Outward Flange Stepped Structure for Fracture-Free Press Forming

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Solution Overview

Problem

Conventional press-forming methods struggle to form floor cross members from high-tensile strength steel sheets without causing stretch flange fractures or wrinkling, especially when forming continuous outward flanges with curving sections, which are essential for enhancing rigidity and load transfer characteristics in automotive body reinforcement.

Innovation Solution

A press-formed article and method that involve shearing deformation to create a stepped portion with specific thickness ratios in the outward flange, allowing it to be formed without cutouts, using a press-forming apparatus with punches and dies that restrict and move the workpiece in an oblique direction to maintain clearance, ensuring the flange's thickness meets specific average, minimum, and maximum thickness criteria.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If conventional press-forming methods are used to form continuous outward flanges with curving sections from high-tensile strength steel sheets, then the joint strength and rigidity are improved, but stretch flange fractures or wrinkling occur

Engineering Contradiction:

Improvejoint strengthVSAvoidformability without fractures

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The continuous outward flange is divided into multiple sections with different curvature radii. The curving section has a larger radius than the straight section, creating a stepped portion that segments the deformation path. This segmentation allows the material to flow more uniformly during forming, preventing both wrinkling (by reducing localized compression) and stretch flange fractures (by distributing tensile stresses across different zones with appropriate curvature transitions).

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different sections of the outward flange are given different local geometric properties. The straight section has zero curvature while the curving section has a specific radius, and the stepped portion connects these with an intermediate curvature. This local quality variation optimizes the stress distribution in each zone during press-forming, allowing the high-tensile strength steel sheet to be formed into the desired continuous flange shape without defects.

Inventive Principle:

Principle #3Local quality

2Strength

If high-tensile strength steel sheets are used to enhance rigidity and strength, then the bending and twisting rigidity are improved, but the formability and ease of manufacture deteriorate

Engineering Contradiction:

Improvebending and twisting rigidityVSAvoidformability

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The blank is pre-designed with an expanded shape that anticipates the final formed geometry. The blank includes provisions for the stepped portion and curving sections in its initial configuration, so that during press-forming, the material flows into the desired shape more easily. This preliminary action on the blank design compensates for the low formability of high-tensile strength steel sheets, enabling successful forming of complex continuous flange geometries without excessive forming forces or defects.

Inventive Principle:

Principle #10Preliminary action

3Ease of manufacture

If cutouts are provided in the outward flange to prevent fractures during forming, then the formability is improved, but the joint strength and rigidity deteriorate

Engineering Contradiction:

ImproveformabilityVSAvoidjoint strength

Core Design Contradiction:

Ease of manufactureVSStrength

Solution Approach 1:

Instead of providing cutouts (removing material) to improve formability, the invention inverts the approach by providing a stepped portion (adding geometric complexity) that enhances formability while maintaining continuity of the flange. This inverted strategy allows the outward flange to remain continuous and intact, preserving joint strength and rigidity, while the stepped geometry with varying curvature radii facilitates successful forming of high-tensile strength steel sheets without fractures or wrinkling.

Inventive Principle:

Principle #13The other way round (Inversion)

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 enables the formation of press-formed articles with enhanced joint strength and rigidity, improving bending and twisting rigidity of the vehicle body, thereby enhancing steering stability, riding comfort, and noise reduction without the need for cutouts that could lead to fractures or wrinkling.

Implementation Method 1

shearing deformation to create a stepped portion with specific thickness ratios in the outward flange

Methodology Applied

Scientific EffectShearing deformation: Shear Stress

Data Source

PatentUS11097331B2Press-formed article, press-forming method, and press-forming apparatus

Publication Date: 2021.08.24 NIPPON STEEL CORPORATION

AI summary

This press-formed article includes: a top sheet portion; a sidewall continuing to the top sheet portion via a convex ridge line portion; a flange continuing to the sidewall via a concaved ridge line portion; and an outward flange continuing from an edge portion of the top sheet portion to an edge portion of the flange, via an edge portion of the convex ridge line portion, an edge portion of the sidewall, and an edge portion of the concaved ridge line portion, wherein in the same unit, an average thickness TAve, a minimum thickness TMin, and a maximum thickness TMax of the outward flange satisfy Equation 1 and Equation 2.0.8×TAve≤TMin<TAve (Equation 1)TAve<TMax≤1.2×TAve (Equation 2).