Multi-process forming judgment method based on two-way tensile ultimate strain

Abstract

The invention relates to a multi-process forming judgment method based on two-way tensile limit strain, which comprises the following steps: on the basis of a deformation mechanism experienced during material forming, associating complex loading characteristics of a two-way tensile test with a complex deformation process of a part, and analyzing the loading history of a plate by utilizing a method of combining the test and simulation; the limit strain of the material in different deformation directions at different stages is ingeniously obtained, so that the forming result of the material is accurately judged; the method can ensure that the limit strain of the sheet cannot be influenced by bending stress and friction force, overcomes the technical problem that the existing method cannot meet the multi-process forming judgment of parts, greatly improves the accuracy and effectiveness of forming simulation analysis, is particularly suitable for occasions of multi-process forming analysis of metal sheet materials, and has wide application prospects. And the application requirements of engineering practice and scientific research work are widely met.

Description

Technical Field

[0001] The invention relates to the technical field of biaxial stretching forming of metal sheets, and in particular to a multi-process forming determination method based on biaxial stretching limit strain. Background Art

[0002] In the process of forming simulation analysis of metal sheets, parts with complex modeling features are often encountered. Such parts often require multiple forming processes to meet the processing and manufacturing requirements of the parts. However, due to the work hardening characteristics of metal materials, the forming ability of the sheet metal will change greatly after undergoing different complex deformation-unloading-re-deformation, which will have a great impact on the analysis results of the forming simulation, resulting in a significant decrease in prediction accuracy.

[0003] At present, the industry mostly uses the traditional hemispherical punch bulging test method to predict the forming results of sheet metal in forming simulation analysis. However, this method ignores the influence of changes in material properties when the sheet metal is deformed multiple times on the forming results. Moreover, during the test, the sheet metal will inevitably be subjected to bending stress and friction. If this method is used to perform forming analysis of multiple processes of parts, it will inevitably produce large judgment errors and cannot meet the application needs of actual engineering and scientific research. Summary of the invention

[0004] In response to the above problems, the purpose of the present invention is to provide a multi-process forming judgment method based on biaxial tensile limit strain, which can ensure that the limit strain of the sheet material will not be affected by bending stress and friction, overcome the technical difficulties that the existing methods cannot meet the multi-process forming judgment of parts, and greatly improve the accuracy and effectiveness of forming simulation analysis.

[0005] The technical solution adopted by the present invention is as follows:

[0006] The present invention proposes a multi-process forming determination method based on biaxial tensile limit strain, comprising the following steps:

[0007] S1. Use forming simulation analysis software to establish a multi-process simulation process for a part, determine the limit strain point of the part after the first forming process through simulation calculation, and obtain the limit strain value generated by the limit strain point along the maximum strain direction and the limit strain value generated perpendicular to the maximum strain direction;

[0008] S2. preparing at least two biaxially stretched specimens;

[0009] S3, using a biaxial tensile testing machine to perform a biaxial tensile test on the sample prepared in step S2, and unloading the sample in sequence after reaching the test termination condition;

[0010] S4, continuing to carry out biaxial tensile tests on the biaxial tensile specimen after the tensile test in step S3 according to different loading ratios, until the biaxial tensile specimen breaks, and obtaining its ultimate strain values ​​in two tensile directions;

[0011] S5. prepare a uniaxial tensile specimen, perform a uniaxial tensile test on the uniaxial tensile specimen, remove the specimen after reaching the termination condition, and perform the uniaxial tensile test again until the uniaxial tensile specimen breaks;

[0012] S6, obtaining the stress-strain curve in the second uniaxial tensile test in step S5, and calculating the instability strain value of the material;

[0013] S7, correcting the limit strain value in the large-scale stretching direction obtained in step S3 to obtain a corrected limit strain value in the large-scale direction;

[0014] S8. Plot the limit strain value in the large-scale stretching direction corrected in step S7 and the limit strain value in another stretching direction obtained in step S3 in the same coordinate system to form a corrected limit strain judgment curve, and input the curve into the forming simulation software of the part to continue the analysis and calculation of the secondary forming process. If the limit strain point of each process condition calculated by the forming simulation software is less than the corrected limit strain value, the result after the part is formed is safe. Otherwise, there is a risk of instability in the forming of the part.

[0015] Furthermore, in step S3, the termination condition of the biaxial tensile test corresponds to the limit strain values ​​of the limit strain point in two directions obtained in step S1.

[0016] Furthermore, in step S4, there are at least two loading ratios.

[0017] Furthermore, in step S5, the termination condition of the uniaxial tensile test is: comparing the ultimate strain values ​​of the ultimate strain point determined in step S1 in two directions, and selecting the larger ultimate strain value in the two directions as the termination condition of the uniaxial tensile test.

[0018] Furthermore, in step S6, the instability strain value of the material=the ultimate strain value of the material-the strain value corresponding to the maximum stress point.

[0019] Furthermore, in step S7, the corrected limit strain value in the large-scale direction = the instability strain value of the material / the limit strain value of the material.

[0020] Furthermore, in step S8, the coordinate system uses the strain value in the small-ratio stretching direction as the horizontal coordinate and the strain value in the large-ratio stretching direction as the vertical coordinate.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The multi-process forming judgment method based on biaxial tensile limit strain proposed in the present invention can ensure that the limit strain of the sheet material will not be affected by bending stress and friction, overcomes the technical difficulty that the existing methods cannot meet the multi-process forming judgment of parts, and can greatly improve the accuracy and effectiveness of forming simulation analysis. It is particularly suitable for multi-process forming analysis of metal sheet materials and can widely meet the application requirements of engineering practice and scientific research work. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of stress-strain curve of the material in Example 1 of the present invention;

[0024] Figure 2 Schematic diagram of the corrected limit strain determination curve in Example 1 of the present invention;

[0025] Figure 3 Schematic diagram of stress-strain curve of the material in Example 2 of the present invention;

[0026] Figure 4 Schematic diagram of the corrected limit strain determination curve in the second embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] The present invention proposes a multi-process forming determination method based on biaxial tensile limit strain, which specifically includes the following steps:

[0029] S1. Use forming simulation analysis software to establish a multi-process simulation process for a part, determine the limit strain point of the part after the first forming process through simulation calculation, and obtain the limit strain value generated by the limit strain point along the maximum strain direction and the limit strain value generated perpendicular to the maximum strain direction;

[0030] S2, preparing at least two or more biaxial tensile specimens to meet the biaxial tensile test of step S3 and step S4;

[0031] S3, using a biaxial tensile testing machine to perform a biaxial tensile test on the biaxial tensile specimen prepared in step S2, wherein the termination condition of the test corresponds to the ultimate strain value of the ultimate strain point in two directions obtained in step S1, and the specimens are unloaded in sequence after reaching the test termination condition;

[0032] S4, continuing to carry out a biaxial tensile test on the biaxial tensile specimen stretched in step S3 according to at least two or more different loading ratios until the specimen breaks, and obtaining its ultimate strain values ​​in two tensile directions;

[0033] S5, preparing a uniaxial tensile test specimen, comparing the ultimate strain values ​​of the ultimate strain point determined in step S1 in two directions, selecting the larger of the ultimate strain values ​​in the two directions as the termination condition of the uniaxial tensile test to perform the uniaxial tensile test, unloading the specimen after reaching the termination condition, and performing the uniaxial tensile test again until the uniaxial tensile test specimen breaks;

[0034] S6, obtaining the stress-strain curve in the second uniaxial tensile test in step S5, and calculating the instability strain value of the material, where the instability strain value = the ultimate strain value of the material - the strain value corresponding to the maximum stress point;

[0035] S7, correcting the limit strain value in the large-scale tensile direction obtained in step S3, the corrected limit strain value in the large-scale direction = (the limit strain value of the material - the strain value corresponding to the maximum stress point) / the limit strain value of the material, wherein the instability strain value is the value obtained in step S6;

[0036] S8. Plot the corrected limit strain value in the large-proportion stretching direction in step S7 and the limit strain value in another stretching direction obtained in step 3 in a coordinate system with the strain value in the small-proportion stretching direction as the horizontal coordinate and the strain value in the large-proportion stretching direction as the vertical coordinate to form a corrected limit strain judgment curve. Input the curve into the forming simulation software of the part to continue the analysis and calculation of the secondary forming process. If the limit strain point of each process condition calculated by the forming simulation software is less than the corrected limit strain value, the result after the part is formed is safe. Otherwise, there is a risk of instability in the forming of the part.

[0037] The present invention will be further described below by specific examples:

[0038] Embodiment 1

[0039] A multi-process forming determination method based on biaxial tensile limit strain, taking seat slide rail parts as an example, the specific implementation process is as follows:

[0040] S1. Use forming simulation analysis software to establish a multi-process simulation process for seat rail parts. Use DP980 steel to determine the limit strain point of the part after the first forming process through simulation calculation. The limit strain value of the limit strain point along the maximum strain direction and the limit strain value perpendicular to the maximum strain direction are 0.018 and 0.011 respectively.

[0041] S2, preparing five biaxially stretched specimens to meet the biaxially stretched test of step S3 and step S4;

[0042] S3, using a biaxial tensile testing machine to perform a biaxial tensile test on the biaxial tensile specimens prepared in step S2, wherein the termination condition of the biaxial tensile test is that the strain in one tensile direction reaches 0.018 and the strain in the other tensile direction reaches 0.011, and the specimens are unloaded in sequence after reaching the test termination condition;

[0043] S4, continuing to carry out biaxial tensile tests on the biaxial tensile specimens stretched in step S3 according to five different loading ratios (4:0, 4:1, 4:2, 4:3, 4:4) until the specimens break and obtain their ultimate strain values ​​in two tensile directions, as shown in Table 1;

[0044]

[0045] S5, preparing a uniaxial tensile test specimen, comparing the ultimate strain values ​​of the ultimate strain point determined in step S1 in two directions, selecting the larger ultimate strain value of 0.018 in the two directions as the termination condition of the uniaxial tensile test to perform the uniaxial tensile test, unloading the specimen after reaching the termination condition, and performing the uniaxial tensile test again until the uniaxial tensile test specimen breaks;

[0046] S6, obtaining the stress-strain curve in the second uniaxial tensile test in step S5, such as Figure 1 As shown, the instability strain value of the calculated material = (the ultimate strain value of the material - the strain value corresponding to the maximum stress point) ÷ the ultimate strain value of the material = (0.0722-0.0616) ÷ 0.0722 = 0.147;

[0047] S7, correcting the limit strain value in the large-scale stretching direction obtained in step S3, the corrected limit strain value in the large-scale stretching direction = the limit strain value in the large-scale stretching direction before correction × (1-instability strain value), wherein the instability strain value is obtained in step S6;

[0048] S8, plotting the ultimate strain value in the large-scale stretching direction corrected in step S7 and the ultimate strain value in another stretching direction obtained in step S3 in a coordinate system with the strain value in the small-scale stretching direction as the horizontal coordinate and the strain value in the large-scale stretching direction as the vertical coordinate, to form a corrected ultimate strain determination curve, such as Figure 2 As shown in the figure, the limit strain points in each deformation mode are 0.078, 0.049, 0.031, 0.033, and 0.035, respectively. The curve is input into the forming simulation software of the part to continue the analysis and calculation of the secondary forming process. The limit strain points of each process calculated in the subsequent forming simulation software are respectively less than the corrected limit strain value ( Figure 20.078, 0.049, 0.031, 0.033, 0.035) calculated in the calculation, the result of the part after forming is safe.

[0049] The present invention is based on the deformation mechanism experienced by materials during forming, associates the unique loading characteristics of the biaxial tensile test with the complex deformation process of the parts, and analyzes the loading history of the sheet material by combining experiments with simulations. The limit strains of the material in different deformation directions at different stages are cleverly obtained to accurately determine the forming results of the material.

[0050] Embodiment 2

[0051] A multi-process forming determination method based on biaxial tensile limit strain is used as an example to describe the A-pillar reinforcement plate parts for automobiles. The specific implementation process is as follows:

[0052] S1. Use forming simulation analysis software to establish a multi-process simulation process for the A-pillar reinforcement plate part. Use DP1180 steel to determine the limit strain point of the part after the first forming process through simulation calculation. The limit strain value generated along the maximum strain direction and the limit strain value perpendicular to the maximum strain direction at the limit strain point are 0.016 and 0.009 respectively.

[0053] S2, preparing five biaxially stretched specimens to meet the biaxially stretched test of step S3 and step S4;

[0054] S3, using a biaxial tensile testing machine to perform a biaxial tensile test on the biaxial tensile specimen prepared in step S2, wherein the termination condition of the biaxial tensile test is that the strain in one tensile direction reaches 0.016 and the strain in the other tensile direction reaches 0.009, and the specimens are unloaded in sequence after reaching the test termination condition;

[0055] S4, continuing to carry out biaxial tensile tests on the biaxial tensile specimens stretched in step S3 according to five different loading ratios (4:0, 4:1, 4:2, 4:3, 4:4) until the specimens break and obtain their ultimate strain values ​​in two tensile directions, as shown in Table 2;

[0056]

[0057] S5, preparing a uniaxial tensile test specimen, comparing the ultimate strain values ​​of the ultimate strain point determined in step S1 in two directions, selecting the larger ultimate strain value of 0.016 in the two directions as the termination condition of the uniaxial tensile test to perform the uniaxial tensile test, unloading the specimen after reaching the termination condition, and performing the uniaxial tensile test again until the uniaxial tensile test specimen breaks;

[0058] S6, obtaining the stress-strain curve in the second uniaxial tensile test in step S5, such as Figure 3As shown, the instability strain value of the calculated material = (the ultimate strain value of the material - the strain value corresponding to the maximum stress point) ÷ the ultimate strain value of the material = (0.152-0.056) ÷ 0.152 = 0.63;

[0059] S7, correcting the limit strain value in the large-scale stretching direction obtained in step S3, the corrected limit strain value in the large-scale stretching direction = the limit strain value in the large-scale stretching direction before correction × (1-instability strain value), wherein the instability strain value is obtained in step S6;

[0060] S8, plotting the ultimate strain value in the large-scale stretching direction corrected in step S7 and the ultimate strain value in another stretching direction obtained in step S3 in a coordinate system with the strain value in the small-scale stretching direction as the horizontal coordinate and the strain value in the large-scale stretching direction as the vertical coordinate, to form a corrected ultimate strain determination curve, such as Figure 4 As shown in the figure, the limit strain points in each deformation mode are 0.066, 0.041, 0.029, 0.031, and 0.033, respectively. The curve is input into the forming simulation software of the part to continue the analysis and calculation of the secondary forming process. The limit strain points of each process calculated in the subsequent forming simulation software are respectively less than the corrected limit strain value ( Figure 4 0.066, 0.041, 0.029, 0.031, 0.033) calculated in the calculation, the result of the part after forming is safe.

[0061] Matters not described in detail in the present invention are all known technologies.

[0062] The embodiments described above are merely descriptions of preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A multi-process forming determination method based on biaxial tensile limit strain, characterized in that: The method comprises the following steps: S1. Use forming simulation analysis software to establish a multi-process simulation process for a part, determine the limit strain point of the part after the first forming process through simulation calculation, and obtain the limit strain value generated by the limit strain point along the maximum strain direction and the limit strain value generated perpendicular to the maximum strain direction; S2. preparing at least two biaxially stretched specimens; S3, using a biaxial tensile testing machine to perform a biaxial tensile test on the sample prepared in step S2, and unloading the sample in sequence after reaching the test termination condition; S4, continuing to carry out biaxial tensile tests on the biaxial tensile specimen after the tensile test in step S3 according to different loading ratios, until the biaxial tensile specimen breaks, and obtaining its ultimate strain values ​​in two tensile directions; S5, preparing a uniaxial tensile specimen, performing a uniaxial tensile test on the uniaxial tensile specimen, removing the specimen after reaching the termination condition, and performing the uniaxial tensile test again until the uniaxial tensile specimen breaks; S6, obtaining the stress-strain curve in the second uniaxial tensile test in step S5, and calculating the instability strain value of the material; S7, correcting the limit strain value in the large-scale stretching direction obtained in step S3 to obtain a corrected limit strain value in the large-scale direction; S8. Plot the limit strain value in the large-scale stretching direction corrected in step S7 and the limit strain value in another stretching direction obtained in step S3 in the same coordinate system to form a corrected limit strain judgment curve, and input the curve into the forming simulation software of the part to continue the analysis and calculation of the secondary forming process. If the limit strain point of each process condition calculated by the forming simulation software is less than the corrected limit strain value, the result after the part is formed is safe. Otherwise, there is a risk of instability in the forming of the part.

2. The multi-process forming determination method based on biaxial tensile limit strain according to claim 1, characterized in that: In step S3, the termination condition of the biaxial tensile test corresponds to the limit strain values ​​of the limit strain point in two directions obtained in step S1.

3. The multi-process forming determination method based on biaxial tensile limit strain according to claim 1, characterized in that: In the step S4, there are at least two loading ratios.

4. The multi-process forming determination method based on biaxial tensile limit strain according to claim 1, characterized in that: In step S5, the termination condition of the uniaxial tensile test is: comparing the ultimate strain values ​​of the ultimate strain point determined in step S1 in two directions, and selecting the larger ultimate strain value in the two directions as the termination condition of the uniaxial tensile test.

5. The multi-process forming determination method based on biaxial tensile limit strain according to claim 1 is characterized in that: In the step S6, the instability strain value of the material=the ultimate strain value of the material-the strain value corresponding to the maximum stress point.

6. The multi-process forming determination method based on biaxial tensile limit strain according to claim 5, characterized in that: In the step S7, the corrected limit strain value in the large-scale direction = the instability strain value of the material / the limit strain value of the material.

7. The multi-process forming determination method based on biaxial tensile limit strain according to claim 6 is characterized in that: In step S8, the coordinate system uses the strain value in the small-ratio stretching direction as the horizontal coordinate and the strain value in the large-ratio stretching direction as the vertical coordinate.

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