A method for removing supports and finishing the inner wall of complex internal cavity structures produced by laser additive manufacturing.

Abstract

This invention discloses a method for removing supports and finishing the inner walls of complex internal cavity structures in laser additive manufacturing. Addressing the current challenges in removing supports and finishing the inner walls of complex internal cavity components in laser additive manufacturing, and specifically targeting precipitation-strengthened alloy systems such as aluminum alloys and nickel-based superalloys, this invention increases the laser energy input at the cavity / support interface to pre-create a rich precipitated corrosion weakening layer. Combined with an electrochemical post-processing step, it achieves controllable dissolution and support removal at the solid / support interface, simultaneously achieving the "step effect" and finishing of slag and powder adhering to the internal wall of the complex cavity. This results in a smooth, support-free complex internal cavity structure manufactured using laser additive manufacturing. This method simultaneously solves the current problems of the inability to remove auxiliary supports and the difficulty in finishing the inner cavity of complex internal cavity structures in laser additive manufacturing, broadening the application of laser additive manufacturing of complex internal cavity structures and offering high operability.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing, specifically relating to a method for removing supports and finishing the inner walls of complex internal cavity structures produced by laser additive manufacturing. Background Technology

[0002] Laser additive manufacturing (LPBF) technology enables the integrated forming of complex components based on a layer-by-layer melting and deposition process. In particular, laser powder bed fusion (LPBF), based on a powder bed laying process, can achieve layer-by-layer powder placement and selective laser melting deposition with micron-level (20-50 μm) thicknesses, offering significant advantages in forming precision and complex components for the aerospace industry. However, current LPBF technology still faces forming constraints. During the forming of overhanging structures, the high-energy laser beam directly acts on the loose powder bed, easily leading to slag buildup at the bottom of the overhanging structure and localized heat accumulation and warping, resulting in a significant reduction in dimensional accuracy and surface finish. Therefore, for forming complex overhanging surfaces, auxiliary support structures are typically designed between the forming substrate and the overhanging surface to suppress slag adhesion, stabilize the forming process, and resist stress deformation. These support structures are crucial for LPBF forming of complex structures. However, current LPBF forming processes with complex internal cavities / channels still face two main technical challenges.

[0003] First, the auxiliary support structure needs to be removed after forming. Currently, cutting and manual grinding are commonly used to remove the auxiliary support structure in LPBF forming. However, for components with complex internal cavity structures, the internal overhanging surfaces require the addition of support structures during forming to ensure forming quality. After forming, cutting is not possible due to three-dimensional space limitations. Therefore, the method for removing the auxiliary support structure inside the complex internal cavity structure formed by LPBF forming is one of the key technological problems that needs to be solved. Second, the layer-by-layer forming characteristic of LPBF easily produces a "step effect" in forming complex internal cavity structures with curvature, resulting in a significant reduction in surface quality. At the same time, complex internal cavities are prone to powder adhesion and overhanging slag during forming, affecting the service characteristics of complex flow channels. Therefore, post-processing finishing of the flow channel inner wall is required. Currently, commonly used internal flow channel finishing methods include abrasive flow, chemical polishing, and electrochemical polishing, but these are not very applicable to complex structures in additive manufacturing, fine diameter, and large-angle internal flow channels, and cannot remove the support structure.

[0004] In summary, LPBF technology has significant advantages in forming complex aerospace structural parts, but it still faces challenges in forming structures with complex internal cavities / flow channels, such as difficulties in removing internal cavity support structures and low forming quality of the inner wall. Currently, there is no process method to simultaneously achieve the removal of internal cavity support structures and the finishing of the inner wall. Summary of the Invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is the difficulty in removing the inner cavity support structure and the low quality of the inner wall forming in the existing laser powder bed fusion (LPBF) technology for forming complex inner cavity / inner flow channel structures. The invention proposes a method for removing the inner cavity support structure and finishing the inner wall.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for removing supports and finishing the inner wall of a complex internal cavity structure produced by laser additive manufacturing includes the following steps:

[0008] S1. Selection of applicable matrix materials: Select matrix materials with precipitation strengthening properties and good laser powder bed melting formability, including any one of lightweight high-strength aluminum alloys and nickel-based high-temperature alloys;

[0009] S2. Interface Feature Recognition: Using support addition software, support design and addition are performed on components with complex internal cavity structures. Interface features are identified and divided in the contact area between the internal cavity support and the component solid, which is divided from top to bottom into "solid material area", "weakened interface area" and "support structure area".

[0010] S3, Laser Additive Manufacturing Process Matching: Differentiated additive manufacturing laser process matching is performed on the interface feature areas of step S2, and the laser energy density method is used to measure its laser energy input;

[0011] The laser energy density in the "solid material region" is η 实 The laser energy density in the "weakened interface region" is η 界 The laser energy density of the "support structure region" is η 支 ;in, η 界 / η 实 ≥1.5, and η 支 / η 实 ≤0.8;

[0012] S4. Electrochemical post-treatment: The above-formed additive component is connected to the anode as the working electrode, and the titanium mesh is connected to the cathode as the counter electrode. It is then placed in an etching tank containing polishing solution and subjected to electrochemical post-treatment to obtain the final product.

[0013] Preferably, in step S1, the lightweight high-strength aluminum alloy includes, but is not limited to, Al-Cu alloy (Cu 4.0-5.5 wt%), Al-Mg-Si alloy (Si 4.0-7.0 wt%, Mg 0.1-1.0 wt%), Al-Zn alloy (Zn 2.0-8.0 wt%, Mg 0.1-3.0 wt%), trace element modified Al-Mg alloy, trace element modified Al-Mn alloy, etc.

[0014] Preferably, the trace elements include, but are not limited to, Sc, Zr, Er, Ti, etc.

[0015] Preferably, in step S1, the nickel-based superalloys include, but are not limited to, GH4169 alloy, Inconel 600 alloy, Inconel 625 alloy, Rene 80 alloy, Rene 125 alloy, Rene 142 alloy, etc.

[0016] Specifically, in step S2, the overhanging surface is identified based on the base alloy, wherein the angle between the aluminum alloy and the substrate is ≤45° and the angle between the nickel-based alloy and the substrate is ≤35°. Self-use supports are added to the marked overhanging surface, and the support types include but are not limited to block supports, conical supports, and hybrid supports.

[0017] Specifically, in step S2, the bottom boundary of the "solid material area" coincides with the model outline; the thickness of the "weakened interface area" is between 0.5 mm and 1 mm, and its top interface coincides with the model outline; the top area of ​​the "support structure area" coincides with the bottom of the "weakened interface area".

[0018] Specifically, in step S3, the laser energy density of each interface feature region is determined by the formula... η = P / Vdh To determine; whereby laser power is defined as P The unit is W, and the suitable range is 200-150 W; the laser scanning speed is defined as... V The unit is mm / s, and the suitable range is 800 mm / s-2500 mm / s; the scanning interval is defined as... h The unit is μm, and the suitable range is 60-120 μm; the scanning layer thickness is defined as... d， The unit is μm, and the suitable range is 30-50μm.

[0019] Preferably, in step S4, the concentration of the electrolyte for electrochemical post-treatment is 0.5-1.0 mol / L, the treatment temperature is 35℃, the treatment time is 0.5-5 h, and the voltage is 6-10 V.

[0020] Preferably, in step S4, for the aluminum alloy substrate material, the electrolyte may be: Na2CO3 80-120 g / L, Na3PO4 45-75 g / L, NaOH 15-40 g / L, complexing agent 15-40 mL / L, and water as the solvent; the bath temperature is 50-80℃, and the current density is 520 A / dm³. 2 Voltage 2-4V, time 15 min - 4 h.

[0021] Preferably, in step S4, for the nickel-based alloy matrix material, the electrolyte can be a mixed aqueous solution of 60-80% phosphoric acid and 20-40% sulfuric acid, the bath temperature is 40-70℃, and the current density is 40-60 A / dm³. 2 Voltage 2-4 V, time 1 min - 30 min. Beneficial effects

[0022] This invention focuses on the collaborative processing of the support structure and inner surface finishing of complex internal cavity components manufactured using additive manufacturing. A 0.5-1 mm thick weakening layer is designed at the interface between the component solid and the support structure. Furthermore, laser technology is used to control the energy input of the weakening layer at the interface. η 界 / η 实 ≥1.5, for precipitation-strengthened alloy systems, the weakened interface designed for complex internal cavity solids / supports undergoes controlled coarsening of precipitates due to increased energy input. In the weakened interface region, the increased laser energy leads to increased molten pool heat accumulation, resulting in higher temperature and slower solidification rate, which in turn promotes the enrichment and coarsening of Al3(Sc,Zr) precipitates along grain boundaries. These enriched and coarsened precipitates distributed along the weakened region have a significant potential difference with the matrix, forming localized microcouples that dissolve rapidly during subsequent electrochemical polishing. By controlling the corrosion and dissolution of the weakened interface layer along the pre-set weakened layer during polishing due to precipitation coarsening, the internal support structure of the complex internal cavity structure can be removed in post-processing. Simultaneously, the "step effect" and slag / powder adhering to the internal wall of the complex internal cavity are addressed, resulting in a smooth, unsupported laser additive manufacturing complex internal cavity structure. This method simultaneously solves the current problems of the inability to remove auxiliary supports and the difficulty of internal cavity finishing in laser additive manufacturing of complex internal cavity structures, broadening the application of laser additive manufacturing of complex internal cavity structures and demonstrating strong operability. Attached Figure Description

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0024] Figure 1 This is a process flow diagram of the method of the present invention.

[0025] Figure 2A schematic diagram of the support / solid interface feature recognition process for additive manufacturing of complex internal cavity structures.

[0026] Figure 3 This is a microstructure diagram of the interface weakening layer after matching the additive manufacturing process proposed in this invention.

[0027] Figure 4 This is a surface SEM image of Example 1 in a specific implementation.

[0028] Figure 5 This is a surface SEM image of Example 3 in a specific implementation.

[0029] Figure 6 This is a surface SEM image of Example 6 in a specific implementation.

[0030] Figure 7 This is a surface SEM image of Example 8 in a specific implementation. Detailed Implementation

[0031] The present invention can be better understood from the following embodiments. Example 1

[0032] Combination Figure 1 The present invention provides a method for removing supports and finishing the inner wall of complex internal cavity structures produced by laser additive manufacturing, comprising the following steps:

[0033] Step 1: Optimize the alloy system with precipitation strengthening properties and good laser powder bed melting formability. The selected material system is an Al-Mg-Mn-Si alloy, with the alloy composition as follows: Mg 7-9 wt.%, Si 0.4-1.2 wt.%, Mn 0.3-0.8 wt.%, Sc 0.5-0.7 wt.%, Zr 0.2-0.5 wt.%, and the balance being Al. The raw material is spherical alloy powder with a particle size of 15-53 μm and D... 50 ≥23 μm. The powder should be dry and have good flowability.

[0034] Step Two: For parts with complex internal cavity structures to be formed, pre-processing software such as MaterialsLise Magics is first used to add supports. Overhanging surfaces are identified based on the original alloy system, where the angle between the overhanging surface and the substrate is ≤45° for aluminum alloys and ≤35° for nickel-based alloys. Supports are then added to the marked overhanging surfaces, including but not limited to block supports, tapered supports, and hybrid supports. Further, the support structures generated within the complex component's internal cavity are selected, and feature areas are identified and divided at the support / solid component interface.

[0035] Feature interface recognition and segmentation process as follows Figure 2As shown, for the contact area between the complex internal cavity support structure and the solid part, from top to bottom, it is divided into the "solid material area," "weakened interface area," and "support structure area." The bottom boundary of the solid material area coincides with the model outline. The thickness of the weakened interface area should be between 0.5 mm and 1 mm, and its top interface coincides with the model outline. The top area of ​​the support structure area coincides with the bottom of the weakened interface area.

[0036] Step 3: After completing the addition of the support structure and feature interface identification in Step 2, perform additive manufacturing process matching design. First, conduct process experiments to determine the laser process range for the "solid material area." Use the laser energy density method to measure the laser energy input, where laser power is defined as... P Laser scanning speed is defined as V The scanning interval is defined as h The scanning layer thickness is defined as d Then the laser energy density can be defined as: η = P / Vdh .

[0037] In step three of the additive manufacturing process matching process, the ratio of laser energy density in the weakened interface region to laser energy density in the solid material region should meet the following requirements: η 界 / η 实 ≥1.5, the ratio of laser energy density in the supporting structure region to the laser energy density in the solid material region should meet the following requirements. η 支 / η 实 ≤0.8. Specifically, the fixed layer thickness is 30 μm, the scanning interval is 60 μm, the laser power in the solid material area is 350 W, and the laser scanning speed is 1200 mm / s; the laser power in the weakened interface area is 400 W, and the laser scanning speed is 800 mm / s; the laser power in the support structure area is 300 W, and the laser scanning speed is 1400 mm / s. Based on this process setting, standardized laser additive manufacturing is performed layer by layer until the processing is completed and the material is removed, and the powder in the inner cavity is removed.

[0038] Step 4: Electrochemical Post-treatment: The additively manufactured complex internal cavity component formed using the above process is connected to the anode as the working electrode, and a titanium mesh is connected to the cathode as the counter electrode. It is then placed in an etching tank containing electrolyte and subjected to electrochemical post-treatment. The electrolyte tank temperature is 50-80℃, and the current density is 5-20 A / dm³. 2 The polishing process involves a voltage of 2-4 V and a polishing time of 1 hour. The polishing temperature is 35℃, the polishing time is 40-60 minutes, and the voltage is 6-8 V. Based on these steps, laser additive manufacturing of components with complex internal cavity structures, removal of internal cavity supports, and finishing of the internal cavity surface are achieved.

[0039] The electrolyte in step four consists of 80-120 g / L Na2CO3, 45-75 g / L Na3PO4, 15-40 g / L NaOH, and 15-40 mL / L complexing agent.

[0040] Figure 3 This is a microstructure diagram of the interface weakening layer after the additive manufacturing process of this invention. Figure 4 This is a SEM image of the surface of the component formed in this embodiment. It can be seen that in the interface weakening region, due to the increased laser energy, the molten pool heat accumulation effect increases, leading to a rise in temperature and a slower solidification rate, which in turn promotes the enrichment and coarsening of Al3(Sc,Zr) precipitates along the grain boundaries. These enriched and coarsened precipitates distributed along the weakening region have a significant potential difference with the matrix, forming localized microcouples that dissolve rapidly during the subsequent electrochemical polishing process. Through controlled corrosion dissolution along the pre-set weakening layer due to precipitation coarsening of the weakened interface layer during polishing (e.g., ... Figure 4 As shown, the process achieves post-processing removal of the internal support structure of the complex internal cavity structure, and simultaneously realizes the "step effect" and slag and powder adhering finishing of the internal wall of the complex internal cavity, so as to obtain a smooth and unsupported laser additive manufacturing complex internal cavity structure. Example 2

[0041] This embodiment differs from Embodiment 1 in that: the alloy system described in step one is a nickel-based high-temperature alloy, specifically GH416 alloy. In step two, the overhanging surface is identified as a nickel-based alloy with an angle ≤35° with the substrate. In step three, the forming parameters are as follows: the fixed layer thickness is 50 μm, the scanning interval is 60 μm, the laser power in the solid material area is 300 W, and the laser scanning speed is 1500 mm / s; the laser power in the weakened interface area is 400 W, and the laser scanning speed is 1000 mm / s; the laser power in the support structure area is 200 W, and the laser scanning speed is 1500 mm / s. In step four, the electrolyte is a mixture of 60-80% phosphoric acid and 20-40% sulfuric acid, the bath temperature is 40-70℃, and the current density is 40-60 A / dm³. 2 Voltage 2-4 V, time 1 min - 30 min. Everything else is the same as in Example 1. Example 3

[0042] The difference between this embodiment and Embodiment 1 is that feature interface identification was not performed in step two, and additive process matching design was not performed in step three. All forming process parameters are fixed at a layer thickness of 30 μm, a scanning spacing of 60 μm, a laser power of 350 W, and a laser scanning speed of 1200 mm / s. Everything else is the same as in Embodiment 1. The SEM image of the surface of the component formed in this embodiment is shown below. Figure 5 As shown. Example 4

[0043] The difference between this embodiment and Embodiment 1 is that the energy density of the "weakened interface region" is reduced during the additive manufacturing process matching design in step three. Specifically, the laser power is 400 W and the laser scanning speed is 1000 mm / s. η 界 / η 实 =1.37 < 1.5. Everything else is the same as in Example 1. Example 5

[0044] The difference between this embodiment and Embodiment 1 is that the thickness of the "weakened interface area" is set to 0.3 mm during the interface identification and segmentation in step two. Everything else is the same as in Embodiment 1. Example 6

[0045] The difference between this embodiment and Embodiment 1 is that the thickness of the "weakened interface area" is set to 1.5 mm during the interface identification and segmentation in step two. Everything else is the same as in Embodiment 1. The SEM image of the surface of the component formed in this embodiment is shown below. Figure 6 As shown. Example 7

[0046] The difference between this embodiment and Embodiment 1 is that the treatment time in step two, the electrochemical post-treatment, is set to 10 minutes. Everything else is the same as in Embodiment 1. Example 8

[0047] The difference between this embodiment and Embodiment 1 is that the treatment time in step two, the electrochemical post-treatment, is set to 6 hours. Everything else is the same as in Embodiment 1. The SEM image of the surface of the component formed in this embodiment is shown below. Figure 7 As shown.

[0048] The inner cavity section of the formed specimen was cut, ground, and polished. The removal of supports was observed, and the roughness of the inner wall was measured. The test results of different embodiments are shown in Table 1.

[0049] Table 1. Support removal effect and inner cavity surface roughness of different embodiments

[0050]

[0051] As can be seen from Table 1:

[0052] Comparing Example 1 and Example 2, it is shown that this method has good effects on systems such as aluminum alloys and nickel-based alloys with precipitation strengthening properties. Figure 4 As shown, the surface treated by this method is smooth and continuous, with no obvious support structure residue or surface slag / powder adhesion. The roughness is better than 1.6μm, achieving good post-treatment surface finishing and support simultaneous removal effect.

[0053] Comparing Examples 1 and 3, when key steps proposed in this invention, such as feature interface identification and additive process matching, are missing, conventional methods cannot simultaneously achieve the removal of the internal cavity support structure and the finishing of the internal wall. (See Appendix) Figure 4 If the feature interface identification step 2 and the additive manufacturing process matching step 3 proposed in this invention are not applied during the processing, the support structure still exists after the same electrochemical polishing treatment, meaning that the support structure cannot be removed. Furthermore, although the surface achieves a certain degree of finishing effect due to the absence of support structure removal, powder adhesion still exists on the surface.

[0054] Comparing Example 1 and Example 4, when the laser energy density of the weakened interface layer is insufficient... η 界 / η 实 =1.37 < 1.5. At this point, the coarsening degree of the weakened stratified precipitates is not significantly different from that of the matrix material, making it impossible to achieve controllable dissolution and support removal along the interface layer.

[0055] Comparing Example 1 and Example 5, when the thickness of the weakened interface layer is insufficient, the local energy is insufficient to generate a continuous coarsening corrosion weakened layer, and the controllable removal of the support structure cannot be achieved at this time.

[0056] Comparing Example 1 and Example 6, when the thickness of the weakened interface layer is too thick, the comparison shows that... Figure 4 With appendix Figure 6 When the weakened interface layer proposed in this method is too thick, the remaining root after the support is removed will result in high roughness. At the same time, the support structure is not completely removed, and it is impossible to achieve simultaneous finishing of the support structure removal and the surface.

[0057] Comparing Example 1 and Example 7, when the electrochemical post-treatment time is too short, the controllable dissolution time of the weakened interface layer is insufficient, and the effect of removing the complex internal cavity support after post-treatment cannot be achieved.

[0058] Comparing Example 1 and Example 8, and comparing Appendix Figure 4 With appendix Figure 7 When the electrochemical post-treatment time is too long, dissolution and corrosion pits appear in the matrix area of ​​the inner cavity. This is because when the electrochemical treatment time is too long, a small amount of precipitated phase in the matrix reacts with the electrolyte to form local microcouples. Under long-term treatment, the matrix material dissolves along the grain boundaries, resulting in corrosion pits and increased surface roughness.

[0059] This invention provides a method for removing supports and finishing the inner walls of complex internal cavity structures created by laser additive manufacturing. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for removing supports and finishing the inner wall of complex internal cavity structures produced by laser additive manufacturing, characterized in that, Includes the following steps: S1. Selection of applicable matrix materials: Select matrix materials with precipitation strengthening properties and good laser powder bed melting formability, including any one of aluminum alloys and nickel-based alloys; S2. Interface Feature Recognition: Using support addition software, support design and addition are performed on components with complex internal cavity structures. Interface features are identified and divided in the contact area between the internal cavity support and the component solid, which is divided into "solid material area", "weakened interface area" and "support structure area" from top to bottom. S3, Laser Additive Manufacturing Process Matching: Differentiated additive manufacturing laser process matching is performed on the interface feature areas of step S2, and the laser energy density method is used to measure its laser energy input; The laser energy density in the "solid material region" is η 实 The laser energy density in the "weakened interface region" is η 界 The laser energy density of the "support structure region" is η 支 ; in, η 界 / η 实 ≥1.5, and η 支 / η 实 ≤0.8; S4. Electrochemical post-treatment: The above-formed additive component is connected to the anode as the working electrode, and the titanium mesh is connected to the cathode as the counter electrode. It is then placed in an etching tank containing polishing solution and subjected to electrochemical post-treatment to obtain the final product. In step S1, the aluminum alloy includes any one of Al-Cu alloy, Al-Mg-Si alloy, Al-Zn alloy, trace element modified Al-Mg alloy, and trace element modified Al-Mn alloy; the nickel-based alloy includes any one of GH4169 alloy, Inconel 600 alloy, Inconel 625 alloy, Rene 80 alloy, Rene 125 alloy, and Rene 142 alloy. In step S2, the bottom boundary of the "solid material area" coincides with the model outline; the thickness of the "weakened interface area" is between 0.5 mm and 1 mm, and its top interface coincides with the model outline; the top area of ​​the "support structure area" coincides with the bottom of the "weakened interface area". In step S3, the laser energy density of each interface feature region is determined by the formula... η = P / Vdh To determine; whereby laser power is defined as P The unit is W; the laser scanning speed is defined as... V Unit: mm / s; Scanning distance is defined as... h Unit: μm; Scan layer thickness is defined as... d， Unit: μm; laser power P The value range is 200-150 W, and the laser scanning speed is... V The value range is 800 mm / s-2500 mm / s, and the scanning interval is... h The value range is 60-120μm, and the value range of the scanning layer thickness is 30-50μm; In step S4, when the base material is aluminum alloy, the electrolyte is: Na2CO3 80-120g / L, Na3PO4 45-75g / L, NaOH 15-40g / L, complexing agent 15-40mL / L, and water as the solvent; the bath temperature is 50-80℃, and the current density is 5-20A / dm³. 2 Voltage 2-4 V, time 15 min - 4 h; In step S4, when the base material is a nickel-based alloy, the electrolyte is a mixed aqueous solution of 60-80% phosphoric acid and 20-40% sulfuric acid, the bath temperature is 40-70℃, and the current density is 40-60 A / dm³. 2 Voltage 2-4 V, time 1 min - 30 min.

2. The method for removing supports and finishing the inner wall of complex internal cavity structures in laser additive manufacturing according to claim 1, characterized in that, The trace elements mentioned are any one or a combination of two or more of Sc, Zr, Er, and Ti.

3. The method for removing supports and finishing the inner wall of complex internal cavity structures in laser additive manufacturing according to claim 1, characterized in that, In step S2, the overhanging surface is identified based on the base alloy. For aluminum alloys, the angle between the overhanging surface and the substrate is ≤45°, and for nickel-based alloys, the angle between the overhanging surface and the substrate is ≤35°. Self-use supports are added to the marked overhanging surface. The support type includes any one of block support, conical support, or hybrid support.

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