Sheet Metal Press Die Design for Sheared Edge Crack Prediction
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Solution Overview
Problem
High-strength steel sheets used in press forming often experience cracking on sheared end faces due to stretch flange and bending deformations, with existing prediction methods failing to accurately predict bending cracks.
Innovation Solution
A deformation limit evaluation method that uses an index value derived from gradients of surface stress distributions in the sheet thickness direction and a direction away from the sheared surface to evaluate and predict crack occurrence, incorporating stress gradients from FEM analysis and testing methods like V-shaped bending and notch tensile tests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-strength steel sheets are used for weight reduction and collision safety, then vehicle body weight is reduced and passenger protection is improved, but cracking occurs on sheared end faces due to stretch flange and bending deformations during press forming
Solution Approach 1:
The invention performs preliminary evaluation of the deformation limit using an index value calculated from stress gradients before actual press forming. By calculating the index value from FEM analysis results that represent stress gradients in the sheet thickness direction and along the sheared end face, the method predicts crack occurrence in advance, allowing prevention measures to be taken before manufacturing defects occur
Solution Approach 2:
The invention replaces traditional empirical or simplified mechanical evaluation methods with a sophisticated FEM-based stress gradient analysis system. By substituting conventional deformation assessment with detailed finite element analysis of stress distribution and gradients, the method achieves more accurate prediction of crack behavior in high-strength steel sheets
2Measurement precision
If existing prediction methods considering strain gradient or stress gradient in in-plane direction are used, then stretch flange crack prediction is improved, but bending cracks on sheared end face cannot be predicted
Solution Approach 1:
The invention creates a universal prediction method that handles both stretch flange cracks and bending cracks through a single index value approach. By formulating the index value to incorporate stress gradients in multiple directions (thickness direction and along the sheared end face), the method becomes adaptable to various crack types occurring during press forming of high-strength steel sheets
Solution Approach 2:
The invention changes the evaluation parameters from traditional single-direction strain or stress gradients to a composite index value that integrates stress gradients in two critical directions. This parameter transformation allows the method to capture the complex stress state causing both stretch flange and bending cracks, expanding its applicability
3Measurement precision
If FEM analysis is performed to obtain stress distribution and gradients, then deformation limit evaluation accuracy is improved, but calculation complexity and time consumption increase
Solution Approach 1:
The invention extracts only the essential information needed for crack prediction from the comprehensive FEM analysis results. Instead of utilizing the entire stress field data, the method specifically extracts stress gradient values in two critical directions (sheet thickness direction and along the sheared end face) to calculate the index value, simplifying the evaluation process while maintaining accuracy
Data Source
AI summary
To prevent a crack from occurring on a sheared end face due to press forming, a technology is provided for evaluating and predicting a crack limit of the sheared end face of a metal sheet and determining press forming conditions. In a deformation limit evaluation method for, when deforming by press forming a metal sheet subjected to shearing, evaluating a deformation limit of the sheared end face of the metal sheet, the deformation limit is evaluated by an index value obtained from two stress gradients at an evaluation position among stress distributions occurring in the vicinity of the sheared end face of the metal sheet due to the press forming, which gradients are a stress gradient in a sheet thickness direction and a stress gradient in a direction away from the sheared end face.