of large-sized additive manufacturing parts, the specific steps include: S1: Select applicable materials, including any materials applicable to selective laser melting forming;

[0007] S2: Model processing: The dimensional specifications of the pre-part can be set as the projection area of the part on the bottom surface during printing and forming. According to the wall thickness of the large-sized part structure, the thickness of the pre-part is set to 1 mm - 20 mm; Draw the pre-part model in CAD software, convert it into STL format, and then import it into Magics software, place it parallel to the substrate plane, the lower surface of the pre-part is 4 mm - 50 mm away from the substrate plane, the bottom of the pre-part is the support structure, and the top is also the support structure, and the part body is located on the support structure at the top;

[0008] S3: Laser scanning strategy setting: The scanning strategy used for printing the pre-part can adopt non-pattern long straight line printing or strip short straight line printing, and the normal strip short straight line printing or checkerboard scanning strategy can be adopted when printing the part body;

[0009] S4: Heat treatment: For the printed part body, pre-part and support structure, together with the substrate, perform heat treatment;

[0010] S5: Wire cutting of the pre-part and the substrate: Perform wire cutting treatment on the printed part;

[0011] S6: Stress relief heat treatment;

[0012] S7: Wire cutting between the part body and the pre-part: The part body and the pre-part are connected by a support, and the part and the pre-part are separated by wire cutting.

[0013] Preferably, in the above S1, the applicable materials include but are not limited to copper, stainless steel, iron, nickel, titanium, tungsten, molybdenum, aluminum, and refractory metal compounds.

[0014] Preferably, in the above S5, the support part between the pre-part and the substrate should be preferentially cut off. The residual stress inside the pre-part will cause it to further shrink and deform, and the part body will also further shrink towards the theoretical model size.

[0015] Preferably, the above S6 can be processed as needed. Since the pre-part and the part body further shrink to the theoretical size in the previous step, in order to control the shape and size stability and prevent cracking, the step of stress relief heat treatment can be selectively carried out.

[0016] Preferably, the function of the above S3: In order to better control the shape of the part body, increase the shrinkage amount of the pre-part by increasing the internal stress.

[0017] Preferably, for the heat treatment in S4, annealing or solution treatment shall be carried out in accordance with the conventional heat treatment systems for various material standards.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: Through the pre-part shape control process, high-quality and high-precision near-net-shaped large-size 3D printed parts can be prepared; by adding pre-part sintering and forming, the role of buffering stress deformation can be achieved, and at the same time, the phenomenon of part cracking caused by uneven stress deformation can be reduced. An optimized process scheme for controlling shape and preventing cracking of 3D printed components by selective laser melting for key components in aerospace is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of the part in this embodiment;

[0020] Figure 2 is a schematic diagram of the pre-part in this embodiment;

[0021] Figure 3 is a schematic diagram of the printing and forming layout in this embodiment;

[0022] Figure 4 is the front view of the printing and forming layout in this embodiment;

[0023] Figure 5 is a partially enlarged schematic diagram of the printing and forming layout in this embodiment; DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] Please refer to Figures 1 - 5 , the present invention provides a technical solution: a pre-part shape control process for selective laser melting of large-size additive manufactured parts, and the specific steps include: S1: Select applicable materials, including any materials applicable to selective laser melting; the applicable materials include but are not limited to copper, stainless steel, iron, nickel, titanium, tungsten, molybdenum, aluminum, and refractory metal compounds;

[0026] S2: Model processing: The dimensional specifications of the pre-part can be set as the projection area of the part on the bottom surface during printing and forming. According to the wall thickness of the large-sized part structure, the thickness of the pre-part is set to be 1 mm - 20 mm. Draw the pre-part model in CAD software, convert it into STL format, and then import it into Magics software. Place it parallel to the substrate plane, with the lower surface of the pre-part 4 mm - 50 mm away from the substrate plane. The bottom of the pre-part is the support, and the top is also the support. The part body is located on the support at the top, as Figure 4 shown;

[0027] S3: Laser scanning strategy setting: To better control the shape of the part body, increase the shrinkage of the pre-part by increasing the internal stress. The scanning strategy for printing the pre-part can be non-pattern long straight line printing or strip short straight line printing. When printing the part body, normal strip short straight line printing or checkerboard scanning strategy can be adopted;

[0028] S4: Heat treatment: For the printed part body, pre-part and support structure, together with the substrate, perform heat treatment. Annealing or solution treatment shall be carried out in accordance with the conventional heat treatment systems for various material standards;

[0029] S5: Wire cutting of the pre-part and the substrate: Perform wire cutting on the printed part. The support part between the pre-part and the substrate should be preferentially cut off. The residual stress inside the pre-part will cause it to further shrink and deform, and the part body will also further shrink towards the theoretical model size;

[0030] S6: Stress relief heat treatment; It can be processed as needed according to the situation. Since the pre-part and the part body further shrink to the theoretical size in the previous step, in order to control the shape and size stability and prevent cracking, the step of stress relief heat treatment can be selectively carried out;

[0031] S7: Wire cutting of the part body and the pre-part: The part body and the pre-part are connected by the support, and the part and the pre-part are separated by wire cutting.

[0032] Although the embodiments of the present invention have been shown and described, see the above detailed description. For those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A pre-part shape control process for large-size additive manufacturing by laser selective melting, characterized in that: The specific steps include: S1: selecting a suitable material, including any material suitable for laser selective melting; S2: Model processing: The size specification of the pre-part can be set as the projection area on the bottom surface when the part is printed. According to the wall thickness of the large-size part structure, the thickness of the pre-part is set to 1mm-20mm; draw the pre-part model in the CAD software, convert it into STL format, and then import it into the Magics software, and place it parallel to the substrate plane. The lower surface of the pre-part is 4mm-50mm away from the substrate plane. The bottom of the pre-part is a support structure, and the top is also a support structure. The part body is located on the top support structure; S3: Laser scanning strategy setting: The scanning strategy used for printing pre-parts can be long straight line printing without pattern or short straight line printing with strips. When printing the part body, the normal short straight line printing with strips or chessboard scanning strategy can be used. S4: Heat treatment: Heat treatment is performed on the printed part body, pre-parts and support structure together with the substrate; S5: Wire cutting of pre-parts and substrates: wire cutting of the printed parts; S6: stress relief heat treatment; S7: Wire cutting of part body and pre-part: The part body and pre-part are connected by support, and the part and pre-part are separated by wire cutting.

2. The pre-part shape control process for large-size additive manufacturing by laser selective melting according to claim 1, characterized in that: In S1, applicable materials include but are not limited to copper, stainless steel, iron, nickel, titanium, tungsten, molybdenum, aluminum and refractory metal compounds.

3. The pre-part shape control process for large-size additive manufacturing by laser selective melting according to claim 1, characterized in that: In the above-mentioned S5, the support portion between the pre-part and the substrate should be removed first, and the residual stress inside the pre-part will cause it to further shrink and deform, and the part body will also further shrink and tend to the theoretical model size.

4. The pre-part shape control process for large-size additive manufacturing by laser selective melting according to claim 1, characterized in that: The S6 can be processed as needed. Since the previous operation pre-component and the part body are further shrunk to the theoretical size, in order to control the shape stability size and prevent cracking, a stress relief heat treatment step can be selectively performed.

5. The pre-part shape control process for large-size additive manufacturing by laser selective melting according to claim 1, characterized in that: The function of S3 is to increase the shrinkage of the preformed part by increasing the internal stress in order to better control the shape of the part body.

6. The pre-part shape control process for large-size additive manufacturing by laser selective melting according to claim 1, characterized in that: The heat treatment of S4 needs to be performed by annealing or solution treatment according to conventional standard heat treatment systems for various materials.

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