Punch Protrusion Shearing for Low-Stress Welded Steel Edges
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Solution Overview
Problem
Existing metal sheet shearing methods, particularly when processing high-strength steel sheets over 1000 MPa, face challenges with high residual stress at the sheared surface, leading to hydrogen embrittlement cracks and reduced fatigue resistance, especially when shearing across weld zones with significant thickness differences.
Innovation Solution
The method involves using a punch with protrusions at the cutting edge to position all or part of the weld zone between the protrusions, which reduces residual stress and enhances surface properties by applying compressive stress through tapered surfaces, thereby improving hydrogen embrittlement resistance and extending punch service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional shearing methods are used on high strength steel sheets over 1000 MPa, then production efficiency is high and processing cost is low, but tensile residual stress becomes high at the sheared surface leading to hydrogen embrittlement cracks and reduced fatigue resistance
Solution Approach 1:
The invention applies local quality by providing protrusions at specific locations on the punch surface that concentrate compressive stress application to the weld zone. The protrusions are positioned to correspond to the weld zone location, applying localized compressive stress only where needed rather than uniformly across the entire workpiece surface, thus improving fatigue resistance at the critical weld area while maintaining overall processing efficiency
Solution Approach 2:
The invention changes the stress state parameter from tensile to compressive at the sheared surface of the weld zone. By applying compressive stress through the protrusions during shearing, the residual stress state is transformed, preventing hydrogen embrittlement cracks and improving fatigue resistance without sacrificing production efficiency
2Adaptability or versatility
If conventional shearing methods are used on tailor welded blanks, then welding joins different types of steel sheets, but hydrogen embrittlement resistance and fatigue resistance further fall at the sheared surface of the weld zone
Solution Approach 1:
The protrusions are specifically positioned to correspond to the weld zone location on tailor welded blanks, applying compressive stress locally to the weld area where hydrogen embrittlement risk is highest. This localized treatment maintains the versatility of joining different steel sheet types while specifically protecting the weld zone from hydrogen embrittlement
Solution Approach 2:
The compressive stress is applied preliminarily during the shearing process itself, before hydrogen embrittlement can occur. This preliminary application of compressive stress counteracts the tensile residual stress that would otherwise lead to hydrogen embrittlement cracks, preventing the problem before it manifests
3Device complexity
If uniform punch shape is used in the direction of cutting ridgeline, then shearing is simple, but cracks easily occur at the weld zone where ductility and toughness are low
Solution Approach 1:
The punch design transitions from uniform to non-uniform by adding protrusions at specific locations. The protrusions create localized variations in the punch shape that correspond to the weld zone position, allowing the punch to apply targeted compressive stress to improve crack resistance at the critical weld area while maintaining simplicity elsewhere
Solution Approach 2:
The punch surface is segmented into different functional zones: areas with protrusions that apply compressive stress to the weld zone, and areas without protrusions for normal shearing. This segmentation allows the punch to perform multiple functions - both general shearing and specific protection of the weld zone from cracking
4Reliability
If clearance is reduced to 1% or less of workpiece thickness to reduce residual stress, then tensile residual stress decreases, but punch and die wear increases and service life decreases
Solution Approach 1:
The invention changes the stress state parameter from tensile to compressive at the sheared surface through the protrusions. This parameter change allows for reduced punch-die clearance without the usual penalty of increased wear, because the compressive stress state prevents the workpiece material from gripping and wearing the cutting edges as aggressively as tensile stress would
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 approach effectively reduces residual stress and improves surface properties, fatigue resistance, and hydrogen embrittlement resistance at the sheared surface, while also extending the service life of the punch by minimizing wear on the protrusions.
Implementation Method 1
applying compressive stress through tapered surfaces
Data Source
AI summary
The present invention provides a method for shear processing whereby a sheared surface having a small residual stress and excellent surface properties is formed and the service life of a punch is prolonged in a shear processing for shearing, by a shear line that crosses a weld zone, a workpiece with a large thickness of level difference of a weld zone and/or obtained by welding together a steel sheet having a strength of 1000 MPa or more and another steel sheet. The shearing for shear processing method according to the present invention is a method for shearing a workpiece having a weld zone using a punch and a die, the method characterized in that two protrusions are provided to a cutting edge of the punch, all or part of the weld zone of the workpiece is flanked from the two sides by the two protrusions, and the workpiece is sheared by a shear line that crosses the weld zone.