Processing residual stress rapid prediction method and system based on cross-scale finite element simulation model

Abstract

The invention belongs to the technical field of cutting machining, and particularly discloses a machining residual stress rapid prediction method and system based on a cross-scale finite element simulation model.The method comprises the steps that in a three-dimensional cutting model of a workpiece, an undeformed section is determined according to the cutting depth, the feeding amount and the geometric shape of a tool, and the machining residual stress is obtained; determining a plurality of section units based on the undeformed section; performing two-dimensional cutting simulation on each section unit to obtain force and heat load distribution of each section unit; carrying out interpolation to obtain force and heat load distribution of the three-dimensional cutting area; and three-dimensional cutting simulation is conducted on the three-dimensional cutting model, no cuttings are formed in the simulation process, the force thermal load directly acts on the machined surface of the workpiece, the cutting and feeding process of the tool is simulated through movement of the force thermal load, and therefore residual stress distribution is obtained through simulation. According to the method, the influence of large grid deformation on the simulation speed can be avoided, so that the residual stress prediction calculation efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of cutting processing, and more specifically, relates to a method and system for quickly predicting machining residual stress based on a cross-scale finite element simulation model. Background Art

[0002] Cutting is widely used in machining various shafts, discs, plates and other parts, including turning, milling, grinding and other machining methods. During the machining process, the interaction between the tool and the workpiece will lead to material removal and temperature changes, which will then generate residual stress on the surface and inside the workpiece. Residual stress will affect the dimensional accuracy, shape accuracy, fatigue strength, etc. of the workpiece, and play a key role in affecting the performance of the workpiece. However, residual stress testing is costly and difficult, and it is difficult to be widely used in actual production through pure experimental means. Therefore, it is urgent to establish an efficient and accurate residual stress prediction model.

[0003] The existing residual stress prediction methods mainly include empirical model method, analytical model method and numerical model method. Invention patent CN115983098A discloses a method for predicting residual stress on grinding surface, which uses empirical model to establish the mapping law between process parameters and processing residual stress based on experimental data. Its essence is to regard the generation process of residual stress in processing as a black box, and its effectiveness depends on the test data itself, which is difficult to reveal the nature of residual stress generation. Invention patent CN116205029A discloses a method for predicting residual stress on cutting surface, which adopts analytical model to apply mechanical and thermal loads to the processing surface for residual stress calculation, and has the characteristics of clear physical process, but it relies on some oversimplified assumptions, such as plane strain state, uniform material, etc., and its accuracy is relatively low, which cannot accurately reflect the complex situation in the actual cutting process. The numerical method for predicting residual stress can simulate the material removal, temperature field and stress field changes in the cutting process, and simulate relatively complex working conditions in detail. Its disadvantage is that the calculation is very time-consuming. These methods have certain limitations in guiding the actual production process. Therefore, there is an urgent need for a method that can quickly and accurately predict the processing residual stress. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a method and system for rapid prediction of machining residual stress based on a cross-scale finite element simulation model, the purpose of which is to improve the calculation efficiency of residual stress prediction.

[0005] To achieve the above object, according to one aspect of the present invention, a method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model is proposed, comprising the following steps:

[0006] S1. In a three-dimensional cutting model of a workpiece, determining an undeformed cross section of the workpiece during machining according to a cutting depth, a feed rate, and a tool geometry; and determining a plurality of cross-sectional units based on the undeformed cross section;

[0007] S2, perform two-dimensional cutting simulation on each cross-sectional unit to obtain the mechanical and thermal load distribution of each cross-sectional unit;

[0008] S3, interpolating the mechanical and thermal load distribution of each cross-sectional unit to obtain the mechanical and thermal load distribution of the three-dimensional cutting area;

[0009] S4. Perform three-dimensional cutting simulation on the three-dimensional cutting model. No chips are formed during the simulation process. The mechanical and thermal loads are directly applied to the workpiece processing surface according to the mechanical and thermal load distribution in the three-dimensional cutting area, and the movement of the mechanical and thermal loads simulates the tool cutting and feeding process, thereby simulating the residual stress distribution.

[0010] As a further preferred method, determining a plurality of cross-sectional units based on the undeformed cross-section includes:

[0011] When the machining method is turning or drilling: multiple cross-sectional units are cut along the direction perpendicular to the cutting edge of the tool, and each cross-sectional unit is perpendicular to the undeformed cross section;

[0012] When the machining method is milling or grinding: multiple cross-sectional units are intercepted along the direction perpendicular to the rotation speed, and each cross-sectional unit is perpendicular to the undeformed cross-section.

[0013] As a further preference, each cross-sectional unit corresponds to a different cutting thickness and extraction length; the cross-sectional unit is extracted at the maximum cutting thickness, and a plurality of cross-sectional units are extracted on both sides of the maximum cutting thickness.

[0014] As a further preference, the extraction length refers to the distance from the contact point between the cutting edge and the workpiece to the machined surface on the corresponding cross-sectional unit; the cross-sectional unit width is not less than the sum of the corresponding cutting thickness and the extraction length.

[0015] As a further preferred embodiment, in step S4, the three-dimensional cutting simulation is performed on the three-dimensional cutting model using the Lagrangian method.

[0016] As further preferred, the thermal loads include heat flux, tangential stress and normal stress.

[0017] As a further preferred method, step S4 is performed after the mechanical and thermal load distribution obtained in step S3 is corrected through a cutting experiment.

[0018] As a further preferred embodiment, three-dimensional cutting force is obtained through cutting experiments, so as to correct the tangential stress and normal stress; and the heat flux density obtained in step S3 is corrected according to the ratio of the tangential force obtained from the cutting experiment and the simulation.

[0019] According to another aspect of the present invention, a system for rapid prediction of machining residual stress based on a cross-scale finite element simulation model is provided, comprising a processor for executing the above-mentioned method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model.

[0020] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0021] 1. When performing 3D cutting simulation, a large number of grids need to be divided in order to simulate chip formation, resulting in large amount of calculation and long calculation time; while the number of grids in 2D cutting is greatly reduced compared to 3D, and the simulation speed is relatively fast. Therefore, by adopting the equivalent load method, the load in 2D cutting simulation is extracted and applied to 3D cutting simulation without chip formation, that is, the relationship between the tool and the workpiece is converted into mechanical and thermal loads and applied to the machining surface, which can avoid the influence of large grid deformation on simulation speed and thus improve efficiency.

[0022] 2. The present invention extracts the load distribution law in the two-dimensional model and applies it to the three-dimensional Lagrangian simulation model to perform residual stress simulation. This can effectively avoid the limitations of the Lagrangian method in solving large deformation problems and the low efficiency of residual stress solution, thereby improving the prediction speed while ensuring the solution accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of a two-dimensional cutting cross section extracted by turning according to an embodiment of the present invention;

[0024] Figure 2 Extract a magnified view of a two-dimensional cutting cross section for turning in an embodiment of the present invention;

[0025] Figure 3 This is a flow chart of a method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model according to an embodiment of the present invention;

[0026] Figure 4 A schematic diagram of the shape of mechanical and thermal load distribution obtained along the extraction path according to an embodiment of the present invention;

[0027] Figure 5 A schematic diagram of applying equivalent loads according to an embodiment of the present invention;

[0028] Figure 6 Schematic diagram of milling, grinding and drilling cutting cross sections obtained according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of 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. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] The embodiment of the present invention provides a method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model, such as Figure 3 As shown, the following steps are included:

[0031] S1. Extract cross-sectional elements from the three-dimensional cutting model to obtain a two-dimensional orthogonal simulation model.

[0032] In the three-dimensional cutting model of the workpiece, an undeformed section is determined according to the cutting depth, the feed amount and the tool geometry, and a plurality of two-dimensional section units are determined based on the undeformed section.

[0033] This embodiment takes turning as an example for specific explanation: the workpiece rotates as the main cutting motion, and the tool performs feed motion. In order to improve the simulation efficiency, only a small area around the cutting area is selected for analysis and it is assumed that the workpiece is fixed and the tool performs feed and cutting motions. The undeformed section of the workpiece can be obtained based on the cutting depth, feed rate and tool geometry. The undeformed section specifically refers to the section of the workpiece that has not been affected by the tool during the cutting motion and maintains its original shape and size. Multiple section units S(i) are intercepted along the direction perpendicular to the cutting edge (i.e., the tool cutting edge). The section units are all perpendicular to the undeformed section. Each section unit S(i) corresponds to a cutting thickness h(i) and an extraction length l(i), such as Figure 1 and Figure 2 As shown in the figure, multiple orthogonal two-dimensional cutting models can be obtained. The extraction length l(i) refers to the distance from the contact point between the cutting edge and the workpiece to the machined surface on the corresponding section unit. Furthermore, because the distribution of the extraction length on the left and right sides of the maximum chip thickness varies with the chip thickness, in order to ensure the subsequent interpolation, multiple sections need to be taken on the left and right sides of the maximum chip thickness, and interpolation calculations are performed on the left and right sides respectively.

[0034] The extraction process of milling, grinding, drilling and other processing methods is similar. Figure 6 The following are cross-sectional schematic diagrams of the three cutting methods. In the milling process, the undeformed section is defined according to the tool diameter, cutting depth and feed rate, and multiple cross-sectional units are extracted along the direction perpendicular to the cutting speed through the contact point between the cutting edge and the workpiece. The grinding extraction method is similar to milling. The undeformed section is defined according to the grinding wheel diameter, grinding depth and feed rate, and multiple cross-sectional units are extracted along the direction perpendicular to the grinding speed. Drilling can be understood as a turning process in which the workpiece is fixed and the tool rotates and feeds at the same time. The cross-sectional extraction method is the same as turning.

[0035] S2. Perform two-dimensional simulation on each selected two-dimensional cross-sectional unit to obtain the distribution of mechanical and thermal loads.

[0036] Specifically, in the two-dimensional simulation, the simulation rate of the chip formation process is faster, so the distribution shape of the mechanical and thermal loads can be obtained without affecting the simulation rate. Various simulation methods can be used for two-dimensional cutting simulation, including but not limited to arbitrary Lagrangian-Euler method, smooth particle flow method, coupled Euler-Lagrangian method, etc. for material removal simulation.

[0037] The mechanical and thermal loads include heat flux, tangential stress and normal stress; the straight line at the intersection of the plane where the machined surface is located and the cross-sectional unit is used as the "extraction path", that is, Figure 4 Y direction; record the heat flux density, tangential stress and normal stress of each point along the "extraction path". These three parameters depend on the cutting thickness h(i), extraction length l(i) and the position along the "extraction path". Fitting their values ​​to functions can obtain the corresponding load distribution shape. like Figure 4 shown.

[0038] S3. Based on the mechanical and thermal load distribution of each cross-sectional unit, the three-dimensional mechanical and thermal load distribution is interpolated.

[0039] Combine the two-dimensional loads and apply them to the three-dimensional cutting model. Each cross-sectional unit S(i) has corresponding heat flux density, tangential stress and normal stress distribution shapes and their values. It is known that the values ​​of each parameter are only related to the position along the "extraction path", i.e., the Y-axis coordinate, the chip thickness h(i) and the extraction length l(i). The three-dimensional cutting thickness is continuous and the cutting thickness range of the selected cross section is large. The load distribution of the remaining uncut parts can be interpolated through several selected cross-sectional units, thereby obtaining the overall load distribution of the three-dimensional cutting surface and calculating and simulating the overall load distribution.

[0040] Furthermore, the three-dimensional load amplitude can be corrected by conducting cutting experiments, so as to obtain a more accurate three-dimensional cutting surface load distribution. Specifically, when performing two-dimensional cutting simulation, the numerical simulation method has a good simulation result for the load distribution shape, but its numerical value often has different errors. In order to obtain more accurate results, the simulation numerical results can be corrected. The three-dimensional overall tangential force and normal force in the simulation results can be calculated by summing, and cutting experiments can be carried out to measure the cutting force during the cutting process, and the simulation results can be corrected by the measured three-dimensional cutting force. That is, the tangential stress is corrected by the ratio of the experimental tangential force and the simulated tangential force, and the normal stress is corrected by the ratio of the experimental normal force and the simulated normal force; for the heat flux density, its distribution mainly depends on the tangential force. According to the ratio of the tangential force obtained by the cutting experiment and the simulation, the heat flux density obtained in step S3 can be corrected to obtain the final force and heat load distribution.

[0041] S4. Based on the three-dimensional Lagrangian method, mechanical and thermal loads are applied to the machined surface to achieve simulation of machining residual stress without chip formation and rapid prediction of residual stress.

[0042] The three-dimensional Lagrangian cutting simulation is carried out to obtain the residual stress distribution. In this model, there is no chip formation simulation. The three-dimensional force and heat load obtained by S3 is directly applied to the machined surface, such as Figure 5 As shown in the figure, the mechanical and thermal loads are first moved along the cutting direction, and the moving speed is equal to the cutting speed. Then cooling is performed, and the cooling time is equal to the workpiece rotation period. Finally, the mechanical and thermal loads are offset along the feed direction by the feed amount per revolution to simulate the tool feed process. The width of the mechanical and thermal load action may be greater than the feed amount. Therefore, some areas may be affected by the mechanical and thermal loads multiple times, and the final residual stress is obtained after superposition, so as to obtain the residual stress distribution.

[0043] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A rapid prediction method for machining residual stress based on a cross-scale finite element simulation model, characterized in that: The steps include: S1. In a three-dimensional cutting model of a workpiece, determining an undeformed cross section of the workpiece during machining according to cutting depth, feed rate, and tool geometry; determining a plurality of cross-sectional elements based on the undeformed cross-section; S2, perform two-dimensional cutting simulation on each cross-sectional unit to obtain the mechanical and thermal load distribution of each cross-sectional unit; S3, interpolating the mechanical and thermal load distribution of each cross-sectional unit to obtain the mechanical and thermal load distribution of the three-dimensional cutting area; S4. Perform three-dimensional cutting simulation on the three-dimensional cutting model. No chips are formed during the simulation process. The mechanical and thermal loads are directly applied to the workpiece processing surface according to the mechanical and thermal load distribution in the three-dimensional cutting area, and the movement of the mechanical and thermal loads simulates the tool cutting and feeding process, thereby simulating the residual stress distribution.

2. The method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model according to claim 1, characterized in that: Determine multiple cross-sectional elements based on the undeformed cross section, including: When the machining method is turning or drilling: multiple cross-sectional units are cut along the direction perpendicular to the cutting edge of the tool, and each cross-sectional unit is perpendicular to the undeformed cross section; When the machining method is milling or grinding: multiple cross-sectional units are intercepted along the direction perpendicular to the rotation speed, and each cross-sectional unit is perpendicular to the undeformed cross-section.

3. The method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model as claimed in claim 2, characterized in that: Each cross-sectional element corresponds to a different cutting thickness and extraction length; the cross-sectional element is extracted at the maximum cutting thickness, and multiple cross-sectional elements are extracted on both sides of the maximum cutting thickness.

4. The method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model according to claim 3, characterized in that: The extraction length refers to the distance from the contact point between the cutting edge and the workpiece to the machined surface on the corresponding cross-sectional unit; the cross-sectional unit width is not less than the sum of the corresponding cutting thickness and the extraction length.

5. The method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model according to claim 1, characterized in that: Step S4, using the Lagrangian method to perform three-dimensional cutting simulation on the three-dimensional cutting model.

6. The method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model according to any one of claims 1 to 5, characterized in that: The mechanical and thermal loads include heat flux, tangential stress and normal stress.

7. The method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model according to claim 6, characterized in that: After the mechanical and thermal load distribution obtained in step S3 is corrected through cutting experiments, step S4 is performed.

8. The method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model according to claim 7, characterized in that: The three-dimensional cutting force is obtained through the cutting experiment, so as to correct the tangential stress and the normal stress; and then the heat flux density obtained in step S3 is corrected according to the ratio of the tangential force obtained from the cutting experiment and the simulation.

9. A rapid prediction system for machining residual stress based on a cross-scale finite element simulation model, characterized in that: It includes a processor, which is used to execute the method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model as described in any one of claims 1-8.

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