Thickness reduction limit safety margin value calculation method

Abstract

The invention relates to the technical field of automobile production, in particular to a thickness reduction limit safety margin value calculation method. According to the method, the safety margin value is reflected as the direct influence of thickness reduction on material stamping, the problems that a traditional calculation method is obscure, difficult to understand and not visual are solved, and the safety margin value of grid analysis is better applied to stamping workshops of automobile factories. According to the method, the problem that the existing grid analysis cannot completely display the thickness reduction rate and has no safety margin value is solved, and more comprehensive analysis and control of the grid analysis on the automobile sheet stamping part are realized. The method can greatly improve the judgment accuracy of the stamping performance of the automobile sheet, meets the requirements of actual stamping production of the automobile sheet, and can ensure the precision of material selection, improve the stamping production efficiency of automobile parts and reduce the processing cost while accurately evaluating the stamping performance of the automobile sheet.

Description

Technical Field

[0001] The invention relates to the technical field of automobile production, and in particular to a method for calculating a thickness reduction limit safety margin value. Background Art

[0002] Automotive steel sheets have very high requirements for their stamping performance, especially some complex automotive panels require the automotive steel sheets to have excellent stamping performance. An accurate judgment of the stamping performance of automotive steel sheets will improve the efficiency of the use of automotive steel sheets and the productivity of automotive parts stamping. On the contrary, if the stamping performance of automotive steel sheets cannot be accurately evaluated, it will affect the actual application of automotive steel sheets, increase the scrap rate of stamping parts in the production process, and increase the difficulty of car users in model design and material selection, and increase the cost of automobile manufacturing.

[0003] At present, the evaluation of the stamping performance of automobile steel plates is mainly based on the sheet metal forming grid strain measurement and analysis technology. The sheet metal forming grid strain measurement and analysis is based on industrial close-range photogrammetry. The position of each small dot in multiple photos is calculated with high precision, and then the spatial coordinates of each dot are calculated based on the data of photos at different angles using the photogrammetry method. Through these dot arrays, the deformed shape of the part can be defined. By calculating the distance change between the dots, the deformation and strain of the part can be obtained. Using the above data, the strain distribution, hot spot area and thickness change of the plate can be calculated (assuming that the volume remains unchanged). High-precision strain measurement can process data of more than 100,000 points at the same time. The dot spacing as the reference length for strain calculation is usually 1mm to 6mm. The strain distribution and thickness change results are displayed on the three-dimensional model of the formed part in the form of a color temperature diagram. Through the usual rotation and other operations, the measurement results and the forming process can be better understood. The sheet metal forming grid strain measurement and analysis technology is often used to measure critical deformation parts, solve complex forming problems, optimize stamping processes, inspect stamping dies, and verify and optimize the results of simulation calculations.

[0004] At present, when the forming limit diagram and the calculation of the safety margin value are applied in the field of automobile factories, it is difficult to see the relationship between the features due to the complex presentation of the data, resulting in the technical personnel of the automobile factory being unable to intuitively understand the data status. Summary of the invention

[0005] In order to overcome the shortcomings of the existing technology, a method for calculating the safety margin value of the thickness thinning limit is provided, which is convenient for automobile factory technicians to intuitively understand the strain distribution of parts, hot spots and thickness changes of plates directly from the perspective of the material thickness thinning rate, which they are more familiar with, and better apply the safety margin value of grid analysis to the stamping workshop of the automobile factory.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for calculating a thickness reduction limit safety margin value, the method specifically comprising the following steps:

[0008] S1: The forming limit diagram (FLD) is converted into the thickness thinning limit diagram (TLD) by formula (1);

[0009] (1+ε1)×(1+ε2)×(1-ε3)=1 (1)

[0010] Where:

[0011] ε1 is the true strain value of the material principal strain;

[0012] ε2 is the true strain value of the secondary strain of the material;

[0013] ε3 is the thickness reduction rate of the material;

[0014] Calculate the material thickness reduction limit using the data from the forming limit curve data pair;

[0015] S2: Reduce the thickness reduction limit diagram by 3% to 15% and 15% to 25% as a whole by formula (2);

[0016] ε 3+ =(1+x%)×ε3 (2)

[0017] Where:

[0018] ε 3+ is the thickness reduction rate value under the latest calculated safety margin;

[0019] x is the set safety margin;

[0020] The safety margin curves of 3% to 9.5% and 10% to 20% of the limit thickness reduction diagram are calculated by increasing the limit values ​​of the thickness reduction rate by 3% to 9.5% and 10% to 20% respectively;

[0021] S3: Compare the TLD curve with the actual material deformation diagram in the grid experiment to obtain the thickness thinning safety margin value. The calculation formula is as follows:

[0022] λ=(ε3-ε0) / ε3×100% (3)

[0023] Where:

[0024] λ is the safety margin value of thickness reduction limit, %;

[0025] ε0 is the value of the actual material thickness thinning rate measured in the grid analysis experiment.

[0026] Furthermore, in S2, the thickness reduction limit diagram is proportionally reduced by 10% and 20% as a whole by formula (2).

[0027] Furthermore, in S2, the limit value of the thickness reduction rate is increased by 5% and 10% respectively to calculate the 5% and 10% safety margin curves of the limit thickness reduction diagram.

[0028] Furthermore, in S2, x is 3≤x<10 or 10≤x<20.

[0029] Furthermore, in S2, x is 5 or 10.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention reflects the safety margin value as the direct effect of thickness reduction on material stamping, overcomes the obscure and non-intuitive problems of traditional calculation methods, and better applies the safety margin value of grid analysis to the stamping workshop of automobile factories.

[0032] In addition, automobile sheet stampings generally have actual requirements for the thickness reduction rate of materials, but most materials will not break even if the thickness reduction rate is too large to meet the requirements of automobile factories; and the stress value is also within a controllable range. Therefore, in this case, the safety margin value of the thickness reduction rate is more important. The present invention solves the problem that the existing grid analysis does not fully display the thickness reduction rate and has no safety margin value, and realizes a more comprehensive analysis and control of automobile sheet stampings by grid analysis.

[0033] It can greatly improve the accuracy of judging the stamping performance of automobile plates, adapt to the needs of actual production of automobile plate stamping, accurately evaluate the stamping performance of automobile plates, ensure the accuracy of material selection, improve the production efficiency of automobile parts stamping, and reduce processing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a diagram of the actual deformation of the material compared with the FLD diagram of the present invention.

[0035] Figure 2 It is a TLD diagram of the present invention compared with an actual deformation diagram of the same material.

[0036] Figure 3 is a forming safety margin diagram of a spare tire compartment part stamped from HC180Y steel in Example 1;

[0037] Figure 4 is a forming safety margin diagram of a left front door inner panel part stamped by DC57D+Z steel in Example 2;

[0038] Figure 5It is a forming safety margin diagram of the DC56D+Z steel stamped roof cover part in Example 3. DETAILED DESCRIPTION

[0039] The following will be combined with examples of the present invention to clearly and completely describe the technical solution of the present invention. Obviously, the implementation case described is only one of the embodiments of the present invention, and those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar replacements and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0040] like Figure 1 , Figure 2 As shown, a method for calculating the thickness reduction limit safety margin value, the method specifically comprises the following steps:

[0041] S1: The forming limit diagram (FLD) is converted into the thickness thinning limit diagram (TLD) by formula (1);

[0042] (1+ε1)×(1+ε2)×(1-ε3)=1 (1)

[0043] Where:

[0044] ε1 is the true strain value of the material principal strain;

[0045] ε2 is the true strain value of the secondary strain of the material;

[0046] ε3 is the thickness reduction rate of the material;

[0047] The thickness reduction limit of the material is calculated using the data from the forming limit curve.

[0048] S2: Reduce the thickness reduction limit diagram by 10% and 20% in proportion as a whole through formula (2);

[0049] ε 3+ =(1+x%)×ε3 (2)

[0050] Where:

[0051] ε 3+ is the thickness reduction rate value under the latest calculated safety margin;

[0052] x is the set safety margin, x is 5 or 10.

[0053] The 5% and 10% safety margin curves of the limit thickness reduction diagram are calculated by increasing the limit value of the thickness reduction rate by 5% and 10% respectively.

[0054] S3: Compare the TLD curve with the actual material deformation diagram in the grid experiment to obtain the thickness thinning safety margin value. The calculation formula is as follows:

[0055] λ=(ε3-ε0)×100% (3)

[0056] Where:

[0057] λ is the safety margin value of thickness reduction limit, unit: %;

[0058] ε0 is the value of the actual material thickness thinning rate measured in the grid analysis experiment.

[0059] Embodiment 1:

[0060] like Figure 3 As shown in the figure, the spare tire compartment parts of a certain vehicle model are stamped and the material used is automotive steel HC180Y.

[0061] A set of ten specimens with a length of 180 mm and widths of 180 mm, 160 mm, 140 mm, 130 mm, 120 mm, 100 mm, 90 mm, 80 mm, 60 mm, and 40 mm were made from HC180Y automobile sheet by laser cutting or wire cutting.

[0062] The sample surface was sprayed with paint and a forming limit test was carried out. The forming limit point of each sample was determined by the rupture line regression method and connected into a line, which is the FLC curve of HC180Y material.

[0063] At the automobile sheet stamping site, a square grid is printed on the surface of the automobile sheet without external force by chemical etching before stamping.

[0064] After the stamping of the stamped parts is completed, the surface grid of the stamped parts is scanned and transmitted to the computer, the grid lines are scanned, the strain value of the surface grid is calculated, and the maximum strain value of the stamped parts is determined. In Example 1, the maximum thickness reduction rate of the HC180Y material roof cover part is measured to be 0.193463, and the secondary strain value under this thinning rate is 0.020835. The thickness reduction rate value on the FLD diagram under this secondary strain value is 0.299802

[0065] The thickness reduction safety margin of the part is calculated, that is, the difference between the maximum thickness reduction rate of the part and the thickness reduction rate on the FLD curve under the same strain is 0.106339. The forming safety margin of the spare tire compartment component Δ = (0.29802-0.193463) × 100% = 10.6339%. See the thickness reduction safety margin diagram Figure 3 .

[0066] Figure 3 The black curve is the TLC thickness thinning limit curve, the dark red line is the 10% safety margin line, and the colored dots are the actual deformation of the material. When all the actual deformation values ​​of the material are below the 10% safety margin line, the material deformation can be considered safe.

[0067] The safety margin of Example 1 is greater than 10%, indicating that the stamping performance of HC180Y steel meets the requirements of the spare tire compartment component.

[0068] Embodiment 2:

[0069] like Figure 4 As shown, according to the method and steps of Example 1, for the DC57D+Z automobile plate left front door inner panel component, the thickness safety margin Δ=2.5288% of the left front door inner panel component is obtained. Figure 4 The black curve is the TLC thickness reduction limit curve, the dark red line is the 10% safety margin line, and the colored dots are the actual deformation of the material. When part of the actual deformation value of the material is above the 10% safety margin line, the material deformation is considered to be risky. The safety margin is less than 10%, indicating that the stamping performance of DC57D+Z steel cannot meet the requirements of the left front door inner panel component, and cracks and hidden cracks may occur in actual production.

[0070] Embodiment 3:

[0071] like Figure 5 As shown in FIG. 1 , for the DC56D+Z automobile panel roof outer panel part, the thickness safety margin Δ of the roof outer panel part is obtained to be 13.7723%. Figure 5 The safety margin is greater than 10%, indicating that the stamping performance of DC56D+Z steel meets the requirements of the roof cover outer panel parts of this model. In this case, from the perspective of reducing automobile production costs, it is recommended that automobile manufacturers use DC56D+Z steel as the material for this part.

[0072] The present invention reflects the safety margin value as the direct effect of thickness reduction on material stamping, overcomes the obscure and non-intuitive problems of traditional calculation methods, and better applies the safety margin value of grid analysis to the stamping workshop of automobile factories.

[0073] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for calculating the safety margin value of thickness reduction limit, characterized in that: The method specifically comprises the following steps: S1: The forming limit diagram (FLD) is converted into the thickness thinning limit diagram (TLD) by formula (1); (1+ε1)×(1+ε2)×(1-ε3)=1 (1) Where: ε1 is the true strain value of the material principal strain; ε2 is the true strain value of the secondary strain of the material; ε3 is the thickness reduction rate of the material; Calculate the material thickness reduction limit using the data from the forming limit curve data pair; S2: Reduce the thickness reduction limit diagram by 3% to 15% and 15% to 25% as a whole by formula (2); e 3+ =(1+x%)×ε3 (2) Where: ε 3+ is the thickness reduction rate value under the latest calculated safety margin; x is the set safety margin; The safety margin curves of 3% to 9.5% and 10% to 20% of the limit thickness reduction diagram are calculated by increasing the limit values ​​of the thickness reduction rate by 3% to 9.5% and 10% to 20% respectively; S3: Compare the TLD curve with the actual material deformation diagram in the grid experiment to obtain the thickness thinning safety margin value. The calculation formula is as follows: λ=(ε3-ε0) / ε3×100% (3) Where: λ is the safety margin value of thickness reduction limit, %; ε0 is the value of the actual material thickness thinning rate measured in the grid analysis experiment.

2. A method for calculating the thickness reduction limit safety margin value according to claim 1, characterized in that: In S2, the thickness reduction limit diagram is proportionally reduced by 10% and 20% as a whole by formula (2).

3. A method for calculating the thickness reduction limit safety margin value according to claim 1, characterized in that: In S2, the limit value of the thickness reduction rate is increased by 5% and 10% respectively to calculate the 5% and 10% safety margin curves of the limit thickness reduction diagram.

4. A method for calculating the thickness reduction limit safety margin value according to claim 1, characterized in that: In S2, x is 3≤x<10 or 10≤x<20.

5. A method for calculating the thickness reduction limit safety margin value according to claim 4, characterized in that: In S2, x is 5 or 10.

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