Sheared Edge Bulging in Pressed Steel Parts to Relax Residual Stress

Solution Overview

Problem

Existing technologies fail to effectively reduce tensile residual stress on sheared edge faces of metal sheets after press forming, leading to delayed fractures in high-strength steel components.

Innovation Solution

A method involving a tensile residual stress relaxation step, where a bulging deformation is applied to the sheared edge face in the sheet thickness direction, forming a bead shape to reduce tensile residual stress generated during springback deformation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If high-strength steel sheets are used for vehicle bodies to achieve weight reduction and collision safety, then vehicle fuel consumption is improved and collision safety is enhanced, but delayed fracture occurs on sheared edge faces after press forming

Engineering Contradiction:

Improvetensile strength of steel sheetVSAvoiddelayed fracture resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The invention applies a preliminary tensile stress to the workpiece before press forming in the same direction as the tensile residual stress that will be generated during springback. This preliminary action counteracts the subsequent tensile residual stress, reducing the total residual stress and preventing delayed fracture on sheared edge faces after press forming

Inventive Principle:

Principle #10Preliminary action

2Reliability

If conventional shearing methods are used to reduce tensile residual stress on sheared edge faces, then delayed fracture is suppressed, but these methods do not address tensile residual stress generated during press forming springback

Engineering Contradiction:

Improvedelayed fracture resistanceVSAvoidapplicability to press forming process

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The invention applies a preliminary tensile stress to the workpiece before press forming in the same direction as the tensile residual stress that will be generated during springback. This preliminary action counteracts the subsequent tensile residual stress, reducing the total residual stress and preventing delayed fracture on sheared edge faces after press forming

Inventive Principle:

Principle #10Preliminary action

3Manufacturing precision

If excess beads are formed on shrink flange portions to reduce springback, then dimensional precision is improved, but tensile residual stress on sheared edge faces is not reduced

Engineering Contradiction:

Improvedimensional precisionVSAvoiddelayed fracture resistance

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The invention applies a preliminary tensile stress to the workpiece before press forming in the same direction as the tensile residual stress that will be generated during springback. This preliminary action counteracts the subsequent tensile residual stress, reducing the total residual stress and preventing delayed fracture on sheared edge faces after press forming

Inventive Principle:

Principle #10Preliminary action

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

The method significantly reduces tensile residual stress on sheared edge faces, thereby enhancing the delayed fracture resistance of high-strength steel components, such as those used in vehicle bodies.

Implementation Method 1

a tensile residual stress relaxation step of bulging, in a sheet thickness direction, a region including at least a site on a sheared edge face where it is estimated that the tensile residual stress is generated

Methodology Applied

Scientific EffectPlastic deformation: Plasticity

Data Source

PatentUS12275052B2Pressed component manufacturing method

Publication Date: 2025.04.15 JFE STEEL CORP

AI summary

A pressing technology for reducing tensile residual stress generated on a sheared edge face of a metal sheet after press forming in order to prevent occurrence of a delayed fracture on the sheared edge face. A pressed component manufacturing method for manufacturing a pressed component by press-forming a metal sheet having a sheared edge face includes a first press forming step in which it is estimated that tensile residual stress is generated in a direction along the sheared edge on a portion of the sheared edge face of the metal sheet after die release, in which the method includes, as a subsequent step to the first press forming step, a tensile residual stress relaxation step of bulging, in the sheet thickness direction, a region that includes at least a site on a sheared edge face where it is estimated that the tensile residual stress is generated.