1. 2.2 Prediction of Trimmed Edge Stretching Performance
Objectives
Understand the mechanism of edge stretching failure
Develop and establish a methodology to predict the trimmed edge performance
To determine and validate the edge stretching limit (ESL)
To identify the factors affecting the edge stretching limit
Technical Benefits
Provide a tool to predict edge cracking in forming feasibility studies, to assess the effectiveness of the counter-measures used to avoid edge cracking and to assess the edge forming severity in the field.
The ESL can also be used to measure the effectiveness in various shearing/trimming processes, optimal shearing/trimming tools setup, material microstructural optimizations, etc.
UNH - 28 October 2016
Sheet Metal Forming

2. 2.2 Prediction of Trimmed Edge Stretching Performance
Technical Obstacles:
High edge stretching limit requirement
Beyond material capability
Poor design
UNH - 28 October 2016
Sheet Metal Forming

3. 2.2 Prediction of Trimmed Edge Stretching Performance
Technical Obstacles:
Poor edges
Worn tools
Wrong die clearance
Continuity of geometry change
Sharp corners
UNH - 28 October 2016
Sheet Metal Forming

4. 2.2 Prediction of Trimmed Edge Stretching Performance
Edge Cracking Mechanism
Edge stretching performance affected by both base material and blanking or trimming processes and their setups
Damages introduced during blanking or trimming cause the edge failure below the forming limit
No consistent correlation has been found between edge shear face properties (roll over, burnish, fracture , burr) and the ESL
Severity of edge damage has been found to correlate with strain hardening in the shear affected zone
UNH - 28 October 2016
Sheet Metal Forming

5. 2.2 Prediction of Trimmed Edge Stretching Performance
Implementations and Discussions
Edge Stretching Limit Test Method?
Factors affecting the ESL:
Material Side?
Tool and Process Side?
How to improve the ESL?
Edge Damage Characterization and Index?
UNH - 28 October 2016
Sheet Metal Forming