Part forming and positioning method

Abstract

The invention discloses a part forming and positioning method, relates to the technical field of additive manufacturing, and aims to solve the problem that a traditional positioning mode easily causes clamping damage to a special part. The positioning method comprises the steps of obtaining a part three-dimensional model; determining a part forming direction; an auxiliary clamping structure used for clamping parts is constructed, a part machining model is obtained, the auxiliary clamping structure comprises a connecting structure, an auxiliary structure and a lattice structure, the connecting structure is connected around the outer walls of the parts, the auxiliary structure is connected with one side edge of the connecting structure, and the auxiliary structure and the connecting structure form a filling cavity with the lattice structure between the parts; the outer wall of the part is connected with the inner wall, close to one side of the part, of the annular plate; performing additive printing based on the processing model to obtain a printed piece; separating the printing piece from the substrate; and the auxiliary clamping structure is clamped, the printing piece is machined, and the part is obtained. The part is machined and positioned through the auxiliary clamping structure, direct contact between machining equipment and the part is avoided, and clamping damage to the surface of the part is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of additive manufacturing, and in particular to a forming and positioning method for a part. Background Art

[0002] Selective laser melting (SLM, also known as additive manufacturing or 3D printing) is a metal additive manufacturing technology that is used to perform high-precision, high-efficiency and repeatable processing on metal materials. It is suitable for complex components of metal materials such as stainless steel, titanium alloy, high-temperature alloy and aluminum alloy, and for special-shaped structures that are usually difficult to complete with traditional processing methods.

[0003] When some special parts with thin walls and complex structures need to be clamped, direct clamping will cause certain damage to the parts, and it is difficult to judge the correct position and difficult to locate. Usually, special tooling is customized, and the special tooling and parts are glued together to form a rough reference block for auxiliary processing. The removal of glue generally uses a high-temperature gun for local heating, which can easily cause deformation or even cracking of the parts. Therefore, traditional positioning methods have the problem that it is difficult to directly clamp special parts with thin walls and complex structures, and it is difficult to locate and easy to cause clamping damage. Summary of the invention

[0004] The object of the present invention is to provide a forming and positioning method for parts, which is used to facilitate the positioning and clamping of parts with special structures and protect the outer walls of the parts with special structures.

[0005] In order to achieve the above object, the present invention provides the following technical solution: a forming and positioning method of a part, comprising:

[0006] Obtain a 3D model of the part;

[0007] Determine the forming direction of the part according to the three-dimensional model so that the axis of the part is perpendicular to the substrate;

[0008] An auxiliary clamping structure for clamping during mechanical processing is constructed in a three-dimensional model to obtain a processing model of the part, wherein the auxiliary clamping structure includes a connecting structure, an auxiliary structure and a lattice structure, the connecting structure is connected around the outer wall of the part, and the connecting structure is inclined relative to the forming direction, the auxiliary structure is connected to the edge of the side of the connecting structure away from the part, the auxiliary structure is an annular plate, the plate surface extension direction of the annular plate is parallel to the forming direction, so that the auxiliary structure and the connecting structure form a filling cavity between the outer wall of the part, the opening direction of the filling cavity is toward the forming direction, and a lattice structure is provided in the filling cavity, the outer wall of the part and the inner wall of the annular plate close to the part are connected through the lattice structure, the lattice structure is composed of a plurality of interconnected cell arrays, the cells are formed by overlapping at least two groups of cross rods, and the cross rods are cross-connected to each other through two support rods;

[0009] Perform additive printing based on the processing model to obtain a printed part;

[0010] Separating the printed part and the substrate;

[0011] The auxiliary clamping structure is clamped to perform mechanical processing on the printed part to obtain the part.

[0012] Optionally, in the above-mentioned forming and positioning method of the part, the connected structure is an annular cone, a plurality of through holes are provided on the surface of the annular cone, and the plurality of through holes are arranged at intervals around the outer wall of the part.

[0013] Optionally, in the above-mentioned part forming and positioning method, the diameter d2 of the through hole satisfies the condition: 1mm≤d2≤3mm.

[0014] Optionally, in the above-mentioned forming and positioning method of parts, clamping the auxiliary clamping structure and mechanically processing the printed part includes:

[0015] Remove the connected structure and keep the auxiliary structure and lattice structure;

[0016] Clamping of auxiliary structures and mechanical processing of printed parts;

[0017] Remove auxiliary structures and lattice structures.

[0018] Optionally, in the above-mentioned forming and positioning method of parts, after clamping the auxiliary clamping structure, the forming and positioning method also includes: using a tool to detect the clamping surface provided by the auxiliary structure to confirm whether the placement of the printed part meets the processing standards.

[0019] Optionally, in the above-mentioned forming and positioning method of parts, after the printed part is mechanically processed to obtain the part, the forming and positioning method further includes: polishing the non-processed surface of the part.

[0020] Optionally, in the above-mentioned forming and positioning method of parts, the diameter d1 of the support rod satisfies the condition: 0.5mm≤d1≤2mm;

[0021] And / or, the angle α1 between the axial direction of the support rod and the horizontal plane meets the condition: α1 ≥ 45°.

[0022] Optionally, in the above-mentioned forming and positioning method of parts, the material thickness N1 of the connected structure is less than the material thickness N2 of the auxiliary structure;

[0023] And / or, the material thickness N1 of the connected structure satisfies the condition: N1 ≥ 1 mm.

[0024] Optionally, in the above-mentioned forming and positioning method of the part, the angle β between the surface of one side of the connecting structure close to the outer wall of the part and the horizontal plane satisfies the condition: 45°≤β<90°.

[0025] Optionally, in the above-mentioned forming and positioning method of the part, the side where the connecting structure is connected to the outer wall of the part is rounded, and the fillet radius α2 of the side where the connecting structure is connected to the outer wall of the part satisfies the condition: α2≥1mm.

[0026] Compared with the prior art, when the above technical scheme is adopted, a three-dimensional model of the part is first obtained, the forming direction of the part is determined according to the three-dimensional model, and then an auxiliary clamping structure for clamping the part is constructed in the three-dimensional model to obtain a processing model of the part, the processing model is additively printed, and the printed part and the substrate are separated, and the printed part is mechanically processed by clamping the auxiliary clamping structure to obtain the part. Compared with the traditional method of clamping directly in contact with the surface of a special part, the present application constructs an auxiliary clamping structure on the surface of the part, so that the processing equipment does not directly contact the surface of the special part during the mechanical processing, thereby avoiding clamping damage to the surface of the part; in addition, the lattice structure has a certain energy absorption effect while meeting the clamping force, which can reduce the extrusion deformation of the part caused by clamping during the mechanical processing, and the lattice structure and the connecting structure have a small connection contact area with the surface of the part, which is easy to remove, reducing the risk of damaging the part during the removal process. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0028] Figure 1 A process flow chart of a forming and positioning method for a part provided in an embodiment of the present invention;

[0029] Figure 2 A schematic structural diagram of a printed part of a forming and positioning method for a part provided in an embodiment of the present invention;

[0030] Figure 3 A schematic diagram of an auxiliary clamping structure in a forming and positioning method for a part provided in an embodiment of the present invention;

[0031] Figure 4 for Figure 3 A schematic cross-sectional structure diagram of ;

[0032] Figure 5 for Figure 3 A schematic diagram of a cross-sectional structure after a lattice structure is arranged in a filling cavity;

[0033] Figure 6 for Figure 5 A top view of

[0034] Figure 7 for Figure 3 Schematic diagram of the structure after removing the connected structure;

[0035] Figure 8 for Figure 7 A front view of

[0036] Fig. 9 for Figure 7 A schematic cross-sectional structure diagram of ;

[0037] Fig.10 A schematic structural diagram of a cell in a lattice structure of a forming and positioning method for a part provided in an embodiment of the present invention;

[0038] Fig.11 for Fig.10 Schematic diagram of the structure of the crossbar in the cell.

[0039] Reference numerals:

[0040] 1-substrate; 2-printed part; 3-auxiliary clamping structure; 31-connecting structure; 32-auxiliary structure; 33-lattice structure; 4-filling cavity; 5-cell; 51-support rod; 6-through hole. DETAILED DESCRIPTION

[0041] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0042] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0043] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. The meaning of "several" is one or more, unless otherwise clearly and specifically defined.

[0044] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by the terms "up", "down", "front", "back", "left", "right", etc. are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0045] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0046] like Figure 1-Figure 11 As shown, an embodiment of the present invention provides a forming and positioning method for a part, the steps comprising:

[0047] Step S100, obtaining a three-dimensional model of a part;

[0048] The 3D model of the part is constructed in 3D software according to the actual size of the part. The 3D software can be selected according to actual needs and is not specifically limited.

[0049] Step S200, determining a forming direction A of the part according to the three-dimensional model so that the axis of the part is perpendicular to the substrate 1;

[0050] Export the Stl format from the 3D software, set the triangular tolerance and adjacent tolerance to 0.0025, use the 3D software to open the Stl format parts, use the repair wizard function to repair and slice the part model, and import it into the equipment to print the 3D model according to the forming direction A.

[0051] Step S300, constructing an auxiliary clamping structure 3 for clamping during mechanical processing in a three-dimensional model to obtain a processing model of the part, wherein the auxiliary clamping structure 3 includes a connecting structure 31, an auxiliary structure 32 and a lattice structure 33, the connecting structure 31 is connected around the outer wall of the part, and the connecting structure 31 is inclined relative to the forming direction A, the auxiliary structure 32 is connected to the edge of the side of the connecting structure 31 away from the part, the auxiliary structure 32 is an annular plate, and the plate surface extension direction of the annular plate is parallel to the forming direction A, so that the auxiliary structure 32 and the connecting structure 31 form a filling cavity 4 between the outer wall of the part, the opening direction of the filling cavity 4 is toward the forming direction, and there is a lattice structure 33 in the filling cavity 4, the outer wall of the part and the inner wall of the annular plate close to the part are connected through the lattice structure 33, the lattice structure 33 is composed of a plurality of interconnected cells 5 arranged in an array, the cell 5 is formed by overlapping at least two groups of cross rods, and the cross rods are cross-connected to each other through two support rods 51;

[0052] Specifically, the part in the above method is a hollow cylinder with a diameter of 200 mm, a height of 300 mm, and a wall thickness of 2 mm. The parts processed by the above method are not limited to the cases listed in this embodiment. In step S300, the processing model of the part is in the optimal forming direction A during processing. Figure 2 As shown, the auxiliary structure 32 formed can be annular or block-shaped, etc. The shape of the auxiliary structure 32 is not limited to the cases listed in this embodiment, as long as the auxiliary structure 32 meets the clamping requirements. When the part is a hollow cylinder, preferably, the auxiliary structure 32 is an annular plate, which improves the processing efficiency and processing quality of the part.

[0053] Step S400, performing additive printing based on the processing model to obtain a printed part 2;

[0054] Step S500, separating the printed part 2 and the substrate 1;

[0055] Specifically, before step S500, the metal powder on the surface of the printed part 2 is cleaned using a vibration platform and compressed air, and then the structure of the printed part 2 and the substrate 1 is heat treated, and the printed part 2 and the substrate 1 are separated using wire cutting. The cutting method between the printed part 2 and the substrate 1 is not limited to the cases listed in this embodiment, which facilitates mechanical processing of the printed part 2.

[0056] Step S600: clamp the auxiliary clamping structure 3 and perform mechanical processing on the printed part 2 to obtain a part.

[0057] Specifically, Figure 3As shown, firstly, the 3D software scanning data is compared and the deformation trend and deformation amount of the part are determined, and corresponding adjustments are made during programming and operation. The printed part 2 obtained by additive printing based on the processing model has an auxiliary clamping structure 3, and a three-axis or five-axis CNC milling machine or other equipment is used to perform mechanical processing with the auxiliary clamping structure 3 as the clamping position, so that in step S600, there is no need to customize special tooling, and the fixture can directly clamp the auxiliary clamping structure 3 without direct contact with the outer wall of the part, thereby reducing structural damage to the surface of the part, completing mechanical processing of the printed part 2 to obtain the part, reducing the production cost of the part, and shortening the manufacturing cycle.

[0058] When implementing it, Figure 1 As shown, a three-dimensional model of the part is first obtained, and a forming direction A of the part is determined according to the three-dimensional model. Then, an auxiliary clamping structure 3 for clamping the part is constructed in the three-dimensional model to obtain a processing model of the part. The processing model is additively printed, and the printed part 2 and the substrate 1 are separated. The printed part 2 is mechanically processed by clamping the auxiliary clamping structure 3 to obtain the part. Compared with the traditional clamping method of directly contacting the surface of a special part, the present application constructs an auxiliary clamping structure 3 on the surface of the part, so that the processing equipment does not directly contact the surface of the special part during the mechanical processing, thereby avoiding clamping damage to the surface of the part. In addition, the lattice structure 33 has a certain energy absorption effect while meeting the clamping force, which can reduce the extrusion deformation of the part caused by clamping during the mechanical processing, and the lattice structure 33 and the connecting structure 31 have a small connection contact area with the surface of the part, which is easy to remove, thereby reducing the risk of damaging the part during the removal process.

[0059] like Figure 3 As shown, in some embodiments, the connected structure 31 is an annular cone, and a plurality of through holes 6 are provided on the surface of the annular cone, and the plurality of through holes 6 are arranged at intervals around the outer wall of the part. The through holes 6 provided may be circular, polygonal or in other shapes, and the through holes 6 provided here are not limited to the cases listed in this embodiment. The plurality of through holes 6 are provided on the surface of the annular cone, which saves printing costs and facilitates the removal of the connected area. Preferably, the shape of the through holes 6 is circular.

[0060] like Figure 3As shown, specifically, in this embodiment, the diameter d2 of the through hole 6 satisfies the condition: 1mm≤d2≤3mm. Among them, the diameter d2 of the through hole 6 can be 1mm, 1.2mm, 2mm, 2.5mm, 3mm, etc. The diameter d2 of the through hole 6 opened here is not limited to the conditions listed in this embodiment. When the diameter d2 of the through hole 6 is ≥1mm, the area of ​​the hollow area on the connecting structure 31 is increased, the required processing materials are reduced, and the processing cost of the auxiliary clamping structure 3 is reduced; when the diameter d2 of the through hole 6 is ≤3mm, the connecting structure 31 has sufficient supporting strength after the through hole 6 is opened.

[0061] like Figure 3 and Figure 7 As shown, specifically, in this embodiment, in step S600, the auxiliary clamping structure 3 is clamped, and the mechanical processing of the printed part 2 specifically includes:

[0062] Step S601, removing the connected structure 31, and retaining the auxiliary structure 32 and the lattice structure 33;

[0063] Step S602, clamping the auxiliary structure 32 and machining the printed part 2;

[0064] Step S603, removing the auxiliary structure 32 and the lattice structure 33, wherein the connected structure 31, the auxiliary structure 32 and the lattice structure 33 can all be removed by using a pneumatic shovel or other tools. The method for removing the connected structure 31, the auxiliary structure 32 and the lattice structure 33 is not limited to the cases listed in this embodiment, as long as it is convenient to remove the auxiliary clamping structure 3.

[0065] During operation, the operator can first remove the connecting structure 31 in the auxiliary clamping structure 3, and then clamp the remaining auxiliary structure 32 and the lattice structure 33. After the mechanical processing of the printed part 2 is completed, the auxiliary structure 32 and the lattice structure 33 on the surface of the part are removed. Before clamping the auxiliary structure 32 and the lattice structure 33, the connecting structure 31 is first removed to reduce the residual stress in the area between the connecting structure 31 and the outer wall of the part during the mechanical processing, avoid the occurrence of local deformation, improve the processing quality, and facilitate the structural stability when the part is clamped by the auxiliary structure 32. At the same time, the lattice structure 33 has a certain energy absorption effect while meeting the clamping force, which can reduce the extrusion deformation of the part caused by clamping during the mechanical processing. The connection contact area between the lattice structure 33 and the surface of the part is small, which is easy to remove, reducing the risk of damaging the part during the removal process.

[0066] In this embodiment, after clamping the auxiliary clamping structure 3 in step S600, the forming and positioning method further includes: using a tool to detect the clamping surface provided by the auxiliary structure 32 to confirm whether the placement of the printed part 2 meets the processing standard.

[0067] The clamping surface of the auxiliary structure 32 needs to be a regular horizontal plane and side surface to meet the clamping and positioning requirements, so as to facilitate the judgment of whether the part status meets the processing standards. Stable clamping and accurate positioning improve the machining quality and facilitate operation.

[0068] In this embodiment, after the printed part 2 is machined to obtain a part in step S600, the forming and positioning method further includes: grinding the non-machined surface of the part.

[0069] In the above steps, the non-machined surface of the part is polished using a grinding tool, and the surface is optimized and adjusted according to the shape of the part to ensure the machining quality of the part.

[0070] like Fig.10 and Fig.11 As shown, specifically, in this embodiment, in step S300, the diameter d1 of the support rod 51 satisfies the condition: 0.5mm≤d1≤2mm; and / or, the angle α1 between the axial direction of the support rod 51 and the horizontal plane satisfies the condition: α1≥45°. The diameter d1 of the support rod 51 can be 0.5mm, 0.6mm, 0.7mm, 1.2mm, 2mm, etc., and the angle α1 between the axial direction of the support rod 51 and the horizontal plane can be 45°, 50°, 55°, 60°, 75°, 80°, etc. The diameter d1 and the angle α1 of the support rod 51 are not limited to the cases listed in this embodiment, so that each cell 5 in the lattice structure 33 can form a smaller contact area between the lattice structure 33 and the outer wall of the part on the basis of having forming stability and providing energy absorption during the clamping process, so as to facilitate the removal of the lattice structure 33, simplify the process flow, and improve production efficiency.

[0071] In this embodiment, in step S300, the material thickness N1 of the connecting structure 31 is less than the material thickness N2 of the auxiliary structure 32; and / or, the material thickness N1 of the connecting structure 31 satisfies the condition: N1 ≥ 1 mm. The material thickness N1 of the connecting structure 31 may be 1 mm, 1.5 mm, 2 mm, etc. The material thickness N1 of the connecting structure 31 is not limited to the cases listed in this embodiment. As long as the material thickness N1 of the connecting structure 31 is less than the material thickness N2 of the auxiliary structure 32, the printing cost can be saved while ensuring the connection strength between the connecting structure 31 and the outer wall of the part.

[0072] like Figure 4 and Figure 5As shown, in this embodiment, in step S300, the angle β between the side surface of the connecting structure 31 close to the outer wall of the part and the horizontal plane meets the condition: 45°≤β<90°. The angle β can be 45°, 50°, 55°, 60°, 75°, 80°, etc., and the angle β is not limited to the cases listed in this embodiment, so as to ensure the stability of the forming between the connecting structure 31 and the outer wall of the part and improve the forming efficiency of the part.

[0073] like Figure 4 and Figure 5 As shown, in this embodiment, in step S300, the side where the connecting structure 31 is connected to the outer wall of the part is rounded, and the fillet radius α2 of the side where the connecting structure is connected to the outer wall of the part satisfies the condition: α2 ≥ 1 mm. The fillet radius α2 can be 1 mm, 1.5 mm, 2 mm, etc., and the fillet radius α2 is not limited to the cases listed in this embodiment. The larger the structure of the part, the larger the fillet radius α2, which reduces the risk of forming cracks in the printed part 2 and improves the forming efficiency of the part.

[0074] In the description of the above embodiments, specific features, structures, materials or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0075] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art who is familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A forming and positioning method for a part, characterized in that: include: Obtain a 3D model of the part; Determining a forming direction of the part according to the three-dimensional model so that the axis of the part is perpendicular to the substrate; An auxiliary clamping structure for clamping during mechanical processing is constructed in the three-dimensional model to obtain a processing model of the part, wherein the auxiliary clamping structure includes a connecting structure, an auxiliary structure and a lattice structure, the connecting structure is connected around the outer wall of the part, and the connecting structure is inclined relative to the forming direction, the auxiliary structure is connected to the edge of one side of the connecting structure away from the part, the auxiliary structure is an annular plate, the plate surface extension direction of the annular plate is parallel to the forming direction, so that the auxiliary structure and the connecting structure form a filling cavity between the outer wall of the part, the opening direction of the filling cavity is toward the forming direction, the lattice structure is provided in the filling cavity, the outer wall of the part and the inner wall of the annular plate close to the part are connected through the lattice structure, the lattice structure is composed of a plurality of interconnected cell arrays, the cell is formed by overlapping at least two groups of cross bars, and the cross bars are cross-connected to each other through two support bars; Perform additive printing based on the processing model to obtain a printed part; separating the printed part and the substrate; The auxiliary clamping structure is clamped, and the printed part is machined to obtain the part.

2. The forming and positioning method of parts according to claim 1, characterized in that: The connecting structure is an annular cone, a plurality of through holes are provided on the surface of the annular cone, and the plurality of through holes are arranged at intervals around the outer wall of the part.

3. The forming and positioning method of parts according to claim 2, characterized in that: The diameter d2 of the through hole satisfies the condition: 1mm≤d2≤3mm.

4. The forming and positioning method of parts according to claim 1, characterized in that: The auxiliary clamping structure is clamped to perform mechanical processing on the printed part, comprising: removing the connected structure and retaining the auxiliary structure and the lattice structure; Clamping the auxiliary structure and machining the printed part; The auxiliary structure and the lattice structure are removed.

5. The forming and positioning method of parts according to claim 1, characterized in that: After clamping the auxiliary clamping structure, the forming and positioning method further comprises: using a tool to detect a clamping surface provided by the auxiliary structure to confirm whether the placement of the printed part meets the processing standard.

6. The forming and positioning method of parts according to claim 1, characterized in that: After the printed part is machined to obtain the part, the forming and positioning method further comprises: grinding the non-machined surface of the part.

7. The forming and positioning method of a part according to any one of claims 1 to 6, characterized in that: The diameter d1 of the support rod meets the condition: 0.5mm≤d1≤2mm; And / or, the angle α1 between the axial direction of the support rod and the horizontal plane satisfies the condition: α1 ≥ 45°.

8. The forming and positioning method of a part according to any one of claims 1 to 6, characterized in that: The material thickness N1 of the connected structure is less than the material thickness N2 of the auxiliary structure; And / or, the material thickness N1 of the connected structure satisfies the condition: N1 ≥ 1 mm.

9. The forming and positioning method of a part according to any one of claims 1 to 6, characterized in that: The angle β between the surface of one side of the connecting structure close to the outer wall of the part and the horizontal plane meets the condition: 45°≤β<90°.

10. The forming and positioning method of a part according to any one of claims 1 to 6, characterized in that: The side where the connecting structure is connected to the outer wall of the part is rounded, and the fillet radius α2 of the side where the connecting structure is connected to the outer wall of the part satisfies the condition: α2≥1mm.

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