Two-Step Press Forming for Side Wall Springback Control
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Solution Overview
Problem
Existing press forming methods face challenges in suppressing wall camber of side wall portions due to springback in high-strength metal sheets, leading to dimensional inaccuracies and increased manufacturing costs, with previous solutions either causing fractures, increasing tool complexity, or being difficult to apply.
Innovation Solution
A two-step press forming method where a preformed part with a flange portion having a concave, convex, or concavo-convex shape is formed in the first step, followed by shaping into the target form in the second step, applying tensile and compressive stresses to reduce residual stress differences and prevent wall camber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a bead is provided in the flange portion to apply large tensile force to eliminate camber, then wall camber is suppressed, but the side wall portion is extended excessively and fracture occurs
Solution Approach 1:
The invention applies local quality by providing the bead only in specific regions (first flange portion and second flange portion) rather than uniformly across the entire flange. The bead in each region has a specific curvature radius (0.5-2.0 times the sheet thickness) tailored to the local geometry, creating localized tensile stress distribution that suppresses wall camber without excessive extension that would cause fracture.
Solution Approach 2:
The invention changes the parameter of bead curvature radius to optimize performance. By setting the curvature radius within a specific range (0.5-2.0 times the sheet thickness), the bead generates appropriate tensile stress to suppress wall camber while avoiding excessive stress concentration that would lead to fracture. This parameter optimization resolves the contradiction between camber suppression and fracture prevention.
2Strength
If high-strength metal sheet is used for weight reduction and collision safety, then strength is improved, but springback increases and dimensional accuracy deteriorates
Solution Approach 1:
The invention applies preliminary action by forming beads in the flange portions before the main press forming process. These pre-formed beads create initial tensile stress states in the side wall portions that counteract the compressive residual stresses generated during subsequent deep drawing. This preliminary stress preparation reduces springback and maintains dimensional accuracy even when using high-strength metal sheets.
3Manufacturing precision
If the entire side wall portion is extended to apply tensile stress, then wall camber is suppressed, but yield is reduced due to post-process cutting
Solution Approach 1:
The invention improves yield by applying local quality - beads are provided only in specific flange regions (first and second flange portions) rather than extending the entire side wall. This localized bead configuration generates sufficient tensile stress to suppress wall camber in the critical areas without requiring excessive material extension, thereby eliminating the need for post-process cutting and maintaining higher production yield.
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 differences between the front and rear surfaces of the side wall portion, preventing fractures and maintaining the shape of the press-formed product while suppressing wall camber without reducing yield.
Implementation Method 1
a phenomenon in which residual stress generated in a press-formed product when a metal sheet is deformed by press forming
Implementation Method 2
springback is generated using the residual stress generated during the press forming as a driving force
Data Source
AI summary
A press forming method for suppressing wall camber of a side wall portion due to springback of a press-formed product including a top portion, the side wall portion and a flange portion includes: a first forming step of press-forming a preformed part including a flange portion having height continuously changed in an axial direction to have a concave shape, a convex shape or a concavo-convex shape more largely than a target shape of the press-formed product in a height direction to provide a height difference; and a second forming step of press-forming the preformed part into the press-formed product having the target shape to reduce the height difference of the flange portion of the preformed part.