Method for additive manufacturing of large sintering metal parts with self-stabilizing powder-saving shell support

Abstract

This invention relates to the field of metal additive manufacturing technology, specifically a method for preparing a self-stabilizing, powder-saving shell support for additive manufacturing of large SLM metal parts. The method includes: acquiring three-dimensional model data of the large metal part to be formed and setting its tilt angle; identifying the suspended structure of the model to determine the support area and contour boundary; generating an initial model of a continuous thin-walled composite shell support through an improved topology optimization algorithm, comprising an outer thin-walled plate, multiple layers of internal reinforcing thin plates parallel to the outer thin-walled plate, and connecting ribs connecting the outer thin-walled plate and the internal reinforcing thin plates; assigning a standard thickness to the thin plate based on a wall thickness grading standardization design system; machining an array of equilateral triangular through-holes on the thin plate; calculating the projection area magnification factor of the support forming direction and directionally adjusting relevant structural parameters; and finally generating a suitable SLM forming process parameter package. This method constructs a dedicated shell support structure, optimizes the support structure performance by combining angle coefficient optimization parameters, and controls powder consumption.

Description

Technical Field

[0001] This invention relates to the field of metal additive manufacturing technology, and in particular to a method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts. Background Technology

[0002] In the current additive manufacturing process for large SLM metal parts, the support structures for the suspended parts of the parts are mostly lattice supports, column supports, or single thin-walled supports. The support structure is generated using conventional topology optimization methods, the wall thickness parameter is set according to a uniform standard, the support plate is mainly a solid structure, and the parameter optimization of the support structure is only carried out around the external dimensions of the part, without taking the tilt angle of the part into account in the parameter adjustment.

[0003] Conventional support structures suffer from high metal powder loss in practical applications. Solid thin-walled supports are cumbersome to remove later. Supports without internal reinforcement are prone to deformation during laser selective melting and forming. Uniform wall thickness designs cannot meet the forming requirements of large parts with different size ranges. Failure to adjust structural parameters in conjunction with tilting angles will result in insufficient matching between the support's projected area and the forming direction, making it difficult to guarantee the overall stability of the support and resulting in low powder utilization efficiency.

[0004] For the support structure in the forming process of large SLM metal parts, it is necessary to use an optimized topology optimization method to generate a dedicated continuous thin-walled composite shell support structure. It is also necessary to calculate the projection area magnification factor in combination with the tilt angle of the parts, and to carry out directional adjustments to the parameters related to the placement angle in the support structure, so as to improve the existing support's problems of material consumption, stability and forming adaptability. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and propose a method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts.

[0006] To achieve the above objectives, the present invention employs the following technical solution: a method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts, comprising: Obtain the 3D model data of the large metal part to be formed and the set tilt angle; The suspended structures in the three-dimensional model data are identified to determine the areas where support structures need to be constructed and their outline boundaries. Using an improved topology optimization algorithm, based on the contour boundary, the tilting angle, and the preset maximum size of the parts, an initial three-dimensional structural model of a continuous thin-walled composite shell support is generated. The continuous thin-walled composite shell support includes an outer wall thin plate, multiple layers of internal reinforcing thin plates parallel to the outer wall thin plate, and connecting ribs connecting the outer wall thin plate and the internal reinforcing thin plates. The wall thickness grading standardization design system is invoked, and the corresponding standard thickness values ​​are assigned to the outer wall thin plate and the inner reinforcing thin plate in the initial three-dimensional structural model according to the design range where the maximum size of the part is located. An opening design is implemented on the outer wall thin plate and the inner reinforcing thin plate to form a uniformly distributed array of equilateral triangular through openings; Based on the tilt angle, the projection area magnification factor of the continuous thin-walled composite shell support in the forming direction is calculated, and the structural parameters related to the tilt angle in the initial three-dimensional structural model are oriented and adjusted according to the projection area magnification factor. Based on the final three-dimensional structural model of the continuous thin-walled composite shell support, a suitable SLM molding process parameter package is generated.

[0007] As a further aspect of the present invention, the step of generating an initial three-dimensional structural model of a continuous thin-walled composite shell support using an improved topology optimization algorithm, based on the contour boundary, the tilting angle, and the preset maximum size of the part, includes: Within the design domain defined by the contour boundary, thermal loads and mechanical constraints are applied during the molding process. These thermal loads and mechanical constraints are calculated based on the maximum size of the part, the properties of the molding material, and the preset molding cycle time. The improved topology optimization algorithm is used to iteratively calculate the design domain. The improved topology optimization algorithm, based on the thermal load and mechanical constraints, aims to minimize the amount of structural material used, provided that the preset structural stiffness threshold and heat dissipation efficiency threshold are met. In each iteration of the calculation, it is simultaneously determined whether the tilt angle is zero. When the tilt angle is not zero, a projection load penalty term related to the tilt angle is introduced into the objective function. After the improved topology optimization algorithm converges, it outputs the material density distribution cloud map, performs geometric reconstruction on the material density distribution cloud map, extracts the region with density greater than a preset threshold, and forms a preliminary shell skeleton composed of an outer wall thin plate, multiple layers of internal reinforcing thin plates and connecting ribs. The initial shell skeleton is smoothed and constrained by minimum feature size to generate an initial three-dimensional structural model of the continuous thin-walled composite shell support with a closed multi-cavity structure.

[0008] As a further aspect of the present invention, the improved topology optimization algorithm is a variable density topology optimization algorithm that combines a bidirectional asymptotic structure optimization method with sensitivity filtering technology. Its working principle includes: The design domain is discretized into a finite element mesh, and each mesh element is assigned a pseudo density variable that varies continuously between zero and one. Based on the pseudo-density variable of each grid cell, the corresponding elastic modulus and thermal conductivity coefficient are calculated through a material interpolation model, and the global stiffness matrix and thermal conductivity matrix are assembled. Under the volume fraction constraint that meets the molding process requirements, with the goal of minimizing the amount of structural material used, and with the dual constraints that the structural compliance corresponding to the global stiffness matrix is ​​less than the structural stiffness threshold and the heat dissipation efficiency corresponding to the heat conduction matrix is ​​greater than the heat dissipation efficiency threshold, an optimization mathematical model is constructed. In each optimization iteration, the sensitivity of the objective function to the pseudo-density variable of each grid cell is calculated, and the sensitivity filtering technique is used to filter the sensitivity field to eliminate the checkerboard phenomenon and control the minimum structure size. The update criteria of the bidirectional progressive structure optimization method are adopted, and the pseudo-density variables of each grid cell are added or deleted synchronously based on the sensitivity information and the current volume fraction constraint, so as to achieve more efficient material layout update. After the iteration converges, the pseudo-density variable field is output as the material density distribution cloud map.

[0009] As a further aspect of the present invention, the step of invoking the wall thickness grading standardization design system, based on the design range in which the maximum size of the part is located, assigns corresponding standard thickness values ​​to the outer wall thin plate and the inner reinforcing thin plate in the initial three-dimensional structural model, including: Four consecutive maximum part size design ranges are predefined, and each design range is associated with a set of standard thickness ranges for outer wall thin plates and internal reinforcing thin plates. Extract the maximum size of the part from the three-dimensional model data, and map the maximum size of the part to one of the four consecutive maximum size design intervals of the part to determine its target design interval; Based on the target design range, the corresponding standard thickness range of the outer wall thin plate and the standard thickness range of the internal reinforcing thin plate are read from the predefined data table; Based on the stress characteristics of each part in the initial three-dimensional structural model of the continuous thin-walled composite shell support, a specific thickness value is assigned to each outer wall thin plate and inner reinforcing thin plate within the corresponding standard thickness range. The thickness value of the main load-bearing area is taken as the upper limit of the standard thickness range, and the thickness value of the secondary area is taken as the median or lower limit of the standard thickness range. The specific thickness values ​​are assigned to the corresponding geometric surfaces of the initial three-dimensional structural model, thereby updating the three-dimensional structural model of the continuous thin-walled composite shell support.

[0010] As a further aspect of the present invention, an opening design is implemented on the outer wall thin plate and the inner reinforcing thin plate to form a uniformly distributed array of equilateral triangular through openings, including: Based on the three-dimensional structural model of the continuous thin-walled composite shell support after the thickness is updated, the geometric surfaces of each outer wall thin plate and inner reinforcing thin plate that require opening design are obtained respectively. On each of the geometric surfaces, an equilateral triangular mesh covering the entire surface is planned. The side length of the equilateral triangular mesh is selected within a preset range according to the target aperture ratio, so that the final aperture ratio meets the coupling requirements of the preset heat dissipation efficiency threshold and the structural stiffness threshold. Using the center of each triangular cell of the equilateral triangular mesh as the center of the opening, an inscribed equilateral triangle with a size slightly smaller than the triangular cell is generated as the opening outline; The opening contour is stretched and cut through along a direction perpendicular to the geometric surface to form a through equilateral triangular hole on the outer wall thin plate or the inner reinforcing thin plate. All edges of the opening contour are rounded to eliminate stress concentration at sharp corners; All the thin plates with completed perforation designs are re-integrated with the connecting ribs through Boolean operations to ensure the geometric continuity between the perforated area and the solid area, ultimately forming a continuous thin-walled composite shell support structure with the equilateral triangle through-hole array.

[0011] As a further aspect of the present invention, based on the tilting angle, the projected area magnification factor of the continuous thin-walled composite shell support in the forming direction is calculated, and the structural parameters related to the tilting angle in the initial three-dimensional structural model are oriented and adjusted according to the projected area magnification factor, including: Based on the tilt angle and the outline dimensions of the initial three-dimensional structural model of the continuous thin-walled composite shell support in the original coordinates, the projected outline of the continuous thin-walled composite shell support on the molded substrate plane is obtained through geometric projection calculation. The ratio of the area of ​​the projected contour to the orthographic projection area of ​​the continuous thin-walled composite shell support in the original coordinates is calculated to obtain the projection area magnification factor; When the projection area magnification factor is greater than one, it indicates the existence of a projection magnification region, and the local structure in the continuous thin-walled composite shell support corresponding to the projection magnification region is identified. According to the projection area magnification factor, the arrangement density of the reinforcing thin plates in the local structure is increased according to the preset scaling ratio formula, and the increase in the arrangement density of the reinforcing thin plates is positively correlated with the projection area magnification factor. The cross-sectional dimensions of the connecting ribs in the local structure are increased simultaneously to match the increased load transfer requirements due to the increased density of the reinforcing thin plates. For the remaining areas where the projection is not magnified, the optimal powder-saving structural parameters determined based on the wall thickness grading standardization design system remain unchanged.

[0012] As a further aspect of the present invention, based on the final three-dimensional structural model of the continuous thin-walled composite shell support, a suitable SLM molding process parameter package is generated, including: The SLM forming process parameters include dedicated laser power, scanning speed, powder layer thickness parameters, and interlayer scanning path rotation strategy for thin-walled regions. Analyze the geometric features of the thin-walled region in the final three-dimensional structural model, identify regions with a wall thickness less than a preset threshold, and mark them as key thin-walled forming areas; A first set of laser process parameters is configured for the critical thin-walled forming area. The laser power of the first set of laser process parameters is lower than that used for forming the solid area, the scanning speed is higher than that used for forming the solid area, and the powder layer thickness is less than that used for forming the solid area, so as to prevent spheroidization and warping defects. A second set of laser process parameters is configured for the solid areas in the final three-dimensional structural model other than the key thin-walled forming area. The laser power of the second set of laser process parameters is higher than that of the first set of laser process parameters, and the scanning speed is lower than that of the first set of laser process parameters, so as to ensure complete melting and densification. For the edge region of the equilateral triangle through-hole array, a third set of laser process parameters is configured. The third set of laser process parameters uses a combination of lower laser power and faster scanning speed to control heat input and prevent overheating and deformation of the hole edge. A rotation strategy for the interlayer scanning path is formulated, and different laser scanning path directions are set for adjacent forming layers. The angle between the scanning path directions of adjacent layers is set to a preset rotation angle. The first set of laser process parameters, the second set of laser process parameters, the third set of laser process parameters, and the interlayer scanning path rotation strategy are integrated and packaged into the SLM forming process parameter package that is uniquely bound to the final three-dimensional structural model.

[0013] As a further aspect of the present invention, within the design domain defined by the contour boundary, thermal loads and mechanical constraints during the molding process are applied, including: Based on the maximum size of the part, the cumulative distribution of molding heat inside the part is calculated within the preset molding cycle time, and the cumulative distribution result is quantified into a heat load function that varies with spatial position according to the thermophysical parameters of the molding material properties. Based on the maximum size of the part and the mechanical parameters of the molding material properties, the deformation trend caused by thermal stress and self-weight during the molding process is estimated, and the deformation trend is converted into displacement constraints applied at the boundary of the design domain and the support connection interface. In the geometric center region of the design domain, a concentrated thermal load positively correlated with the maximum size of the part and the height of the molding layer is applied to simulate the thermal influence of the molding heat source center. In the design domain, corresponding to the area where the support structure connects to the solid part to be formed, fully constrained mechanical boundary conditions are applied to simulate the rigid connection between the support structure and the part. In the design domain, corresponding to the area where the bottom of the support structure contacts the molding substrate, a mechanical constraint condition with zero displacement along the molding direction is applied to simulate the fixed connection between the support structure and the substrate. The thermal load function, concentrated thermal load, fully constrained mechanical boundary conditions, and displacement constraint conditions are collectively applied as the thermal load and mechanical constraint conditions to the computational model of the improved topology optimization algorithm.

[0014] As a further aspect of the present invention, all edges of the opening contour are rounded to eliminate stress concentration at sharp corners, including: Based on the thin plate structure model that has been completed through stretching and cutting, all the inner side lines formed by the opening contour in three-dimensional space are identified. The inner side lines are the geometric edges formed by the intersection of the equilateral triangular hole and the thin plate solid. Based on the thickness value of the current thin plate in the thin plate structure model and the side length of the opening profile, a matching recommended chamfer radius value range is queried from the preset process rule library. The recommended chamfer radius value range is positively correlated with the thickness value of the thin plate and the side length of the opening profile. Within the recommended chamfer radius range, based on the stress characteristics of the thin plate and the current position of the thin plate in the continuous thin-walled composite shell support structure, a specific chamfer radius value is determined for each inner edge line. The chamfer radius value of the opening edge located on the main load-bearing path is taken as the upper limit of the recommended chamfer radius range, and the chamfer radius value of the opening edge located on the non-main load-bearing path is taken as the median or lower limit of the recommended chamfer radius range. Using the edge rounding function of 3D modeling software, based on the specific chamfer radius value determined for each inner edge line, the rounding modeling operation is performed on all inner edge lines in sequence, so that the original sharp corners are transformed into smooth arc surfaces. Perform geometric topology consistency checks and repairs on all models after rounding operations to ensure seamless connection between rounded corner features and the original thin plate entity and holes, with no redundant or missing geometric surfaces.

[0015] As a further aspect of the present invention, the method also includes a closed-loop fine-tuning step of process parameters based on online monitoring data during the SLM molding process: During the SLM forming process supported by the continuous thin-walled composite shell, the thermal radiation signal of the molten pool area is collected in real time by a coaxial infrared thermal imager. The thermal radiation signal is processed to obtain the average melt pool temperature and temperature distribution uniformity index of the key thin-walled forming area during the forming process of each layer; The average molten pool temperature obtained in real time is compared with the preset temperature reference range. If the average molten pool temperature continues to deviate from the temperature reference range, the laser power or scanning speed in the first set of laser process parameters used in the critical thin-wall forming area of ​​the next forming layer is dynamically adjusted according to the degree and direction of the deviation. The temperature distribution uniformity index obtained in real time is compared with a preset uniformity threshold. If the temperature distribution uniformity index is lower than the uniformity threshold, the interlayer scanning path rotation strategy is activated, and the specific value of the rotation angle is adjusted in the subsequent forming layer. All process parameter adjustment instructions are recorded and synchronously updated to the SLM molding process parameter package to form a dynamically adjusted set of process parameters.

[0016] Compared with the prior art, the advantages and positive effects of the present invention are as follows: An improved topology optimization algorithm generates an initial 3D structural model of a continuous thin-walled composite shell support based on the support area's contour boundary, tilt angle, and the maximum size of the part. This model consists of an outer thin-walled plate, multiple layers of internal reinforcing plates parallel to the outer thin-walled plate, and connecting ribs. The combination of multiple thin plates and connecting ribs enhances the overall structural stiffness of the support, disperses the stress load borne by the support during molding, and maintains the structural stability of the support during processing. A standardized design system with graded wall thickness matches the corresponding standard thickness values ​​for the outer thin-walled plate and internal reinforcing plates according to the design range of the part's maximum size, ensuring that the support wall thickness is compatible with the molding conditions of large parts. A uniformly distributed array of equilateral triangular through-holes on the outer thin-walled plate and internal reinforcing plates reduces the amount of support material used, decreases the amount of metal powder adhering and remaining during molding, reduces powder accumulation inside the support structure, optimizes powder flow in the processing area, and simultaneously reduces the bonding strength between the support and the part's molding surface, facilitating subsequent processing of the support structure.

[0017] The projection area magnification factor of the continuous thin-walled composite shell support in the forming direction is calculated based on the tilt angle. This factor is used to orient the structural parameters related to the tilt angle in the initial 3D structural model, ensuring the spatial shape of the support structure matches the forming direction. This optimizes the stress distribution of the support under tilt conditions, reduces stress concentration caused by insufficient angle adaptation, and improves the structural stability of the support under non-perpendicular placement. Orienting the structural parameters allows the support's projection shape to match the processing path, reducing the possibility of support displacement or deformation during forming and ensuring the forming accuracy of suspended parts in large parts. The combination of the perforated structure and parameter adjustments further reduces the amount of support material used, improves powder utilization efficiency, and maintains the stable working state of the support structure during SLM forming, while ensuring the support's load-bearing capacity. Attached Figure Description

[0018] Figure 1 This is a flowchart of the method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts according to the present invention; Figure 2 A flowchart for designing the application of thermal loads and mechanical constraints in the design domain and improving the iterative calculation of topology optimization. Figure 3 This is a flowchart of the process for planning an equilateral triangle mesh, creating a through-hole array, and rounding corners. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] In the description of this invention, it should be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, in the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0021] See Figure 1 This invention provides a method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts. The specific method includes: Acquire the 3D model data of the large metal part to be formed and the set tilt angle. Identify the suspended structures in the 3D model data to determine the areas and contour boundaries where a support structure needs to be constructed. Using an improved topology optimization algorithm, based on the contour boundaries, tilt angle, and preset maximum part size, generate an initial 3D structural model of a continuous thin-walled composite shell support. This continuous thin-walled composite shell support includes an outer thin-walled plate, multiple layers of internal reinforcing thin plates parallel to the outer thin-walled plate, and connecting ribs connecting the outer thin-walled plate and the internal reinforcing thin plates. Call the wall thickness grading standardization design system and assign corresponding standard thickness values ​​to the outer thin-walled plate and internal reinforcing thin plates in the initial 3D structural model according to the design range where the maximum part size is located. Perform opening design on the outer thin-walled plate and internal reinforcing thin plates to form a uniformly distributed array of equilateral triangular through openings. Based on the tilt angle, calculate the projection area magnification factor of the continuous thin-walled composite shell support in the forming direction, and adjust the structural parameters related to the tilt angle in the initial 3D structural model according to the projection area magnification factor. Based on the final three-dimensional structural model supported by a continuous thin-walled composite shell, a suitable SLM molding process parameter package is generated.

[0022] In one embodiment of the present invention, see [reference] Figure 2Within the design domain defined by the contour boundary, thermal loads and mechanical constraints during the molding process are applied. These thermal loads and mechanical constraints are calculated based on the maximum part size, molding material properties, and a preset molding cycle length. An improved topology optimization algorithm is used to iteratively calculate the design domain. Based on the thermal loads and mechanical constraints, the improved topology optimization algorithm aims to minimize the amount of structural material used, while satisfying preset structural stiffness and heat dissipation efficiency thresholds. In each iteration, it is simultaneously determined whether the tilt angle is zero. If the tilt angle is not zero, a projection load penalty term related to the tilt angle is introduced into the objective function. After the improved topology optimization algorithm converges, it outputs a material density distribution cloud map. The material density distribution cloud map is geometrically reconstructed to extract regions with densities greater than preset thresholds, forming a preliminary shell skeleton composed of an outer thin plate, multiple layers of internal reinforcing thin plates, and connecting ribs. The preliminary shell skeleton is then smoothed and constrained to a minimum feature size, generating an initial three-dimensional structural model of a continuous thin-walled composite shell support with a closed multi-cavity structure. The improved topology optimization algorithm is a variable-density topology optimization algorithm that combines a two-way progressive structural optimization method with sensitivity filtering technology. Its working principle is to discretize the design domain into a finite element mesh and assign a pseudo-density variable that continuously varies between zero and one to each mesh element. Based on the pseudo-density variable of each mesh element, the corresponding elastic modulus and thermal conductivity coefficient are calculated using a material interpolation model, and a global stiffness matrix and thermal conductivity matrix are assembled. Under the volume fraction constraint that meets the forming process requirements, the algorithm aims to minimize the amount of structural material used, with the dual constraints of structural compliance (corresponding to the global stiffness matrix) being less than the structural stiffness threshold and heat dissipation efficiency (corresponding to the thermal conductivity matrix) being greater than the heat dissipation efficiency threshold. An optimization mathematical model is constructed. In each optimization iteration, the sensitivity of the objective function to the pseudo-density variable of each mesh element is calculated, and sensitivity filtering technology is used to filter the sensitivity field to eliminate checkerboard patterns and control the minimum structural size. The update criterion of the two-way progressive structural optimization method is adopted, and based on the sensitivity information and the current volume fraction constraint, the pseudo-density variable of each mesh element is added or deleted synchronously to achieve more efficient material layout updates. After the iteration converges, the pseudo-density variable field is output as a material density distribution cloud map.

[0023] In the specific implementation, the large metal part to be formed is a ring-shaped structural component similar to an aero-engine casing. The maximum size of the part is set at 1200 mm, the tilt angle is set at 45°, and the forming material is the nickel-based superalloy Inconel 718. Within the design domain defined by the contour boundary, based on the maximum part size of 1200 mm, the forming material properties of Inconel 718, and the preset forming cycle length of 72 hours, the thermal load and mechanical constraints during the forming process are calculated. The applied thermal load reflects the periodic temperature field formed inside the part during the movement of the forming heat source, and the mechanical constraints reflect the role of the supporting structure in suppressing thermal deformation and resisting its own weight.

[0024] In some embodiments, an improved topology optimization algorithm is used to iteratively calculate the design domain. This algorithm, under the premise of satisfying a structural stiffness threshold of 500 MPa and a heat dissipation efficiency threshold of 200 W / m² Kelvin, uses minimizing the amount of structural material as the objective function. In each iteration, it is simultaneously determined whether the tilt angle is 0. When the tilt angle is 45° and not 0, a projected load penalty term related to the tilt angle is introduced into the objective function. The mathematical expression for the projected load penalty term is:

[0025] in: This represents the total value of the projected load penalty term. It is a weighting coefficient with a value of 0.15. It's the angle at which it's tilted. It is the total number of grid cells within the design domain. It is the first Volume of each grid cell It is the first The pseudo-density variable of each grid cell. This penalty term is introduced to preferentially remove inefficient material with an excessively large projected area in the forming direction under inclined conditions, thereby reducing the risk of thermal stress concentration in the support structure during the forming process.

[0026] The improved topology optimization algorithm is understood to be a variable-density topology optimization algorithm that combines a two-way progressive structural optimization method with sensitivity filtering technology. Its working principle involves discretizing the design domain into a hexahedral finite element mesh with a size of 2 mm, and assigning a pseudo-density variable that continuously varies between 0 and 1 to each mesh element. Based on the pseudo-density variable of each mesh element, the corresponding elastic modulus and thermal conductivity coefficient are calculated using a SIMP material interpolation model, and the global stiffness matrix and thermal conductivity matrix are assembled. Under the constraint of a volume fraction of 0.35 that meets the molding process requirements, the optimization mathematical model is constructed with the objective of minimizing the amount of structural material used, and the dual constraints of the structural compliance corresponding to the global stiffness matrix being less than the structural stiffness threshold and the heat dissipation efficiency corresponding to the thermal conductivity matrix being greater than the heat dissipation efficiency threshold.

[0027] In one embodiment of the present invention, four consecutive maximum part size design intervals are predefined, each interval being associated with a set of standard thickness ranges for outer wall thin plates and inner reinforcing thin plates. The maximum part size is extracted from the 3D model data and mapped to one of the four consecutive maximum part size design intervals to determine its target design interval. Based on the target design interval, the corresponding standard thickness ranges for outer wall thin plates and inner reinforcing thin plates are read from a predefined data table. According to the stress characteristics of each part in the initial 3D structural model of the continuous thin-walled composite shell support, a specific thickness value is assigned to each outer wall thin plate and inner reinforcing thin plate within the corresponding standard thickness range. The thickness value of the main load-bearing area is taken as the upper limit of the standard thickness range, and the thickness value of the secondary area is taken as the median or lower limit of the standard thickness range. The assigned specific thickness values ​​are assigned to the corresponding geometric surfaces of the initial 3D structural model, updating the 3D structural model of the continuous thin-walled composite shell support.

[0028] In practical implementation, the four predefined maximum part size design ranges are: Range A (800 mm to 1100 mm), Range B (1100 mm to 1400 mm), Range C (1400 mm to 1700 mm), and Range D (1700 mm to 2000 mm). The standard thickness range for the outer wall sheet associated with Range A is 0.8 mm to 1.2 mm, and the standard thickness range for the internal reinforcing sheet is 0.6 mm to 1.0 mm; the standard thickness range for the outer wall sheet associated with Range B is 1.0 mm to 1.4 mm, and the standard thickness range for the internal reinforcing sheet is 0.8 mm to 1.2 mm; the standard thickness range for the outer wall sheet associated with Range C is 1.2 mm to 1.6 mm, and the standard thickness range for the internal reinforcing sheet is 1.0 mm to 1.4 mm; the standard thickness range for the outer wall sheet associated with Range D is 1.4 mm to 1.8 mm, and the standard thickness range for the internal reinforcing sheet is 1.2 mm to 1.6 mm.

[0029] In practice, the maximum part size extracted from the 3D model data is 1250 mm. This size is mapped to a predefined interval system, determining that it belongs to interval B (1100 mm to 1400 mm). Based on interval B, the corresponding standard thickness range of the outer wall thin plate (1.0 mm to 1.4 mm) and the standard thickness range of the internal reinforcing thin plate (0.8 mm to 1.2 mm) are read from the predefined data table.

[0030] In some embodiments, based on the stress characteristics of each part in the initial three-dimensional structural model of the continuous thin-walled composite shell support, specific thickness values ​​are assigned to each outer wall thin plate and internal reinforcing thin plate. For the main load-bearing areas that directly bear the weight of the suspended parts, the thickness value of the outer wall thin plate is taken as the upper limit of the standard thickness range, 1.4 mm, and the thickness value of the internal reinforcing thin plate is taken as the upper limit of the standard thickness range, 1.2 mm. For secondary areas that only serve an auxiliary connection function, the thickness value of the outer wall thin plate is taken as the median of the standard thickness range, 1.2 mm, and the thickness value of the internal reinforcing thin plate is taken as the lower limit of the standard thickness range, 0.8 mm. The assignment of thickness values ​​is based on the importance of the thin plate in the force transmission path of the supporting overall structure, where the thin plates on the main load-bearing paths bear greater bending moments and shear forces.

[0031] It is understandable that assigning lower thickness values ​​to secondary areas can effectively reduce the overall weight and powder consumption of the support structure, thereby achieving powder saving without affecting stiffness. By traversing all geometric surfaces in the initial three-dimensional structural model, the assigned thickness values ​​of 1.4 mm, 1.2 mm, and 0.8 mm are assigned to the corresponding outer wall thin plates and internal reinforcing thin plates, completing the update of the three-dimensional structural model of the continuous thin-walled composite shell support. Optionally, when the maximum size of the part falls within different ranges, the upper and lower limits of the standard thickness range are adjusted accordingly. For example, if the maximum size of the part is 1600 mm, it falls into range C, and its standard thickness range for the outer wall thin plate becomes 1.2 mm to 1.6 mm. At this time, the thickness value of the outer wall thin plate in the main load-bearing area will be 1.6 mm, and the secondary area will be 1.4 mm or 1.2 mm. This mapping and assignment mechanism ensures that parts of different sizes can obtain suitable support wall thicknesses. In some embodiments, the median and lower limit of the standard thickness range are selected according to a specific proportional relationship, and the calculation formula is expressed as follows:

[0032] in: This represents the median thickness of the thin plate assigned to a specific area. This corresponds to the lower limit of the standard thickness range. This corresponds to the upper limit of the standard thickness range. It is an adjustment coefficient set to 0.5. This formula ensures that the thickness value exhibits a gradient change under the distribution strategy of taking the upper limit in the main load-bearing area and the middle or lower limit in the secondary area.

[0033] In one embodiment of the present invention, see [reference] Figure 3Based on the updated thickness of the continuous thin-walled composite shell support's 3D structural model, the geometric surfaces of each outer wall thin plate and internal reinforcing thin plate requiring perforation design are obtained. On each geometric surface, an equilateral triangular mesh covering the entire surface is planned. The side length of the equilateral triangular mesh is selected within a preset range according to the target perforation ratio, ensuring that the final perforation ratio meets the coupling requirements of the preset heat dissipation efficiency threshold and structural stiffness threshold. Using the center of each triangular element of the equilateral triangular mesh as the perforation center, an inscribed equilateral triangle with a size slightly smaller than the triangular element is generated as the perforation outline. The perforation outline is then stretched and cut along a direction perpendicular to the geometric surface, forming through equilateral triangular holes in the outer wall thin plate or internal reinforcing thin plate. All edges of the perforation outline are rounded to eliminate stress concentration at sharp corners. All thin plates with completed perforation designs are then integrated with the connecting ribs using Boolean operations to ensure geometric continuity between the perforated area and the solid area, forming a continuous thin-walled composite shell support structure with an array of through equilateral triangular perforations. Based on the tilt angle and the initial 3D structural model of the continuous thin-walled composite shell support in the original coordinate system, the projected profile of the continuous thin-walled composite shell support on the molded substrate plane is obtained through geometric projection calculation. The ratio of the area of ​​the projected profile to the orthographic projection area of ​​the continuous thin-walled composite shell support in the original coordinate system is calculated to obtain the projection area magnification factor. When the projection area magnification factor is greater than one, it indicates the existence of a projection magnification region, and the local structure in the continuous thin-walled composite shell support corresponding to the projection magnification region is identified. According to the projection area magnification factor, the arrangement density of the reinforcing thin plates in the local structure is increased according to a preset scaling formula. The increase in the arrangement density of the reinforcing thin plates is positively correlated with the projection area magnification factor. Simultaneously, the cross-sectional dimensions of the connecting ribs in the local structure are increased to match the increased load transfer requirements due to the increased arrangement density of the reinforcing thin plates. For the remaining areas where the projection is not magnified, the optimal powder-saving structural parameters determined based on the wall thickness grading standardized design system remain unchanged. When rounding all edges of the opening contour, based on the thin plate structure model that has undergone through-stretch cutting, all inner edges formed by the opening contour in three-dimensional space are identified. These inner edges are the geometric edges formed by the intersection of an equilateral triangular hole and the thin plate solid. Based on the current thickness of the thin plate and the side length of the opening contour in the thin plate structure model, a recommended chamfer radius range is retrieved from a preset process rule library. The recommended chamfer radius range is positively correlated with the thickness of the thin plate and the side length of the opening contour. Within the recommended chamfer radius range, based on the stress characteristics of the thin plate and its position in the continuous thin-walled composite shell support structure, a specific chamfer radius value is determined for each inner edge. Specifically, the chamfer radius value for opening edges located on the main load-bearing path is the upper limit of the recommended chamfer radius range, while the chamfer radius value for opening edges located on non-main load-bearing paths is the median or lower limit of the recommended chamfer radius range.Using the edge rounding function of 3D modeling software, rounding is performed on all inner edges sequentially based on the specific chamfer radius value determined for each inner edge, transforming the original sharp corners into smooth arc surfaces. After all rounding operations, the models undergo geometric topology consistency checks and repairs to ensure seamless connection between the rounded features and the original thin plate entity and holes, with no redundant or missing geometric surfaces.

[0034] In practical implementation, based on the three-dimensional structural model of the continuously thin-walled composite shell supported by the updated thickness, the geometric surfaces of each outer wall thin plate and internal reinforcing thin plate requiring opening design are obtained. On each geometric surface, an equilateral triangular mesh covering the entire surface is planned. The side length of the equilateral triangular mesh is selected within a preset range of 12 mm to 18 mm according to the target opening ratio, so that the final opening ratio is maintained between 55% and 65%, to meet the coupling requirements of the preset heat dissipation efficiency threshold and structural stiffness threshold. Taking the center of each triangular unit of the equilateral triangular mesh as the opening center, an inscribed equilateral triangle with a size of 80% of the side length of the triangular unit is generated as the opening contour. The opening contour is stretched and cut through along a direction perpendicular to the geometric surface to form a through equilateral triangular hole in the outer wall thin plate or the internal reinforcing thin plate.

[0035] In practice, all edges of the opening contour are rounded to eliminate stress concentration at sharp corners. All thin plates with completed opening designs are then integrated with the connecting ribs using Boolean operations to ensure geometric continuity between the opening area and the solid area, forming a continuous thin-walled composite shell support structure with an array of equilateral triangular through-holes.

[0036] In practical implementation, based on the 45° tilt angle and the initial 3D structural model of the continuous thin-walled composite shell support in the original coordinate system, the projected profile of the continuous thin-walled composite shell support on the molded substrate plane is obtained through geometric projection calculation. The ratio of the area of ​​the projected profile to the orthographic projection area of ​​the continuous thin-walled composite shell support in the original coordinate system is calculated to obtain the projection area magnification factor. When the projection area magnification factor is greater than 1, it indicates the existence of a projection magnification region, and the local structure in the continuous thin-walled composite shell support corresponding to the projection magnification region is identified. According to the projection area magnification factor, the arrangement density of the reinforcing thin plates in the local structure is increased according to a preset scaling formula. The increase in the arrangement density of the reinforcing thin plates is positively correlated with the projection area magnification factor. Simultaneously, the cross-sectional dimensions of the connecting ribs in the local structure are increased to match the increased load transfer requirements due to the increased arrangement density of the reinforcing thin plates. For the remaining areas where the projection is not magnified, the optimal powder-saving structural parameters determined based on the wall thickness grading standardized design system remain unchanged.

[0037] In practical implementation, when rounding all edges of the opening contour, based on the thin plate structure model that has undergone through-stretch cutting, all inner edges formed by the opening contour in three-dimensional space are identified. These inner edges are the geometric edges formed by the intersection of an equilateral triangular hole and the thin plate entity. Based on the current thickness of the thin plate and the side length of the opening contour in the thin plate structure model, a recommended chamfer radius range is retrieved from a preset process rule library. The recommended chamfer radius range is positively correlated with the thickness of the thin plate and the side length of the opening contour. Within the recommended chamfer radius range, based on the stress characteristics of the thin plate and its position in the continuous thin-walled composite shell support structure, a specific chamfer radius value is determined for each inner edge. Specifically, the chamfer radius value for opening edges located on the main load-bearing path is the upper limit of the recommended chamfer radius range, while the chamfer radius value for opening edges located on non-main load-bearing paths is the median or lower limit of the recommended chamfer radius range. Using the edge rounding function of 3D modeling software, rounding is performed on all inner edges sequentially based on the specific chamfer radius value determined for each inner edge, transforming the original sharp corners into smooth arc surfaces. After all rounding operations, the models undergo geometric topology consistency checks and repairs to ensure seamless connection between the rounded features and the original thin plate entity and holes, with no redundant or missing geometric surfaces.

[0038] In some embodiments, the relationship between the side length of the equilateral triangular mesh and the final aperture ratio is shown in Table 1, which guides the parameter selection when designing apertures: Table 1: Comparison of Side Length and Aperture Ratio of Equilateral Triangular Mesh ; It is understood that the data in the table above is derived from the geometric area calculation formula and is used to quickly determine grid parameters in the design to meet specific opening ratio requirements. In some embodiments, the calculation of the projected area magnification factor depends on the tilt angle and the height of the supporting structure, and their relationship is described by the following formula:

[0039] in: Indicates the magnification factor of the projected area. It is the total height of the continuous thin-walled composite shell support in the forming direction. It's the angle at which it's tilted. It is the average width of the supporting structure in the direction perpendicular to the inclination. When When, the adjustment factor for the arrangement density of locally reinforced thin plates is given by the formula. Decision, among which It is a density adjustment factor. It is a constant amplification factor set based on experience, and is usually taken as 1.2.

[0040] In one embodiment of the present invention, the SLM forming process parameters include dedicated laser power, scanning speed, powder layer thickness parameters, and interlayer scanning path rotation strategy for thin-walled regions. The geometric features of the thin-walled regions in the final 3D structural model are analyzed, and regions with a wall thickness less than a preset threshold are identified and marked as critical thin-walled forming areas. A first set of laser process parameters is configured for the critical thin-walled forming areas. The laser power of this first set is lower than that used for forming solid regions, the scanning speed is higher than that used for forming solid regions, and the powder layer thickness is lower than that used for forming solid regions, to prevent spheroidization and warping defects. A second set of laser process parameters is configured for the solid regions in the final 3D structural model other than the critical thin-walled forming areas. The laser power of this second set is higher than that of the first set, and the scanning speed is lower than that of the first set, to ensure complete melting and densification. For the edge regions of the equilateral triangular through-hole array, a third set of laser process parameters is configured. This third set uses a combination of lower laser power and faster scanning speed to control heat input and prevent overheating and deformation of the hole edges. A layer-by-layer scanning path rotation strategy is formulated, assigning different laser scanning path directions to adjacent forming layers, with the angle between the scanning path directions of adjacent layers set to a preset rotation angle. The first, second, and third sets of laser process parameters, along with the layer-by-layer scanning path rotation strategy, are integrated and encapsulated into a SLM forming process parameter package uniquely bound to the final 3D structural model. During the SLM forming process supported by a continuous thin-walled composite shell, thermal radiation signals from the molten pool region are acquired in real time using a coaxial infrared thermal imager. The thermal radiation signals are processed to obtain the average molten pool temperature and temperature distribution uniformity index of the key thin-walled forming area during each layer's forming process. The real-time average molten pool temperature is compared with a preset temperature reference range. If the average molten pool temperature continuously deviates from the temperature reference range, the laser power or scanning speed in the first set of laser process parameters used in the key thin-walled forming area of ​​the next forming layer is dynamically adjusted according to the degree and direction of the deviation. The real-time temperature distribution uniformity index is compared with a preset uniformity threshold. If the temperature distribution uniformity index is lower than the uniformity threshold, the layer-by-layer scanning path rotation strategy is activated, and the specific value of the rotation angle is adjusted in subsequent forming layers. All process parameter adjustment instructions are recorded and synchronously updated to the SLM molding process parameter package to form a dynamically adjusted set of process parameters.

[0041] In practical implementation, the SLM forming process parameters include dedicated laser power, scanning speed, powder layer thickness parameters, and interlayer scanning path rotation strategies for thin-walled regions. Analyzing the geometric features of the thin-walled regions in the final 3D structural model, areas with a wall thickness of 1.4 mm or less are identified and marked as critical thin-walled forming areas. A first set of laser process parameters is configured for these critical thin-walled forming areas. This first set features a lower laser power, a higher scanning speed, and a thinner powder layer thickness than the solid regions used for forming, to prevent spheroidization and warping defects. A second set of laser process parameters is configured for the solid regions in the final 3D structural model, excluding the critical thin-walled forming areas. This second set features a higher laser power and a lower scanning speed than the first set, to ensure complete melting and densification. A third set of laser process parameters is configured for the edge regions of the equilateral triangular through-hole array. This third set combines lower laser power with a faster scanning speed to control heat input and prevent overheating and deformation of the hole edges. A layer-to-layer scanning path rotation strategy was developed, assigning different laser scanning path directions to adjacent forming layers, with the included angle between the scanning path directions of adjacent layers set to 67°. The first set of laser process parameters, the second set of laser process parameters, the third set of laser process parameters, and the layer-to-layer scanning path rotation strategy were integrated and packaged into an SLM forming process parameter package uniquely bound to the final 3D structural model.

[0042] In specific implementation, during the SLM forming process supported by a continuous thin-walled composite shell, a coaxial infrared thermal imager is used to collect thermal radiation signals of the molten pool area in real time. The thermal radiation signals are processed to obtain the average molten pool temperature and temperature distribution uniformity index of the key thin-walled forming area during each layer forming process. The real-time average molten pool temperature is compared with a preset temperature reference range. If the average molten pool temperature continuously deviates from the temperature reference range, the laser power or scanning speed in the first set of laser process parameters used in the key thin-walled forming area of ​​the next forming layer is dynamically adjusted according to the degree and direction of the deviation. The real-time temperature distribution uniformity index is compared with a preset uniformity threshold. If the temperature distribution uniformity index is lower than the uniformity threshold, an inter-layer scanning path rotation strategy is activated, and the specific value of the rotation angle is adjusted in subsequent forming layers. All process parameter adjustment instructions are recorded and synchronously updated to the SLM forming process parameter package, forming a dynamically adjusted process parameter set. In some embodiments, for the nickel-based superalloy Inconel 718 material, the specific configuration values ​​of the first, second, and third sets of laser process parameters are shown in Table 2, where the powder layer thickness is uniformly set to 30 micrometers. Table 2: Inconel 718SLM Molding Zone Process Parameters ; It is understandable that the first set of laser process parameters uses a relatively low laser power of 180 watts combined with a high scanning speed of 900 mm / s, reducing the energy input per unit area and helping to suppress spheroidization of molten metal and structural warping deformation caused by heat accumulation in thin-walled areas. The second set of laser process parameters uses a combination of 250 watts laser power and a scanning speed of 700 mm / s, providing sufficient energy density to ensure the depth of the molten pool and the quality of metallurgical bonding in the solid area. The third set of laser process parameters further reduces the laser power to 150 watts and increases the scanning speed to 1050 mm / s, significantly reducing the risk of overheating in thin structures at the opening edges. In some embodiments, the rotation angle of the interlayer scanning path rotation strategy is not fixed but adjusted according to monitoring data. The formula for calculating the temperature distribution uniformity index is defined as:

[0043] in: This represents an index of temperature distribution uniformity. It is the standard deviation of the temperature at all measurement points within the critical thin-walled forming zone of the current forming layer. It is the average temperature of all measurement points within the critical thin-walled forming zone of the current forming layer. When When the value is lower than the preset uniformity threshold of 0.85, it indicates that the molten pool temperature distribution is uneven, which can easily lead to anisotropic stress. Optionally, when it is detected... At this time, the system automatically activates the interlayer scanning path rotation strategy, adjusting the originally fixed 67° interlayer rotation angle to 90° to change the heat flow direction and promote uniform heat diffusion within the plane. This adjustment is recorded as a process parameter adjustment command and simultaneously fed back to the SLM forming process parameter package to guide the subsequent forming process. It can be understood that online monitoring and parameter adjustment form a closed-loop control system, enabling the forming process to adapt to the actual thermal state of the molten pool and maintain the thermal stability of the critical thin-walled forming zone.

[0044] In one embodiment of the present invention, based on the maximum size of the part, the cumulative distribution of molding heat within the part during a preset molding cycle is calculated. The cumulative distribution result is quantified into a thermal load function varying with spatial position based on the thermophysical parameters of the molding material properties. Based on the maximum size of the part and the mechanical parameters of the molding material properties, the deformation trend caused by thermal stress and self-weight during the molding process is estimated, and this deformation trend is transformed into displacement constraints applied at the boundary of the design domain and the support connection interface. In the geometric center region of the design domain, a concentrated thermal load positively correlated with the maximum size of the part and the molding layer height is applied to simulate the thermal influence of the molding heat source center. In the region of the design domain corresponding to the connection between the support structure and the solid part to be molded, fully constrained mechanical boundary conditions are applied to simulate the rigid connection between the support structure and the part. In the region of the design domain corresponding to the contact between the bottom of the support structure and the molding substrate, a mechanical constraint condition with zero displacement along the molding direction is applied to simulate the fixed connection between the support structure and the substrate. The thermal load function, concentrated thermal load, fully constrained mechanical boundary conditions, and displacement constraint conditions are collectively applied as thermal loads and mechanical constraints to the computational model of the improved topology optimization algorithm.

[0045] In the specific implementation, the large metal part to be formed is a ring-shaped structural component similar to an aero-engine casing, with a maximum size of 1200 mm. The forming material is the nickel-based superalloy Inconel 718, the preset forming cycle time is 72 hours, and the single-layer powder thickness is set to 0.03 mm. Based on the maximum part size of 1200 mm, the cumulative distribution of forming heat inside the part during the 72-hour forming cycle is calculated. Using the thermophysical parameters of the Inconel 718 forming material, the cumulative distribution result is quantified as a thermal load function varying with spatial location. The thermal load function describes the equivalent heat input power density at any time and location during the forming process, with its peak appearing in the area directly affected by the heat source. Based on the maximum part size of 1200 mm and the mechanical parameters of the Inconel 718 forming material, the deformation trend caused by thermal stress and self-weight during the forming process is estimated, and this deformation trend is transformed into displacement constraints applied at the boundary of the design domain and the support connection interface. The displacement constraints limit the rigid body displacement and rotation of the support structure in specific directions to balance the gravity and thermal expansion force of the part.

[0046] In specific implementation, a concentrated thermal load positively correlated with the maximum part size and the forming layer height is applied in the geometric center region of the design domain to simulate the thermal influence of the forming heat source center. The value of the concentrated thermal load is determined based on the product of the maximum part size of 1200 mm and the layer height of 0.03 mm, reflecting the high energy density characteristics of the heat source center. In the region of the design domain corresponding to the connection between the support structure and the solid part to be formed, fully constrained mechanical boundary conditions are applied to simulate the rigid connection between the support structure and the part. The fully constrained mechanical boundary conditions restrict six degrees of freedom, ensuring that the support structure can provide sufficient positioning and support reaction forces for the part. In the region of the design domain corresponding to the contact between the bottom of the support structure and the forming substrate, a mechanical constraint condition with zero displacement along the forming direction is applied to simulate the fixed connection between the support structure and the substrate. The mechanical constraint condition with zero displacement along the forming direction prevents vertical movement of the support structure relative to the substrate, establishing a stable forming reference. In some embodiments, the spatial distribution of the thermal load function is described using an exponential decay model, the mathematical expression of which is:

[0047] in: Indicates the location and time The heat load power density, in watts per cubic meter; It is a reference heat input intensity related to the maximum size of the part and the molding cycle, and its value is [value missing]. Tiles per cubic meter; It is the attenuation coefficient characterizing the thermal diffusion properties of Inconel 718 material, with a value of 50 per meter; It is the spatial distance from the calculation point to the center of the heat source, in meters; This is a time-varying normalized modulation function that reflects the periodic thermal fluctuations caused by the laser switching and scanning path during the forming process. This formula links the macroscopic forming cycle with the microscopic heat source behavior, quantifying the spatial gradient distribution of heat. It can be understood that the fully constrained mechanical boundary conditions and the mechanical constraint condition with zero displacement along the forming direction constitute the basic boundary of the supporting structure's mechanical model. The thermal load function, concentrated thermal load, fully constrained mechanical boundary conditions, and displacement constraint conditions are collectively used as the computational model of an improved topology optimization algorithm that applies thermal loads and mechanical constraints. This drives the topology optimization process to generate a supporting structure configuration that can effectively dissipate heat and resist mechanical deformation.

[0048] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a self-stabilizing, powder-saving shell support for additive manufacturing of large SLM metal parts, characterized in that, The method includes: Obtain the 3D model data of the large metal part to be formed and the set tilt angle; The suspended structures in the three-dimensional model data are identified to determine the areas where support structures need to be constructed and their outline boundaries. Using an improved topology optimization algorithm, based on the contour boundary, the tilting angle, and the preset maximum size of the parts, an initial three-dimensional structural model of a continuous thin-walled composite shell support is generated. The continuous thin-walled composite shell support includes an outer wall thin plate, multiple layers of internal reinforcing thin plates parallel to the outer wall thin plate, and connecting ribs connecting the outer wall thin plate and the internal reinforcing thin plates. The wall thickness grading standardization design system is invoked, and the corresponding standard thickness values ​​are assigned to the outer wall thin plate and the inner reinforcing thin plate in the initial three-dimensional structural model according to the design range where the maximum size of the part is located. An opening design is implemented on the outer wall thin plate and the inner reinforcing thin plate to form a uniformly distributed array of equilateral triangular through openings; Based on the tilt angle, the projection area magnification factor of the continuous thin-walled composite shell support in the forming direction is calculated, and the structural parameters related to the tilt angle in the initial three-dimensional structural model are oriented and adjusted according to the projection area magnification factor. Based on the final three-dimensional structural model of the continuous thin-walled composite shell support, a suitable SLM molding process parameter package is generated.

2. The method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts according to claim 1, characterized in that, The process of generating an initial three-dimensional structural model of a continuous thin-walled composite shell support using an improved topology optimization algorithm, based on the contour boundary, the tilt angle, and the preset maximum size of the parts, includes: Within the design domain defined by the contour boundary, thermal loads and mechanical constraints are applied during the molding process. These thermal loads and mechanical constraints are calculated based on the maximum size of the part, the properties of the molding material, and the preset molding cycle time. The improved topology optimization algorithm is used to iteratively calculate the design domain. The improved topology optimization algorithm, based on the thermal load and mechanical constraints, aims to minimize the amount of structural material used, provided that the preset structural stiffness threshold and heat dissipation efficiency threshold are met. In each iteration of the calculation, it is simultaneously determined whether the tilt angle is zero. When the tilt angle is not zero, a projection load penalty term related to the tilt angle is introduced into the objective function. After the improved topology optimization algorithm converges, it outputs the material density distribution cloud map, performs geometric reconstruction on the material density distribution cloud map, extracts the region with density greater than a preset threshold, and forms a preliminary shell skeleton composed of an outer wall thin plate, multiple layers of internal reinforcing thin plates and connecting ribs. The initial shell skeleton is smoothed and constrained by minimum feature size to generate an initial three-dimensional structural model of the continuous thin-walled composite shell support with a closed multi-cavity structure.

3. The method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts according to claim 2, characterized in that, The improved topology optimization algorithm is a variable-density topology optimization algorithm that combines a bidirectional asymptotic structure optimization method with sensitivity filtering technology. Its working principle includes: The design domain is discretized into a finite element mesh, and each mesh element is assigned a pseudo density variable that varies continuously between zero and one. Based on the pseudo-density variable of each grid cell, the corresponding elastic modulus and thermal conductivity coefficient are calculated through a material interpolation model, and the global stiffness matrix and thermal conductivity matrix are assembled. Under the volume fraction constraint that meets the molding process requirements, with the goal of minimizing the amount of structural material used, and with the dual constraints that the structural compliance corresponding to the global stiffness matrix is ​​less than the structural stiffness threshold and the heat dissipation efficiency corresponding to the heat conduction matrix is ​​greater than the heat dissipation efficiency threshold, an optimization mathematical model is constructed. In each optimization iteration, the sensitivity of the objective function to the pseudo-density variable of each grid cell is calculated, and the sensitivity filtering technique is used to filter the sensitivity field to eliminate the checkerboard phenomenon and control the minimum structure size. The update criteria of the bidirectional progressive structure optimization method are adopted, and the pseudo-density variables of each grid cell are added or deleted synchronously based on the sensitivity information and the current volume fraction constraint, so as to achieve more efficient material layout update. After the iteration converges, the pseudo-density variable field is output as the material density distribution cloud map.

4. The method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts according to claim 1, characterized in that, The invocation of the wall thickness grading standardization design system assigns corresponding standard thickness values ​​to the outer wall thin plate and the internal reinforcing thin plate in the initial three-dimensional structural model based on the design range where the maximum size of the part is located, including: Four consecutive maximum part size design ranges are predefined, and each design range is associated with a set of standard thickness ranges for outer wall thin plates and internal reinforcing thin plates. Extract the maximum size of the part from the three-dimensional model data, and map the maximum size of the part to one of the four consecutive maximum size design intervals of the part to determine its target design interval; Based on the target design range, the corresponding standard thickness range of the outer wall thin plate and the standard thickness range of the internal reinforcing thin plate are read from the predefined data table; Based on the stress characteristics of each part in the initial three-dimensional structural model of the continuous thin-walled composite shell support, a specific thickness value is assigned to each outer wall thin plate and inner reinforcing thin plate within the corresponding standard thickness range. The thickness value of the main load-bearing area is taken as the upper limit of the standard thickness range, and the thickness value of the secondary area is taken as the median or lower limit of the standard thickness range. The specific thickness values ​​are assigned to the corresponding geometric surfaces of the initial three-dimensional structural model, thereby updating the three-dimensional structural model of the continuous thin-walled composite shell support.

5. The method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts according to claim 1, characterized in that, An opening design is implemented on the outer wall thin plate and the inner reinforcing thin plate to form a uniformly distributed array of equilateral triangular through openings, including: Based on the three-dimensional structural model of the continuous thin-walled composite shell support after the thickness is updated, the geometric surfaces of each outer wall thin plate and inner reinforcing thin plate that require opening design are obtained respectively. On each of the geometric surfaces, an equilateral triangular mesh covering the entire surface is planned. The side length of the equilateral triangular mesh is selected within a preset range according to the target aperture ratio, so that the final aperture ratio meets the coupling requirements of the preset heat dissipation efficiency threshold and the structural stiffness threshold. Using the center of each triangular cell of the equilateral triangular mesh as the center of the opening, an inscribed equilateral triangle with a size slightly smaller than the triangular cell is generated as the opening outline; The opening contour is stretched and cut through along a direction perpendicular to the geometric surface to form a through equilateral triangular hole on the outer wall thin plate or the inner reinforcing thin plate. All edges of the opening contour are rounded to eliminate stress concentration at sharp corners; All the thin plates with completed perforation designs are re-integrated with the connecting ribs through Boolean operations to ensure the geometric continuity between the perforated area and the solid area, ultimately forming a continuous thin-walled composite shell support structure with the equilateral triangle through-hole array.

6. The method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts according to claim 1, characterized in that, Based on the tilt angle, the projected area magnification factor of the continuous thin-walled composite shell support in the forming direction is calculated, and the structural parameters related to the tilt angle in the initial three-dimensional structural model are oriented and adjusted according to the projected area magnification factor, including: Based on the tilt angle and the outline dimensions of the initial three-dimensional structural model of the continuous thin-walled composite shell support in the original coordinates, the projected outline of the continuous thin-walled composite shell support on the molded substrate plane is obtained through geometric projection calculation. The ratio of the area of ​​the projected contour to the orthographic projection area of ​​the continuous thin-walled composite shell support in the original coordinates is calculated to obtain the projection area magnification factor; When the projection area magnification factor is greater than one, it indicates the existence of a projection magnification region, and the local structure in the continuous thin-walled composite shell support corresponding to the projection magnification region is identified. According to the projection area magnification factor, the arrangement density of the reinforcing thin plates in the local structure is increased according to the preset scaling ratio formula, and the increase in the arrangement density of the reinforcing thin plates is positively correlated with the projection area magnification factor. The cross-sectional dimensions of the connecting ribs in the local structure are increased simultaneously to match the increased load transfer requirements due to the increased density of the reinforcing thin plates. For the remaining areas where the projection is not magnified, the optimal powder-saving structural parameters determined based on the wall thickness grading standardization design system remain unchanged.

7. The method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts according to claim 1, characterized in that, Based on the final three-dimensional structural model of the continuous thin-walled composite shell support, a suitable SLM molding process parameter package is generated, including: The SLM forming process parameters include dedicated laser power, scanning speed, powder layer thickness parameters, and interlayer scanning path rotation strategy for thin-walled regions. Analyze the geometric features of the thin-walled region in the final three-dimensional structural model, identify regions with a wall thickness less than a preset threshold, and mark them as key thin-walled forming areas; A first set of laser process parameters is configured for the critical thin-walled forming area. The laser power of the first set of laser process parameters is lower than that used for forming the solid area, the scanning speed is higher than that used for forming the solid area, and the powder layer thickness is less than that used for forming the solid area, so as to prevent spheroidization and warping defects. A second set of laser process parameters is configured for the solid areas in the final three-dimensional structural model other than the key thin-walled forming area. The laser power of the second set of laser process parameters is higher than that of the first set of laser process parameters, and the scanning speed is lower than that of the first set of laser process parameters, so as to ensure complete melting and densification. For the edge region of the equilateral triangle through-hole array, a third set of laser process parameters is configured. The third set of laser process parameters uses a combination of lower laser power and faster scanning speed to control heat input and prevent overheating and deformation of the hole edge. A rotation strategy for the interlayer scanning path is formulated, and different laser scanning path directions are set for adjacent forming layers. The angle between the scanning path directions of adjacent layers is set to a preset rotation angle. The first set of laser process parameters, the second set of laser process parameters, the third set of laser process parameters, and the interlayer scanning path rotation strategy are integrated and packaged into the SLM forming process parameter package that is uniquely bound to the final three-dimensional structural model.

8. The method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts according to claim 2, characterized in that, Within the design domain defined by the contour boundary, thermal loads and mechanical constraints are applied during the molding process, including: Based on the maximum size of the part, the cumulative distribution of molding heat inside the part is calculated within the preset molding cycle time, and the cumulative distribution result is quantified into a heat load function that varies with spatial position according to the thermophysical parameters of the molding material properties. Based on the maximum size of the part and the mechanical parameters of the molding material properties, the deformation trend caused by thermal stress and self-weight during the molding process is estimated, and the deformation trend is converted into displacement constraints applied at the boundary of the design domain and the support connection interface. In the geometric center region of the design domain, a concentrated thermal load positively correlated with the maximum size of the part and the height of the molding layer is applied to simulate the thermal influence of the molding heat source center. In the design domain, corresponding to the area where the support structure connects to the solid part to be formed, fully constrained mechanical boundary conditions are applied to simulate the rigid connection between the support structure and the part. In the design domain, corresponding to the area where the bottom of the support structure contacts the molding substrate, a mechanical constraint condition with zero displacement along the molding direction is applied to simulate the fixed connection between the support structure and the substrate. The thermal load function, concentrated thermal load, fully constrained mechanical boundary conditions, and displacement constraint conditions are collectively applied as the thermal load and mechanical constraint conditions to the computational model of the improved topology optimization algorithm.

9. The method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts according to claim 5, characterized in that, All edges of the opening profile are rounded to eliminate stress concentration at sharp corners, including: Based on the thin plate structure model that has been completed through stretching and cutting, all the inner side lines formed by the opening contour in three-dimensional space are identified. The inner side lines are the geometric edges formed by the intersection of the equilateral triangular hole and the thin plate solid. Based on the thickness value of the current thin plate in the thin plate structure model and the side length of the opening profile, a matching recommended chamfer radius value range is queried from the preset process rule library. The recommended chamfer radius value range is positively correlated with the thickness value of the thin plate and the side length of the opening profile. Within the recommended chamfer radius range, based on the stress characteristics of the thin plate and the current position of the thin plate in the continuous thin-walled composite shell support structure, a specific chamfer radius value is determined for each inner edge line. The chamfer radius value of the opening edge located on the main load-bearing path is taken as the upper limit of the recommended chamfer radius range, and the chamfer radius value of the opening edge located on the non-main load-bearing path is taken as the median or lower limit of the recommended chamfer radius range. Using the edge rounding function of 3D modeling software, based on the specific chamfer radius value determined for each inner edge line, the rounding modeling operation is performed on all inner edge lines in sequence, so that the original sharp corners are transformed into smooth arc surfaces. Perform geometric topology consistency checks and repairs on all models after rounding operations to ensure seamless connection between rounded corner features and the original thin plate entity and holes, with no redundant or missing geometric surfaces.

10. The method for preparing a self-stabilizing powder-saving shell support for additive manufacturing of large SLM metal parts according to claim 7, characterized in that, The method also includes a closed-loop fine-tuning step for process parameters based on online monitoring data during the SLM molding process: During the SLM forming process supported by the continuous thin-walled composite shell, the thermal radiation signal of the molten pool area is collected in real time by a coaxial infrared thermal imager. The thermal radiation signal is processed to obtain the average melt pool temperature and temperature distribution uniformity index of the key thin-walled forming area during the forming process of each layer; The average molten pool temperature obtained in real time is compared with the preset temperature reference range. If the average molten pool temperature continues to deviate from the temperature reference range, the laser power or scanning speed in the first set of laser process parameters used in the critical thin-wall forming area of ​​the next forming layer is dynamically adjusted according to the degree and direction of the deviation. The temperature distribution uniformity index obtained in real time is compared with a preset uniformity threshold. If the temperature distribution uniformity index is lower than the uniformity threshold, the interlayer scanning path rotation strategy is activated, and the specific value of the rotation angle is adjusted in the subsequent forming layer. All process parameter adjustment instructions are recorded and synchronously updated to the SLM molding process parameter package to form a dynamically adjusted set of process parameters.

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