Weak rigid cylindrical thin-walled part composite medium variable temperature filling residual stress regulation method

Abstract

The present application relates to a kind of methods for eliminating residual stress of thin-walled weak rigid structure of cylinder after processing by volume change of solution caused by temperature.The present application generates controllable bulging force by volume change of high expansion coefficient composite medium due to solid-liquid conversion, so that stress release or stress relaxation of thin-walled cylinder part occurs, and the purpose of eliminating residual stress is achieved. Thus, under the action of more accurate and effective temperature change filling, the occurrence conditions and rules of stress release and plastic strengthening of weak rigid thin-walled cylinder part are mastered, which is of great significance for reducing residual stress of thin-walled weak rigid structure of cylinder.

Description

Technical Field

[0001] This invention relates to a method for eliminating residual stress after processing of a thin-walled, weakly rigid cylindrical structure by utilizing the volume change of a solution caused by temperature. Background Technology

[0002] Cylindrical thin-walled parts are characterized by large material removal, numerous features, low rigidity, and strict machining tolerances. During the forming and machining of these weakly rigid cylindrical thin-walled structures, residual stress is introduced and released and redistributed during the semi-finishing / finishing stages (external factors), causing warping or torsional deformation and reducing machining accuracy. Due to the inherently weak rigidity of cylindrical structures and the driving forces of cutting loads and residual stress loads, thin-walled parts are highly susceptible to machining deviations and surface defects, even leading to part scrap and delayed product delivery.

[0003] Metal pre-stretching can significantly remove residual stress and is one of the existing methods for releasing residual stress. Meanwhile, some media, such as water, exhibit a phenomenon where the solid density is less than the liquid density when undergoing a liquid-solid transition due to temperature changes. For example, during a liquid-solid transition, the volume of ice can become 1.09 times that of water. When water fills a thin-walled, weakly rigid structure and undergoes a liquid-solid transition, calculated based on uniform expansion in the length, width, and height directions, the length in a single direction can become 1.03 times that of water, meaning a 3% deformation can occur in a single direction. The pre-stretching deformation in metal pre-stretching is generally 1.5%-3%, and the deformation from ice expansion is comparable to that of pre-stretching.

[0004] Therefore, this invention proposes a method for eliminating residual stress in cylindrical thin-walled structures by utilizing solution volume changes. First, data is acquired using EBSD to construct a plastic-finite element model, a macroscopic geometric model, and a finite element model. Then, the composition of the medium solution is determined based on temperature-varying experiments. Water or aqueous solutions, polystyrene, and high-molecular-weight resins are all high-expansion-coefficient materials that undergo significant volume changes during temperature variations. These materials are used as the medium matrix, and incompressible materials are used as the filling structure. The filling structure and the matrix together form a high-expansion-coefficient composite medium with controllable structure and composition. After filling the cylindrical thin-walled part with the composite medium, the ambient temperature is changed to induce quantitative and directional expansion of the composite medium, achieving precise control of residual stress and thus eliminating it. Sampling experiments are then conducted on the workpiece after residual stress elimination to verify the residual stress removal effect. This method is of great significance for reducing residual stress in cylindrical thin-walled, weakly rigid structures. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for eliminating residual stress in cylindrical thin-walled structures by utilizing changes in solution volume. This method solves the problem of releasing residual stress inside cylindrical thin-walled weakly rigid structures after processing, and has significant effects and important value in reducing residual stress in such weakly rigid structures.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for controlling residual stress during temperature-dependent filling of a weakly rigid cylindrical thin-walled component using a composite medium, characterized by comprising the following steps:

[0008] S1: First, the fine grain morphology, orientation and texture of the workpiece sample are obtained by scanning electron backscatter diffraction (EBSD), and the *.ctf or *.ang file is exported. Then, the Spectral solver based on fast Fourier transform is applied to construct the microstructure geometric model of the cylindrical thin-walled metal material.

[0009] S2: Establish a Crystal Plasty Finite Element Method (CP-FEM) model for cylindrical thin-walled metal parts, fully consider the state variables of the microstructure evolution process, and solve the nonlinear state dynamic equations describing the evolution of state parameters under the application boundary or initial conditions by writing macro programs, thereby obtaining the change curves of state variables in the phase transition process.

[0010] S3: Using general-purpose finite element software, establish the macroscopic geometric model and finite element model of thin-walled parts, and assign the state variables obtained from the crystal plasticity model to the macroscopic finite element model. At the same time, define the macroscopic mechanical properties of materials such as composite media and thin-walled parts, and carry out thermo-mechanical coupled finite element simulation to solve the physical field results such as stress, strain, deformation, and temperature in the variable temperature filling process, so as to realize the cross-scale simulation of the variable temperature filling process.

[0011] S4: Based on the constructed cross-scale macro-micro simulation model, the effects of different filling medium pressures, filling amounts, and filling structure forms on expansion volume, bulging force, and residual stress are analyzed. The evolution law of tensile and compressive residual stress states in the bulging process is compared, and a quantitative relationship between filling parameters, bulging volume, and bulging load is established. Through quantitative iterative calculation, the range of filling process parameters that meet the requirements for residual stress control is obtained.

[0012] S5: Select media with high solidification expansion ratio, low cost and solidification point close to room temperature, such as water and aqueous solution, to conduct freezing expansion characteristic analysis of different media solutions, explore the expansion force distribution law of the media matrix in different cavity shapes, and consider the dissolution rate and the matching with cutting process after melting to determine the composition of the media solution and use it as the composite media matrix.

[0013] S6: To avoid excessive deformation and uncontrollable deformation caused by the complete filling of the inner cavity of the weak rigid cylindrical thin-walled part with aqueous matrix, a filling structure is added to the inner cavity of the weak rigid thin-walled part to control the volume and the direction of thermal expansion.

[0014] S7: In order to make the medium solidify only in the inner cavity of the cylindrical thin-walled part and not on the outer surface, after filling the matrix, the opening of the thin-walled part is sealed with a permeable membrane, and then sodium chloride solute is added to the outside. The freezing point of the outer solution is lowered. Then, the entire container is cooled by a refrigeration device to a temperature below the freezing point of the inner medium and above the freezing point of the outer medium. The temperature is maintained for a period of time until the matrix is ​​completely solidified and the expansion is completed.

[0015] S8: Samples were taken from different specimens and tensile tests, EBSD analysis and transmission electron microscopy (TEM) were carried out to investigate the effects of different parameters on the residual stress relief effect, mechanical properties and microstructure of the specimens. The simulation effect of temperature-controlled bulging of the medium on the residual stress relief effect of the specimens was verified. Based on the experimental results, the simulation model was corrected to improve the calculation accuracy of the model.

[0016] Preferably, in step S2, the state variables are set as microstructure parameters, such as dislocation density, dislocation rate, stacking fault energy, twin integral number, volume fraction of phase transition, and related variables, and an evolution equation for each state variable is established.

[0017] Preferably, the exploration of the expansion force distribution law of the medium matrix in different cavity shapes in S5 can be used to analyze the influence of parameters such as different solute mass fractions, cooling rates, and holding times on expansion deformation and expansion load.

[0018] Preferably, in step S7, since the permeation membrane only allows the solution to pass through but not the solute, the freezing point of the inner cavity of the cylindrical thin-walled component remains unchanged. The composite medium is cooled to a temperature slightly lower than the freezing point of the solution inside the cylindrical thin-walled component but higher than the freezing point of the solution outside. At this temperature, the inner medium solidifies and expands, while the outer medium remains in a low-temperature liquid state, ensuring that the thin-walled component can expand freely. To prevent excessive expansion of the opening of the thin-walled component from causing insufficient internal expansion force, the support and limiting device is adjusted to the opening of the thin-walled component. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the analysis process of the present invention.

[0020] Figure 2 This is a schematic diagram of the internal filling structure of the present invention.

[0021] Figure 3 This is a schematic diagram of the single-phase permeation membrane of the present invention. Detailed Implementation

[0022] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] like Figure 1 As shown, a method for controlling residual stress during temperature-dependent filling of a weakly rigid cylindrical thin-walled component using a composite medium includes the following steps:

[0024] First, the fine grain morphology, orientation and texture of the workpiece sample are obtained by scanning electron microscopy electron backscatter diffraction, and the *.ctf or *.ang file is exported. Then, the Spectral solver based on fast Fourier transform is applied to construct the geometric model of the microstructure of the thin-walled metal material.

[0025] Secondly, a Crystal Plasty Finite Element Method (CP-FEM) model for thin-walled metal parts is established. In the model, the state variables are actual microstructure parameters, such as dislocation density, dislocation rate, stacking fault energy, twin integral number, volume fraction of phase transition, and related variables. The evolution equation of each state variable is established. By writing macro programs, the nonlinear state dynamic equations describing the evolution of state parameters under application boundary or initial conditions are solved, thereby obtaining the change curves of state variables in the phase transition process.

[0026] Next, using general-purpose finite element software, we established a macroscopic geometric model and a finite element model of the thin-walled part, and solved the physical field results such as stress, strain, deformation, and temperature during the variable-temperature filling process, thus realizing cross-scale simulation of the variable-temperature filling process.

[0027] Furthermore, based on the constructed cross-scale macro-micro simulation model, the effects of different filling medium pressures, filling amounts, and filling structure forms on expansion volume, bulging force, and residual stress are analyzed. The evolution law of tensile and compressive residual stress states during the bulging process is compared, and a quantitative relationship between filling parameters, bulging volume, and bulging load is established. Through quantitative iterative calculation, the range of filling process parameters that enable the residual stress control effect to meet the requirements is obtained.

[0028] Furthermore, a medium with a high solidification expansion ratio, low cost, and a freezing point close to room temperature was selected to conduct liquid-solid change expansion characteristics analysis of different medium solutions. The effects of parameters such as different solute mass fractions, cooling rates, and holding times on expansion deformation and expansion load were analyzed to determine the composition of the medium solution and use it as the composite medium matrix.

[0029] Furthermore, such as Figure 2 As shown, to avoid excessive deformation and uncontrollable deformation caused by completely filling the inner cavity of the cylindrical, weakly rigid, thin-walled component with an aqueous matrix, a filling structure is added to the inner cavity of the component, as indicated by arrow number 1 in the figure, to control the volume and the direction of thermal expansion. Silicone rubber is an incompressible material whose elasticity decreases significantly at low temperatures. Currently, additive manufacturing technology for this material is relatively mature, and complex porous structures can be obtained through 3D printing at a relatively low cost. Therefore, silicone rubber can be used as an ideal filling structure material for this invention.

[0030] Furthermore, such as Figure 3 As shown, to ensure that the medium solidifies only within the inner cavity of the thin-walled component and not on the outer surface, after filling the substrate, the opening of the thin-walled component is sealed with a permeable membrane, as indicated by arrow number 2 in the figure. Then, sodium chloride solute is added to the periphery, lowering the freezing point of the outer solution. Subsequently, the entire container is cooled using a refrigeration device until the temperature is below the freezing point of the internal medium but above the freezing point of the external medium. This temperature is maintained for a period of time until the substrate has completely solidified and bulged.

[0031] Furthermore, samples were taken from different specimens, and tensile tests, EBSD analysis, and transmission electron microscopy were conducted to investigate the effects of different parameters on the residual stress relief, mechanical properties, and microstructure of the specimens. The experimental results were compared with CP-FEM simulation results to verify the residual stress removal effect and revise the simulation model.

[0032] The workflow of this invention is as follows: First, an electron backscatter diffraction (ESD) microscope is used to construct a geometric model of the microstructure of the thin-walled metal material. Second, a crystal plasticity-finite element model of the thin-walled metal part is established. Next, a cross-scale simulation of the temperature-dependent filling process is performed using general-purpose finite element software. Next, the parameter range of the filling process that meets the requirements is determined. Next, the composition of the medium solution is determined and used as the composite medium matrix. Next, a filling structure is added to the inner cavity of the weakly rigid thin-walled part to control the volume and the direction of thermal expansion. Next, a permeable membrane is used to change the concentration of the solution inside and outside the specimen, causing the matrix to completely solidify and complete the expansion, eliminating residual stress. Finally, the simulation model is modified according to the actual stress condition of the specimen to verify the residual stress elimination effect.

[0033] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0034] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for controlling residual stress during temperature-dependent filling of a weakly rigid cylindrical thin-walled component using a composite medium, characterized in that... It includes the following steps: S1: First, the fine grain morphology, orientation, and texture of the workpiece sample are obtained by scanning electron microscopy electron backscattered diffraction (EBSD), and then the results are derived. .ctf or The .ang file is then used to construct the microstructure geometric model of the cylindrical thin-walled metal material by applying the Spectral solver based on the fast Fourier transform. S2: Establish a Crystal Plasty Finite Element Method (CP-FEM) model for cylindrical thin-walled metal parts, fully consider the state variables of the microstructure evolution process, and solve the nonlinear state dynamic equations describing the evolution of state parameters under application boundary or initial conditions by writing macro programs, thereby obtaining the change curves of state variables in the phase transition process. S3: Using general-purpose finite element software, establish the macroscopic geometric model and finite element model of the thin-walled part, and assign the state variables obtained from the crystal plasticity model to the macroscopic finite element model. At the same time, define the macroscopic mechanical properties of the composite medium and the thin-walled part, and carry out thermo-mechanical coupled finite element simulation to solve the stress, strain, deformation and temperature results of the variable temperature filling process, so as to realize the cross-scale simulation of the variable temperature filling process. S4: Based on the constructed cross-scale macro-micro simulation model, the effects of different filling medium pressures, filling amounts, and filling structure forms on expansion volume, bulging force, and residual stress are analyzed. The evolution law of tensile and compressive residual stress states in the bulging process is compared, and a quantitative relationship between filling parameters, bulging volume, and bulging load is established. Through quantitative iterative calculation, the range of filling process parameters that meet the requirements for residual stress control is obtained. S5: Select a medium with a high solidification expansion ratio, low cost and a freezing point close to room temperature. The medium is an aqueous solution. Conduct an analysis of the freezing expansion characteristics of different medium solutions, explore the distribution law of expansion force of the medium matrix in different cavity shapes, and consider the dissolution rate and the matching with the cutting process after melting to determine the composition of the medium solution and use it as the composite medium matrix. S6: To avoid excessive deformation and uncontrollable deformation caused by the complete filling of the inner cavity of the weak rigid cylindrical thin-walled part with aqueous matrix, a filling structure is added to the inner cavity of the weak rigid thin-walled part to control the volume and the direction of thermal expansion. S7: In order to make the medium solidify only in the inner cavity of the cylindrical thin-walled part and not on the outer surface, after filling the matrix, the opening of the thin-walled part is sealed with a permeable membrane, and then sodium chloride solute is added to the outside. The freezing point of the outer solution is lowered. Then, the entire container is cooled by a refrigeration device to a temperature below the freezing point of the inner medium and above the freezing point of the outer medium. The temperature is maintained for a period of time until the matrix is ​​completely solidified and the expansion is completed. S8: Samples were taken from different specimens and tensile tests, EBSD analysis, and transmission electron microscopy (TEM) were carried out to investigate the effects of different parameters on the residual stress relief, mechanical properties, and microstructure of the specimens. The simulation was verified to show the effect of temperature-controlled bulging on the residual stress relief of the specimens. Based on the experimental results, the simulation model was corrected to improve the calculation accuracy of the model and address the simulation calculation errors.

2. The method for controlling residual stress during temperature-dependent filling of a weakly rigid cylindrical thin-walled composite medium according to claim 1, characterized in that: In S1, the actual EBSD experimental results of materials are extracted to construct a crystal plasticity-finite element simulation model of thin-walled metal parts, which greatly improves the simulation accuracy and avoids the modeling errors introduced by the traditional representative volume element model.

3. The method for controlling residual stress during temperature-dependent filling of a weakly rigid cylindrical thin-walled composite medium according to claim 1, characterized in that: In S2, the state variables are set as microstructure parameters, including dislocation density, dislocation rate, stacking fault energy, twin integral number, volume fraction of phase transition, and related variables, and an evolution equation for each state variable is established.

4. The method for controlling residual stress during temperature-dependent filling of a weakly rigid cylindrical thin-walled composite medium according to claim 1, characterized in that: In S5, the distribution law of expansion force of the medium matrix in different cavity shapes is investigated. The analysis includes the effects of different solute mass fractions, cooling rates and holding times on expansion deformation and expansion load.

5. The method for controlling residual stress during temperature-dependent filling of a weakly rigid cylindrical thin-walled composite medium according to claim 1, characterized in that: In step S7, the permeation membrane is used to make the solution concentration inside and outside the thin-walled part different, resulting in different freezing points inside and outside. This causes the solution inside the thin-walled part to solidify while the solution outside does not solidify. In order to prevent the expansion of the opening of the thin-walled part from being too large and causing insufficient internal expansion force, the support limiting device is adjusted to the opening of the thin-walled part.

6. The method for controlling residual stress during temperature-dependent filling of a weakly rigid cylindrical thin-walled composite medium according to claim 1, characterized in that: In S7, the cylindrical thin-walled weakly rigid structure expands in volume due to the temperature-changing filling of the composite medium, thereby providing expansion force to the thin-walled structure and adjusting the residual stress.

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