A metal additive manufacturing specimen design method

Abstract

The present invention discloses a metal additive manufacturing specimen design method, which belongs to the field of metal additive technology and includes the following steps: S1. Determine the shape and size of the free design area based on the shape and size of the target part for additive manufacturing, which is recorded as shape Q; S2. Determine the shape and size of the upper surface of the transition area and the shape of the lower surface based on the cross-sectional shape of the connection between shape Q and the transition area; S3. Determine the area of ​​the lower surface and the taper θ of the transition area, thereby designing the metal additive manufacturing specimen. 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 can basically eliminate the impact of substrate removal on the residual stress state inside the component, making 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 the optimization of process parameters.

Description

Technical Field

[0001] The present invention relates to the field of metal additive manufacturing technology, 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. This can lead to further component deformation during processes such as substrate removal and heat treatment. Ultimately, this stress, combined with the workload during component operation, can affect the component's service life. Improving the quality of additively manufactured products requires both solutions to reduce residual stress levels within components and methods to understand their magnitude and distribution.

[0003] In terms of reducing residual stress levels, the methods widely adopted in the industry include optimizing process parameters, preheating the substrate, 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 temperature differences. Substrate design refers to optimizing the substrate structure to reduce the substrate's constraints on the component, or using elastic or flexible substrates to absorb some of the stress during the cooling process, thereby reducing the residual stress level of 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 measuring residual stress in components, neutron diffraction, X-ray diffraction, drilling, ultrasonic methods and other methods are usually used. These methods can more accurately obtain the size and distribution of residual stress on parts, providing an important reference for inspection or process optimization in R&D and production. However, in actual operation, metal specimens for additive manufacturing usually need to be printed on a substrate. Removing the printed specimen from the substrate will lead to a redistribution of residual stress inside the specimen. Therefore, the residual stress distribution of the specimen after removal from the substrate is significantly different from that before removal. When carrying a substrate for residual stress measurement, it is often impossible to put it into the testing equipment because the substrate is too large or too heavy.

[0005] To address the issue of removing the substrate affecting the residual stress distribution of the sample, the industry's currently widely adopted solution is to pre-print a platform of a certain thickness on the substrate before printing the sample. This platform is then stress-eliminated by heat treatment, and the sample is then printed on this platform. Finally, the sample and the platform are removed from the substrate and residual stress is measured. This method ensures that the residual stress of the sample changes little before and after removal. However, for alloys such as high-temperature alloys where residual stress cannot be eliminated by heat treatment, it is impossible to eliminate the residual stress of the pre-printed platform. Therefore, this method has certain material limitations.

[0006] Based on this background, the present invention proposes a new additive manufacturing specimen design method to solve the problem of difficulty in reducing the residual stress level in the component and the inevitable redistribution of residual stress 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 the 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:

[0009] S1. Determine the shape and size of the free design area based on the target part shape and size of the additive manufacturing, and record it as shape Q.

[0010] S2. Determine the shape and size of the upper surface and the shape of the lower surface of the transition region based on the cross-sectional shape of the connection between the shape Q and the transition region;

[0011] S3. Determine the area of ​​the lower surface and the taper θ of the transition region to design the metal additive manufacturing specimen to ensure the stability of the structure.

[0012] 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.

[0013] 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 that of the upper surface.

[0014] Preferably, the lower surface of the transition region is the contact surface between the sample and the substrate.

[0015] Preferably, the raw material for metal additive manufacturing is metal powder.

[0016] Preferably, when performing residual stress testing using the design method, any one of neutron diffraction technology, X-ray diffraction technology, profilometry, drilling method or ultrasonic method is adopted.

[0017] 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 completed printing 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 the optimization of process parameters.

[0018] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of an embodiment of a metal additive manufacturing specimen design method of the present invention;

[0020] Figure 2 This is a schematic diagram of a sample designed for testing residual stress and reducing residual stress levels according to an embodiment of a metal additive manufacturing sample design method of the present invention;

[0021] Figure 3 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;

[0022] Figure 4 This is a cloud diagram of the residual stress distribution inside the sample "Special Sample Cone" in an embodiment of the metal additive manufacturing sample design method of the present invention after the cladding deposition process is completed and cooled to room temperature, and after the substrate is removed, as well as a comparison of the Z-direction residual stress numerical curves of the sample in these two states;

[0023] Figure 5 This 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;

[0024] Figure 6 This is a cloud diagram of the residual stress distribution inside the sample of a "normal sample column" in an embodiment of the metal additive manufacturing sample design method of the present invention after the cladding deposition process is completed and the sample is cooled to room temperature, and after the substrate is removed, as well as a comparison of the Z-direction residual stress numerical curves of the sample in these two states;

[0025] Figure 7This is a comparison chart of the Z-direction residual stress levels on the Z axis of a "special specimen Cone" and a "normal specimen Column" in an embodiment of a metal additive manufacturing specimen design method of the present invention after the substrate is removed.

[0026] Reference numerals

[0027] 1. Transition area; 2. Free design area; A. Lower surface of transition area; B. Upper surface of transition area. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0029] Unless otherwise defined, technical or scientific terms used herein shall have the ordinary meanings understood by persons of ordinary skill in the art to which this invention pertains. Terms such as "upper" and "lower" are used herein solely to indicate relative positions. When the absolute positions of the objects being described change, the relative positions may also change accordingly.

[0030] This invention provides a metal additive manufacturing specimen design method for reducing residual stress and making residual stress testing more convenient and accurate. The resulting specimens exhibit low residual stress levels, and the magnitude and distribution of internal residual stress are largely unaffected by substrate removal. Even when residual stress is measured after the substrate is removed, the pre-existing residual stress can be determined.

[0031] In terms of the geometric design of the specimen, the specimen can be divided into two areas, namely the transition area 1 and the free design area 2, such as Figure 1 As shown in the figure, the transition region 1 is characterized by having a lower surface A connected to the substrate that is as small as possible. Its shape can be circular, triangular, rectangular, or other polygonal, and can be adjusted according to the shape of the interface between the free design region 2 and the transition region 1 or the requirements of the residual stress measurement equipment. The upper surface B of the transition region 1 has the same shape as the lower surface A, and its size is determined by the size of the interface between the free design region 2 and the transition region 1.

[0032] 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 the 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 convenient for measurement; 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.

[0033] Example 1

[0034] This invention reduces the contact area between the component and the substrate, alleviating the substrate's constraints on the component, thereby lowering residual stress levels within the component. Based on Saint-Venant's principle, the inverted tapered structure of transition region 1 distances the target component in free design region 2 to a certain extent from the substrate, thereby eliminating the effect of substrate removal on the magnitude and distribution of residual stress within the target component. If the area of ​​surface A is sufficiently small, residual stress within transition region 1 can be largely unaffected when the substrate is removed.

[0035] by Figure 2 Taking the sample design shown as an example, it demonstrates the effect of the sample designed using the method proposed in the present invention in reducing residual stress and eliminating the effect of substrate removal on the magnitude and distribution of residual stress during finite element simulation of additive manufacturing.

[0036] First, a finite element simulation is performed on the process of producing components using metal additive manufacturing technology under certain process parameters. The components are designed using the special sample design method with an inverted cone transition area proposed in this invention, and the shape is as follows: Figure 2 As shown, this sample is recorded as "special sample Cone". Figure 3The figure shows the relative positions of the substrate and specimen in the finite element model. The size of the substrate is 50mm*50mm*10mm. The specimen transition region 1 is a regular rectangular pyramid with a height of 10mm, the free design region 2 is a regular rectangular prism with a height of 20mm, and the total height of the specimen is 30mm. The lower surface A of the transition region 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 magnitude 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 Specimen Cone" exhibits residual stress distribution contours within the specimen after the cladding deposition process completes and the substrate is removed, along with a comparison of Z-axis residual stress curves for the specimen in these two states. It can be observed that substrate removal has little effect on the residual stress distribution and magnitude within the special specimen with an inverted tapered transition region designed using the specimen design method proposed in this invention.

[0037] Then, a finite element simulation is performed on the cladding deposition process of a common cuboid that does not adopt the sample design method proposed in the present invention. The relative positions of the cuboid and the substrate are as follows: Figure 5 As shown, the rectangular specimen is designated "Normal Specimen Column." To compare the residual stress distribution at the same height between the "Normal Specimen Column" and the "Special Specimen Cone" with an inverted tapered transition zone, and to examine the impact of the residual stress distribution after substrate removal, the rectangular specimen was designed with the same height of 30 mm as the "Special Specimen Cone," and its cross-section was also designed as a square with a side length of 10 mm. The additive manufacturing process parameters, substrate material properties, and powder material properties were consistent with the finite element model of the "Special Specimen Cone." Figure 6 The exhibit displays residual stress distribution contours for the "normal specimen column" after the cladding deposition process completes and the specimen cools to room temperature, and after the substrate is removed. Comparisons of Z-direction residual stress curves for these two conditions are also provided. It can be seen that substrate removal significantly impacts both the distribution and magnitude of residual stress in the normal specimen. Figure 7 The figure shows a comparison of the Z-direction residual stress levels of the "Special Cone" and "Normal Column" specimens after the substrate is removed. It can be clearly seen that the "Special Cone" specimen has a lower residual stress level.

[0038] according to Figure 4 、 Figure 6 and Figure 7These observations confirm that the specimens designed using the proposed specimen design method significantly reduce residual stress levels and essentially eliminate the effect of substrate removal on the magnitude and distribution of residual stress within the component. This allows for the determination of residual stress after the specimen is removed from the substrate, while providing a reliable indicator of the stress state after cladding deposition, without the risk of residual stress redistribution.

[0039] 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 impact of substrate removal on the residual stress state inside the component, making 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.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. 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 solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A metal additive manufacturing specimen design method, characterized in that: The following steps are involved: S1. Determine the shape and size of the free design area based on the target part shape and size of the additive manufacturing, and record it as shape Q. S2. Determine the shape and size of the upper surface and the shape of the lower surface of the transition region based on the cross-sectional shape of the connection between shape Q and the transition region; the cross-sectional shape and size of the connection between shape Q and the transition region are the shape and size of the upper surface of the transition region; the upper and lower surfaces of the transition region have the same shape, and the area of ​​the lower surface of the transition region is smaller than that of the upper surface; the lower surface of the transition region is the contact surface between the sample and the substrate; S3. Determine the area of ​​the lower surface and the taper θ of the transition region to design the metal additive manufacturing specimen.

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

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

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