Metal additive manufacturing sample design method

Abstract

The invention discloses a metal additive manufacturing sample design method, which belongs to the technical field of metal additive manufacturing, and comprises the following steps: S1, determining the shape and size of a free design area according to the shape and size of a target part for additive manufacturing, and recording the shape and size as a shape Q; s2, the shape and size of the upper surface and the shape of the lower surface of the transition area are determined according to the section shape of the joint of the shape Q and the transition area; and S3, the area of the lower surface and the taper theta of the transition area are determined, and therefore metal additive manufacturing sample design is conducted. By the adoption of the metal additive manufacturing sample design method, the residual stress level in a component in the cladding deposition process can be remarkably reduced, the influence of substrate removal on the internal residual stress state of the component can be basically eliminated, residual stress evaluation is more convenient and accurate, and the working efficiency is improved. And help is provided for research, development and production work such as additive manufacturing new alloy development and technological parameter optimization.

Description

Technical Field

[0001] The invention relates to the technical field of metal additive manufacturing, and in particular to a method for designing a metal additive manufacturing specimen. Background Art

[0002] Residual stress is generated during the metal additive manufacturing process. Excessive residual stress can cause deformation and cracking of the substrate and components, further deformation of the components during processing such as substrate removal and heat treatment, and finally superimposed with the working load during the service of the components, jointly affecting the service life of the components. Improving the quality of additive manufacturing products requires both solutions to reduce the level of residual stress inside the components and means to obtain the size and distribution of residual stress inside the components.

[0003] In terms of reducing the level of residual stress, the methods widely adopted in the industry are to optimize process parameters, preheat substrates, and substrate design. Optimizing process parameters mainly includes the following three aspects: first, adjusting laser power, scanning speed, and path planning to reduce heat input, thereby reducing temperature gradients; second, using thicker powder layers to improve heat conduction, enhance thermal uniformity, and reduce thermal gradients, thereby reducing stress generated during cooling; third, adjusting the scanning strategy, using cross scanning, sequential scanning, or adaptive scanning paths to evenly distribute heat to reduce stress concentration. Substrate preheating is to reduce the accumulation of thermal stress by reducing the temperature difference. Substrate design refers to optimizing the structure of the substrate to reduce the constraints of the substrate on the component, or using an elastic or flexible substrate to absorb part of the stress during the cooling process, thereby reducing the level of residual stress in the component. However, the above methods still have certain limitations. For example, reducing the laser power will reduce production efficiency and prolong manufacturing time. Increasing the thickness of the powder layer will increase the roughness of the component surface and may also cause insufficient melting of the metal powder, thereby increasing the porosity. The substrate preheating method has limited effect on some materials with low thermal expansion coefficients. For components that need to work in low-temperature environments, this method may also change the microstructure of the material and affect the final performance.

[0004] In terms of residual stress measurement of components, neutron diffraction, X-ray diffraction, drilling, ultrasonic and other methods are usually used. These methods can more accurately obtain the size and distribution of residual stress on parts, and provide important references for inspection or process optimization in R&D and production. However, in actual operation, metal samples manufactured by additive manufacturing usually need to be printed on a substrate. Removing the printed sample from the substrate will lead to the redistribution of residual stress inside the sample. Therefore, the residual stress distribution of the sample after being removed from the substrate is quite different from that before being removed. Carrying the substrate together for residual stress measurement often makes it impossible to put it into the detection equipment because the substrate is too large or too heavy.

[0005] In order to solve the problem that removing the substrate will affect the residual stress distribution of the sample, the solution currently widely adopted in the industry is: before printing the sample, first pre-print a platform with a certain thickness on the substrate, then eliminate the stress of this pre-printed platform through heat treatment, then print the sample on this platform, and finally remove the sample and the platform from the substrate and measure the residual stress. This method ensures that the residual stress of the sample changes little before and after removal, but for alloys such as high-temperature alloys that cannot eliminate residual stress through heat treatment, it is impossible to eliminate the residual stress of the pre-printed platform, so this method has certain material limitations.

[0006] Based on this background, the present invention proposes a novel additive manufacturing specimen design method to solve the problem that the residual stress level in the component is difficult to reduce and the inevitable residual stress redistribution after the specimen is removed from the substrate. Summary of the invention

[0007] The purpose of the present invention is to provide a metal additive manufacturing specimen design method, which can not only significantly reduce the residual stress level in the component during the cladding deposition process, but also basically eliminate the influence of substrate removal on the residual stress state inside the component, making the residual stress evaluation more convenient and accurate, and providing assistance for research and development and production work such as the development of new alloys for additive manufacturing and optimization of process parameters.

[0008] To achieve the above object, the present invention provides a metal additive manufacturing specimen design method, comprising the following steps: S1. According to the shape and size of the target part of additive manufacturing, determine the shape and size of the free design area, which is recorded as shape Q; S2. Determine the shape and size of the upper surface and the shape of the lower surface of the transition area according to the cross-sectional shape of the connection between the shape Q and the transition area; S3. Determine the area of ​​the lower surface and the taper θ of the transition area to design the metal additive manufacturing specimen to ensure the stability of the structure.

[0009] Preferably, the cross-sectional shape and size of the connection between the shape Q and the transition region are the shape and size of the upper surface of the transition region.

[0010] Preferably, the upper surface and the lower surface of the transition region have the same shape, and the area of ​​the lower surface of the transition region is smaller than the area of ​​the upper surface.

[0011] Preferably, the lower surface of the transition area is the contact surface between the sample and the substrate.

[0012] Preferably, the raw material for metal additive manufacturing is metal powder.

[0013] Preferably, when the residual stress test is performed using the design method, any one of neutron diffraction technology, X-ray diffraction technology, profile method, drilling method or ultrasonic method is adopted.

[0014] Therefore, the present invention adopts the above-mentioned metal additive manufacturing specimen design method to avoid stress redistribution when the specimen is removed from the substrate, thereby realizing the evaluation of the residual stress level of the specimen in the printing completed state (rather than the state after the substrate is removed); through the new specimen design method, the residual stress level inside the additively manufactured component is significantly reduced, and the influence of the substrate removal on the residual stress state inside the component can be basically eliminated, making the residual stress evaluation more convenient and accurate, and providing assistance for research and development and production work such as the development of new alloys for additive manufacturing and optimization of process parameters.

[0015] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of an embodiment of a metal additive manufacturing specimen design method of the present invention; Figure 2 It is a schematic diagram of a sample designed for testing residual stress and reducing the residual stress level according to an embodiment of a metal additive manufacturing sample design method of the present invention; Figure 3 It is a schematic diagram of the relative positions of a substrate and a "special sample Cone" in an embodiment of a metal additive manufacturing sample design method of the present invention; Figure 4 It is a residual stress distribution cloud diagram of a metal additive manufacturing sample design method embodiment "special sample Cone" of the present invention after the cladding deposition process is completed and cooled to room temperature, and after the substrate is removed, and a comparison diagram of the Z-direction residual stress numerical curves on the Z axis of the sample in these two states; Figure 5 It is a schematic diagram of the relative positions of a substrate and a "normal sample Column" in an embodiment of a metal additive manufacturing sample design method of the present invention; Figure 6 It is a residual stress distribution cloud diagram of a metal additive manufacturing sample design method embodiment of the present invention, "ordinary sample Column", in a state where the cladding deposition process is completed and cooled to room temperature, and in a state where the substrate is removed, and a comparison diagram of the Z-direction residual stress numerical curves on the Z axis of the sample in these two states; Figure 7 This is a comparison chart of the Z-direction residual stress levels on the Z axis of a "special sample Cone" and a "normal sample Column" in an embodiment of a metal additive manufacturing sample design method of the present invention after the substrate is removed.

[0017] Reference numerals 1. Transition area; 2. Free design area; A. Lower surface of transition area; B. Upper surface of transition area. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0019] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the common meanings understood by persons with ordinary skills in the field to which the present invention belongs. The terms "upper", "lower", etc. used in the present invention are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0020] The present invention provides a metal additive manufacturing sample design method for reducing residual stress and making the residual stress test process more convenient and the results more accurate. The sample designed by this method has a lower residual stress level inside and the size and distribution of the internal residual stress are basically not affected by the removal of the substrate. Even if the residual stress inside the sample is measured after the substrate is removed, the residual stress situation before the substrate is removed can be obtained.

[0021] In terms of the geometric design of the specimen, the specimen can be divided into two regions, namely the transition region 1 and the free design region 2, such as Figure 1 As shown. The transition area 1 is characterized in that the area of ​​the lower surface A connected to the substrate is as small as possible, and its shape can be circular, triangular, rectangular or other polygonal shapes, and can be adjusted according to the shape of the connection surface between the free design area 2 and the transition area 1 or the requirements of the residual stress measurement equipment; the upper surface B of the transition area 1 has the same shape as the lower surface A, and the size is set according to the size of the connection surface between the free design area 2 and the transition area 1.

[0022] Transition region 1 is a three-dimensional entity generated by the smooth transition between the lower surface A and the upper surface B. This entity has a certain taper angle. In order to ensure sufficient stability during the sample printing process, the taper angle should be reasonably designed according to the size and weight of the free design area 2. The free design area 2 can be freely designed according to the different needs of users. If it is necessary to measure the residual stress distribution and size inside the sample before the substrate is removed, the area 2 can be designed to be a shape that is easy to measure; if it is necessary to reduce the residual stress level inside a special structure, the area 2 is designed to be the shape of the structure. For example, to produce a regular quadrangular prism using an additive manufacturing process, it is necessary to reduce the residual stress level inside it, and at the same time accurately measure the residual stress value after the cladding deposition is completed and before the substrate is removed to evaluate the quality of the component. At this time, the shape of the free design area 2 is a regular quadrangular prism, the shapes of the lower surface A and the upper surface B of the transition area 1 are squares, and the shape of the transition area 1 is a regular quadrangular pyramid, such as Figure 2 shown.

[0023] Embodiment 1 The present invention reduces the contact area between the component and the substrate and reduces the constraint of the substrate on the component, thereby reducing the residual stress level inside the component. According to the Saint-Venant principle, the inverted cone-shaped solid structure of the transition area 1 is added to make the target part of the free design area 2 away from the substrate to a certain extent, so as to achieve the purpose of eliminating the effect of the removal of the substrate on the residual stress size and distribution in the target part. If the area of ​​surface A is small enough, when the substrate is removed, the residual stress in the transition area 1 can also be basically unaffected.

[0024] by Figure 2 Taking the sample design shown as an example, it demonstrates the effect of reducing residual stress and eliminating the effect of substrate removal on the size and distribution of residual stress by using the sample designed using the method proposed in the present invention during finite element simulation of additive manufacturing.

[0025] First, a finite element simulation is performed on the process of producing components using metal additive manufacturing technology under certain process parameters. The components adopt the special sample design method with an inverted cone transition area proposed in the present invention, and the shape is as follows: Figure 2 As shown, this sample is recorded as "Special Sample Cone". Figure 3 The relative positions of the substrate and the specimen in the finite element model are shown in the figure. The size of the substrate is 50mm*50mm*10mm. The transition area 1 of the specimen is a regular tetrahedron with a height of 10mm, the free design area 2 is a regular tetrahedron with a height of 20mm, and the total height of the specimen is 30mm. The lower surface A of the transition area 1 is a square with a side length of 1mm, and the upper surface B is a square with a side length of 10mm. The finite element simulation method adopts the component-scale thermal-mechanical coupling modeling method proposed by Mohammed Bayat et al., which can accurately predict the residual stress distribution and size inside the specimen. This modeling method can simulate the residual stress during the cladding deposition process, and can also simulate the residual stress field inside the component after cooling to room temperature and after the substrate is removed. Figure 4 The "special sample Cone" is shown, with the residual stress distribution cloud diagram inside the sample after the cladding deposition process is completed and cooled to room temperature, and after the substrate is removed, as well as the Z-direction residual stress numerical curve comparison diagram on the Z axis of the sample in these two states. It can be observed that the removal of the substrate has little effect on the residual stress distribution and size in the special sample with an inverted cone transition area designed by the sample design method proposed in the present invention.

[0026] Then, a finite element simulation is performed on the cladding deposition process of a common cuboid without using the sample design method proposed in the present invention. The relative positions of the cuboid and the substrate are shown in FIG. Figure 5As shown, the rectangular specimen is recorded as "normal specimen Column". In order to compare the residual stress distribution of the "normal specimen Column" and the "special specimen Cone" with an inverted cone transition area design at the same height and the degree of influence on the residual stress distribution after the substrate is removed, the height of the rectangular specimen is 30mm, the same as the "special specimen Cone", and the cross-section of the rectangular specimen is also designed as a square with a side length of 10mm. The additive manufacturing process parameters, substrate material properties, and powder material properties are consistent with the finite element model of the "special specimen Cone". Figure 6 The "Ordinary Sample Column" shows the residual stress distribution cloud diagram inside the sample after the cladding deposition process is completed and cooled to room temperature, and after the substrate is removed, as well as the Z-direction residual stress numerical curve comparison diagram on the Z axis of the sample in these two states. It can be observed that the removal of the substrate has a great influence on the residual stress distribution and size of the ordinary sample. Figure 7 The comparison of the residual stress levels in the Z direction of the "Special Specimen Cone" and the "Ordinary Specimen Column" on the Z axis after the substrate is removed is shown. It can be clearly observed that the "Special Specimen Cone" has a lower residual stress level inside.

[0027] according to Figure 4 , Figure 6 and Figure 7 The conclusions observed can verify that the sample designed by the sample design method proposed in the present invention has the important effect of significantly reducing the residual stress level and can basically eliminate the influence of substrate removal on the residual stress size and distribution inside the component. In this way, even if the sample is removed from the substrate and then the residual stress is measured, the stress state after the cladding deposition is completed can be obtained without worrying about the redistribution of residual stress.

[0028] Therefore, the present invention adopts the above-mentioned metal additive manufacturing specimen design method, which can not only significantly reduce the residual stress level in the component during the cladding deposition process, but also basically eliminate the influence of substrate removal on the residual stress state inside the component, making the residual stress evaluation more convenient and accurate, and providing assistance for research and development and production work such as the development of new alloys for additive manufacturing and optimization of process parameters.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A metal additive manufacturing specimen design method, characterized in that: The following steps are involved: S1. According to the shape and size of the target part of additive manufacturing, determine the shape and size of the free design area, which is recorded as shape Q; S2. Determine the shape and size of the upper surface and the shape of the lower surface of the transition area according to the cross-sectional shape of the connection between the shape Q and the transition area; S3. Determine the area of ​​the lower surface and the taper θ of the transition region to design a metal additive manufacturing specimen.

2. A metal additive manufacturing specimen design method according to claim 1, characterized in that: The cross-sectional shape and size of the connection between the shape Q and the transition region are the shape and size of the upper surface of the transition region.

3. A metal additive manufacturing specimen design method according to claim 1, characterized in that: The upper surface and the lower surface of the transition region have the same shape, and the area of ​​the lower surface of the transition region is smaller than the area of ​​the upper surface.

4. A metal additive manufacturing specimen design method according to claim 1, characterized in that: The lower surface of the transition area is the contact surface between the sample and the substrate.

5. The metal additive manufacturing sample design method according to claim 1, characterized in that: The raw material for metal additive manufacturing is metal powder.

6. A metal additive manufacturing specimen design method according to claim 1, characterized in that: When the residual stress test is performed using the design method, any one of neutron diffraction technology, X-ray diffraction technology, profile method, drilling method or ultrasonic method is adopted.

Images