Two-Stage Press-Forming for High Strength Steel Warping Control
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Solution Overview
Problem
High strength steel sheets used in press-forming often experience significant warping and torsion due to residual stress, making it challenging to achieve precise shape accuracy, especially in parts with bent sections, which can lead to assembly issues and increased costs due to the need for trial-and-error die design and correction.
Innovation Solution
A press-forming method involving a two-stage shaping process: first, bending the flange part until a specific angle α1 is achieved, and second, further bending until angle α2, with the additional bending angle β falling within a predetermined range to minimize warping and torsion, applicable to high strength steel sheets with tensile strengths between 440 to 1600 MPa.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high strength steel sheet is used to improve collision safety and reduce weight, then tensile strength is improved, but warping and torsion of the final shaped article increase due to residual stress
Solution Approach 1:
The press-forming process is divided into multiple stages: a first press-forming process that forms an intermediate shaped article, and a second press-forming process that forms the final shaped article. This segmentation allows residual stress to be managed in controlled steps, reducing overall warping and torsion while maintaining the high strength properties of the steel sheet.
Solution Approach 2:
The first press-forming process performs preliminary shaping to create an intermediate form that pre-manages stress distribution. By forming the intermediate shaped article first, the process prepares the material in a controlled state before the final forming operation, reducing the magnitude of residual stress that would otherwise cause excessive warping and torsion.
2Device complexity
If conventional single-stage press-forming is used, then the process is simple, but shape precision deteriorates due to large warping and torsion
Solution Approach 1:
The press-forming operation is segmented into two distinct processes: first press-forming to create an intermediate shaped article, and second press-forming to create the final shaped article. This segmentation transforms a complex precision problem into two manageable forming steps, each with controlled stress states.
Solution Approach 2:
The invention changes the forming parameters by introducing an intermediate state with specific geometric characteristics (tapered parts between vertical wall parts and flange parts). This intermediate geometry serves as a stress-distributing configuration that enables the final high-precision form to be achieved.
3Manufacturing precision
If bead is imparted to suppress warping and torsion, then shape precision is improved, but the method becomes limited to specific article shapes
Solution Approach 1:
Instead of adding localized beads to specific areas, the invention segments the entire press-forming process into two stages. This global segmentation approach suppresses warping and torsion throughout the entire article without requiring shape-specific modifications, making it universally applicable to various article geometries.
Solution Approach 2:
The invention changes the fundamental parameter of the forming process from a single-stage to a two-stage operation. This parameter change enables warping and torsion suppression through process structure rather than geometric modification, maintaining versatility across different article shapes.
4Manufacturing precision
If trial and error die design is used to reduce warping and torsion, then shape precision can be achieved, but time and cost increase significantly
Solution Approach 1:
The two-stage press-forming process provides a systematic approach that reduces reliance on trial-and-error die design. By controlling stress distribution through process segmentation, the method achieves consistent shape precision with minimal die corrections needed.
Solution Approach 2:
Changing from single-stage to two-stage press-forming fundamentally alters the stress management approach, providing a predictable method for reducing warping and torsion. This parameter change reduces the need for extensive die design iterations and corrections.
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 warping and torsion in final shaped articles with bent parts, maintaining shape precision without forming beads, and reduces the need for costly die corrections, enabling the use of high strength steel sheets while achieving similar results to softer steel sheets.
Implementation Method 1
a first shaping process in which high strength steel sheet with a tensile strength of 440 to 1600 MPa is used, a flange part is bent at an intersecting part until an angle of the flange part with a horizontal line becomes α1
Data Source
AI summary
A press-forming method which press-forms a final shaped article which comprises a top sheet part, vertical wall parts, and flange parts and which has at least one bent part in a longitudinal direction, which method forms the top sheet part, vertical wall parts, bent part, and flange parts, includes a first shaping process of bending a flange part at an intersecting part until an angle of the flange part with a horizontal line becomes α1 in a plane which includes a horizontal line which connects an intersecting part of a vertical wall part and a flange part and a center of curvature of the bent part and which is vertical to the high strength steel sheet and a second shaping process of additionally bending the flange part after the first shaping process at the intersecting part until the angle of the flange part with the horizontal line becomes α2 in that plane, makes the additional bending angle β of α1-α2 predetermined ranges, and thereby reduces the warping and torsion of the final shaped article.