A forming method of an SLM large-inclination-angle structure without support

Abstract

The application provides a forming method of an SLM non-support large-inclination structure, which can manufacture an extreme overhanging structure with an inclination less than 15 degrees without a support structure, and makes the SLM technology application expanded. The method is characterized in that: for the extreme overhanging structure, the process parameters need to be dynamically regulated, the ratio of the solid and profile process parameters is dynamically optimized, and the energy density relationship between the upper and lower surfaces and the inner surface is strictly controlled; the scanning strategy adopts a short scanning vector length and a random scanning sequence, and the overhanging area is divided into multiple small blocks, and a random jumping scanning mode from the boundary to the center is adopted; and the substrate preheating and the forming cavity environment control are simultaneously performed.

Description

Technical Field

[0001] This invention relates to the field of selective laser melting (SLM), specifically to a method for forming an unsupported, large-angle SLM structure. Background Technology

[0002] Selective laser melting (SLM) technology uses a high-energy laser beam to melt metal powder layer by layer, producing complex metal parts with high density and mechanical properties approaching those of forgings. However, SLM technology has inherent limitations when processing overhanging structures: 1. "Step Effect" and Critical Angle Limitation: Currently, the industry generally believes that 45° is the critical angle for unsupported SLM forming. Below this angle, the thermal conductivity and mechanical support provided by the unmelted powder in the lower layer of the overhang area are insufficient, resulting in: (a) Unstable molten pool: The molten pool is prone to flow and spheroidization under the action of gravity, causing surface roughness, holes, or even forming failure; (b) Thermal stress accumulation: The huge temperature gradient in the overhang area leads to thermal stress concentration, which can easily cause warping and cracking of parts; (c) Powder adhesion: Incompletely melted powder adheres to the surface at low angles, seriously affecting surface quality and dimensional accuracy. 2. Disadvantages of Support Structures: To solve the above problems, the only current method is to add a solid support structure. However, the following problems exist: (a) Waste of materials and energy: The support structure consumes a large amount of metal powder and printing time; (b) Difficult post-processing: The metal support structure has high mechanical strength and is extremely difficult to remove. It requires wire cutting, grinding, etc., which can easily damage the part body, introduce stress or deformation, and cannot remove the support for internally closed structures such as hollow spheres; (c) Restriction of design freedom: The component process design must compromise for manufacturability, and the design potential of additive manufacturing cannot be fully utilized.

[0003] Existing technologies attempt to improve the quality of overhanging surfaces through single parameters (such as reducing laser power or increasing scanning speed), but the effects are limited, typically only barely addressing overhang angles above 30°. For extreme overhanging structures below 15°, conventional parameter adjustments cannot overcome their physical forming problems. Therefore, developing a method to achieve high-quality forming of extreme overhanging structures without the need for supports is of great significance. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a method for forming SLM unsupported large tilt angle structures, which can produce extreme overhang structures below 15° without the need for supporting structural components, thereby expanding the application of SLM technology.

[0005] A method for forming an unsupported, large-angle SLM structure, characterized in that: For extreme overhanging structural components, the process parameters need to be dynamically adjusted. This dynamic adjustment optimizes the ratio of solid to contour process parameters and strictly controls the energy density relationship between the upper and lower surfaces and the inner surface. The scanning strategy employs a short scan vector length and a random scan order, and divides the overhanging region into multiple small blocks, using a random skip scan method from the boundary to the center; Simultaneously, substrate preheating and molding cavity environment control are performed.

[0006] Its further features are: When dynamically adjusting process parameters, the ratio of solid to contour process parameters is optimized. When the layer thickness is 40~60μm, the relationship between the inner surface solid and contour is as follows: its laser power P 实体 / P 轮廓 =0.5~0.8, scanning speed V 实体 / V 轮廓 =1.4~1.8, and the scanning interval is generally 0.07~0.12; When controlling the energy density relationship between the upper and lower surfaces and the inner surface, the relationship between various parameters of the inner surface and the lower surface is: P 内表面 / P 下表面 =1.3~1.8, V 内表面 / V 下表面 =0.6~0.9, S 内表面 / S 下表面 =1.2~1.9; Relationship between parameters of the inner and upper surfaces: P 内表面 / P 上表面 =1.2~1.4, V 内表面 / V 上表面 =1.0~1.2, S 内表面 / S 上表面 =1.1~1.3; Scanning strategies should avoid using long scan lines to prevent heat buildup in overhang areas; The scanning strategy divides the overhanging region into multiple small blocks, adopts a random jump scanning method from the boundary to the center, and the end point of each short scan line can provide an anchor point for the next segment; When the substrate is preheated, it is preheated to a relatively high temperature. The higher base temperature significantly reduces the temperature gradient between the molten pool and the base, slows down the cooling rate, and thus effectively reduces thermal stress and suppresses warping tendency. The forming cavity environment control specifically involves precisely controlling the protective gas flow field within the forming cavity to prevent airflow from directly impacting the tiny molten pool in the overhanging area and to prevent disturbance. The scanning strategy employs a short scan vector length and a random scan sequence, and resolves stress through geometric reconstruction. It has corresponding planning algorithms for ordinary overhanging areas, spirals, and hollow spheres, respectively. For ordinary overhanging areas, an overhanging area micro-guide scanning and edge enhancement algorithm is adopted. This algorithm automatically divides large overhanging areas into hundreds of micro-guides with micro-scale dimensions. The scanning path adopts a random jump scanning sequence from the boundary to the center, which avoids heat accumulation and stress concentration caused by long vector scanning, so that each micro-area can be independently and stably formed and provides solid anchor points for its adjacent areas. At the same time, the algorithm will prioritize and scan the outer contour of the overhanging area with higher energy density to form a solid frame and lock the internal material. For the spiral, a three-dimensional self-supporting path algorithm for the spiral is adopted. This algorithm generates a non-coplanar three-dimensional continuous scanning path with a specific radial offset in the Z-axis direction, which allows the newly melted weld to be partially remelted and anchored on the solidified sidewall of the lower structure, forming a mechanically self-stabilizing arch or catenary structure, thereby fundamentally avoiding the limitation of the plane projection angle. For hollow spheres, a partitioned variable-direction tangential scanning algorithm is adopted. This algorithm triangulates the surface of the sphere and plans a path within each micro-unit. The direction of the scanning vector is forcibly constrained to be close to the tangential direction of the sphere at that point. At the same time, the scanning directions of adjacent layers are staggered at a certain angle, so that the stress distribution is uniform and that the new material of each layer can be firmly bonded to the lower layer in multiple directions, together weaving a stable spherical mesh structure.

[0007] The unsupported structural components prepared by the above method can be processed by SLM technology for extreme overhang structures with an angle of less than 15°. The overhanging area, spiral structure and hollow sphere are well formed, without defects such as spheroidization and cracking. The surface roughness Ra of the overhanging surface is <6.3μm and the density is >99.5%. Attached Figure Description

[0008] Figure 1 A physical diagram of a structure with a common overhang region obtained by the method of this invention; Figure 2 A physical diagram of a structure with a helix obtained by the method of this invention; Figure 3 A physical diagram of the structure with a hollowed-out sphere obtained by the method of this invention; Figure 4 for Figure 3 Another location marker diagram. Detailed Implementation

[0009] A method for forming unsupported, large-angle inclined structures using SLM (Surface Mount Technology): For extreme overhanging structural components, process parameters need to be dynamically adjusted. This dynamic adjustment optimizes the ratio of solid to contour process parameters and strictly controls the energy density relationship between the upper and lower surfaces and the inner surface. The corresponding positions of the upper, lower, and inner surfaces are described in [reference needed]. Figure 2 , Figure 3 The corresponding marker in; The scanning strategy employs a short scan vector length and a random scan order, dividing the overhanging region into multiple small blocks and using a random skip scan method from the boundary to the center. The locations of the boundary and center are detailed in [reference needed]. Figure 4 The corresponding marker; Simultaneously, substrate preheating and molding cavity environment control are performed.

[0010] When dynamically adjusting process parameters, the ratio of solid to contour process parameters is optimized. When the layer thickness is 40~60μm, the relationship between the inner surface solid and contour is as follows: its laser power P 实体 / P 轮廓 =0.5~0.8, scanning speed V 实体 / V 轮廓 =1.4~1.8, and the scanning interval is generally 0.07~0.12; When controlling the energy density relationship between the upper and lower surfaces and the inner surface, the relationship between various parameters of the inner surface and the lower surface is: P 内表面 / P 下表面 =1.3~1.8, V 内表面 / V 下表面 =0.6~0.9, S 内表面 / S 下表面 =1.2~1.9; Relationship between parameters of the inner and upper surfaces: P 内表面 / P 上表面 =1.2~1.4, V 内表面 / V 上表面 =1.0~1.2, S 内表面 / S 上表面 =1.1~1.3; Scanning strategies should avoid using long scan lines to prevent heat buildup in overhang areas; The scanning strategy divides the overhanging region into multiple small blocks, adopts a random jump scanning method from the boundary to the center, and the end point of each short scan line can provide an anchor point for the next segment; When preheating the substrate, the substrate is preheated to a relatively high temperature, such as 200~400℃ for steel materials and 400~600℃ for titanium alloys. The higher base temperature significantly reduces the temperature gradient between the molten pool and the base, slows down the cooling rate, and thus effectively reduces thermal stress and suppresses warping tendency. The forming cavity environment control specifically involves precisely controlling the protective gas flow field within the forming cavity to prevent airflow from directly impacting the tiny molten pool in the overhanging area and to prevent disturbance. The scanning strategy employs a short scan vector length and a random scan sequence, and resolves stress through geometric reconstruction. It has corresponding planning algorithms for ordinary overhanging areas, spirals, and hollow spheres, respectively. For ordinary overhang areas, such as Figure 1 The structural diagrams shown depict three products with dimensions of 36×25×11mm, 43×25×23mm, and 42×25×15mm from left to right. This group of products employs a micro-guided scanning and edge enhancement algorithm for overhanging areas. This algorithm automatically divides large overhanging areas into hundreds of micrometer-sized microguides. The scanning path adopts a random, skipping scanning sequence from the boundary to the center, which avoids heat accumulation and stress concentration caused by long vector scanning. This allows each micro-area to form independently and stably, and provides solid anchor points for its adjacent areas. At the same time, the algorithm prioritizes scanning the outer contour of the overhanging area with higher energy density, forming a robust frame that locks in the internal material.

[0011] For spirochetes, such as Figure 2 The structural diagram shown has product dimensions of 46×46×23mm. It adopts a three-dimensional self-supporting path algorithm of a spiral body. This algorithm generates a non-coplanar three-dimensional continuous scanning path. This path has a specific radial offset in the Z-axis direction. In the specific embodiment, the radial offset is 10~50μm, which allows the newly melted weld to be partially remelted and anchored on the solidified sidewall of the lower structure, forming a mechanically self-stabilizing arch or catenary structure, thereby fundamentally avoiding the limitation of the plane projection angle. For hollow spheres, such as Figure 3 , Figure 4 The structural diagram shown shows a product with dimensions of 50×50×50mm. It employs a partitioned, variable-direction tangential scanning algorithm for a hollow sphere. This algorithm triangulates the surface of the sphere into a mesh and plans a path within each micro-unit. The direction of the scanning vector is forcibly constrained to be close to the tangential direction of the sphere at that point. At the same time, the scanning directions of adjacent layers are staggered at certain angles (e.g., 0°, 67°, 120°) to ensure uniform stress distribution and to allow each new layer of material to firmly bond with the lower layer in multiple directions, together weaving a stable spherical mesh structure.

[0012] The unsupported structural component prepared by the above method (see...) Figures 1-4 Its suspended area, spiral structure, and hollow spheres are well formed, without defects such as spheroidization or cracking. The surface roughness of the suspended surface Ra < 6.3 μm and the density > 99.5%.

[0013] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0014] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for forming an unsupported, large-angle SLM structure, characterized in that: For extreme overhanging structural components, the process parameters need to be dynamically adjusted. This dynamic adjustment optimizes the ratio of solid to contour process parameters and strictly controls the energy density relationship between the upper and lower surfaces and the inner surface. The scanning strategy employs a short scan vector length and a random scan order, and divides the overhanging region into multiple small blocks, using a random skip scan method from the boundary to the center; Simultaneously perform substrate preheating and molding cavity environment control; When dynamically adjusting process parameters, the ratio of solid to contour process parameters is optimized. When the layer thickness is 40~60μm, the relationship between the inner surface solid and contour is as follows: its laser power P 实体 / P 轮廓 =0.5~0.8, scanning speed V 实体 / V 轮廓 =1.4~1.8, and the scanning interval is generally 0.07~0.12; When controlling the energy density relationship between the upper and lower surfaces and the inner surface, the relationship between various parameters of the inner surface and the lower surface is: P 内表面 / P 下表面 =1.3~1.8, V 内表面 / V 下表面 =0.6~0.9, S 内表面 / S 下表面 =1.2~1.9; Relationship between parameters of the inner and upper surfaces: P 内表面 / P 上表面 =1.2~1.4, V 内表面 / V 上表面 =1.0~1.2, S 内表面 / S 上表面 =1.1~1.3; The scanning strategy employs a short scan vector length and a random scan sequence, and resolves stress through geometric reconstruction. It has corresponding planning algorithms for ordinary overhanging areas, spirals, and hollow spheres, respectively. For ordinary overhanging areas, the overhanging area micro-guide scanning and edge enhancement algorithm is adopted. The overhanging area micro-guide scanning and edge enhancement algorithm automatically divides the large overhanging area into hundreds of micro-guides with micron-sized dimensions. The scanning path adopts a random jump scanning sequence from the boundary to the center, which avoids heat accumulation and stress concentration caused by long vector scanning, so that each micro-area can be independently and stably formed, and provides solid anchor points for its adjacent areas. At the same time, the overhanging area micro-guide scanning and edge enhancement algorithm will prioritize and scan the outer contour of the overhanging area with higher energy density to form a solid frame and lock the internal material. For the spiral, a three-dimensional self-supporting path algorithm for the spiral is adopted. The three-dimensional self-supporting path algorithm for the spiral generates a non-coplanar three-dimensional continuous scanning path. The non-coplanar three-dimensional continuous scanning path has a specific radial offset in the Z-axis direction, which allows the newly melted weld to be partially remelted and anchored on the solidified sidewall of the lower structure, forming a mechanically self-stabilizing arch or catenary structure, thereby fundamentally avoiding the limitation of the plane projection angle. For hollow spheres, a partitioned variable-direction tangential scanning algorithm is adopted. The partitioned variable-direction tangential scanning algorithm triangulates the surface of the sphere and plans a path within each micro-unit. The direction of the scanning vector is forcibly constrained to be close to the tangential direction of the sphere at that point. At the same time, the scanning directions of adjacent layers are staggered at a certain angle, so that the stress distribution is uniform and the new material of each layer can be firmly bonded to the lower layer in multiple directions, together weaving a stable spherical mesh structure.

2. The forming method of an unsupported large-angle SLM structure according to claim 1, characterized in that: The scanning strategy divides the overhanging region into multiple small blocks, adopts a random jump scanning method from the boundary to the center, and the end point of each short scan line can provide an anchor point for the next segment.

3. The forming method of an unsupported large-angle SLM structure according to claim 1, characterized in that: When preheating the substrate, steel materials should be preheated to 200~400℃, and titanium alloys should be preheated to 400~600℃. The forming cavity environment control specifically involves precisely controlling the protective gas flow field within the forming cavity to prevent airflow from directly impacting the tiny molten pool in the overhanging area and to prevent disturbance.

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