Method for evaluating influence of pre-deformation on formability of high-strength steel edge portion

Abstract

The application discloses an evaluation method for the influence of pre-deformation on the edge forming property of high-strength steel, which comprises the following steps: (1) processing a sample to be measured into a rectangular wide and long strip sample; (2) stretching the wide and long strip sample until it is broken to determine the maximum uniform deformation A that can be borne; (3) taking a plurality of wide and long strip samples, respectively applying different degrees of pre-deformation to obtain pre-deformation samples; (4) punching each pre-deformation sample into a standard tensile sample; (5) directly stretching each standard tensile sample until it is broken and fails; (6) measuring the uniform elongation A and the total elongation A0 of each broken sample, and calculating the instability elongation PUE=A0-A of each broken sample, which is used as an evaluation index of the edge forming property of high-strength steel. g The method is convenient, simple, easy to operate, has a wide application range and strong engineering application guiding property, and requires a small number of samples. g ​

Description

Technical Field

[0001] This invention relates to the field of sheet metal forming performance testing technology, and in particular to an evaluation method for the influence of pre-deformation on the edge forming performance of high-strength steel. Background Technology

[0002] High-strength steel and advanced high-strength steel, due to their high strength and good plasticity, can meet the dual goals of lightweighting and collision safety requirements of automobiles, and their application in car body is increasing. As a result, more and more quality problems such as edge cracking are being exposed.

[0003] As the surface features of parts become increasingly complex, single-pass forming is no longer sufficient to capture the characteristics of the target part. High-strength steel parts typically require five or six processes to complete, including drawing, trimming, flanging / bending / expansion, shaping, and punching. During the initial drawing process, the sheet metal undergoes varying degrees of pre-deformation. When flanging / bending / expansion is performed after blanking and punching, the edge forming performance differs from that of sheet metal without pre-deformation loading and without drawing. Currently, research generally considers the expansion rate to be the most direct and effective way to characterize the edge forming performance of materials. However, the measured expansion rate is an indicator of the edge forming performance of the original sheet metal and has limited engineering guidance for parts that have undergone pre-deformation before bending / flanging. Therefore, there is an urgent need to develop a method to evaluate the impact of pre-deformation on the edge forming performance of high-strength steel, providing guidance for material selection and engineering applications of complex high-strength steel parts. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a rapid and reasonable method for evaluating the influence of pre-deformation on the edge forming performance of high-strength steel.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention includes the following steps: (1) processing the sample to be tested into a rectangular wide strip sample;

[0006] (2) Stretch the wide strip specimen until it breaks, and determine the maximum uniform deformation A that it can withstand.

[0007] (3) Take several wide strip specimens and apply different degrees of pre-deformation to obtain pre-deformed specimens;

[0008] (4) Punch each pre-deformed specimen into a standard tensile specimen.

[0009] (5) Each standard tensile specimen is directly stretched until it breaks.

[0010] (6) Measure the uniform elongation value A of each tensile specimen. g Given the total elongation value A0, the buckling elongation PUE of each tensile specimen is calculated as: PUE = A0 - A gThe instability elongation is used as an evaluation index for the edge forming performance of high-strength steel.

[0011] Furthermore, in step (3), the range of the pre-deformation amount is 0% to (A-2)%.

[0012] Furthermore, the pre-deformation amount is gradient-selected within the selection range.

[0013] Furthermore, in step (4), the same blanking gap as the trimming process on the production floor is used for blanking.

[0014] Furthermore, the following steps are also included: calculate and sort out the instability elongation rate (PUE) values ​​under different pre-deformation amounts, and plot the relationship curve between pre-deformation amount and PUE to obtain the relationship curve of the influence of pre-deformation amount on edge forming performance.

[0015] The beneficial effects of adopting the above technical solution are as follows: This invention first applies a certain amount of pre-deformation to a large rectangular strip sample to simulate the drawing deformation in the production site, and then punches and stretches the sample to simulate the edge quality of the punching blank in the production site. The instability elongation rate (PUE) calculated after tensile failure is used to evaluate the local forming performance after pre-deformation. This invention is convenient, simple, and easy to operate. It requires a small number of samples and has a wide range of applications. It can effectively simulate the edge forming ability of high-strength steel parts after edge deformation following drawing and trimming, and has strong guidance for engineering applications. The forming performance of any part obtained by edge forming methods such as bending / flanging / drilling after drawing, trimming, and punching can be evaluated using this method. It has high testing efficiency, less human intervention, and a short test cycle. Attached Figure Description

[0016] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0017] Figure 1 These are images of rectangular strip specimens after different pre-deformation amounts were applied, as shown in Embodiment 1 of the present invention.

[0018] Figure 2 This is a drawing of a tensile specimen punched from a rectangular strip specimen according to Embodiment 1 of the present invention;

[0019] Figure 3 This is a sample image of the specimen after it was directly pulled apart without grinding the edges according to Embodiment 1 of the present invention;

[0020] Figure 4 This is a graph showing the relationship between the pre-deformation amount and the edge forming performance obtained in Embodiment 1 of the present invention.

[0021] Figure 5 This is a graph showing the relationship between the pre-deformation amount and the edge forming performance obtained in Embodiment 2 of the present invention. Detailed Implementation

[0022] Example 1: The evaluation method for the influence of pre-deformation on the edge forming performance of high-strength steel takes 1.2mm thick 590DP produced by a steel material supplier as an example and adopts the following steps.

[0023] (1) The sample to be tested is processed into a rectangular wide strip specimen. The size of the wide strip specimen is only required to achieve uniform deformation in the middle of the specimen, and the uniform deformation area can be punched out into a tensile specimen. The specific length and width dimensions of the specimen can be adjusted according to the shape of the clamp of the tensile testing machine. That is, the width of the specimen should be greater than the width of the punched tensile specimen after tensile pre-deformation, and the length of the specimen should be to ensure that the uniform deformation area during the pre-stretching process covers the stress area of ​​the subsequent punched specimen, and preferably covers the clamping end. In this embodiment, the width of the wide strip specimen is 40 mm and the length is 400 mm.

[0024] (2) The wide strip specimen was stretched on a tensile testing machine until it broke, and the maximum uniform deformation A that it could withstand was determined to be 14.32%.

[0025] (3) Take several wide strip specimens and apply different degrees of pre-deformation within the range of 0% to (A-2)% to obtain pre-deformed specimens; the interval gradient of the pre-deformation amount can be equal or unequal, as long as the deformation amount is uniform and equal at all points in the deformation area; it is best to perform three or more repeated tests for each pre-deformation amount. Figure 1 As shown, in this embodiment, seven different pre-deformation amounts were selected within the range of 0% to 12.32%, namely 0%, 1%, 3%, 5%, 7%, 9%, and 12%. Each pre-deformation amount was subjected to three repeated tests. Therefore, in this embodiment, 21 wide strip samples were taken, and a total of 21 tests were conducted.

[0026] (4) Using the same blanking clearance as the production site, each pre-deformed specimen is blanked into a standard tensile specimen, such as... Figure 2 As shown, in actual production, the blanking gap is generally 10% to 15% of the material thickness, which can be adjusted according to the actual situation. In this embodiment, a blanking gap of 0.1 times the material thickness is used, with a gap of 0.12mm.

[0027] (5) Each standard tensile specimen after punching is subjected to tensile testing without grinding the edges until it breaks. Figure 3 As shown.

[0028] (6) Measure the uniform elongation value A of each tensile specimen. g Given the total elongation value A0, the instability elongation PUE is calculated as PUE = A0 - A g The average value of the repeated tests for each pre-deformation amount is used as the material performance evaluation index; the measurement and calculation results of the 21 tests in this embodiment are shown in Table 1;

[0029] Table 1: Measurement and Calculation Results of Example 1

[0030]

[0031] In Table 1, the average PUE is the average of the PUE obtained from the three tests.

[0032] (7) Based on the measurements in step (6), calculate the instability elongation (PUE) value under different pre-deformation amounts, and take the average value of three tests as the final instability elongation of the material, as shown in Table 1; plot the relationship curve between pre-deformation amount and PUE to obtain the relationship curve of the influence of pre-deformation amount on edge forming performance, as shown in Table 1. Figure 4 As shown.

[0033] Example 2: The evaluation method for the influence of pre-deformation on the edge forming performance of high-strength steel takes 1.0 mm thick 980QP produced by a steel material supplier as an example, and adopts the following steps.

[0034] (1) The sample to be tested is processed into a rectangular wide strip specimen. The size of the wide strip specimen is only required to achieve uniform deformation in the middle of the specimen, and the uniform deformation area can be punched out into a tensile specimen. The specific length and width dimensions of the specimen can be adjusted according to the shape of the clamp of the tensile testing machine. That is, the width of the specimen should be greater than the width of the punched tensile specimen after tensile pre-deformation, and the length of the specimen should be to ensure that the uniform deformation area during the pre-stretching process covers the stress area of ​​the subsequent punched specimen, and preferably covers the clamping end. In this embodiment, the width of the wide strip specimen is 40 mm and the length is 400 mm.

[0035] (2) The wide strip specimen was stretched on a tensile testing machine until it broke, and the maximum uniform deformation A that it could withstand was determined to be 13.49%.

[0036] (3) Take several wide strip specimens and apply different degrees of pre-deformation within the range of 0% to (A-2)% to obtain pre-deformed specimens; the interval gradient of the pre-deformation amount can be equal or unequal, as long as the deformation amount is uniform and equal at all points in the deformation area; it is best to perform three or more repeated tests for each pre-deformation amount. Figure 1 As shown, in this embodiment, six different pre-deformation amounts were selected within the range of 0% to 11.49%, namely 0%, 2%, 4%, 6%, 8%, and 10%. Each pre-deformation amount was subjected to three repeated tests. Therefore, in this embodiment, 18 wide strip samples were taken, and a total of 18 tests were conducted.

[0037] (4) Using the same blanking clearance as the production site, each pre-deformed specimen is blanked into a standard tensile specimen, such as... Figure 2 As shown, in actual production, the blanking gap is generally 10% to 15% of the material thickness, which can be adjusted according to the actual situation. In this embodiment, a blanking gap of 0.1 times the material thickness is used, with a gap of 0.10 mm.

[0038] (5) Each standard tensile specimen after punching is subjected to tensile testing without grinding the edges until it breaks. Figure 3 As shown.

[0039] (6) Measure the uniform elongation value A of each tensile specimen. g Given the total elongation value A0, the instability elongation PUE is calculated as PUE = A0 - A g The average value of the repeated tests for each pre-deformation amount is used as the material performance evaluation index; the measurement and calculation results of the 18 tests in this embodiment are shown in Table 2;

[0040] Table 2: Measurement and Calculation Results of Example 2

[0041]

[0042] In Table 2, the average PUE is the average of the PUE obtained from the three tests.

[0043] (7) Based on the measurements in step (6), calculate the instability elongation (PUE) value under different pre-deformation amounts, and take the average value of the three tests as the final instability elongation of the material, as shown in Table 2; plot the relationship curve between pre-deformation amount and PUE to obtain the relationship curve of the influence of pre-deformation amount on edge forming performance, as shown in Table 2. Figure 5 As shown.

Claims

1. A method for evaluating the influence of pre-deformation on the edge forming performance of high-strength steel, characterized in that, The steps include: (1) processing the sample to be tested into a rectangular strip sample; (2) Stretch the wide strip specimen until it breaks, and determine the maximum uniform deformation A that it can withstand. (3) Take several wide strip specimens and apply different degrees of pre-deformation to obtain pre-deformed specimens; (4) Punch each pre-deformed specimen into a standard tensile specimen. (5) Each standard tensile specimen is directly stretched until it breaks. (6) Measure the uniform elongation value A of each tensile specimen. g Given the total elongation value A0, the buckling elongation PUE of each tensile specimen is calculated as: PUE = A0 - A g The instability elongation is used as an evaluation index for the edge forming performance of high-strength steel.

2. The method for evaluating the influence of pre-deformation on the edge forming performance of high-strength steel according to claim 1, characterized in that: In step (3), the range of the pre-deformation amount is 0% to (A-2)%.

3. The method for evaluating the influence of pre-deformation on the edge forming performance of high-strength steel according to claim 2, characterized in that: The pre-deformation amount is selected in a gradient within the selected range.

4. The method for evaluating the influence of pre-deformation on the edge forming performance of high-strength steel according to claim 1, characterized in that: In step (4), the same blanking gap as the trimming process on the production floor is used for blanking.

5. The method for evaluating the influence of pre-deformation on the edge forming performance of high-strength steel according to any one of claims 1-4, characterized in that, The process also includes the following steps: calculating the instability elongation (PUE) value under different pre-deformation amounts, and plotting the relationship curve between the pre-deformation amount and PUE to obtain the relationship curve of the influence of the pre-deformation amount on the edge forming performance.

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