Punch Protrusion Shearing Across Weld Zones in High-Strength Steel
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Solution Overview
Problem
Shear processing of high-strength steel sheets over 1000 MPa results in high tensile residual stress at the sheared surface, leading to hydrogen embrittlement cracks and reduced fatigue resistance, especially at the weld zone, and existing methods fail to effectively control residual stress and extend punch service life.
Innovation Solution
The use of a punch with wedge-shaped protrusions positioned to sandwich the weld zone, reducing residual stress and wear on the cutting edge, thereby improving surface properties and extending punch service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional shearing is 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
Solution Approach 1:
The invention changes the geometric parameters of the cutting edge by providing protrusions that extend in the sheet thickness direction. This modifies the shearing mechanism to apply compressive stress instead of tensile stress at the sheared surface, thereby reducing residual stress while maintaining production efficiency
Solution Approach 2:
The cutting edge is extended in the sheet thickness direction (third dimension) to form protrusions. This dimensional change allows the cut to engage the material differently, applying compression rather than tension at the surface, thus resolving the residual stress issue without sacrificing productivity
2Ease of manufacture
If conventional shearing is used on high-strength steel sheets, then processing cost is low, but hydrogen embrittlement cracks easily form at the sheared surface
Solution Approach 1:
By modifying the cutting edge geometry to include protrusions in the thickness direction, the shearing process generates compressive residual stress that counteracts tensile stresses that would otherwise promote hydrogen embrittlement cracking, thereby improving reliability without significantly increasing processing cost
3Productivity
If conventional shearing is used on high-strength steel sheets, then production efficiency is high, but fatigue resistance falls at the sheared surface
Solution Approach 1:
The protrusions on the cutting edge change the stress state at the sheared surface from tensile to compressive, creating a more favorable condition for fatigue resistance while maintaining the high production efficiency of conventional shearing processes
4Productivity
If shearing is performed on tailor welded blanks at the weld zone, then production efficiency is maintained, but hydrogen embrittlement resistance and fatigue resistance further fall
Solution Approach 1:
The protrusions modify the shearing action at the weld zone to generate compressive residual stress, which counteracts the detrimental effects of welding on hydrogen embrittlement resistance and fatigue resistance, thereby improving reliability while maintaining production efficiency
5Stress or pressure
If clearance is reduced to 25% or less of sheet thickness, then work hardening and tensile residual stress are reduced, but cracks easily occur at the weld zone with low ductility and toughness
Solution Approach 1:
By extending the cutting edge in the thickness direction to form protrusions, the invention changes the shearing mechanism to apply compressive stress at the surface, thereby reducing residual stress without requiring such small clearance that would cause cracking at the weld zone
Solution Approach 2:
The geometric parameter of the cutting edge is changed to include protrusions, which modifies the stress distribution during shearing to generate compression rather than tension, resolving the contradiction between residual stress reduction and crack resistance
6Ease of manufacture
If uniform punch shape is used in the direction of cutting ridgeline, then manufacturing is simple, but cracks easily occur at the weld zone
Solution Approach 1:
The cutting edge is given local quality by providing protrusions at specific locations, particularly at positions that will engage the weld zone during shearing. This localized modification improves crack resistance at the weld zone while keeping the rest of the punch simple and easy to manufacture
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 results in a sheared surface with reduced residual stress, enhanced fatigue and hydrogen embrittlement resistance, and prolonged punch service life, even when processing thick weld zones or high-strength steel sheets.
Implementation Method 1
perform shear processing while sandwiching all or part of the weld zone of the workpiece from two sides by protrusions... forming a sheared surface small in residual stress
Implementation Method 2
shear processing... shearing a metal sheet by a press
Data Source
Figure 1~2
Figure 3
Figure 4A~4C
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.