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

Abstract

The application belongs to the technical field of cutting processing, and particularly discloses a machining residual stress rapid prediction method and system based on a cross-scale finite element simulation model, which comprises the following steps: in a three-dimensional cutting model of a workpiece, determining an undeformed section according to a cutting depth, a feed amount and a tool geometry, determining a plurality of section units based on the undeformed section; performing two-dimensional cutting simulation on each section unit respectively to obtain force-thermal load distribution of each section unit; then, interpolating to obtain force-thermal load distribution of a three-dimensional cutting region; performing three-dimensional cutting simulation on the three-dimensional cutting model, in which no chip is formed, the force-thermal load is directly applied to a machining surface of the workpiece, and movement of the force-thermal load simulates a cutting and feeding process of the tool, so that residual stress distribution is simulated and obtained. The application can avoid the influence of large deformation of a grid on simulation speed, thereby improving residual stress prediction and calculation efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cutting machining, and more particularly relates to a machining residual stress rapid prediction method and system based on a cross-scale finite element simulation model. BACKGROUND

[0002] Cutting machining is widely used in machining various shafts, discs and flat plates and other parts, including turning, milling, grinding and other machining methods. In the machining process, the interaction between the tool and the workpiece will cause material removal and temperature change, which will in turn cause residual stress on the surface and inside of the workpiece. Residual stress affects the dimensional accuracy, shape accuracy, fatigue strength and other properties of the workpiece, and plays a key role in affecting the performance of the workpiece. However, residual stress testing is costly and difficult, and it is difficult to apply it universally through pure experimental means in actual production, so 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. The patent CN115983098A discloses a grinding surface residual stress prediction method, which uses an empirical model to establish a mapping rule between process parameters and machining residual stress based on experimental data. Its essence is to regard the generation process of residual stress in machining as a black box, and its effectiveness depends on the test data itself, which cannot reveal the nature of the generation of residual stress. The patent CN116205029A discloses a cutting machining surface residual stress prediction method, which uses an analytical model to calculate residual stress by applying force and thermal load to the machining surface, and has the characteristics of clear physical process, but it relies on some oversimplified assumptions, such as plane strain state and uniform material, and its accuracy is relatively low, which cannot accurately reflect the complex situation in actual cutting process. The numerical method for residual stress prediction can simulate the material removal, temperature field and stress field changes in the cutting machining process, and can simulate the relatively complex working conditions in detail, but its disadvantage is that the calculation is very time-consuming. These methods have certain limitations for guiding the actual production process, therefore, it is urgent to develop a method for quickly and accurately predicting machining residual stress. SUMMARY

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

[0005] To achieve the above-mentioned purpose, according to one aspect of the application, a machining residual stress rapid prediction method based on a cross-scale finite element simulation model is provided, which includes the following steps:

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

[0007] S2, performing two-dimensional cutting simulation on each cross section unit respectively to obtain a force and heat load distribution of each cross section unit;

[0008] S3, interpolating the force and heat load distribution of each cross section unit to obtain a force and heat load distribution of a three-dimensional cutting region;

[0009] S4, performing three-dimensional cutting simulation on the three-dimensional cutting model, no chip is formed during the simulation process, the force and heat load is directly applied to the machining surface of the workpiece according to the force and heat load distribution of the three-dimensional cutting region, and the movement of the force and heat load simulates the cutting and feeding process of the tool, so that the residual stress distribution is simulated.

[0010] As a further optimization, the plurality of cross section units is determined based on the undeformed cross section, comprising:

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

[0012] When the machining method is milling or grinding: a plurality of cross section units are taken along a direction perpendicular to the rotational speed, and each cross section unit is perpendicular to the undeformed cross section.

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

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

[0015] As a further optimization, step S4 adopts Lagrange method to perform three-dimensional cutting simulation on the three-dimensional cutting model.

[0016] As a further optimization, the force and heat load includes heat flux density, tangential stress and normal stress.

[0017] As a further optimization, the force and heat load distribution obtained in step S3 is corrected through cutting experiment, and then step S4 is performed.

[0018] As a further optimization, the three-dimensional cutting force is obtained through cutting experiment, so that the tangential stress and the normal stress are corrected; the heat flux density obtained in step S3 is corrected according to the ratio of the tangential force obtained by cutting experiment and simulation.

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

[0020] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages:

[0021] 1. In three-dimensional cutting simulation, a large number of grids need to be divided to simulate chip formation, resulting in large amount of calculation and long calculation time; while in two-dimensional cutting, the number of grids is greatly reduced compared with three-dimensional cutting, and the simulation speed is relatively fast. Therefore, by using the equivalent load method, the load in two-dimensional cutting simulation is extracted and applied to three-dimensional cutting simulation without chip formation, i.e. the tool and workpiece interaction is converted into force and thermal load applied to the machining surface, which can avoid the influence of grid large deformation on simulation speed and improve efficiency.

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

[0023] Figure 1 A two-dimensional cutting section extraction diagram for turning of the embodiment of the present application is shown in the figure;

[0024] Figure 2 An enlarged view of the two-dimensional cutting section extraction for turning of the embodiment of the present application is shown in the figure;

[0025] Figure 3 A flowchart of the machining residual stress fast prediction method based on a cross-scale finite element simulation model of the embodiment of the present application is shown in the figure;

[0026] Figure 4 A schematic diagram of force and thermal load distribution shape along the extraction path of the embodiment of the present application is shown in the figure;

[0027] Figure 5 A schematic diagram of applying equivalent load of the embodiment of the present application is shown in the figure;

[0028] Figure 6 A schematic diagram of milling, grinding and drilling cutting section extraction of the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0029] In order to make the objects, technical solutions and advantages of the present application clearer, further detailed description will be made to the present application in combination with the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0030] The machining residual stress rapid prediction method based on the cross-scale finite element simulation model provided by the embodiment of the present application comprises the following steps as shown in Figure 3 The machining residual stress rapid prediction method based on the cross-scale finite element simulation model provided by the embodiment of the present application comprises the following steps as shown in

[0031] S1, extracting a cross-section element from a three-dimensional cutting model to obtain a two-dimensional orthogonal simulation model.

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

[0033] This embodiment takes turning as an example for specific description: the workpiece rotates to make main cutting motion, and the tool makes feed motion. In order to improve the simulation efficiency, only a small area around the cutting area is selected for analysis and the workpiece is assumed to be fixed, and the tool makes feed and cutting motion. The undeformed cross-section of the workpiece can be obtained according to the cutting depth, the feed amount and the tool geometry. The undeformed cross-section specifically refers to the cross-section of the workpiece that has not been affected by the tool and keeps the original shape and size when the tool makes cutting motion. A plurality of cross-section elements S(i) are taken along the direction perpendicular to the cutting edge (i.e. the cutting edge of the tool), and each cross-section element S(i) corresponds to a cutting thickness h(i) and an extraction length l(i), as shown in Figure 1 and Figure 2 Thus, a plurality of orthogonal two-dimensional cutting models can be obtained. The extraction length l(i) refers to the distance from the contact point of the cutting edge to the machined surface on the corresponding cross-section element. Further, because the extraction length on the left and right of the maximum chip thickness is different from the chip thickness distribution law, in order to ensure subsequent interpolation, a plurality of cross-sections are taken on the left and right of the maximum chip thickness, and interpolation calculation is performed on the left and right respectively.

[0034] The extraction process for machining methods such as milling, grinding and drilling is similar, Figure 6 is a schematic diagram of the cross-section for the three cutting methods. In the milling process, the undeformed cross-section is defined according to the tool diameter, the cutting depth and the feed amount, and a plurality of cross-section elements are extracted along the direction perpendicular to the cutting speed from the contact point of the cutting edge and the workpiece. The grinding extraction method is similar to milling. The undeformed cross-section is defined according to the grinding wheel diameter, the grinding depth and the feed amount, and a plurality of cross-section elements 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 while feeding, and the cross-section extraction method is the same as turning.

[0035] S2, respectively, each selected two-dimensional cross-section unit is simulated, to obtain the force thermal load distribution.

[0036] Specifically, in the two-dimensional simulation with chip formation process simulation rate is faster, so you can not affect the simulation rate while obtaining force thermal load distribution shape. Two-dimensional cutting simulation can be used in a variety of simulation methods, including but not limited to arbitrary Lagrangian-Eulerian method, smoothed particle hydrodynamics method, coupled Euler-Lagrangian method and other material removal simulation.

[0037] Thermal load includes heat flux, tangential stress and normal stress; with the plane and the intersection of the cross-section unit as the "extraction path", that is Figure 4 Y direction; along the "extraction path" record each point heat flux, tangential stress and normal stress size, the three parameters depend on the cutting thickness h (i), the extraction length l (i) and along the "extraction path" position, its numerical fitting function, can get the corresponding load distribution shape As Figure 4 shown.

[0038] S3, based on the force thermal load distribution of each cross-section unit, interpolation to get three-dimensional force thermal load distribution.

[0039] Combination of two-dimensional load, applied to the three-dimensional cutting model. Each cross-section unit S (i) unit has corresponding heat flux, tangential stress and normal stress distribution shape and its value, the parameter value is only related to the position along the "extraction path", that is, the Y axis coordinate, chip thickness h (i) and extraction length l (i), and three-dimensional cutting thickness has continuity, the selected cross-section cutting thickness range is large, can be selected by several cross-section unit interpolation of the remaining uncut part load distribution, so as to obtain the three-dimensional cutting surface overall load distribution, the calculation of the overall load distribution

[0040] Furthermore, the three-dimensional load amplitude can be corrected by conducting cutting experiments, thereby obtaining a more accurate three-dimensional cutting surface load distribution. Specifically, in two-dimensional cutting simulation, numerical simulation methods provide good simulation results for the load distribution shape, but the values ​​often have varying degrees of error. To obtain more accurate results, the simulation numerical results can be corrected. The three-dimensional overall tangential and normal forces in the simulation results can be calculated by summation, and cutting experiments can be conducted to measure the cutting forces during the cutting process. The measured three-dimensional cutting forces are then used to correct the obtained simulation results. That is, the tangential stress is corrected by the ratio of the experimental tangential force to the simulated tangential force, and the normal stress is corrected by the ratio of the experimental normal force to the simulated normal force. For heat flux density, its distribution mainly depends on the tangential force. The heat flux density obtained in step S3 can be corrected according to the ratio of the tangential forces obtained from the cutting experiment and simulation to obtain the final force and heat load distribution.

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

[0042] Three-dimensional Lagrangian cutting simulation was conducted to obtain the residual stress distribution. This model does not include chip formation simulation; instead, the three-dimensional force and thermal loads obtained from S3 are directly applied to the machined surface. Figure 5 As shown, the thermal load is first moved along the cutting direction at a speed equal to the cutting speed. Then, cooling is performed for a time equal to the workpiece's rotation cycle. Finally, the thermal load is moved along the feed direction offset by the feed per revolution to simulate the tool feed process. The width of the thermal load application may be greater than the feed rate; therefore, some areas may be affected by the thermal load multiple times, and the final superposition results in the final residual stress, thus revealing the residual stress distribution.

[0043] Those skilled in the art will readily understand that the above description is merely 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 within the scope of protection of the present invention.

Claims

1. A method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model, characterized in that, Includes the following steps: S1. In the three-dimensional cutting model of the workpiece, determine the undeformed cross section of the workpiece during machining based on the cutting depth, feed rate and tool geometry; Multiple section elements are determined based on the undeformed section, including: When the machining method is turning or drilling: multiple cross-sectional elements are cut along the direction perpendicular to the cutting edge of the tool, and each cross-sectional element is perpendicular to the undeformed cross-section; When the machining method is milling or grinding: multiple cross-sectional elements are cut along the direction perpendicular to the rotation speed, and each cross-sectional element is perpendicular to the undeformed cross-section; Each cross-sectional element corresponds to a different cutting thickness and extraction length; cross-sectional elements are extracted at the maximum cutting thickness, and multiple cross-sectional elements are extracted on both sides of the maximum cutting thickness; S2. Perform two-dimensional cutting simulation on each cross-sectional element to obtain the force and thermal load distribution of each cross-sectional element; S3. Based on the force and heat load distribution of each cross-sectional element, interpolation is performed to obtain the force and heat load distribution of the three-dimensional cutting region; S4. Perform three-dimensional cutting simulation on the three-dimensional cutting model. No chips are formed during the simulation. Based on the force and heat load distribution in the three-dimensional cutting area, the force and heat load is directly applied to the workpiece machining surface. The movement of the force and heat load 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 as described in claim 1, 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 width of the cross-sectional unit is not less than the sum of the corresponding cutting thickness and the extraction length.

3. The method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model as described in claim 1, characterized in that, Step S4: Perform three-dimensional cutting simulation on the three-dimensional cutting model using the Lagrange method.

4. 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 1-3, characterized in that, The thermal loads include heat flux density, tangential stress, and normal stress.

5. The method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model as described in claim 4, characterized in that, After correcting the force and heat load distribution obtained in step S3 through a cutting experiment, step S4 is then performed.

6. The method for rapid prediction of machining residual stress based on a cross-scale finite element simulation model as described in claim 5, characterized in that, The three-dimensional cutting force is obtained through cutting experiments, thereby correcting the tangential stress and normal stress; then, the heat flux density obtained in step S3 is corrected based on the ratio of the tangential force obtained from the cutting experiments and simulations.

7. A rapid prediction system for machining residual stress based on a cross-scale finite element simulation model, characterized in that, Includes a processor for executing the rapid prediction method for machining residual stress based on a cross-scale finite element simulation model as described in any one of claims 1-6.

Images