A method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process

Abstract

This invention discloses a method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process, belonging to the field of metal material additive manufacturing technology. The method includes the following steps: S1, setting the process parameters for metal additive manufacturing and planning the area and timing for synchronously applying pulsed current; S2, during the layer-by-layer deposition process of the component, when a high-energy laser beam, electron beam, or electric arc acts on the deposition area to form a molten pool, a pulsed power supply is triggered by a synchronous control unit to apply a pulsed current with preset parameters to the molten pool and the heat-affected zone; S3, through the synergistic effect of the electroplasticity and Joule heating of the pulsed current, thermal stress relaxation, grain refinement, and microstructure homogenization are simultaneously achieved during the manufacturing process. This invention, by employing the above method and precisely controlling the electrical pulse parameters, simultaneously achieves stress relaxation and solidification microstructure optimization during the manufacturing process, significantly improving the dimensional stability, fatigue life, and mechanical properties of the formed component.

Description

Technical Field

[0001] This invention relates to the field of metal additive manufacturing technology, and in particular to a method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process. Background Technology

[0002] Metal additive manufacturing is an advanced manufacturing technology that achieves near-net-shape forming of complex components by cladding or solidifying metal materials layer by layer. This technology is characterized by high forming accuracy, high design freedom, and wide material applicability. Its basic principle is based on the discrete-stacking principle, using high-energy beams or mechanical energy to achieve layer-by-layer bonding and accumulation of materials. Metal additive manufacturing technologies mainly include powder bed fusion (PBF), directed energy deposition (DED), electric arc additive manufacturing (WAAM), solid-state additive stirring friction deposition (AFSD), and selective laser sintering (SLS). Among these, PBF mainly includes typical processes such as laser powder bed fusion (LPBF) and electron beam powder bed fusion (EBPBF). Metal additive manufacturing technology has been widely used in aerospace, biomedicine, and high-end mold making. However, in molten additive manufacturing processes, due to the high concentration of energy and extremely rapid cooling rate of the molten pool, there are severe temperature gradients and thermal stress cycles within the components, which easily generate significant residual stress and promote the formation of coarse columnar crystals and crystalline textures. These problems mainly stem from the unbalanced "rapid melting-solidification" thermal cycle process, which may lead to warping, interlaminar cracking, dimensional instability, and seriously affect the fatigue life, corrosion resistance, and uniformity of mechanical properties of components.

[0003] Currently, common methods for addressing stress issues in metal additive manufacturing include substrate preheating, scanning path optimization, and post-forming heat treatment. However, substrate preheating has limited effectiveness in high-layer deposition areas because the temperature gradient upwards from the substrate significantly decreases with increasing printing height, resulting in insufficient preheating in areas far from the heat source. High-energy beam heat source scanning path optimization cannot fundamentally eliminate stress. Post-forming heat treatment is costly, time-consuming, and prone to causing excessive grain growth, failing to effectively solve the problems of residual stress accumulation, deformation, and cracking during manufacturing. Currently, no publicly reported methods for stress organization control in metal additive manufacturing based on pulsed current have been published. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of residual stress accumulation, uneven microstructure, and grain coarsening caused by rapid non-equilibrium solidification during metal additive manufacturing, and to provide a method for synergistic control of residual stress and microstructure in the metal additive manufacturing process assisted by pulsed current.

[0005] To achieve the above objectives, the present invention provides a method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process, comprising the following steps: S1. Set the process parameters for metal additive manufacturing and plan the area and timing for synchronously applying pulse current; S2. During the layer-by-layer deposition process of the component, when a high-energy laser beam, electron beam or electric arc acts on the deposition area to form a molten pool, a pulse power supply is triggered by the synchronous control unit to apply a pulse current with preset parameters to the molten pool and the heat-affected zone. S3. Through the synergistic effect of the electroplastic effect of pulsed current and the Joule heating effect, thermal stress relaxation, grain refinement and microstructure homogenization are achieved simultaneously during the manufacturing process.

[0006] Preferably, S1 specifically includes: Based on the material and geometric characteristics of the target component, the main process parameters for metal additive manufacturing are set, and a spatiotemporal matching scheme for pulsed current application is planned. The metal additive manufacturing includes high-energy beam metal additive manufacturing and friction stir solid-state additive manufacturing.

[0007] Preferably, the spatiotemporal matching scheme for the planned pulse current application specifically involves: determining which scanning / deposition path segments, interlayer time periods, or specific regions to apply the pulse current, and identifying its application mode.

[0008] Preferably, the material of the target component includes titanium alloy, nickel-based superalloy, high-strength steel or aluminum alloy and their composite materials; The main process parameters of the high-energy beam metal additive manufacturing include energy beam power or arc current / voltage, scanning / travel speed, powder laying / powder feeding / wire feeding speed, layer thickness and scanning strategy. The main process parameters of the friction stir solid additive manufacturing include the stirring head rotation speed, axial pressure, and travel speed.

[0009] Preferably, S2 specifically includes: When the energy beam melts the material to form a molten pool, the synchronous control unit triggers the pulse power supply and applies a high-density pulse current to the molten pool and its adjacent heat-affected zone through the conductive contact device according to preset parameters, forming a local closed loop.

[0010] Preferably, the synchronous control unit receives energy beam switching signals and real-time coordinate information of the scanning path from the additive manufacturing CNC system. The additive manufacturing CNC system, driven by intelligent software and supported by precision hardware, accurately controls the printing process to achieve timing matching between pulse application and scanning path.

[0011] Preferably, S3 specifically includes: applying the pulsed current to the molten pool region through electro-thermal-mechanical-fluid multi-field coupling in a very short time, thereby achieving core control at two levels.

[0012] Preferably, the synergy between the electroplastic effect and the Joule heating effect is as follows: the Joule heating generated in the material by the high-density pulsed current forms transient and local thermal disturbances, effectively homogenizing the temperature gradient of the molten pool and its front, and interfering with the directional growth conditions of columnar crystals; at the same time, through the interaction between current carriers and atoms / defects, the stability of the solid / liquid interface, solute distribution and nucleation process are affected, jointly promoting the formation of fine equiaxed crystals and the weakening of texture.

[0013] Preferably, the pulsed current is connected to the substrate or the formed area through a conductive clamp to form a local current loop in the molten pool or high-temperature area; The pulse current is applied in a continuous mode synchronized with the scanning path or in a fixed-point mode triggered according to a specific region. The parameters of the pulse current are as follows: pulse frequency of 1-30kHz, pulse width of 20μs-20ms, and current density of 0.5-20kA / mm². 2 .

[0014] Preferably, the molten pool temperature is monitored by a temperature sensor, and the feedback signal is input to the synchronous control unit for adaptive fine-tuning of the pulse current parameters to cope with the thermal history differences caused by the complex geometry.

[0015] Therefore, the method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process described above has the following beneficial effects: (1) In the process of metal additive manufacturing, by synchronizing the high-density pulsed current with the energy beam scanning path in real time, the electro-induced effect and the controllable Joule heating effect are used to conduct in-situ multi-field intervention on the molten pool and its adjacent heat-affected zone, dynamically relax thermal stress, disturb the solidification process and suppress columnar crystal epitaxial growth and texture formation, thereby obtaining a low stress state and a uniform and refined microstructure in the manufacturing process. Through the above-mentioned in-situ comprehensive control, the residual stress level of the formed component is significantly reduced, the microstructure uniformity is significantly improved, and the comprehensive mechanical properties are comprehensively improved.

[0016] (2) This invention utilizes the real-time synchronous coupling of pulsed current and metal additive manufacturing process to effectively utilize the synergistic effect of electro-induced effect and controllable Joule heating. During the forming process, it achieves in-situ multi-field control of the thermo-mechanical-structural state of the molten pool, significantly suppressing the accumulation of residual stress and epitaxial growth of columnar crystals caused by rapid non-equilibrium solidification, thereby improving the internal stress distribution and microstructure uniformity of the component from the source. After forming, the optimized pulsed current post-processing process can be used to replace or simplify the traditional high-temperature heat treatment process, effectively reducing residual stress while maintaining or even refining the grain structure, avoiding abnormal grain growth and performance fluctuation problems in conventional heat treatment, thereby comprehensively improving the dimensional stability, mechanical property consistency and overall service performance of the component.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating a method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process, according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the PBF in-situ printing device according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of the DED in-situ printing device according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the AFSD in-situ printing device according to an embodiment of the present invention; Figure Labels 1. Powder; 2. Nozzle; 3. High-energy electron beam; 4. Molten pool; 5. Processed layer; 6. Substrate; 7. Friction stir head; 8. Alloy rod. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0020] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] like Figure 1 As shown, this invention provides a method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process. It is applicable to additive manufacturing of metallic materials such as titanium alloys, aluminum alloys, and nickel-based superalloys, and can also be extended to the field of solid-state additive manufacturing, such as stirring additive manufacturing processes. The method includes the following steps: S1. Set the process parameters for metal additive manufacturing (including high-energy beam metal additive manufacturing and friction stir solid additive manufacturing), and plan the region and timing for synchronously applying pulsed current, specifically including: Based on the material (e.g., titanium alloy, nickel-based superalloy, high-strength steel, or aluminum alloy) and geometric characteristics of the target component, set the basic process parameters for high-energy beam metal additive manufacturing, including energy beam power or arc current / voltage, scanning / travel speed, powder laying / feeding / wire feeding speed (depending on the process), layer thickness, and scanning strategy. For friction stir solid-state additive manufacturing such as AFSD, it is necessary to set the main process parameters, such as stirring head rotation speed, axial pressure, and travel speed. Plan the spatiotemporal matching scheme for pulsed current application: clarify in which scanning / deposition path segments, interlayer periods, or specific regions pulsed current is applied, and determine the pulsed current application mode.

[0022] S2. During the layer-by-layer deposition process of the component, when a high-energy laser beam, electron beam, or electric arc acts on the deposition area to form a molten pool 4, a pulse power supply is triggered by the synchronization control unit (which achieves precise coordination during the additive manufacturing process) to apply a pulse current with preset parameters to the molten pool 4 and the heat-affected zone, specifically including: When the energy beam melts the material to form a molten pool 4, the synchronous control unit immediately triggers the pulse power supply and applies a high-density pulse current to the molten pool 4 and its adjacent heat-affected zone through the conductive contact device according to preset parameters, forming a local closed loop.

[0023] The synchronous control unit receives energy beam switching signals and real-time coordinate information of the scanning path from the additive manufacturing CNC system in real time. The additive manufacturing CNC system, driven by intelligent software and supported by precision hardware, accurately controls the printing process to achieve precise timing matching between pulse application and scanning path.

[0024] The conductive contact device can be equipped with a water cooling system to prevent it from being damaged by high temperature or sticking to the workpiece.

[0025] The pulsed current is connected to the substrate 6 or the formed area through the conductive clamp, forming a local current loop in the molten pool 4 or the high temperature area.

[0026] The pulsed current can be applied in a continuous mode synchronized with the scanning path or in a fixed-point mode triggered according to a specific region. The parameters of the pulsed current are as follows: pulse frequency 1-30kHz, pulse width 20μs-20ms, and current density 0.5-20kA / mm². 2 .

[0027] The introduction of pulsed current can alter melt flow and heat transfer behavior, promoting nucleation and inhibiting columnar crystal growth, thereby refining the solidification structure, weakening the crystal texture, and effectively reducing the accumulation of thermal stress caused by rapid non-equilibrium solidification. Furthermore, pulsed current can also optimize phase composition and precipitated phase morphology by influencing solid-liquid interface stability and solute distribution, further enhancing the overall performance of the material.

[0028] S3. Through the synergistic effect of the electroplastic effect and the Joule heating effect of the pulsed current, thermal stress relaxation, grain refinement and microstructure homogenization are achieved simultaneously during the manufacturing process. Specifically, the applied pulsed current is applied to the molten pool region 4 through electro-thermal-mechanical-fluid multi-field coupling in a very short time to achieve core regulation at two levels.

[0029] The synergistic effect of electroplasticity and Joule heating is specifically manifested in the following ways: Joule heating generated in the material by high-density pulsed current creates transient and localized thermal disturbances, effectively homogenizing the temperature gradient of the molten pool 4 and its leading edge, thus interfering with the directional growth conditions of columnar crystals. Simultaneously, through the interaction between current carriers and atoms / defects, it affects the stability of the solid / liquid interface, solute distribution, and nucleation process, jointly promoting the formation of fine equiaxed crystals and textural weakening.

[0030] Thermal stress relaxation, grain refinement, and microstructure homogenization are specifically achieved through the combination of the aforementioned electro-induced effect and Joule heating effect. This significantly reduces the material's resistance to deformation at high temperatures and promotes the dynamic relaxation of transient thermal stresses generated during manufacturing. Furthermore, the electromagnetic stirring effect induced by the electric current can enhance melt convection, further breaking down dendrites and homogenizing the composition, thereby achieving in-situ refinement and homogenization of the microstructure while depositing layer by layer.

[0031] By cyclically executing S2 and S3 in each deposition layer, the regulatory effect of pulse current is deeply integrated into the manufacturing process, achieving source suppression of residual stress accumulation and simultaneous optimization of solidification structure.

[0032] The temperature of the molten pool 4 can be monitored by a temperature sensor, and the feedback signal is input to the synchronous control unit for adaptive fine-tuning of the pulse current parameters to cope with the thermal history differences caused by the complex geometry.

[0033] Example 1: Reference Figure 2Using pure titanium powder as raw material, in an inert gas protective atmosphere, the powder is selectively melted layer by layer in a laser powder bed melting technology. The powder 1 is accumulated layer by layer after being scanned by a high-energy electron beam 3. During the manufacturing process, a pulse current is applied simultaneously for auxiliary control. The pulse parameters are matched in real time according to the state of the molten pool 4. Residual stress is tested at three locations before and after the application of the pulse current using high-energy X-rays.

[0034] Example 2: Reference Figure 3 Laser fused wire additive manufacturing is carried out using TC4 titanium alloy wire. A molten pool 4 is formed on the substrate 6 by a high-energy laser beam. The raw material is fed into the molten pool 4 by the nozzle 2 to melt. After cooling, the processed layer 5 is formed on the substrate 6 by layer accumulation. Pulsed current is introduced during the process to cooperate with the process. Residual stress is tested at three positions before and after the pulsed current is applied using high-energy X-rays.

[0035] Example 3: Reference Figure 4 Using titanium 55531 alloy as the material, the alloy rod 8 is deposited layer by layer through friction stir additive manufacturing technology. A plasticized zone is generated on the substrate 6 by a high-speed rotating friction stir head 7. The alloy rod 8 is plasticized and deposited layer by layer by the rotation and lateral movement of the friction stir head. After cooling, the layers are accumulated to form a processed layer 5 on the substrate 6. A pulsed current is introduced during the deposition process to achieve a synergistic effect. Residual stress is tested at three locations before and after the application of the pulsed current using high-energy X-rays.

[0036] The test results for the three embodiments are shown in Table 1. High-energy X-ray diffraction was used to measure the residual stress distribution inside the component before and after the application of the pulsed current at three different locations. Comparative analysis shows that after the application of the pulsed current, the residual stress values ​​at each detection point decreased, and the stress concentration phenomenon was alleviated. This result confirms that the introduction of pulsed current can effectively control the thermo-mechanical coupling effect in the additive manufacturing process, thereby achieving active reduction and homogenization of residual stress.

[0037] Table 1: Test Results

[0038] Therefore, the present invention adopts the above-mentioned method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process. By synchronously applying the pulsed current and the energy beam scanning path to the molten pool and its adjacent heat-affected zone, the electro-thermal-mechanical multi-field coupling effect generated by the pulsed current is utilized to achieve dynamic relaxation of residual stress and in-situ control of solidification microstructure while the component is formed layer by layer.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process, characterized in that, Includes the following steps: S1. Set the process parameters for metal additive manufacturing and plan the area and timing for synchronously applying pulse current; S2. During the layer-by-layer deposition process of the component, when a high-energy laser beam, electron beam or electric arc acts on the deposition area to form a molten pool, a pulse power supply is triggered by the synchronous control unit to apply a pulse current with preset parameters to the molten pool and the heat-affected zone. S3. Through the synergistic effect of the electroplastic effect of pulsed current and the Joule heating effect, thermal stress relaxation, grain refinement and microstructure homogenization are achieved simultaneously during the manufacturing process.

2. The method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process according to claim 1, characterized in that, S1 specifically includes: Based on the material and geometric characteristics of the target component, the main process parameters for metal additive manufacturing are set, and a spatiotemporal matching scheme for pulsed current application is planned. The metal additive manufacturing includes high-energy beam metal additive manufacturing and friction stir solid-state additive manufacturing.

3. The method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process according to claim 1, characterized in that, The specific spatiotemporal matching scheme for the planned pulse current application is as follows: clearly define which scanning / deposition path segments, interlayer time periods, or specific regions to apply the pulse current, and determine its application mode.

4. The method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process according to claim 2, characterized in that, The target component is made of titanium alloys, nickel-based superalloys, high-strength steel or aluminum alloys and their composite materials. The main process parameters of the high-energy beam metal additive manufacturing include energy beam power or arc current / voltage, scanning / travel speed, powder laying / powder feeding / wire feeding speed, layer thickness and scanning strategy. The main process parameters of the friction stir solid additive manufacturing include the stirring head rotation speed, axial pressure, and travel speed.

5. The method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process according to claim 1, characterized in that, S2 specifically includes: When the energy beam melts the material to form a molten pool, the synchronous control unit triggers the pulse power supply and applies a high-density pulse current to the molten pool and its adjacent heat-affected zone through the conductive contact device according to preset parameters, forming a local closed loop.

6. The method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process according to claim 5, characterized in that, The synchronous control unit receives energy beam switching signals and real-time coordinate information of the scanning path from the additive manufacturing CNC system, thereby achieving timing matching between pulse application and the scanning path.

7. The method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process according to claim 1, characterized in that, Specifically, S3 includes: applying the pulsed current to the molten pool region through electro-thermal-mechanical-fluid multi-field coupling in a very short time, thereby achieving core control at two levels.

8. The method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process according to claim 1, characterized in that, The synergy between the electroplastic effect and the Joule heating effect is as follows: the Joule heating generated in the material by the high-density pulsed current forms transient and local thermal disturbances, effectively homogenizing the temperature gradient of the molten pool and its front, and interfering with the directional growth conditions of columnar crystals; at the same time, through the interaction between current carriers and atoms / defects, it affects the stability of the solid / liquid interface, solute distribution and nucleation process, jointly promoting the formation of fine equiaxed crystals and the weakening of texture.

9. The method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process according to claim 5, characterized in that, The pulsed current is connected to the substrate or the formed area through a conductive clamp, forming a local current loop in the molten pool or high-temperature area. The pulse current is applied in a continuous mode synchronized with the scanning path or in a fixed-point mode triggered according to a specific region. The parameters of the pulse current are as follows: pulse frequency of 1-30kHz, pulse width of 20μs-20ms, and current density of 0.5-20kA / mm². 2 .

10. The method for synergistic control of residual stress and microstructure in a pulsed current-assisted metal additive manufacturing process according to claim 1, characterized in that, The molten pool temperature is monitored by a temperature sensor, and the feedback signal is input to the synchronous control unit to adaptively fine-tune the pulse current parameters in order to cope with the thermal history differences caused by the complex geometry.

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