Finite element judgment method for predicting hole flanging cracks

Abstract

The invention relates to a finite element judgment method for predicting hole flanging cracks, which comprises the following steps of: screening hole flanging meeting conditions according to a priority sequence of minimum hole flanging corner radius > minimum hole flanging diameter > maximum flanging height, and carrying out a hole flanging simulation test by utilizing finite element software. Comparing the stress value of the unit with the maximum stress of the neutral layer with the hole flanging crack in the simulation test with the maximum stress in the input stress-strain curve so as to correct the stress curve of the material until the stress value of the unit with the maximum stress in the simulation test result is equal to the maximum stress in the input original stress-strain curve; predicting hole flanging deformation characteristics and hole flanging cracks of the material; according to the method, the technical problem that only fixed-aperture hole flanging deformation characteristics can be predicted by adopting a traditional fixed-aperture method is solved, the hole flanging crack prediction precision of the part is greatly improved, the method is very suitable for occasions where parts with various different-aperture characteristics are predicted, and the application requirements of engineering practice and scientific research work are widely met.

Description

Technical Field

[0001] The present invention relates to the technical field of finite element determination, and in particular to a finite element determination method for predicting hole-turning cracks. Background Art

[0002] In the stamping process of automobile parts, the punching process is often used to make holes of various shapes at a perpendicular angle to the sheet material to meet the functional requirements of the parts. However, since the sheet material will undergo complex deformation modes such as radial, tangential, and bending during the punching process, the material is prone to microcracks of varying degrees during the punching process, which will lead to insufficient rigidity of the parts after the punching. If the parts with punching cracks are assembled with other parts, the assembly stability between the parts will be seriously reduced and the service requirements of the parts cannot be met. Therefore, it is very important to develop a finite element determination method for predicting punching cracks.

[0003] At present, the existing technical means in the industry often use a fixed aperture as a benchmark to perform fixed aperture punching on the material on the punching die to predict the punching characteristics of all different apertures of the material. In fact, this method can only predict the punching deformation of the fixed aperture characteristics, and the prediction error for the punching cracks caused by different fixed aperture characteristics is large, which cannot meet the needs of engineering practice and scientific research work.

[0004] The Chinese patent with publication number CN111898220A discloses a method for prejudging cracking of a punched hole, a storage medium and an electronic device, including: reading a structural model in a 3D drawing of a product; defining the opening direction of a concave hole used for punching a hole in the 3D drawing of the product as a vertical direction, and obtaining the concave hole selected by the engineer on the 3D drawing and the input material tensile strength σ, the inner diameter D of the hole after punching the hole, the material thickness t0, and the inner radius r of the punched hole; calculating the maximum straight height h of the punched hole according to the tensile strength σ of the material, the inner diameter D of the hole after punching the hole, the material thickness t0, and the inner radius r of the punched hole, and calculating the maximum straight height h of the punched hole according to the straight height of the concave hole and the maximum straight height h of the punched hole. The comparison results are used to predict the risk of cracking after the recessed hole is punched; however, this patent judges the cracking for a single punching feature, and the whole process requires a large number of integral operations to obtain the required punching height h. This process is not efficient, and it requires repeated mathematical operations for parts with multiple punching features, which is time-consuming, labor-intensive and inefficient. Moreover, they are all purely theoretical calculations without actual verification, so the prediction accuracy cannot be examined. Because the higher the strength of the material, the lower the hole expansion rate, and the hole expansion rate of materials with the same tensile strength is not unique, therefore, predicting the hole cracking according to the curve fitting results described in the patent will inevitably produce huge errors. Summary of the invention

[0005] The present invention provides a finite element determination method for predicting hole punching cracks, which can effectively predict hole punching cracks with different aperture characteristics, overcomes the technical difficulty that the traditional fixed aperture method can only predict the deformation characteristics of fixed aperture punching, and greatly improves the prediction accuracy of hole punching cracks of parts.

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

[0007] A finite element determination method for predicting hole-turning cracks comprises the following steps:

[0008] S1. Determine the number of holes to be punched, the radius of the punching angle, the punching diameter and the punching height according to the characteristics of the target part;

[0009] S2, screening all the holes determined according to step S1 in the order of smallest hole bending radius > smallest hole diameter > largest flanging height, determining the holes that meet the screening conditions in the above priority order, and establishing a finite element hole-cutting process model according to the characteristics of the screened holes;

[0010] S3, inputting the uniaxial tensile stress-strain curve of the material into the finite element model to define it as material properties, and using finite element software to carry out hole-flanging simulation tests;

[0011] S4, comparing and correcting the maximum stress value of the unit of the neutral layer where the hole-turning crack appears in the simulation test with the maximum stress in the input stress-strain curve. If the maximum stress unit in the simulation test is less than the maximum stress of the material itself, the overall stress on the stress curve of the material is increased; if the maximum stress unit in the simulation test is greater than the maximum stress of the material itself, the overall stress on the stress curve of the material is reduced;

[0012] S5, defining the corrected stress-strain curve as a new material property, continuing to carry out the hole-turning simulation test, and then repeating step S4 until the stress value of the unit with the maximum force in the simulation test result is equal to the maximum stress in the input original stress-strain curve;

[0013] S6. The corrected stress-strain curve input at this time can effectively describe the mechanical behavior of the material itself in the simulation analysis, predict the material's hole deformation characteristics and hole cracks, and also meet the use requirements of other hole diameters of the parts.

[0014] Furthermore, in step S4, the overall stress increase on the stress curve of the material specifically includes: if the maximum stress unit in the simulation test is less than the maximum stress of the material itself, the maximum stress difference between the two is calculated as X=(maximum stress of material-maximum stress of simulation) / maximum stress of material×100%, and the overall stress in the material curve is increased by X / 10.

[0015] Furthermore, in step S4, reducing the overall stress on the stress curve of the material specifically includes: if the maximum stress unit in the simulation test is greater than the maximum stress of the material itself, calculating the maximum stress difference ratio Y=(simulation maximum stress-material maximum stress) / material maximum stress×100%, then reducing the overall stress in the material curve by Y / 10.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention is based on the material deformation mechanism in the punching process, associates the punching deformation characteristics of the material with the punching characteristic parameters, and cleverly combines the microscopic deformation mechanism of the punching process with the finite element analysis method to accurately and effectively predict the punching cracks of materials with different aperture characteristics. It can cover all the punching characteristics on the entire part for prediction, and overcomes the technical difficulty that the traditional fixed aperture method can only predict the fixed aperture punching deformation characteristics. The finite element curve is compared and optimized with the results of the actual test curve, which greatly improves the prediction accuracy of the punching cracks of parts and components, ensures the prediction accuracy of the actual punching results, improves work efficiency and reduces mold manufacturing costs. It is very suitable for predicting parts with a variety of different aperture characteristics, and widely meets the application requirements of engineering practice and scientific research work. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the characteristic structure of the hole turning according to the present invention.

[0019] Figure 2 It is a comparison diagram of the original input curve and the simulated output curve described in the present invention.

[0020] Figure 3 It is a comparison diagram between the modified input curve and the simulated output curve of the present invention.

[0021] In the figure: 1. Radius of the bend of the hole 2. Bend of the hole 3. Height of the hole DETAILED DESCRIPTION

[0022] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings:

[0023] The present invention discloses a finite element determination method for predicting punching cracks. The method is based on the deformation mechanism of materials in the punching process, associates the punching deformation characteristics of the material with the punching characteristic parameters, and accurately predicts the punching cracks of the material by ingeniously combining the microscopic deformation mechanism of the punching process with the finite element analysis method. The specific method and steps are as follows:

[0024] S1. Determine the number of holes to be punched, the radius of the punching angle 1, the punching diameter and the punching height 3 according to the characteristics of the target part. Figure 1In this embodiment, the number of holes to be punched is determined to be 6 according to the characteristics of the target part, and the punching angle radius 1, the punching diameter and the punching height 3 of each hole are shown in Table 1.

[0025] Table 1

[0026] Flip hole number Flanging corner radius / mm Hole diameter / mm Hole height / mm 1 2.4 31 2.1 2 2.6 35 2.4 3 2.2 32 2.2 4 3.2 32 2.3 5 3.1 38 2.2 6 2.8 34 2.3

[0027] S2. According to the priority order of the smallest radius of the punching angle 2 > the smallest punching diameter > the largest flanging height, all the punching holes determined according to step S1 are screened, and the punching hole that can meet the screening conditions is determined to be hole No. 3 in Table 1. A finite element punching process model is established according to the characteristics of the punching hole.

[0028] S3. Input the uniaxial tensile stress-strain curve of the material into the finite element model to define it as the material property, and use the finite element software to carry out the hole-flanging simulation test.

[0029] S4. Compare and correct the maximum unit stress value of the neutral layer with the hole-turning crack in the simulation test, 642MPa, with the maximum stress of 612MPa in the input original stress-strain curve, as shown in the following example: Figure 2 As shown, the maximum stress unit in the simulation test is greater than the maximum stress of the material itself, and the maximum stress difference between the two is calculated as Y=(642-612) / 612×100%=4.9%, which reduces the overall stress of the material curve by 0.49%.

[0030] S5, the modified stress-strain curve is positioned as the new material property, the hole-turning simulation test is continued, and then step S4 is repeated until the stress value of the maximum stress unit in the simulation test result is equal to the maximum stress of 612MPa in the input original stress-strain curve, such as Figure 3 shown.

[0031] S6. The corrected stress-strain curve input at this time can effectively describe the mechanical behavior of the material itself in the simulation analysis, so as to accurately predict the material's hole deformation characteristics and hole cracks, and at the same time meet the use requirements of the other 6 apertures of the part.

[0032] The above embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the above embodiments. The methods used in the above embodiments are conventional methods unless otherwise specified.

Claims

1. A finite element determination method for predicting hole-turning cracks, characterized in that: The following steps are involved: S1. Determine the number of holes to be punched, the radius of the punching angle, the punching diameter and the punching height according to the characteristics of the target part; S2, screening all the holes determined according to step S1 in the order of smallest hole bending radius > smallest hole diameter > largest flanging height, determining the holes that meet the screening conditions in the above priority order, and establishing a finite element hole-cutting process model according to the characteristics of the screened holes; S3, inputting the uniaxial tensile stress-strain curve of the material into the finite element model to define it as material properties, and using finite element software to carry out hole-flanging simulation tests; S4, comparing and correcting the maximum stress value of the unit of the neutral layer where the hole-turning crack appears in the simulation test with the maximum stress in the input stress-strain curve. If the maximum stress unit in the simulation test is less than the maximum stress of the material itself, the overall stress on the stress curve of the material is increased; if the maximum stress unit in the simulation test is greater than the maximum stress of the material itself, the overall stress on the stress curve of the material is reduced; S5, defining the corrected stress-strain curve as a new material property, continuing to carry out the hole-turning simulation test, and then repeating step S4 until the stress value of the unit with the maximum force in the simulation test result is equal to the maximum stress in the input original stress-strain curve; S6. The corrected stress-strain curve input at this time can effectively describe the mechanical behavior of the material itself in the simulation analysis, predict the material's hole deformation characteristics and hole cracks, and also meet the use requirements of other hole diameters of the parts.

2. A finite element determination method for predicting hole-turning cracks according to claim 1, characterized in that: In step S4, the overall stress on the stress curve of the material is increased specifically including: if the maximum stress unit in the simulation test is less than the maximum stress of the material itself, the maximum stress difference between the two is calculated as X=(maximum stress of material-maximum stress of simulation) / maximum stress of material×100%, and the overall stress in the material curve is increased by X / 10.

3. The finite element determination method for predicting hole-turning cracks according to claim 2 is characterized in that: The step S4 of reducing the overall stress on the stress curve of the material specifically includes: if the maximum stress unit in the simulation test is greater than the maximum stress of the material itself, the maximum stress difference between the two is calculated as a ratio Y=(simulation maximum stress-material maximum stress) / material maximum stress×100%, and the overall stress in the material curve is reduced by Y / 10.

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