Sheared Blank Edge Structure for Stretch Flange Crack Suppression
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Solution Overview
Problem
Existing methods for suppressing stretch flange cracking in sheared edges during press forming often lead to fatigue failure in workpieces, as they increase the proportion of fractured surfaces with cracks, reducing the fatigue strength of the material.
Innovation Solution
A sheet-shaped blank with a sheared edge that has a loop shape in plan view, featuring a curved portion with a longer fractured surface in the sheet thickness direction, which can easily stretch and deform, while the remaining areas have a shorter fractured surface, maintaining sufficient fatigue strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing methods are used to suppress stretch flange cracking in sheared edges, then formability is improved, but fatigue strength decreases due to increased fractured surfaces with cracks
Solution Approach 1:
The patent applies local quality by creating different surface characteristics at different locations on the sheared edge. The curved portion (which requires stretch flanging) is given a longer fractured surface with more cracks that can open and close, while the straight portion (which does not require stretch flanging) maintains a shorter fractured surface with fewer cracks. This localized differentiation allows the curved portion to suppress stretch flange cracking through crack opening/closing action, while the straight portion maintains high fatigue strength by minimizing crack formation.
2Ease of operation
If the sheared edge is made to stretch and deform easily, then stretch flange cracking is suppressed, but fatigue strength may decrease due to increased fractured surface
Solution Approach 1:
The patent implements local quality by providing different fractured surface characteristics to different portions of the sheared edge based on their functional requirements. The curved portion has a longer fractured surface that enables easy stretching and deformation through crack opening/closing, while the straight portion has a shorter fractured surface that maintains fatigue strength. This localized approach ensures each portion has the properties needed for its specific function.
Solution Approach 2:
The patent applies segmentation by dividing the sheared edge into distinct functional zones: curved portions that require stretch flanging and straight portions that do not. Each zone is given appropriate fractured surface characteristics - the curved portions receive longer fractured surfaces with more cracks for enhanced stretchability, while straight portions maintain shorter fractured surfaces for fatigue resistance. This segmentation allows optimized performance in each zone without compromising the other.
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3(a)~3(c)
AI summary
A sheet-shaped blank (10) for press forming is produced by shearing a metal sheet (30). The blank (10) includes a sheared edge (14), which includes a sheared surface (14b) and a fractured surface (14c) in the sheet thickness direction and has a loop shape in plan view. In plan view, an edge of the sheared edge (14) includes concavely curved portions (20). The average of lengths of the fractured surface (14c) in the sheet thickness direction in the curved portions (20) is greater than the average of lengths of the fractured surface (14c) in the sheet thickness direction over the entire perimeter of the sheared edge (14).