Stamping Press Shearing Across Weld Zones to Lower Edge Residual Stress
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Solution Overview
Problem
Existing cutting methods using a stamping press to shear metal sheets with weld portions often result in high residual stress at sheared faces, leading to hydrogen embrittlement cracking and deteriorated fatigue properties, particularly at weld and heat-affected zones, where uniform edge characteristics are difficult to achieve and misalignment issues cause galling and increased stress.
Innovation Solution
A cutting method employing a punch with a projecting portion that initiates cutting at the heat-affected zone or weld portion before the flat portion, reducing residual stress by shearing across these areas, using a configuration where the projecting portion projects further than the flat portion and has a specific shape and dimensions to minimize stress concentration and prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional shearing is applied to high strength steel sheets with tensile strength exceeding 1000 MPa, then productivity is improved and machining cost is reduced, but residual stress is high at edges of blanks, hydrogen embrittlement cracking is liable to occur, and fatigue properties deteriorate
Solution Approach 1:
The punch is designed with a rounded tip portion that performs preliminary action by creating a dimple or shallow deformation zone before the main cutting edge engages the workpiece. This preliminary action redistributes stress and reduces residual stress concentration at the sheared edges, preventing hydrogen embrittlement cracking while maintaining high productivity in shearing high strength steel sheets
Solution Approach 2:
The cutting edge of the punch is modified with a rounded or curved tip portion instead of a sharp edge. This curvature distributes the shearing stress more uniformly across the material, reducing peak residual stress at the blank edges and improving hydrogen embrittlement resistance while maintaining efficient cutting performance
2Manufacturing precision
If clearance and tool shape are adjusted to achieve prescribed amounts of die roll, shear face, fracture face, and burr generation, then edge face properties are improved with respect to stretch flange formability, fatigue properties, and hydrogen embrittlement resistance, but it is difficult to produce blanking faces having uniform end face characteristics at weld portions and heat-affected zones
Solution Approach 1:
The punch is designed with different geometric characteristics at different locations: a rounded tip portion that contacts the workpiece first to create controlled deformation, followed by a cutting edge portion. This local differentiation in geometry allows the tip to manage stress distribution while the cutting edge produces the final shear, achieving uniform end face characteristics across weld portions and heat-affected zones while maintaining improved edge face properties
3Stress or pressure
If the clearance to thickness ratio is not greater than 1% to reduce residual tensile stress, then residual stress is reduced, but galling occurs due to slight punch misalignment, and when clearance changes due to wear, residual stress is increased and sufficient improvement effect is no longer obtainable
Solution Approach 1:
The rounded tip portion performs preliminary action by creating a dimple or shallow deformation zone before the main cutting edge engages. This preliminary deformation zone acts as a stress distributor that reduces sensitivity to clearance variations and misalignment, maintaining low residual stress even when clearance changes due to wear, while the subsequent cutting action proceeds normally without galling
Solution Approach 2:
The rounded tip portion serves as a cushioning element that absorbs misalignment and clearance variations before the main cutting edge engages the workpiece. This beforehand cushioning prevents galling caused by slight punch misalignment and maintains process stability even as clearance changes due to tool wear, ensuring consistent residual stress reduction
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively reduces residual stress at sheared faces, suppressing hydrogen embrittlement cracking and fatigue cracks, even in high-strength steel sheets, while maintaining excellent tensile and fatigue properties and hydrogen embrittlement resistance.
Implementation Method 1
cutting the workpiece by moving the punch and a die relative to each other at the positioned position so as to shear across the weld portion on the workpiece
Data Source
AI summary
A cutting method using a stamping press according to the present disclosure is a method to cut a workpiece that is configured from a first metal sheet and a second metal sheet joined at a weld portion and that has a heat-affected zone around the weld portion, in which the workpiece is cut using a punch. The punch includes a flat portion and a projecting portion projected more toward the workpiece than a flat portion of the punch. The workpiece is positioned with respect to the punch at a position such that the projecting portion starts cutting at least at one out of the heat-affected zone or the weld portion before the flat portion cuts the workpiece. The workpiece is then cut by moving the punch and a die relative to each other in this state of positioning so as to shear across the weld portion on the workpiece.