A multi-process forming determination method based on bidirectional tensile ultimate strain

Abstract

The present application relates to a kind of multi-process forming determination methods based on bidirectional tensile limit strain, to the deformation mechanism experienced by material forming as basis, the complex loading characteristics of bidirectional tensile test is associated with the complex deformation process of part, the loading history of sheet metal is analyzed using the method of test and simulation, limit strain of material in different stages under different deformation direction is ingeniously obtained, to accurately determine the forming result of material;The present application can ensure that the limit strain of sheet metal will not be affected by bending stress and friction, overcome the technical problems that existing method cannot meet the multi-process forming determination of part, greatly improve the accuracy and effectiveness of forming simulation analysis, especially suitable for the occasion of multi-process forming analysis of metal sheet material, widely meet the application requirements of engineering practice and scientific research work.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal sheet bidirectional stretch forming, and particularly relates to a multi-process forming determination method based on bidirectional stretch limit strain. BACKGROUND

[0002] In the forming simulation analysis process of a metal sheet, a part with complex features is often encountered, and the part often needs to be formed by multiple processes to meet the processing and manufacturing requirements of the part. However, due to the work hardening characteristics of the metal material, the forming capacity of the sheet after different complex deformation-unloading-redeformation will change greatly, which will greatly affect 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 the sheet in the forming simulation analysis, but this method ignores the influence of the change of the material properties of the sheet during multiple deformations on the forming results, and the sheet will inevitably bear bending stress and friction force during the test. If this method is used for multi-process forming analysis of the part, a large determination error will inevitably occur, which cannot meet the application requirements of engineering practice and scientific research. SUMMARY

[0004] In view of the above problems, the purpose of the present application is to provide a multi-process forming determination method based on bidirectional stretch limit strain, which can ensure that the limit strain of the sheet is not affected by bending stress and friction, overcome the technical difficulties that the existing method cannot meet the multi-process forming determination of the part, and greatly improve the accuracy and effectiveness of the forming simulation analysis.

[0005] The technical scheme adopted by the present application is as follows:

[0006] The multi-process forming determination method based on bidirectional stretch limit strain provided by the present application comprises the following steps:

[0007] S1, a multi-process simulation process of a part is established by using a forming simulation analysis software, the limit strain point after the first forming process of the part is determined after simulation calculation, the limit strain value generated along the maximum strain direction and the limit strain value generated perpendicular to the maximum strain direction of the limit strain point are obtained;

[0008] S2, at least two bidirectional stretch samples are prepared;

[0009] S3, the samples prepared in step S2 are subjected to bidirectional stretch test by using a bidirectional stretch testing machine, and the samples are unloaded in turn after reaching the test termination condition;

[0010] S4. Continue to conduct biaxial tensile tests on the biaxial tensile specimens after the tensile test in step S3 according to different loading ratios until the biaxial tensile specimens break and obtain their 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 a uniaxial tensile test again until the uniaxial tensile specimen breaks.

[0012] S6. Obtain the stress-strain curve from the second uniaxial tensile test in step S5, and calculate the instability strain value of the material.

[0013] S7. Correct the ultimate strain value in the large-proportion tensile direction obtained in step S3 to obtain the corrected ultimate strain value in the large-proportion direction.

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

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

[0016] Furthermore, in step S4, the loading ratio is at least two different types.

[0017] Furthermore, in step S5, the termination condition for 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 of the ultimate strain values ​​in the two directions as the termination condition for 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 ultimate strain value in the large-proportion direction = the material's instability strain value ÷ the material's ultimate strain value.

[0020] Furthermore, in step S8, the coordinate system uses the strain value in the small-proportion tensile direction as the abscissa and the strain value in the large-proportion tensile direction as the ordinate.

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

[0022] The present invention proposes a multi-process forming determination method based on biaxial tensile ultimate strain, which can ensure that the ultimate strain of sheet metal is not affected by bending stress and friction. It overcomes the technical problem that existing methods cannot meet the multi-process forming determination of parts, and can greatly improve the accuracy and effectiveness of forming simulation analysis. It is especially suitable for multi-process forming analysis of thin metal sheet materials and can widely meet the application requirements of engineering practice and scientific research. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the stress-strain curve of the material in Embodiment 1 of the present invention;

[0024] Figure 2 This is a schematic diagram of the modified limit strain determination curve in Embodiment 1 of the present invention;

[0025] Figure 3 This is a schematic diagram of the stress-strain curve of the material in Embodiment 2 of the present invention;

[0026] Figure 4 This is a schematic diagram of the modified limit strain determination curve in Embodiment 2 of the present invention. Detailed Implementation

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] The multi-process forming judgment method based on biaxial tensile ultimate strain proposed in this invention specifically includes the following steps:

[0029] S1. Use forming simulation analysis software to establish a multi-process simulation process of the part. After simulation calculation, determine the limit strain point after the first forming process of the part, and obtain 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.

[0030] S2. Prepare at least two or more biaxial tensile specimens to meet the requirements of steps S3 and S4 for biaxial tensile testing.

[0031] S3. Use a biaxial tensile testing machine to perform a biaxial tensile test on the biaxial tensile specimen prepared in step S2. The termination condition of the test corresponds to the ultimate strain value in two directions of the ultimate strain point obtained in step S1. After the test termination condition is reached, the specimens are removed one by one.

[0032] S4. Continue to conduct biaxial tensile tests on the biaxial tensile specimens that have been stretched in step S3 according to at least two or more different loading ratios until the specimens break and the ultimate strain values ​​in the two tensile directions are obtained.

[0033] S5. Prepare a uniaxial tensile specimen. Compare the ultimate strain values ​​of the ultimate strain point determined in step S1 in two directions. Select the larger of the ultimate strain values ​​in the two directions as the termination condition for the uniaxial tensile test. After the termination condition is reached, remove the specimen and carry out the uniaxial tensile test again until the uniaxial tensile specimen breaks.

[0034] S6. Obtain the stress-strain curve from the second uniaxial tensile test in step S5, and calculate the unstable strain value of the material. The unstable strain value = the ultimate strain value of the material - the strain value corresponding to the maximum stress point.

[0035] S7. Correct the ultimate strain value in the large-proportion tensile direction obtained in step S3. The corrected ultimate strain value in the large-proportion direction = (ultimate strain value of the material - strain value corresponding to the maximum stress point) ÷ ultimate strain value of the material, where the instability strain value is obtained in step S6.

[0036] S8. Plot the corrected ultimate strain value in the large-scale tensile direction obtained in step S7 and the ultimate strain value in the other tensile direction obtained in step 3 on a coordinate system with the strain value in the small-scale tensile direction as the abscissa and the strain value in the large-scale tensile direction as the ordinate to form a corrected ultimate 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 ultimate strain point of each process condition calculated by the forming simulation software is less than the corrected ultimate strain value, the result of the part forming is safe. Otherwise, the part forming has the risk of instability.

[0037] The invention will be further illustrated below with specific examples:

[0038] Example 1

[0039] A multi-process forming judgment method based on biaxial tensile ultimate strain, taking a seat slide rail part as an example, is implemented as follows:

[0040] S1. Using forming simulation analysis software, a multi-process simulation process for the seat slide rail part is established. Using DP980 steel, the ultimate strain point after the first forming process of the part is determined through simulation calculation. The ultimate strain value generated along the maximum strain direction and the ultimate strain value generated perpendicular to the maximum strain direction at this ultimate strain point are 0.018 and 0.011, respectively.

[0041] S2. Prepare five biaxial tensile specimens to meet the biaxial tensile test requirements of steps S3 and S4.

[0042] S3. Use a biaxial tensile testing machine to perform a biaxial tensile test on the biaxial tensile specimen prepared in step S2. 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. After the test termination condition is reached, the specimens are removed one by one.

[0043] S4. The biaxial tensile specimens stretched in step S3 are subjected to biaxial tensile tests at five different loading ratios (4:0, 4:1, 4:2, 4:3, 4:4) until the specimens break and the ultimate strain values ​​in the two tensile directions are obtained, as shown in Table 1.

[0044]

[0045] S5. Prepare a uniaxial tensile specimen. Compare the ultimate strain values ​​of the ultimate strain point determined in step S1 in two directions. Select the larger of the ultimate strain values ​​in the two directions, 0.018, as the termination condition for the uniaxial tensile test. After reaching the termination condition, remove the specimen and repeat the uniaxial tensile test until the uniaxial tensile specimen breaks.

[0046] S6. Obtain the stress-strain curve from the second uniaxial tensile test in step S5, such as... Figure 1 As shown, the calculated instability strain value of the material is: (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. Correct the ultimate strain value in the large-proportion tensile direction obtained in step S3. The corrected ultimate strain value in the large-proportion tensile direction = the original ultimate strain value in the large-proportion tensile direction × (1 - instability strain value), where the instability strain value is obtained in step S6.

[0048] S8. Plot the ultimate strain value in the large-scale tensile direction (corrected in step S7) and the ultimate strain value in the other tensile direction (obtained in step S3) on a coordinate system with the strain value in the small-scale tensile direction as the abscissa and the strain value in the large-scale tensile direction as the ordinate, to form the corrected ultimate strain determination curve, as shown below. Figure 2 As shown, the limiting strain points for each deformation mode are 0.078, 0.049, 0.031, 0.033, and 0.035, respectively. This curve is input into the forming simulation software for this part for further analysis and calculation of the secondary forming process. The limiting strain points calculated in the subsequent forming simulation software for each process are smaller than the corrected limiting strain values. Figure 2If the values ​​calculated are 0.078, 0.049, 0.031, 0.033, and 0.035, then the result after the part is formed is safe.

[0049] Based on the deformation mechanism experienced during material forming, this invention associates the unique loading characteristics of biaxial tensile testing with the complex deformation process of parts. By combining experimental and simulation methods to analyze the loading history of sheet metal, it cleverly obtains the ultimate strain of the material in different deformation directions at different stages, so as to accurately determine the forming result of the material.

[0050] Example 2

[0051] A multi-process forming judgment method based on biaxial tensile ultimate strain, taking an automotive A-pillar reinforcement plate part as an example, is implemented as follows:

[0052] S1. Using forming simulation analysis software, a multi-process simulation process for the A-pillar reinforcement plate part was established. After simulation calculation using DP1180 steel, the ultimate strain point after the first forming process of the part was determined. The ultimate strain value generated along the maximum strain direction and the ultimate strain value generated perpendicular to the maximum strain direction at the ultimate strain point were obtained as 0.016 and 0.009, respectively.

[0053] S2. Prepare five biaxial tensile specimens to meet the biaxial tensile test requirements of steps S3 and S4.

[0054] S3. Use a biaxial tensile testing machine to perform a biaxial tensile test on the biaxial tensile specimen prepared in step S2. 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. After the test termination condition is reached, the specimens are removed one by one.

[0055] S4. The biaxial tensile specimens stretched in step S3 are subjected to biaxial tensile tests at five different loading ratios (4:0, 4:1, 4:2, 4:3, 4:4) until the specimens break and the ultimate strain values ​​in the two tensile directions are obtained, as shown in Table 2.

[0056]

[0057] S5. Prepare a uniaxial tensile specimen. Compare the ultimate strain values ​​of the ultimate strain point determined in step S1 in two directions. Select the larger of the ultimate strain values ​​in the two directions, 0.016, as the termination condition for the uniaxial tensile test. After reaching the termination condition, remove the specimen and repeat the uniaxial tensile test until the uniaxial tensile specimen breaks.

[0058] S6. Obtain the stress-strain curve from the second uniaxial tensile test in step S5, such as... Figure 3As shown, the calculated instability strain value of the material is: (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. Correct the ultimate strain value in the large-proportion tensile direction obtained in step S3. The corrected ultimate strain value in the large-proportion tensile direction = the original ultimate strain value in the large-proportion tensile direction × (1 - instability strain value), where the instability strain value is obtained in step S6.

[0060] S8. Plot the ultimate strain value in the large-scale tensile direction (corrected in step S7) and the ultimate strain value in the other tensile direction (obtained in step S3) on a coordinate system with the strain value in the small-scale tensile direction as the abscissa and the strain value in the large-scale tensile direction as the ordinate, to form the corrected ultimate strain determination curve, as shown below. Figure 4 As shown, the limiting strain points for each deformation mode are 0.066, 0.041, 0.029, 0.031, and 0.033, respectively. This curve is input into the forming simulation software for this part for further analysis and calculation of the secondary forming process. The limiting strain points calculated in the subsequent forming simulation software for each process are smaller than the corrected limiting strain values. Figure 4 If the values ​​calculated are 0.066, 0.041, 0.029, 0.031, and 0.033, then the result of the formed part is safe.

[0061] All matters not covered in this invention are common knowledge.

[0062] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A multi-process forming judgment method based on biaxial tensile ultimate strain, characterized in that, The method includes the following steps: S1. Use forming simulation analysis software to establish a multi-process simulation process of the part. After simulation calculation, determine the limit strain point after the first forming process of the part, and obtain 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. S2. Prepare at least two biaxial tensile specimens; S3. Use a biaxial tensile testing machine to perform a biaxial tensile test on the specimens prepared in step S2. After the test termination condition is reached, remove the specimens one by one. S4. Continue to conduct biaxial tensile tests on the biaxial tensile specimens after the tensile test in step S3 according to different loading ratios until the biaxial tensile specimens break and obtain their ultimate strain values ​​in two tensile directions. 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 a uniaxial tensile test again until the uniaxial tensile specimen breaks. S6. Obtain the stress-strain curve from the second uniaxial tensile test in step S5, and calculate the instability strain value of the material. S7. Correct the ultimate strain value in the large-proportion tensile direction obtained in step S3 to obtain the corrected ultimate strain value in the large-proportion direction. S8. Plot the ultimate strain value in the large-scale tensile direction corrected in step S7 and the ultimate strain value in the other tensile direction obtained in step S3 on the same coordinate system to form a corrected ultimate strain judgment curve. Input the curve into the part forming simulation software to continue the analysis and calculation of the secondary forming process. If the ultimate strain point of each process condition calculated by the forming simulation software is less than the corrected ultimate strain value, the result of the part forming is safe. Otherwise, the part forming has the risk of instability.

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

3. The multi-process forming determination method based on biaxial tensile ultimate strain according to claim 1, characterized in that: In step S4, the loading ratio is at least two different types.

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

5. The multi-process forming determination method based on biaxial tensile ultimate strain according to claim 1, characterized in that: 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.

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

7. The multi-process forming determination method based on biaxial tensile ultimate strain according to claim 6, characterized in that: In step S8, the coordinate system uses the strain value in the small-proportion tensile direction as the abscissa and the strain value in the large-proportion tensile direction as the ordinate.

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