Active design and control method for internal defects of molten structure of laser powder bed

Abstract

The invention discloses an active design and control method for internal defects of a laser powder bed melting structure, which comprises the following steps of: 1, marking a defect target area in an integral model of the laser powder bed melting structure, dividing the integral model of the laser powder bed melting structure into a defect-free area model and a defect area model, and designing a defect type of the target area; 2, printing layer thicknesses are set for the laser powder bed fusion structure overall model, the defect-free area model and the defect area model, layer cutting treatment is carried out, and path planning is carried out; and 3, independently allocating different process parameters to the three types of models according to the defect types of the target area in the step 1, manufacturing a laser powder bed melting structure according to the path planned in the step 2, and actively controlling different types of internal defects in each area. The invention provides a technical means for LPBF defect online monitoring calibration test sample manufacturing and controllable density, and provides an active design and manufacturing method for different types of defects in a local area for an LPBF energy absorption structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser additive manufacturing, and in particular relates to a method for actively designing and controlling internal defects of a laser powder bed fusion structure. Background Art

[0002] Laser powder bed fusion (LPBF) is a typical additive manufacturing technology that uses metal powder as raw material. The metal powder is laid on a substrate using a powder laying device, and then a high-energy laser beam is used to melt the metal powder on the powder bed along a set scanning path. After cooling and solidification, the metal powder is stacked layer by layer to manufacture the target structure. It has technical advantages such as high forming freedom, high material utilization, and short production cycle. It is widely used in the integrated manufacturing of complex structures with high dimensional accuracy and forming quality requirements.

[0003] Defects are easily generated within the structure during the laser powder bed fusion manufacturing process. Currently, online monitoring technology is mainly used to analyze the changes in physical signals during the LPBF manufacturing process to determine whether defects have occurred in local areas. Before online monitoring technology is applied to the actual manufacturing process, the defect signal characteristics must be calibrated and tested, so it is necessary to manufacture calibration test specimens containing defects. Currently, calibration test specimens are often manufactured by not printing local areas (such as CN114839010A), prefabricating defects in auxiliary materials (CN117900507A), and external mechanical processing. The main type of defect manufactured by these methods is unfused defects. Active control of the spatial position of spherical pore defects is not achieved, and it is difficult to simulate the spatial characteristics of the discrete distribution of a large number of defects in local areas during the actual manufacturing process. As a result, the defects of the currently actively manufactured LPBF structures have large morphological differences compared to the actual defects and the spatial distribution is difficult to design. The defective calibration test specimens ultimately manufactured affect the accuracy of the online monitoring signal calibration.

[0004] Internal defects generated during LPBF manufacturing can significantly reduce the mechanical properties of the structure. Conventional structural manufacturing often avoids internal defects through process optimization. For laser powder bed fusion structures with special application scenarios, such as energy-absorbing structures, improved energy absorption and controlled deformation and fracture are primarily achieved through structural design and dimensional feature optimization. Local defect design and controlled manufacturing can effectively reduce the mechanical properties of the target area, providing a new process solution for guiding the controlled deformation and fracture of LPBF structures.

[0005] In summary, a new method is urgently needed to achieve the active design and control of the internal defect types and spatial positions of laser powder bed structures. Summary of the Invention

[0006] In response to the above-mentioned deficiencies in the existing technologies, the present invention proposes a method for active design and control of internal defects in laser powder bed fusion structures. This method provides technical means for the manufacture of LPBF defect online monitoring and calibration test specimens and controllable density, and provides a method for active design and manufacturing of different types of defects in local areas of LPBF energy-absorbing structures. The method can also be extended to different types of typical structures.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for actively designing and controlling internal defects of a laser powder bed fusion structure comprises the following steps:

[0009] Step 1: Mark the defect target area in the overall model of the laser powder bed fusion structure, divide the overall model of the laser powder bed fusion structure into a defect-free area model and a defect area model, and design the defect type of the target area;

[0010] Step 2: Set the printing layer thickness for the three types of models in step 1: the laser powder bed fusion structure overall model, the defect-free area model, and the defect area model, and perform layer slicing, and perform path planning for each model.

[0011] Step 3: Based on the defect type in the target area in step 1, different process parameters are independently assigned to the three types of models. The laser powder bed fusion structure is manufactured according to the path planned in step 2, and different types of internal defects in each area are actively controlled.

[0012] Furthermore, the step 1 specifically includes:

[0013] Step 1.1: Mark the defect target area in the overall model of the laser powder bed fusion structure;

[0014] Step 1.2: Cut the defect target area from the overall model of the laser powder bed fusion structure, and divide the overall model of the laser powder bed fusion structure into a defect-free area model and a defect area model.

[0015] Furthermore, in step 1.2, the target area defect types are designed to include spherical pore defects and unfused defects, and the size of the overlapping area of ​​the interface between the defect-free area model and the defect area model is set.

[0016] Furthermore, the step 2 specifically includes:

[0017] Step 2.1: Set the layer thickness for the three types of models: the laser powder bed fusion structure overall model, the defect-free area model, and the defect area model. Set the laser spot compensation parameters to control the distance between the laser scanning path and the outer contour of the structure for the three types of models. Slice the three types of models and output the contour information files for each layer of the three types of models.

[0018] Step 2.2: Import the contour information file into the laser powder bed fusion manufacturing equipment and set the laser movement path, inter-pass distance, and inter-layer rotation strategy parameters;

[0019] Step 2.3: Design the steering scanning strategies for the defect-free area model and the defect area model. Set the laser steering scanning strategy for the spherical pore defect area to continuous scanning, and set the laser steering scanning strategy for the defect-free area to jump scanning.

[0020] Furthermore, the step three specifically includes:

[0021] Step 3.1: Based on the material properties and laser powder bed fusion manufacturing equipment parameters, material-grade specimens are manufactured to characterize the cross-sectional forming quality and defect distribution of the specimens, and to determine the material's dense, spherical pore, and unfused process ranges.

[0022] Step 3.2: Assign process parameters within the dense range to the overall laser powder bed fusion structure model and the defect-free model. Assign different process parameters to the unfused defect region model and the spherical pore defect region model based on the target region defect type in step 1.2.

[0023] Step 3.3: Add supports to the overhanging feature areas of the laser powder bed fusion structure to ensure that the manufacturing process in the forming chamber is carried out under an argon protective gas atmosphere;

[0024] Step 3.4: Based on the contour information file and the planned path in step 2, laser powder bed fusion is performed to manufacture the defect-free structure as a whole to obtain the first set of samples;

[0025] Step 3.5: Based on the contour information file and the planned path in Step 2, print the defect-free area of ​​the laser powder bed fusion structure and the node unfused defect area to obtain the second set of samples, realizing LPBF structure combination manufacturing;

[0026] Step 3.6: Based on the contour information file and planned path in step 2, print the spherical pore defect area, defect-free area, and unfused defect area of ​​the laser powder bed fusion structure to obtain the third set of samples, realizing LPBF structure combination manufacturing.

[0027] Furthermore, the process parameters in step three include laser power and scanning speed.

[0028] Furthermore, the overall model of the laser powder bed fusion structure is an overall model of the energy absorbing plate lattice structure.

[0029] Furthermore, in step 3.3, the oxygen content in the forming chamber is lower than 0.1% throughout the entire process.

[0030] Compared with the prior art, the advantages of the present invention include:

[0031] The method for active design and control of internal defects in laser powder bed fusion structures of the present invention can realize active design and controllable manufacturing of different types of defects in local areas of LPBF structures by dividing the model area and planning the scanning path, laser power, and scanning speed process parameters in different areas. It provides a new technical means for the preparation of LPBF online monitoring capability calibration test samples, and provides a new method for the zoning density and controllable deformation and fracture of LPBF structures.

[0032] In addition to the features and advantages described above, the principles and other features and advantages of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a flow chart of the method for actively designing and controlling internal defects of a laser powder bed fusion structure according to the present invention;

[0034] Figure 2 It is the overall model of the lattice structure of the energy absorbing plate and the division diagram of the defect target area model;

[0035] Figure 3 Schematic diagram of continuous scanning and jump scanning strategies;

[0036] Figure 4 This is the internal defect characterization diagram of the AlSi10Mg material grade sample;

[0037] Figure 5 It is the CT scan cross-section entity and defect distribution grayscale image of the energy absorption plate lattice structure specimen;

[0038] Figure 6 Reconstruct three-dimensional feature maps for the relatively dense energy-absorbing plate lattice structure CT;

[0039] Figure 7 Reconstructed diagram of the unfused defect control results at the node position of the energy absorbing plate lattice structure;

[0040] Figure 8 Reconstructed image of the control results of spherical pore defects in the target area of ​​the energy absorbing plate lattice structure;

[0041] Figure 9 This is the grayscale image of the unfused defect control cross-section entity and defect distribution in the target area of ​​the energy absorbing plate lattice structure. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. The implementation of the present invention is described in detail below with reference to the specific embodiments.

[0043] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings. The following examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0044] Combine Figure 1 , a method for actively designing and controlling internal defects of a laser powder bed fusion structure, comprising the following steps:

[0045] Step 1: Mark the defect target area in the overall model of the laser powder bed fusion structure, divide the overall model of the laser powder bed fusion structure into a defect-free area model and a defect area model, and design the defect type of the target area (including spherical pore defects and unfused defects);

[0046] Step 2: Set the printing layer thickness for the three types of models in step 1: the laser powder bed fusion structure overall model, the defect-free area model, and the defect area model, and perform layer slicing, and perform path planning for each model.

[0047] Step 3: Based on the defect type in the target area in step 1, different process parameters (including laser power and scanning speed) are independently assigned to the three types of models. The laser powder bed fusion structure is manufactured according to the path planned in step 2, and different types of internal defects in each area are actively controlled.

[0048] The step 1 specifically includes:

[0049] Step 1.1: The laser powder bed fusion structure overall model is specifically selected as the energy absorbing plate lattice structure overall model. The energy absorbing plate lattice structure overall model is as follows: Figure 2 In Figure (a), the three-dimensional size of the model is 19mm×18.4mm×19mm. Mark the defect target area in the STL file of the overall model of the energy absorbing plate lattice structure. The marking methods include: (1) local micro-size area marking, such as Figure 2 (b) The cylindrical area with a diameter of 200 μm at the node of the plate lattice; (2) The division mark of the overall model, such as Figure 2 (c) The overall model division of the plate lattice;

[0050] Step 1.2: Cut the defect target area from the overall model of the energy absorbing plate lattice structure, thereby dividing the original model into a defect-free area model and a defect area model, and design the internal defect types of the target area including spherical pore defects (too high energy input) and unfused defects (insufficient energy input). Figure 2 Figure (b) generates a non-defective area model and an unfused defect area model (the design position is the plate lattice node). Figure 2Figure (c) generates a model for a defect-free region, a model for a spherical pore defect region, and a model for an unfused defect region. A 50μm overlap is set between the interface between the defect-free and defect region models to ensure the integrity of the manufacturing process for multiple models.

[0051] The second step specifically includes:

[0052] Step 2.1: Use Magics software to perform layer slicing on the three models: the overall model of the energy absorbing plate lattice structure, the model of the defect-free area, and the model of the defect area. Set the layer thickness of the three models to 30 μm during printing, set the laser spot compensation parameter to control the distance between the laser scanning path and the outer contour of the structure (0 μm in this embodiment), perform layer slicing on the three models, and output the contour information files of each layer of the three models;

[0053] Step 2.2: Import the profile information file into the LPBF manufacturing equipment and set the parameters for the laser movement path, inter-pass distance, and inter-layer rotation strategy. In this embodiment, the laser movement path within the printing layer is set to scan adjacent deposition passes in a 180° bidirectional manner, the inter-pass distance is set to 70μm, and the inter-layer rotation strategy is set to rotate the entire scanning path of adjacent printing layers by 90°.

[0054] Step 2.3: Design the steering scanning strategy for the defect-free area model and the defect area model. For the spherical pore defect area, the laser steering scanning strategy is set to continuous scanning. The laser is turned on and off between adjacent scanning paths. There is no laser shutdown and restart stage. The laser energy input in the target area is increased by continuous scanning. The local scanning path is as follows: Figure 3 Figure (a); The laser steering scanning strategy is set to jump scanning in the defect-free area. The laser is turned off at the end of the scanning path at the outer contour of the part, and jumps directly to the next path and then turns on. There is no scanning path between adjacent deposition paths. The local scanning path is as follows Figure 3 Figure (b) in the figure;

[0055] The step three specifically includes:

[0056] Step 3.1: In this example, AlSi10Mg is used as the raw material for the powder processing. Based on the material properties and LPBF manufacturing equipment parameters, material-grade samples are manufactured. The samples are ground and polished using SiC sandpaper and diamond polishing agent. The cross-sectional forming quality and defect distribution of the samples are characterized and observed using an optical microscope. The internal characteristics of the samples under different process parameters (including laser power and scanning speed) are as follows: Figure 4 As shown, the dense, spherical pore and unfused process range of AlSi10Mg material are determined;

[0057] Step 3.2: Assign laser power and scanning speed process parameters within the dense range to the overall energy absorbing plate lattice structure model and the defect-free region model. Based on the internal defect type of the target region in step 1.2, assign different laser power and scanning speed process parameters to the unfused defect region model and the spherical pore defect region model. Based on the dimensional characteristics of the energy absorbing plate lattice structure and a comprehensive analysis of the differences in process ranges between the structural and material-level samples, the process parameter assignments for the samples in this example are shown in Table 1.

[0058] Table 1 Manufacturing process parameters of energy absorption plate lattice structure

[0059]

[0060]

[0061] Step 3.3: Add supports to the overhanging feature areas of the lattice structure of the energy absorbing plate to ensure that the manufacturing process in the forming chamber is carried out under an argon protective gas atmosphere and the oxygen content in the forming chamber is less than 0.1% throughout the entire process;

[0062] Step 3.4: According to the contour information file and planning path in step 2, the energy absorbing plate lattice structure defect-free overall LPBF is manufactured, and the two sets of laser power and scanning speed in Table 1 are used to manufacture sample 1 and sample 2 respectively (the target area is divided as follows Figure 2 (a) in Figure 1);

[0063] Step 3.5: Based on the contour information file and planned path in step 2, different laser power and scanning speed parameters in Table 1 are used to print the energy absorbing plate lattice structure defect-free area and the node unfused defect area, and the energy absorbing plate lattice structure samples 3 and 4 are manufactured in combination (the defect target area is divided as follows Figure 2 (b) in the figure);

[0064] Step 3.6: Based on the contour information file and planned path in step 2, different laser power and scanning speed parameters in Table 1 are used to print the spherical pore defect area, non-defect area, and unfused defect area of ​​the energy absorbing plate lattice structure, and the energy absorbing plate lattice structure samples 5 and 6 are manufactured in combination (the defect target area is divided as follows Figure 2 (c) in Figure 5);

[0065] Perform CT reconstruction and characterization of the internal defect characteristics of the laser powder bed fusion structure in step 3 to obtain information on defect size, morphology, and spatial distribution characteristics, and verify the defect control effect in the target area:

[0066] (1) Cut the manufactured energy absorbing plate lattice structure sample from the substrate using an electric spark cutting device, confirm the interface quality between the defect-free area and the defect target area in samples 3, 4, 5, and 6, and confirm the overall forming consistency of the sample. If there is no interface problem between the defect-free area and the defect target area, proceed to the next step; otherwise, return to step 1.2 to adjust the size of the overlapping area (there is no interface bonding problem in this example);

[0067] (2) Micron-level X-ray computed tomography (CT) equipment was used to detect the internal features of the six samples of the energy absorbing plate lattice structure, and the two-dimensional cross-sectional solid and defect distribution grayscale images of the sample were obtained. The two-dimensional cross-sectional solid and defect distribution grayscale images of the different defect target areas in the typical sample 5 are shown in FIG. Figure 5 As shown, Figure 5 Figure (a) corresponds to the 5-1 unfused defect area in Table 1. The cross-sectional grayscale image is dominated by irregular unfused defects with a unidirectional size greater than 100 μm. Figure 5 Figure (b) corresponds to the defect-free area 5-2 in Table 1. There are no obvious defects in the figure; Figure 5 Figure (c) corresponds to the 5-3 spherical pore defect area in Table 1. The figure is mainly composed of spherical pores with a unidirectional size of less than 100 μm;

[0068] (3) Set the minimum voxel resolution to 17 μm in the CT data processing software. By processing the two-dimensional cross-sectional solid and defect distribution grayscale image in step (2), the overall morphology and internal defect three-dimensional characteristics of the six energy absorbing plate lattice structure specimens are reconstructed. The results are as follows: Figure 6 、 Figure 7 、 Figure 8 As shown;

[0069] (4) Figure 6 The 3D morphology of the energy-absorbing plate lattice structure model, sample 1 and sample 2, was reconstructed by CT. Sample 1 had no obvious internal defects except for a small amount of spherical pores at the top of the thin-walled feature. Sample 2 also had no obvious internal defects. Calculations based on CT results showed that the density of both samples 1 and 2 was higher than 99.9%.

[0070] (5) The results of the control of unfused defects at the node positions of the energy absorbing plate lattice structure are as follows Figure 7 As shown in the figure, the internal defects of sample 3 and sample 4 are concentrated in the node cylindrical mark unfused defect area, and the defect-free area is relatively dense and defect-free. Combining the defect size and regional energy input, it is determined that the node position unfused defect control is achieved;

[0071] (6) The control results of spherical pore defects and unfused defects in the lattice structure area of ​​the energy absorbing plate are as follows Figure 8 As shown, combined Figure 2From the regional model division in Figure (c), it can be seen that the defect-free areas of samples 5 and 6 are relatively dense, with no internal defect concentration. Spherical pore defects are concentrated in the 5-1 and 6-1 spherical pore defect areas. Combining high energy input and defect sphericity, it is determined that spherical pore defect control in the target area has been achieved.

[0072] (7) Aiming at the problem of surface extraction of the unfused defect area of ​​the energy absorbing plate lattice structure specimens 5 and 6 by CT reconstruction, the two-dimensional size and morphological characteristics of the defect are analyzed through the two-dimensional cross-sectional entity and defect distribution grayscale image of the unfused defect area of ​​the specimen. Figure 9 The cross-sectional features of the target area of ​​unfused defects of Samples 5 and 6 are mainly irregular defects with a unidirectional size greater than 100 μm. Combined with the low energy input in the area, it is determined that the unfused defects in the target area are controlled.

[0073] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for active design and control of internal defects in laser powder bed fusion structures, characterized in that: The following steps are involved: Step 1: Mark the defect target area in the overall model of the laser powder bed fusion structure, divide the overall model of the laser powder bed fusion structure into a defect-free area model and a defect area model, and design the defect type of the target area; Step 2: Set the printing layer thickness for the three types of models in step 1: the laser powder bed fusion structure overall model, the defect-free area model, and the defect area model, and perform layer slicing, and perform path planning for each model. Step 3: Based on the defect type in the target area in step 1, different process parameters are independently assigned to the three types of models. The laser powder bed fusion structure is manufactured according to the path planned in step 2, and different types of internal defects in each area are actively controlled.

2. The method for active design and control of internal defects of laser powder bed fusion structure according to claim 1, characterized in that: The step 1 specifically includes: Step 1.1: Mark the defect target area in the overall model of the laser powder bed fusion structure; Step 1.2: Cut the defect target area from the overall model of the laser powder bed fusion structure, and divide the overall model of the laser powder bed fusion structure into a defect-free area model and a defect area model.

3. The method for active design and control of internal defects of laser powder bed fusion structure according to claim 2, characterized in that: In step 1.2, the target area defect types are designed to include spherical pore defects and unfused defects, and the overlapping area size of the interface between the defect-free area model and the defect area model is set.

4. The method for active design and control of internal defects of laser powder bed fusion structure according to claim 3, characterized in that: The second step specifically includes: Step 2.1: Set the layer thickness for the three types of models: the laser powder bed fusion structure overall model, the defect-free area model, and the defect area model. Set the laser spot compensation parameters to control the distance between the laser scanning path and the outer contour of the structure for the three types of models. Slice the three types of models and output the contour information files for each layer of the three types of models. Step 2.2: Import the contour information file into the laser powder bed fusion manufacturing equipment and set the laser movement path, inter-pass distance, and inter-layer rotation strategy parameters; Step 2.3: Design the steering scanning strategies for the defect-free area model and the defect area model. Set the laser steering scanning strategy for the spherical pore defect area to continuous scanning, and set the laser steering scanning strategy for the defect-free area to jump scanning.

5. The method for active design and control of internal defects of laser powder bed fusion structure according to claim 4, characterized in that: The step three specifically includes: Step 3.1: Based on the material properties and laser powder bed fusion manufacturing equipment parameters, material-grade specimens are manufactured to characterize the cross-sectional forming quality and defect distribution of the specimens, and to determine the material's dense, spherical pore, and unfused process ranges. Step 3.2: Assign process parameters within the dense range to the overall laser powder bed fusion structure model and the defect-free model. Assign different process parameters to the unfused defect region model and the spherical pore defect region model based on the target region defect type in step 1.

2. Step 3.3: Add supports to the overhanging feature areas of the laser powder bed fusion structure to ensure that the manufacturing process in the forming chamber is carried out under an argon protective gas atmosphere; Step 3.4: Based on the contour information file and the planned path in step 2, laser powder bed fusion is performed to manufacture the defect-free structure as a whole to obtain the first set of samples; Step 3.5: Based on the contour information file and the planned path in Step 2, print the defect-free area of ​​the laser powder bed fusion structure and the node unfused defect area to obtain the second set of samples, realizing LPBF structure combination manufacturing; Step 3.6: Based on the contour information file and planned path in step 2, print the spherical pore defect area, defect-free area, and unfused defect area of ​​the laser powder bed fusion structure to obtain the third set of samples, realizing LPBF structure combination manufacturing.

6. The method for active design and control of internal defects of laser powder bed fusion structure according to claim 5, characterized in that: The process parameters in step three include laser power and scanning speed.

7. The method for active design and control of internal defects in laser powder bed fusion structures according to claim 6, characterized in that: The overall model of the laser powder bed fusion structure is an overall model of the energy absorbing plate lattice structure.

8. The method for active design and control of internal defects in laser powder bed fusion structures according to claim 6, characterized in that: In step 3.3, the oxygen content in the forming chamber is lower than 0.1% throughout the entire process.

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