Two-Stage Press Forming for Curved Wall Wrinkle Prevention
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Solution Overview
Problem
Press-formed products with convexly curved wall parts are prone to wrinkling, especially when using high tensile strength steel sheets, due to compressive stress generated during the forming process, which complicates achieving target product quality and increases maintenance costs.
Innovation Solution
A two-stage forming process using a specific forming die and method that forms a primary formed product with an intermediate wall portion and flange, followed by a secondary formed product with an extended flange to align with the intermediate wall portion, reducing compressive stress by varying the depth and height of boundary valley and ridge lines based on curvature sections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single-step forming method is used to form a convexly curved wall part, then the forming process is simple and quick, but compressive stress concentrates and causes wrinkling
Solution Approach 1:
The forming process is divided into multiple stages: a first forming step that creates an intermediate formed product with a partially formed wall part and flange, followed by a second forming step that completes the wall part formation. This segmentation distributes the compressive stress across multiple steps, preventing wrinkling while maintaining process efficiency.
Solution Approach 2:
In the first forming step, an intermediate flange is preliminarily formed extending from the intermediate wall portion. This preliminary action prepares the material distribution and stress state for the second forming step, enabling complete wall part formation without excessive compressive stress concentration.
2Adaptability or versatility
If the wall part has large length or large curvature, then the product design flexibility is improved, but compressive stress increases and wrinkling occurs
Solution Approach 1:
The multi-stage forming process segments the deformation of long or highly curved wall parts into manageable steps. The intermediate flange formation in the first step accommodates material flow for complex geometries, while the second step completes the shaping without generating excessive compressive stress that would cause wrinkling.
Solution Approach 2:
The forming parameters are changed between stages: the first forming step uses parameters suitable for creating the intermediate structure with controlled material flow, while the second step uses parameters optimized for completing the wall part formation. This parameter adjustment allows handling of various wall part lengths and curvatures without wrinkling.
3Weight of moving object
If high tensile strength steel sheet is used to make the product thinner and lighter, then the weight is reduced, but the material is more prone to wrinkling under compressive stress
Solution Approach 1:
The multi-stage forming process is particularly effective for high tensile strength steel sheets because it segments the compressive stress application. The intermediate flange formation in the first step prepares the material in a controlled manner, and the second step completes the forming without subjecting the thin, high-strength material to excessive compressive stress that would cause wrinkling.
Solution Approach 2:
The preliminary formation of the intermediate flange in the first step creates a favorable stress state and material distribution for the second forming step. This preliminary action is crucial for high tensile strength steel sheets as it prevents stress concentration before the final wall part formation, enabling successful forming of thin-walled components without wrinkling.
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 prevents wrinkling in press-formed products, especially those with long convex-side slanted wall portions, allowing for high-quality production without special equipment, reducing die complexity and costs, and enhancing design flexibility.
Implementation Method 1
forming of a press-formed product by pressing the blank with a forming die
Implementation Method 2
compressive stress is generated at the convexly curved wall part due to shrink flanging
Data Source
AI summary
A pressing step of forming a press-formed product includes: a primary formed product forming step of forming a primary formed product having an intermediate wall portion which will be a part of a convex-side wall part, and an intermediate flange continuous with the intermediate wall portion; and a secondary formed product forming step of forming a secondary formed product having a wall part which will be the convex-side wall part by extending at least a portion, on the intermediate wall portion side, of the intermediate flange formed in the primary formed product forming step such that the portion is aligned with the intermediate wall portion. In the primary formed product forming step, the intermediate wall portion is formed such that a boundary valley line between the intermediate wall portion and the intermediate flange is deeper at a large-curvature section than at a small-curvature section.