Press Forming Blank Edge Shape for Stretch Flange Failure Control
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Solution Overview
Problem
Existing methods for preventing stretch flange fractures and wrinkles during press forming are complex and limited in design versatility, often requiring multiple prototype iterations and increased designer workload, as they struggle to uniformly suppress strain concentration across the entire component edge.
Innovation Solution
A blank shape determining method that involves analyzing forming failures through sheet thickness and plastic strain distributions, estimating failure regions, generating corrected blanks by adjusting edge shapes, and determining the optimal shape to minimize forming failure indices, thereby reducing the likelihood of stretch flange fractures and wrinkles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-strength steel sheet is adopted to reduce vehicle body weight and improve collision safety, then weight reduction and collision safety performance are improved, but formability and stretch flange formability deteriorate
Solution Approach 1:
The invention applies local quality by modifying only the end edge portion shape of the blank rather than changing the entire blank geometry or material properties. By locally adjusting the curvature radius at the end edge portion, the patent addresses strain concentration issues specifically where they occur without affecting the overall formability requirements of the component
Solution Approach 2:
The invention implements preliminary action by pre-modifying the blank shape before press forming to prevent forming failures. The end edge portion is designed with a specific curvature radius ratio (R2/R1 ≥ 2) in advance, which pre-regulates strain distribution during subsequent forming operations, preventing stretch flange fractures before they occur
2Reliability
If conventional methods are used to suppress strain concentration at end edge portions, then stretch flange fracture prevention is improved, but design versatility is limited and device complexity increases
Solution Approach 1:
The invention applies parameter changes by modifying geometric parameters of the blank - specifically the curvature radius ratio (R2/R1) at the end edge portion. This simple parameter adjustment provides a quantitative design criterion that is easy to implement and evaluate, avoiding complex forming processes while effectively preventing stretch flange fractures
3Reliability
If multiple prototype iterations are performed to optimize blank shape, then forming failure prevention is improved, but productivity decreases and time consumption increases
Solution Approach 1:
The invention implements feedback by establishing a clear evaluation criterion (curvature radius ratio R2/R1 ≥ 2) that provides immediate feedback on whether a blank design will prevent stretch flange fractures. This allows designers to evaluate blank shapes analytically rather than through trial-and-error prototyping, significantly reducing development time and improving productivity
Data Source
Figure 1A~1B
Figure 2
Figure 3~4A
AI summary
A blank shape determining method includes: a process of making a forming analysis of forming a reference blank into a reference formed product and a acquiring sheet thickness distribution and a plastic strain distribution; a process of acquiring a forming failure evaluation index for the reference blank; a process of estimating a region, which includes an end edge portion at which the forming failure evaluation index exceeds a predetermined threshold, within the reference blank as a forming failure region; a process of generating a plurality of corrected blanks; a process of making a forming analysis of forming the corrected blanks into corrected formed products and acquiring a sheet thickness distribution and a plastic strain distribution; a process of acquiring the forming failure evaluation index for the corrected formed product; and a process of determining a shape of the corrected blank having a smallest maximum value of the forming failure evaluation index as a shape of a blank provided for press forming.