Two-Step Flange Press Forming for Wrinkle and Fracture Suppression
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Solution Overview
Problem
Existing press forming methods struggle to suppress wrinkles and fractures in the flange portion of automotive parts made from high-strength steel sheets, which are prone to buckling and material processing defects due to their low elongation and thinning during sheet metal forming.
Innovation Solution
A two-step press forming method where the first step forms a preformed part with a torsional shape portion to alleviate excess metal in shrink flange areas, and the second step converts this portion into a flange, while forming the stretch flange portion to prevent material shortages, using either different dies or a single die for both steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If high-strength steel sheets are used for weight reduction, then weight of the automotive part is reduced, but the steel sheet becomes poor in elongation and tends to cause fracture during material processing
Solution Approach 1:
The flange portion is divided into multiple zones based on wall depth: a first curved portion with large wall depth, an inclined side portion, and a second curved portion with small wall depth. This segmentation allows different forming strategies to be applied to different regions, preventing fracture by avoiding excessive strain in critical areas while achieving the desired flange shape.
Solution Approach 2:
The press forming process is divided into two steps: a first forming step that creates a preformed part with a torsional shape portion, and a second forming step that completes the flange formation. This preliminary action distributes strain more evenly during the initial forming stage, preventing concentration of stress that would lead to fracture in high-strength steel.
2Weight of moving object
If sheet metal thinning is performed for further weight reduction, then weight of the automotive part is reduced, but the likelihood of occurrence of buckling and wrinkles during press forming increases
Solution Approach 1:
Different regions of the flange portion are formed with different local qualities: the first curved portion with large wall depth is formed to create a shrink flange that resists wrinkling, while the second curved portion with small wall depth is formed to create a stretch flange. This local differentiation allows thinning to be managed regionally, maintaining surface quality despite overall weight reduction.
Solution Approach 2:
The forming process uses dynamic control of the blank holder and punch to adapt to the thinning behavior of the high-strength steel sheet. By adjusting forming parameters during the two-step process, the method dynamically responds to material flow and thickness changes, preventing buckling and wrinkles while achieving weight reduction through controlled thinning.
3Manufacturing precision
If a wrinkle suppression pad is used to hold down the inside of the product, then wrinkles inside the product are suppressed, but the method cannot be applied to shapes having occurrence of wrinkles or fractures in the flange portion itself
Solution Approach 1:
The flange portion is segmented into different zones (first curved portion with large wall depth, inclined side portion, and second curved portion with small wall depth) that require different forming approaches. This segmentation allows the method to address wrinkles and fractures in the flange itself by applying appropriate forming strategies to each zone, enhancing adaptability to various shapes.
Solution Approach 2:
The first forming step creates a preformed part with a torsional shape portion that prepares the material distribution before the final flange formation. This preliminary action prevents wrinkles and fractures in the flange portion by establishing favorable stress states and material flow patterns before the second forming step completes the shape, making the method applicable to a wider range of geometries.
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 suppresses wrinkles and fractures throughout the entire forming process by dispersing strain in critical areas, resulting in high-quality press forming parts without defects in the flange portion.
Implementation Method 1
a press forming method for forming a press forming part from a metal sheet
Data Source
AI summary
A press forming method for forming a press forming part includes: a first forming step of forming a preformed part, the preformed part including a side wall portion, a flange portion formed in a bottom edge being a portion having a large wall depth and a torsional shape portion formed in an inclined side portion continuous from the flange portion to reach a second curved portion; and a second forming step of further processing the preformed part formed in the first forming step, including processes of forming the torsional shape portion into the flange portion and forming the flange portion in the second curved portion continuous from the inclined side portion and in a recessed side portion having a small wall depth so as to achieve formation of a target shape.