Forming method of SLM (selective laser melting) support-free large-dip-angle structure

Abstract

The invention provides a forming method of an SLM (selective laser melting) support-free large-dip-angle structure, which can be used for manufacturing an extreme overhanging structure lower than 15 degrees without a support structural part, so that the application of an SLM technology is expanded. The method is characterized in that technological parameters need to be dynamically regulated and controlled for an extreme overhanging structural component, the ratio of the entity technological parameters to the outline technological parameters is dynamically optimized, and the energy density relation between the upper surface, the lower surface and the inner surface is strictly controlled; the scanning strategy adopts a short scanning vector length and a random scanning sequence, the overhanging area is divided into a plurality of small blocks, and a random jump scanning mode from the boundary to the center is adopted; and meanwhile, substrate preheating and forming cavity environment control are carried out.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of selective laser melting, in particular to a forming method of SLM large-inclination-angle structure without support. BACKGROUND

[0002] Selective laser melting (SLM) technology melts metal powder layer by layer through high-energy laser beam to manufacture complex metal parts with high density and mechanical properties close to forged parts. However, SLM technology has inherent bottlenecks in dealing with overhanging structures: 1 "step effect" and critical angle limitation: it is generally believed in the industry that 45° is the critical angle for SLM support-free forming. Below this angle, the heat conduction and mechanical support provided by the lower layer of un-melted powder in the overhanging area are insufficient, resulting in: (a) unstable molten pool: the molten pool is prone to flow and spheroidization under the action of gravity, causing rough surface, holes and even forming failure; (b) heat stress accumulation: the huge temperature gradient in the overhanging area causes heat stress concentration, which easily causes the part to warp and crack; (c) powder adhesion: the un-melted powder adheres to the low-angle lower surface, seriously affecting the surface quality and dimensional accuracy; 2 disadvantages of support structure: to solve the above problems, the only method at present is to add a solid support structure. However, there are the following problems: (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, which needs to be removed by wire cutting, grinding, etc., which easily damages the part body, introduces stress or deformation, and the support for internal closed structures such as hollow spheres cannot be removed; (c) limit design freedom: the component process design must be compromised for manufacturability, and the design potential of additive manufacturing cannot be fully utilized.

[0003] The prior art attempts to improve the overhanging surface quality by a single parameter (such as reducing laser power or increasing scanning speed), but the effect is limited, and usually only 30° or more overhanging angle can be barely dealt with. For extreme overhanging structures below 15°, conventional parameter adjustment cannot overcome the physical level forming problems. Therefore, it is of great significance to develop a method that can realize high-quality forming of extreme overhanging structures without support. SUMMARY

[0004] In view of the above problems, the present application provides a forming method of SLM large-inclination-angle structure without support, which can manufacture extreme overhanging structures below 15° without support structure, and expands the application of SLM technology.

[0005] A forming method of SLM large-inclination-angle structure without support, characterized in that: For the extreme overhanging structure, the process parameters need to be dynamically adjusted, and the ratio of the solid and contour process parameters is optimized, and the energy density relationship between the upper and lower surfaces and the inner surface is strictly controlled; The scanning strategy adopts short scanning vector length and random scanning order, and divides the overhanging area into multiple small blocks, and adopts random jumping scanning mode from the boundary to the center. The substrate is preheated and the forming cavity environment is controlled at the same time.

[0006] It further comprises the following features: When the process parameters are dynamically adjusted, the ratio of the solid and contour process parameters is optimized, and when the layer thickness is 40-60 μm, the relationship between the inner surface solid and the contour is: the laser power P 实体 / P 轮廓 =0.5-0.8, the scanning speed V 实体 / V 轮廓 =1.4-1.8, and the scanning pitch is generally 0.07-0.12. When the energy density relationship between the upper and lower surfaces and the inner surface is controlled, the relationship between the 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; the relationship between the parameters of the inner surface and the upper surface is: 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 avoids using long scanning lines to prevent heat accumulation in the overhanging area. The scanning strategy divides the overhanging area into multiple small blocks, adopts random jumping scanning mode from the boundary to the center, and the end point of each short scanning line can provide an anchor point for the next segment. When the substrate is preheated, the substrate is preheated to a relatively high temperature, and a higher base temperature significantly reduces the temperature gradient between the molten pool and the base, slows down the cooling rate, thereby effectively reducing the thermal stress and suppressing the warping tendency. The forming cavity environment control is to precisely control the protective gas flow field in the forming cavity to avoid direct impact of the gas flow on the small molten pool in the overhanging area and prevent disturbance. The scanning strategy adopts short scanning vector length and random scanning order, and solves the stress through geometric reconstruction, which has corresponding planning algorithms for ordinary overhanging areas, spirals, and hollow spheres. For ordinary overhanging area, the overhanging area micro-guide scanning and edge strengthening algorithm is adopted, the algorithm automatically divides the large-area overhanging area into hundreds of micron-level micro-guides, the scanning path adopts the random jumping scanning sequence from the boundary to the center, which avoids the heat accumulation and stress concentration caused by long vector scanning, makes each micro-area independently and stably form, and provides a solid anchor point for the adjacent area, at the same time, the algorithm will preferentially scan the outer contour of the overhanging area with higher energy density, and form a solid frame to lock the internal material; For the spiral body, a three-dimensional self-supporting path algorithm for the spiral body is adopted, the algorithm generates a non-coplanar three-dimensional continuous scanning path, which has a specific radial offset in the Z-axis direction, so that the newly melted weld can partially remelt and anchor on the sidewall of the solidified lower structure, forming a mechanically self-stable arch or catenary structure, thereby fundamentally avoiding the limitation of the plane projection angle; For the hollow sphere, a partition variable direction tangential scanning algorithm for the hollow sphere is adopted, the algorithm triangulates the surface of the sphere, and plans the path in each micro-unit, the direction of the scanning vector is forced to be close to the direction of the tangent of the sphere at the 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 combined with the lower layer in multiple directions to weave a stable spherical net structure.

[0007] The unsupported structure prepared by the above method can be processed by SLM technology for extreme overhanging structures below 15°, the suspended area, spiral structure and hollow sphere are well formed without defects such as spheroidization and cracking, the suspended surface roughness Ra is less than 6.3μm, and the density is greater than 99.5%. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 A structure with ordinary overhanging area prepared by the method of the application; Figure 2 A structure with spiral body prepared by the method of the application; Figure 3 A structure with hollow sphere prepared by the method of the application; Figure 4 Another position marking schematic view of Figure 3 . DETAILED DESCRIPTION

[0009] A forming method of SLM unsupported large-inclination-angle structure: for extreme overhanging structure members: the process parameters need to be dynamically adjusted, the ratio of the entity to the contour process parameters is optimized dynamically, and the energy density relationship between the upper surface and the lower surface and the inner surface is strictly controlled, wherein the corresponding positions of the upper surface, the lower surface and the inner surface are shown in Figure 2 ,Figure 3 corresponding marks in the figures; The scanning strategy adopts short scanning vector length and random scanning sequence, and divides the overhanging area into multiple small blocks, adopts random jumping scanning mode from the boundary to the center, and the positions of the boundary and the center are shown in Figure 4 corresponding marks in the figures; The substrate preheating and the forming cavity environment control are simultaneously performed.

[0010] When the process parameters are dynamically regulated, the ratio of the entity and the contour process parameters is optimized, and when the layer thickness is 40-60 μm, the relationship between the inner surface entity and the contour is that the laser power P 实体 / P 轮廓 =0.5-0.8, the scanning speed V 实体 / V 轮廓 =1.4-1.8, and the scanning pitch is generally 0.07-0.12. When the energy density relationship of the upper and lower surfaces and the inner surface is controlled, the relationship between the parameters of the inner surface and the lower surface is that P 内表面 / P 下表面 =1.3-1.8, V 内表面 / V 下表面 =0.6-0.9, and S 内表面 / S 下表面 =1.2-1.9; and the relationship between the parameters of the inner surface and the upper surface is that P 内表面 / P 上表面 =1.2-1.4, V 内表面 / V 上表面 =1.0-1.2, and S 内表面 / S 上表面 =1.1-1.3. The scanning strategy avoids using long scanning lines to prevent heat accumulation in the overhanging area; The scanning strategy divides the overhanging area into multiple small blocks, adopts random jumping scanning mode from the boundary to the center, and the end point of each short scanning line can provide an anchor point for the next segment; When the substrate is preheated, the substrate is preheated to a relatively high temperature, the preheating temperature is 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 the thermal stress and suppresses the warping tendency; The forming cavity environment control specifically refers to precisely controlling the protective gas flow field in the forming cavity to avoid direct impact of the gas flow on the small molten pool in the overhanging area and prevent disturbance; The scanning strategy adopts short scanning vector length and random scanning sequence, and resolves stress through geometric reconstruction, which has corresponding planning algorithms for ordinary overhanging areas, spirals, and hollow spheres, respectively; For ordinary overhanging areas, such asFigure 1 The structure of the product is shown in the physical diagram, and the sizes of the three products from left to right are 36x25x11mm, 43x25x23mm and 42x25x15mm respectively; the product set adopts a micro-guide scanning and edge strengthening algorithm, which automatically divides a large area of overhanging area into hundreds of micron-level micro-guides, and the scanning path adopts a random jumping scanning sequence from the boundary to the center, which avoids heat accumulation and stress concentration caused by long vector scanning, enables each micro area to be independently and stably formed, and provides a solid anchor point for the adjacent area, and at the same time, the algorithm will preferentially scan the outer contour of the overhanging area with higher energy density to form a solid frame to lock the internal material.

[0011] For a spiral body, such as Figure 2 The structure of the product is shown in the physical diagram, and the size of the product is 46x46x23mm, which adopts a three-dimensional self-supporting path algorithm of a spiral body, which generates a non-coplanar three-dimensional continuous scanning path, which has a specific radial offset in the Z-axis direction, and the radial offset in the specific embodiment is 10-50μm, so that the newly melted weld can partially remelt and anchor on the side wall of the solidified lower structure to form a mechanically self-stable arch or catenary structure, thereby fundamentally avoiding the limitation of the plane projection angle; For a hollow sphere, such as Figure 3 , Figure 4 The structure of the product is shown in the physical diagram, and the size of the product is 50x50x50mm, which adopts a partitioned variable-direction tangential scanning algorithm of a hollow sphere, which triangulates the surface of the sphere and plans a path in each micro unit, and the direction of the scanning vector is forced to be close to the direction of the tangent of the sphere at the point, and at the same time, the scanning directions of adjacent layers are staggered at a certain angle (for example, 0°, 67°, 120°), so that the stress distribution is uniform, and the new material of each layer can be firmly combined with the lower layer in multiple directions to weave a stable spherical net-like structure.

[0012] The unsupported structure piece (see Figures 1-4 ) prepared by the above method has a good overhanging area, spiral structure and hollow sphere forming, and has no defects such as spheroidization and cracking, and the surface roughness Ra of the overhanging surface is less than 6.3μm, and the density is greater than 99.5%.

[0013] It will be obvious to a person skilled in the art that the application is not limited to the details of the foregoing exemplary embodiments and can be implemented in other concrete forms without departing from the spirit or essential characteristics of the application. The embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. No reference signs in the claims should be considered as limiting the scope of the claims to the identity of the reference signs therein.

[0014] Furthermore, it should be understood that although the description is made on the basis of the embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity, and 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 those skilled in the art can understand.

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, substrate preheating and molding cavity environment control are performed.

2. The forming method of an unsupported large-angle SLM structure according to claim 1, characterized in that: 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.

3. The forming method of an unsupported large-angle SLM structure according to claim 2, characterized in that: 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.

4. The forming method of an unsupported large-angle SLM structure according to claim 1, characterized in that: The scanning strategy avoids using long scan lines to prevent heat buildup in the overhanging area.

5. The forming method of an unsupported large-angle SLM structure according to claim 4, 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.

6. The forming method of an unsupported large-angle SLM structure according to claim 1, characterized in that: The substrate is preheated to a relatively high temperature during substrate preheating; 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.

7. The forming method of an unsupported large-angle SLM structure according to claim 1, characterized in that: The scanning strategy employs a short scan vector length and a random scan sequence, and uses geometric reconstruction to resolve stress. It has corresponding planning algorithms for ordinary overhanging areas, spirals, and hollow spheres, respectively.

8. The forming method of an unsupported large-angle SLM structure according to claim 7, characterized in that: For ordinary overhanging areas, a micro-guided scanning and edge enhancement algorithm is used. This algorithm automatically divides large overhanging areas into hundreds of micro-guides with micrometer-level 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, allowing each micro-area to be independently and stably formed, and providing 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 in the internal material.

9. The forming method of an unsupported large-angle SLM structure according to claim 7, characterized in that: For the helical body, a three-dimensional self-supporting path algorithm for the helical body 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 planar projection angle.

10. The forming method of an unsupported large-angle SLM structure according to claim 7, characterized in that: 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.

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