Lightweight high-thermal-stability joint based on invar alloy and design method thereof

Abstract

A lightweight, thermally stable joint based on Invar alloy includes a support, a joint skeleton, and a connecting frame. The joint skeleton and connecting frame are connected by the support and rotate around a spatial joint axis under the drive of a driving component. The spatial axis joint configuration proposed in this invention simplifies two joints with orthogonal axes to a single spatial axis joint, achieving the target position and posture with a single rotation, reducing the number of joints and the number of movements, thus optimizing the joint composition. This invention combines topology optimization technology to propose a lightweight joint configuration with irregular geometry, reducing joint weight by removing some material while maintaining stiffness and strength. Furthermore, it employs 3D printing technology based on variable skin thickness design to manufacture the support, joint skeleton, and connecting frame, achieving high surface quality, high internal quality, and high dimensional accuracy in the molding of irregularly shaped parts, further reducing weight. This invention uses Invar alloy powder as raw material, which possesses high thermal stability.

Description

Technical Field

[0001] This invention relates to a lightweight, thermally stable joint based on Invar alloy and its design method, belonging to the aerospace field. Background Technology

[0002] Efficient lightweighting methods have always been one of the research directions in the aerospace field. With the development of aerospace technology and the continuous improvement of requirements, spacecraft structures are developing towards larger scale, higher precision, and lighter weight. When the size increases and the precision improves, the change in precision caused by thermal deformation can no longer be ignored. The thermal stability of high-precision products is one of the important performance indicators of the products.

[0003] Currently, the commonly used joint axis has a parallel or perpendicular relationship with the mounting surface. Such joints have a regular configuration, which facilitates the processing and testing of the joints. However, the regular joint configuration limits the design of the deployable arm configuration. Sometimes, more joints must be arranged to deploy to the target position, making it impossible to achieve a large proportion of weight reduction.

[0004] The commonly used method for lightweighting parts is to drill holes in the parts to reduce weight. However, this reduces the product's rigidity and makes it impossible to maintain the product's rigidity and other performance indicators while achieving weight reduction.

[0005] Currently, common methods to improve thermal stability include introducing materials with low coefficients of thermal expansion and symmetrical product configurations. However, the coefficients of thermal expansion of commonly used aerospace metals such as Ti and Al are still around 10 × 10⁻⁶. -6 At this scale, carbon fiber materials with near-zero expansion are difficult to manufacture complex parts, and symmetrical product configurations are also difficult to adapt to the current complex configuration requirements. Summary of the Invention

[0006] The technical problem to be solved by this invention is: This invention provides a lightweight, highly thermally stable joint based on Invar alloy and its design method, which simplifies a joint with two orthogonal axes into a single spatial axis joint, optimizes the system composition, achieves high surface quality, high internal quality, high dimensional accuracy in the forming of irregularly shaped parts, and further reduces weight; the joint of this invention has high thermal stability.

[0007] The technical solution adopted in this invention is: a lightweight, highly thermally stable joint based on Invar alloy, comprising a support, a joint skeleton, and a connecting frame;

[0008] The joint frame and connecting frame are connected by a bracket, and rotate around the joint space rotation axis under the drive of the drive component installed in the mounting hole of the bracket; there is a spatial angle between the joint space rotation axis and the flange mounting surface XOY of the joint.

[0009] Furthermore, the joint material is an Invar alloy with an average coefficient of linear expansion ≤1.34×10⁻⁶. -6 .

[0010] Furthermore, while maintaining the set strength and stiffness, the bracket, joint skeleton, and connecting frame are subjected to material removal using a topology optimization method based on mechanical analysis and a 3D printing material distribution optimization method with variable skin thickness, forming a hollow structure with skin envelope.

[0011] A design method for lightweight, thermally stable joints based on Invar alloys, comprising:

[0012] Based on the design technical requirements of the joint, the overall structure of the joint is designed using regular geometric configurations to obtain the preliminary shapes of the support, joint skeleton, and connecting frame.

[0013] Based on the preliminary shape of the support, joint skeleton, and connecting frame, the topology of the support, joint skeleton, and connecting frame is optimized based on mechanical analysis. While keeping the strength and stiffness unchanged, the material of the support, joint skeleton, and connecting frame is removed to obtain support, joint skeleton, and connecting frame structures with irregular curved surface shapes.

[0014] Based on the irregular curved surface shape of the support, joint skeleton and connecting frame structure, while keeping the strength and stiffness constant, the distribution of 3D printing material with variable skin thickness is optimized to transform the solid irregular structure of the support, joint skeleton and connecting frame into a hollow structure with skin covering.

[0015] Furthermore, the design technical requirements for the joint include the overall size of the joint envelope, bearing type, motor type, and position of the joint's spatial rotation axis.

[0016] Furthermore, mechanical simulation software was used to perform topology optimization of the support, joint skeleton, and connecting frame based on mechanical analysis. During the calculation, joint material parameters, motion constraints, and applied load conditions were set. The optimization variable was the removable joint material, and the constraint condition was the mechanical properties, including stiffness and strength. The objective function was to minimize the mass of the support, joint skeleton, and connecting frame.

[0017] Furthermore, in the process of optimizing the distribution of 3D printing materials with variable skin thickness, joint material parameters, motion constraints, and applied load conditions are set. The optimization variable is the joint skin thickness, the constraint condition is the mechanical properties, including stiffness and strength, and the objective function is to minimize the mass of the support, joint skeleton, and connecting frame.

[0018] The advantages of this invention compared to the prior art are:

[0019] (1) This invention proposes a joint structure with a spatial axis configuration. The joint rotation axis and the mounting plane are no longer in a traditional parallel or perpendicular relationship, but are in any spatial angle direction. In practical applications, this can make the movement trajectory of the unfolding arm more flexible, use fewer joints to make the unfolding arm reach the unfolding target position, and realize on-orbit application.

[0020] (2) This invention proposes a two-stage weight reduction design approach for 3D printing, which involves structural topology optimization and variable skin thickness design. First, structural topology optimization based on mechanical analysis is performed, retaining only the material along the force transmission path and removing material from other locations to achieve weight reduction. This first step of weight reduction optimization is achieved while maintaining the product's stiffness and other properties. On this basis, lightweight thin-walled structural components with skin envelopment and lattice filling are shaped, and a second weight reduction optimization is performed from the perspective of process design.

[0021] (3) This invention proposes to use 3D printing technology to process and manufacture core components, which solves the problem that it is difficult to achieve high-precision part forming by traditional processing methods such as turning, milling, cutting, and casting for irregularly shaped parts obtained after structural topology optimization.

[0022] (4) This invention proposes to use Invar alloy powder as a 3D printing raw material, which greatly reduces the coefficient of thermal expansion and has better thermal stability. Attached Figure Description

[0023] Figure 1 A schematic diagram of a lightweight, thermally stable joint based on Invar alloy;

[0024] Figure 2 This is a schematic diagram of the spatial rotation axis of a lightweight, highly thermally stable joint based on Invar alloy.

[0025] Figure 3 A flowchart illustrating the design method for lightweight, thermally stable joints based on Invar alloys;

[0026] Figure 4 This diagram illustrates the motion constraints and applied load positions during the optimization calculation of a lightweight, thermally stable joint connector based on Invar alloy. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and specific examples.

[0028] A spatial axis joint needs to be designed to rotate the joint flange surface to a specified position and orientation in one operation. Simultaneously, to meet lightweight requirements, the joint itself needs to be designed to reduce weight while maintaining stiffness and strength. Furthermore, the irregular configuration caused by the spatial axis, the difficulty in machining components, and the challenge of creating a symmetrical structure to ensure thermal stability must be addressed. To solve these problems, this invention proposes a method based on Invar alloy, combined with mechanical analysis for structural topology optimization. Only material along the force transmission path is retained, while material in other locations is removed to achieve the initial weight reduction. Building upon this, 3D printing technology based on variable skin thickness is used to manufacture irregularly shaped metal parts, achieving further weight reduction through the molding of lightweight, irregularly shaped structural components. The introduction of 3D printing technology effectively solves the problem of machining irregularly shaped components. Moreover, Invar alloy has a significantly lower coefficient of thermal expansion compared to traditional metals such as Ti and Al, exhibiting better thermal stability.

[0029] like Figure 1 The present invention provides a lightweight, thermally stable joint based on Invar alloy, comprising a support 1, a joint frame 2, and a connecting frame 3;

[0030] The joint frame 2 and the connecting frame 3 are connected by the bracket 1 and rotate around the joint space rotation axis 5 under the drive of the drive component 4.

[0031] The present invention provides a lightweight, high thermal stability joint based on Invar alloy, which is a joint with a spatial rotation axis. The spatial rotation axis of the joint is neither parallel nor perpendicular to the flange mounting surface of the joint, but has a spatial angle.

[0032] like Figure 2 The flange mounting surface is set as the XOY plane, and the vertical direction is the Z axis. The joint space rotation axis 5 is neither parallel nor perpendicular to the flange mounting surface. For ease of labeling, the space axis 5 is translated to position 5-1 passing through point O. In this embodiment, the angle between the joint space rotation axis and the flange mounting surface is represented in the OXYZ space coordinate system as i = 42.9932°, j = 46.9663°, and k = 88.47913°.

[0033] like Figure 3 This document outlines a design methodology for lightweight, thermally stable joints. First, a preliminary regular geometric configuration is designed. Based on this, topological optimization based on mechanical analysis is performed for the first weight reduction optimization, resulting in an irregular geometric configuration. Then, based on this irregular geometric configuration, a 3D printing envelope lattice design with variable skin thickness is implemented, transforming the solid irregular structure into a hollow-like structure with a skin envelope, achieving further weight reduction optimization. Finally, based on the skin envelope lattice design results, the joint is manufactured. The specific operational steps are as follows:

[0034] Step 1: Conduct preliminary design of the overall joint configuration. Based on the design technical requirements of the joint (including but not limited to the overall size of the joint envelope, bearing model, motor model, position of the joint spatial rotation axis, etc.), use regular geometric configuration to design the overall joint structure and obtain the preliminary shape of the three core parts: support, joint skeleton, and connecting frame.

[0035] Step 2: Based on the preliminary shape of the parts obtained in Step 1, the topology of the three core parts is optimized based on mechanical analysis. Under the premise of unchanged strength and stiffness, mechanical simulation software including but not limited to Abaqus, ANSYS, COMSOL, etc. is used to design the removal of materials for the parts, resulting in the part structure with irregular curved surface shape, thus achieving the first weight reduction.

[0036] In this embodiment, the material parameters in the calculation process are set as follows: elastic modulus 140 GPa, Poisson's ratio 0.3, and material density 8100 kg / m³. 3 ;

[0037] like Figure 4 The motion constraint conditions are set as follows: apply six degrees of freedom constraints on the inner walls of the nine connecting holes 3-1 that connect with other parts;

[0038] The load conditions are set as follows: a bending moment of 100 N·m in each of the three directions is applied to the top equipment mounting hole 3-2, which is connected to the external load.

[0039] The optimization variables are specifically set to materials other than motion constraint hole 3-1 and load application hole 3-2, in order to ensure the strength and stiffness of the connection with other parts;

[0040] The specific constraint conditions are set as follows: stress less than 300MPa, rotation angle of the loading point in the X direction not greater than 0.002°, rotation angle of the loading point in the Y direction not greater than 0.0002°, and rotation angle of the loading point in the X direction not greater than 0.001°.

[0041] The objective function is set to minimize mass, resulting in a lightweight, irregularly configured connecting frame.

[0042] Step 3: Based on the irregular curved surface part structure obtained in Step 2, under the premise of unchanged strength and stiffness, we will optimize the 3D printing material distribution design with variable skin thickness to transform the solid irregular structure into a hollow structure with skin covering. We will further achieve the weight reduction effect by designing the manufacturing process scheme.

[0043] In this embodiment, the material parameters are set as follows: elastic modulus 140 GPa, Poisson's ratio 0.3, and material density 8100 kg / m³. 3 ;

[0044] like Figure 4 The motion constraint conditions are set as follows: apply six degrees of freedom constraints on the inner walls of the nine connecting holes 3-1 that connect with other parts;

[0045] The load conditions are set as follows: a bending moment of 100 N·m is applied in each of the three directions to the top equipment mounting hole 3-2, which is connected to the external load.

[0046] The optimization variable is specifically set to allow the skin thickness to vary continuously from 0.4mm to 6mm;

[0047] The specific constraint conditions are set as follows: stress less than 50 MPa, rotation angle of the loading point in the X direction not greater than 0.002°, rotation angle of the loading point in the Y direction not greater than 0.0002°, and rotation angle of the loading point in the X direction not greater than 0.001°.

[0048] The objective function is set to minimize the mass, resulting in the internal structure of the 3D printed connector with a hollow skin lattice envelope;

[0049] Functional verification was performed on the lightweight, thermally stable joint structure based on Invar alloy of the present invention. The average linear expansion coefficient of the Invar alloy joint support in the heat-treated state is ≤1.34×10⁻⁶. -6 ;

[0050] Thermal deformation tests were conducted on a lightweight, highly thermally stable joint based on Invar alloy, with test temperatures ranging from -50℃ to +70℃. The results showed that the angle change over three cycles on the two measuring end faces of the joint was approximately 0.024° at high temperature and approximately 0.021° at low temperature, indicating good thermal stability.

[0051] This invention discloses a lightweight, thermally stable joint based on Invar alloy, which has broad application prospects in deployable arm products. Thanks to the joint's unique spatial axis design, multiple consecutive pose changes of the deployable arm product can be equivalent to a single pose change around a specified spatial coordinate axis. This reduces the number of axes in the deployable arm product from a system composition perspective, achieving the goal of deploying the load to a specified position using fewer joints and arms.

[0052] Compared to traditional regular joint configurations, the joints of this invention achieve a 32% weight reduction. Furthermore, thanks to the unique spatial axis design, the system composition of this deployable arm is simplified from the initial 4 joints and 3 arms to 3 joints and 2 arms, contributing to a 30% weight reduction at the system design level. In addition, the excellent thermal stability of the joints ensures smooth deployment in orbit, achieving ultra-high on-orbit deployment accuracy.

[0053] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific implementation of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A design method for a lightweight, high thermal stability joint based on Invar alloy, characterized in that, include: Based on the design technical requirements of the joint, the overall structure of the joint is designed using regular geometric configurations to obtain the preliminary shapes of the support, joint skeleton, and connecting frame. Based on the preliminary shape of the support, joint skeleton, and connecting frame, the topology of the support, joint skeleton, and connecting frame is optimized based on mechanical analysis. While keeping the strength and stiffness unchanged, the material of the support, joint skeleton, and connecting frame is removed to obtain support, joint skeleton, and connecting frame structures with irregular curved surface shapes. Based on the irregular curved surface shape of the support, joint skeleton and connecting frame structure, while keeping the strength and stiffness constant, the 3D printing material distribution of variable skin thickness is optimized to transform the solid irregular structure of the support, joint skeleton and connecting frame into a hollow structure with skin covering, resulting in a lightweight and thermally stable joint based on Invar alloy. The lightweight, thermally stable joint based on Invar alloy includes a support frame, a joint skeleton, and a connecting frame. The joint frame and connecting frame are connected by a bracket, and rotate around the joint space rotation axis under the drive of the drive component installed in the mounting hole of the bracket; there is a spatial angle between the joint space rotation axis and the flange mounting surface XOY of the joint; The joint material is Invar alloy powder, with an average coefficient of linear expansion ≤1.34×10⁻⁶. -6 .

2. The design method for a lightweight, high thermal stability joint based on Invar alloy according to claim 1, characterized in that, The design technical requirements for the joint include the overall size of the joint envelope, bearing model, motor model, and the position of the joint's spatial rotation axis.

3. The design method for a lightweight, high thermal stability joint based on Invar alloy according to claim 2, characterized in that, The mechanical simulation software was used to perform topology optimization of the support, joint skeleton and connecting frame based on mechanical analysis. During the calculation, joint material parameters, motion constraints and applied load conditions were set. The optimization variable was the removable joint material, the constraint condition was the mechanical properties, including stiffness and strength, and the objective function was to minimize the mass of the support, joint skeleton and connecting frame.

4. The design method for a lightweight, high thermal stability joint based on Invar alloy according to claim 3, characterized in that, In the process of optimizing the distribution of 3D printing materials with variable skin thickness, joint material parameters, motion constraints, and applied load conditions are set. The optimization variable is the joint skin thickness, the constraint condition is the mechanical properties, including stiffness and strength, and the objective function is to minimize the mass of the support, joint skeleton, and connecting frame.

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