A method of repairing a titanium alloy additively manufactured piece by laser directed energy deposition

Abstract

This invention proposes a method for repairing titanium alloy additive manufacturing parts by laser-directed energy deposition, comprising: material pretreatment: removing cracks by machining, dividing the workpiece into a main body and corner blocks according to the crack location, and beveling the main body and corner blocks according to the nozzle forming direction; repairing the titanium alloy additive manufacturing parts by laser-directed energy deposition technology: (1) forming a receiving platform on the cut of the main body and corner blocks; (2) formal filling: the three parts to be filled according to the repair sequence are the corner part, the side boundary and the top boundary in the same direction as the forming direction, fixing and calibrating the position of the main body and corner blocks with a fixture, filling the corner part first, and connecting the corner block and the main body; completing the filling of the side boundary by the method of positive and negative symmetry repair, and then completing the filling of the top boundary by the method of positive and negative symmetry repair; this invention can improve the repair quality of additive manufacturing parts.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology, and in particular to a method for repairing titanium alloy additive manufacturing parts by laser-directed energy deposition. Background Technology

[0002] Additive manufacturing is a technology that creates three-dimensional objects by depositing materials layer by layer. This technology is currently widely used in aerospace, automotive, medical, and precision engineering fields.

[0003] In the aerospace field, additive manufacturing technology is used to manufacture complex parts, such as engine components, structural assemblies, and specialized tools. These applications typically require parts with high geometric complexity, excellent mechanical properties, and stringent quality standards.

[0004] Titanium alloys are particularly important in the aerospace field due to their excellent strength, weight ratio, and corrosion resistance. However, the additive manufacturing process of titanium alloys is complex and susceptible to the effects of heat input and cooling rates, which can lead to defects such as thermal stress and cracking in components. Traditional repair methods to address these issues include welding and machining. Traditional welding methods can easily introduce new stresses and deformations when repairing high-performance materials, especially for complex additively manufactured parts. The high heat input during welding can cause over-hardening or softening of the heat-affected zone, affecting the overall performance of the component. Furthermore, the welding thermal cycle can also cause microstructural changes, reducing the material's fatigue life. While machining can provide high dimensional accuracy, it is often inefficient when repairing additively manufactured parts with complex geometries. In addition, machining may remove excessive material, altering the component's design intent and performance specifications. For internal defects, such as internal cracks, machining is almost ineffective in repairing them. Therefore, traditional repair methods often fail to meet the required accuracy and material performance requirements, or may lead to additional stress concentration and structural weakening.

[0005] To address these issues, laser-directed energy deposition (LDED) has been applied to the repair of additively manufactured parts. LDED is a technique that uses a high-energy laser beam to melt metal powder and form a solid material. By using a precisely controlled laser beam, material is added directly to the surface of the material, allowing for the precise repair of damaged areas in additively manufactured parts. Compared to traditional repair methods, LDED offers the following advantages:

[0006] (1) Precise control of the repair process: Laser-directed energy deposition technology can precisely control laser parameters (such as power, scanning speed, etc.) and effectively manage the morphology of the molten pool, thereby ensuring the accuracy and consistency of the repair area.

[0007] (2) Minimize thermal impact: The thermal impact zone of laser-directed energy deposition technology is smaller than that of traditional welding, which reduces the risk of changes in material properties and stress concentration.

[0008] (3) Adapting to complex geometries: Laser-directed energy deposition technology can adapt to the complex geometries of additively manufactured parts, and can even effectively repair internal structures, which is difficult to achieve with traditional machining.

[0009] (4) Improve material utilization: Laser-directed energy deposition technology repairs defects by adding a precise amount of material, which greatly reduces material waste compared with machining.

[0010] However, implementing laser-directed energy deposition (LDED) technology faces several challenges. First, the selection of laser parameters is crucial to the morphology and temperature distribution of the molten pool, directly affecting the microstructure and mechanical properties of the repaired area. Second, the repair strategy needs careful design to ensure the overall performance and reliability of the repaired component. Summary of the Invention

[0011] The purpose of this invention is to provide a method for repairing titanium alloy additive manufacturing parts by laser-directed energy deposition, so as to improve the repair quality of additive manufacturing parts, extend their service life, and reduce manufacturing costs.

[0012] The technical solution to achieve the purpose of this invention is as follows:

[0013] A method for repairing titanium alloy additively manufactured parts by laser-directed energy deposition includes:

[0014] The first step is material pretreatment: the cracks are removed by machining, the workpiece is divided into main body and corner blocks according to the location of the cracks, and the main body and corner blocks are beveled according to the nozzle forming direction.

[0015] The second step involves repairing the titanium alloy additively manufactured parts using laser-directed energy deposition technology.

[0016] (1) Form the receiving platform on the cuts of the main body and corner pieces;

[0017] (2) Perform formal filling: The three parts that need to be filled according to the repair order are the corner part, the side boundary and the top boundary in the same direction as the forming direction. Use a clamp to fix and check the position of the main body and the corner block. Fill the corner part first and connect the corner block and the main body. Complete the filling of the side boundary by the positive and negative symmetry repair method, and then complete the filling of the top boundary by the positive and negative symmetry repair method.

[0018] (3) Remove excess material from both sides of the melt channel.

[0019] The significant advantages of this invention compared to existing technologies are:

[0020] (1) By pre-processing, i.e., machining a 45° bevel at the defect and then forming a frustum / triangular prism-shaped receiving platform, a wider pose transformation space can be provided for the coaxial nozzle in subsequent steps, avoiding interference between the workpiece and the coaxial powder flow in spatial geometry during the repair process, ensuring sufficient powder flow filling, and enabling effective metal cladding at the repair site, thus avoiding defects. The repair sequence is the corner part, the side boundary and the top boundary in the same direction as the forming direction. Because the angle of the corner part is small, the interference problem during the filling process is serious, so filling is performed first. After completing the deposition forming of the bevel on the plane, the main body and corner block positions are fixed and checked using a fixture. By using a symmetrical repair method, the two sides of the workpiece are filled and repaired in sequence to reduce the influence of thermal stress and residual stress caused by forming, and the filling is completed.

[0021] (2) It can set the path for the repair area. Laser directional energy deposition technology can adapt to the complex geometry of additive manufacturing parts and can effectively repair even the internal structure, which is difficult to achieve with traditional machining. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the laser-directed energy deposition repair process for deep or penetrating defects at corner locations.

[0023] Figure 2 Case 1: Laser-directed energy deposition repair.

[0024] Figure 3 To repair the non-destructive film image in Case 1. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0026] This invention discloses a method for repairing titanium alloy additively manufactured parts using laser-directed energy deposition (EDD) technology. For complex-shaped titanium alloy parts with defects, after removing the defects, a precisely controlled laser beam is used to melt and deposit energy at the defect removal site, thereby achieving efficient repair of the damaged portion. The repaired workpiece undergoes non-destructive testing and meets the required standards. The specific steps are as follows:

[0027] Step 1: Material pretreatment: Pretreatment of the repair area. First, according to the actual defect, the crack is removed by mechanical processing. The workpiece is divided into the main body and corner pieces. After removal, a trapezoidal opening is made at the repair area according to the nozzle forming direction and orientation. A bevel is machined with a bevel angle of 45°.

[0028] Step 2: Repairing the titanium alloy additively manufactured part using laser-directed energy deposition (LDED) technology. This includes the following steps:

[0029] Step 2-1: Select the process parameters for material consumption: Precisely adjust the parameters of laser directional energy deposition according to the workpiece structure and defect type. The laser power is 500-800w, the laser radius is 0.5-1.5mm, the scanning rate is 6-10mm / s, and the powder feeding rate is 4-6g / min.

[0030] Step 2-2: Inert gas sealing. Since the forming material is a Ti alloy, its cladding forming needs to be carried out in an oxygen-free and nitrogen-free environment. Therefore, the workpiece is placed in a sealed chamber for sealing, and protective gas is continuously introduced into the sealed environment. The preparation is completed when the oxygen content is less than 10 ppm.

[0031] Steps 2-3: Repairing the workpiece using a coaxial laser nozzle cladding process involves two steps. First, pre-treatment of the cut interface is performed, forming frustum or triangular prism-shaped receiving platforms on the planar cuts of the main body and corner blocks. This step provides a wider pose transformation space for the coaxial nozzle in subsequent steps, avoiding spatial geometric interference between the workpiece and the coaxial powder flow during repair, ensuring sufficient powder filling, and polishing to improve laser energy absorption and powder utilization during forming. Polishing requires thorough removal of the oxide film, revealing the metallic color of the surface. Then, formal filling is performed: based on the forming parameters of the laser-directed energy deposition powder, a repair path planning program is written for the specific defects in the workpiece, and laser cladding repair is carried out. Quality is checked every three layers during forming, and process parameters are adjusted promptly according to the repair quality. During this process, the three parts to be filled according to the repair sequence are the corner parts, the side boundaries in the same direction as the forming direction, and the top boundary. After the deposition and forming of the receiving platform is completed on the plane, the main body and corner blocks are fixed and aligned using a fixture. The corner parts are filled first to connect the corner blocks and the main body. The side boundaries are filled using a symmetrical repair method (filling one layer on the front, then one layer on the back, repeating the filling and repair on both sides). The top boundary is then filled using the same symmetrical repair method. The two sides of the workpiece are filled and repaired sequentially to reduce the influence of thermal stress and residual stress caused by forming, thus completing the filling process.

[0032] Steps 2-4: Shape Refinement. During the material repair process in the forming process, there is material overflow on both sides of the melt channel. The excess material on both sides is removed by grinding and polishing.

[0033] Step 3: Perform heat treatment on the workpiece repaired in step 2. The heat treatment regime should refer to standard Q / PC 1177.

[0034] Step 4: Perform non-destructive testing on the workpiece that has undergone heat treatment in step 3.

[0035] Non-destructive testing includes internal quality inspection, namely X-ray inspection, and surface quality inspection, namely fluorescence penetrant testing.

[0036] Example 1

[0037] A structural sample has a defect of thermal stress cracking. During the selected area laser melting process, due to stress accumulation, residual thermal stress-induced cracking occurs at the bottom in the forming direction. Figure 2 a) Based on the aforementioned research results, and considering the comprehensive factors of mechanical properties and stability of the repaired components, a repair strategy is proposed that involves first forming the bevel (connecting platform) through cladding, and then filling the bevel to connect the workpiece. The specific steps are as follows.

[0038] The first step involves cutting away the crack-prone areas, performing beveling cuts according to the nozzle's forming direction. A certain structure fractured along a crack caused by thermal stress. Based on the crack location, the workpiece was cut into two parts: the main body and corner pieces. Due to the complex geometry of the workpiece, interference during cutting was likely. The main body used a straight cut, and the cut shape was modified using laser deposition to create beveling cuts to facilitate subsequent laser deposition for connection and repair. The corner pieces had a complex geometric design; during cutting, the original structural features were preserved as much as possible. After cutting, the cut surfaces were polished to improve the laser energy absorption rate and powder utilization rate during forming.

[0039] The second step is to adjust the equipment and process for the powder material to be formed. The material of this workpiece is TA15, and the repair material used is a powder suitable for laser directional energy deposition (DED) process. Single-pass testing shows that the repair parameters are the same as above: power P = 500-800W, laser radius r = 0.5-1.5mm, scanning rate v = 6-10mm / s, and powder feed rate ρ = 4-6g / min. When these parameters are met, the height and width of the formed melt channel are stable along the scanning direction, and the depth-to-width ratio is uniform. Therefore, these parameters are used.

[0040] Then, an inert gas sealing process is performed. Because the forming material is a Ti alloy, its cladding forming needs to be carried out in an oxygen-free and nitrogen-free environment. Therefore, the workpiece is placed in a sealed chamber for sealing, and protective gas is continuously introduced. The process is complete when the oxygen content is less than 10 ppm.

[0041] Laser cladding repair of workpieces. Laser forming repair mainly consists of two steps. The first step is pre-treatment of the cut interface for connection repair. This process mainly involves forming a frustum-shaped or triangular prism-shaped access platform on the planar cut of a structural body and corner block. Figure 2(b) To adapt to the connection repair, at this time, the power P = 500W, the laser radius r = 0.5mm, the scanning rate v = 6mm / s, and the powder feeding rate ρ = 4g / min. This step can provide a wider pose transformation space for the coaxial nozzle in subsequent steps, avoid interference between the workpiece and the coaxial powder flow in spatial geometry during the repair process, and ensure that the powder flow is fully filled. During the formal filling, the power P = 800W, the laser radius r = 1.5mm, the scanning rate v = 10mm / s, and the powder feeding rate ρ = 6g / min. In this process, the three parts that need to be filled according to the repair sequence are the corner part, the side boundary in the same direction as the forming direction, and the top boundary ( Figure 2 a). Due to the small angle of the bend, interference during the filling process is severe. Therefore, filling is performed first. After the bevel of the corner is deposited and formed on the plane, a fixture is used to fix and calibrate the position of the main body and the corner block, and the bend is filled first. Near the side boundary of the corner block, for structural features with grooves, heat dissipation is difficult during the cladding process, which can easily lead to melt-through. Therefore, copper material is filled into the grooves to promote heat transfer. Figure 2 c). The reason is that copper has a high thermal conductivity and poor compatibility with the forming material, so it was chosen as the backing. The workpiece was repaired by filling both sides sequentially using a symmetrical repair method. Figure 2 d) Reduce the influence of thermal stress and residual stress caused by forming to complete the filling.

[0042] After the repair is completed, the morphology is adjusted. The overflowing deposited material on both sides is removed by grinding and polishing.

[0043] The third step is to perform heat treatment on the workpiece, following the process specifications in Q / PC 1177.

[0044] The fourth step is to perform non-destructive testing on the repaired area. (See...) Figure 3 Table 1 shows that after repair, there are no cracks and the tensile properties do not show obvious anisotropy in any direction, all of which meet the technical requirements specified in Q / PC 1177, and the test results show that they are qualified.

[0045] Table 1 Mechanical properties of the repaired samples from the furnace

[0046]

[0047]

[0048] The components repaired using this method not only meet or exceed the standards of the original materials in terms of mechanical properties, but also have a more uniform and consistent microstructure, significantly improving repair efficiency and quality, and providing a new solution for the repair of high-performance components.

Claims

1. A method for repairing titanium alloy additively manufactured parts by laser-directed energy deposition, characterized in that, include: The first step is material pretreatment: the cracks are removed by machining, the workpiece is divided into main body and corner blocks according to the location of the cracks, and the main body and corner blocks are beveled according to the nozzle forming direction. The second step involves repairing the titanium alloy additively manufactured parts using laser-directed energy deposition technology. (1) Form the receiving platform on the cuts of the main body and corner pieces; (2) Perform formal filling: The three parts that need to be filled according to the repair order are the corner part, the side boundary and the top boundary in the same direction as the forming direction. Use a clamp to fix and check the position of the main body and the corner block. Fill the corner part first and connect the corner block and the main body. Complete the filling of the side boundary by the method of positive and negative symmetry repair, and then complete the filling of the top boundary by the method of positive and negative symmetry repair. (3) Remove excess material from both sides of the melt channel; During the forming stage, the forming power P = 500W, the laser radius r = 0.5mm, the scanning rate v = 6mm / s, and the powder feeding rate ρ = 4g / min; during the formal filling, the forming power P = 800W, the laser radius r = 1.5mm, the scanning rate v = 10mm / s, and the powder feeding rate ρ = 6g / min.

2. The method for repairing titanium alloy additively manufactured parts by laser-directed energy deposition according to claim 1, characterized in that, During the actual filling process, the quality is checked every three layers.

3. The method for repairing titanium alloy additively manufactured parts by laser-directed energy deposition according to claim 1, characterized in that, When repairing titanium alloy additive manufacturing parts, the workpiece is placed in a sealed chamber for sealing.

4. The method for repairing titanium alloy additively manufactured parts by laser-directed energy deposition according to claim 1, characterized in that, For structures with grooves on the side edges of corner pieces, copper material is filled into the grooves as a liner.

5. The method for repairing titanium alloy additively manufactured parts by laser-directed energy deposition according to claim 1, characterized in that, It also includes heat treatment and non-destructive testing of the repaired workpiece.

6. The method for repairing titanium alloy additively manufactured parts by laser-directed energy deposition according to claim 5, characterized in that, Non-destructive testing includes X-ray inspection and fluorescence penetrant testing.

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