High-Tensile Steel Press Forming with Ridge Line Pad
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Solution Overview
Problem
It is challenging to form a press-formed body made of high-tensile strength steel sheets with a groove-shaped cross section, including a groove bottom part, ridge line parts, and side wall parts, while maintaining a continuous outward flange across the end part in a longitudinal direction without cutouts at the ridge line part flange portion, as conventional methods often result in stretch flange cracks and wrinkling due to the high material strength and steep cross-sectional wall angles.
Innovation Solution
A manufacturing method and apparatus that utilize a ridge line pad to bind and shape the press-forming material, ensuring the ridge line parts are formed in conjunction with the groove bottom parts, thereby suppressing material deformation and preventing cracks and wrinkling by pressing the material in a manner that maintains a sufficient pad load across the ridge line part flange portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional press-forming methods are used on high-tensile strength steel sheets, then material strength is maintained, but formability deteriorates and design flexibility is reduced
Solution Approach 1:
The press-forming process is divided into multiple stages: first forming the groove-shaped cross section, then forming the outward flange. This segmentation allows each stage to be optimized independently, enabling complex shapes to be formed on high-tensile strength steel without causing formability issues
Solution Approach 2:
The groove-shaped cross section is formed preliminarily before forming the outward flange. This preliminary action creates a pre-shaped blank that facilitates subsequent flange formation while maintaining material strength, effectively solving the formability problem of high-tensile strength steel
2Strength
If a continuous outward flange is formed across the ridge line part, then joining strength is enhanced, but stretch flange cracks occur due to high material strength and steep wall angles
Solution Approach 1:
The forming process is segmented into two distinct operations: first forming the groove-shaped cross section with controlled wall angles, then forming the continuous outward flange. This segmentation prevents crack formation by avoiding attempts to form both features simultaneously under excessive stress
Solution Approach 2:
The cross-sectional shape parameters are optimized by controlling the wall angles and curvature radii during the first forming stage. These parameter changes create a favorable geometry that reduces stress concentration during subsequent flange formation, preventing stretch flange cracks while maintaining joining strength
3Ease of manufacture
If cutouts are provided at the ridge line part flange portion, then forming is easier, but structural integrity is reduced
Solution Approach 1:
The groove-shaped cross section is formed preliminarily with optimized geometry before flange formation. This preliminary action creates a blank that is easier to form without cutouts, thereby maintaining structural integrity while improving formability
4Strength
If the cross-sectional wall angle is increased to enhance rigidity, then structural performance improves, but wrinkling occurs during press-forming
Solution Approach 1:
The forming process is segmented so that the groove-shaped cross section with high wall angles is formed in the first stage when the material is more formable. The second stage then forms the outward flange on this pre-shaped blank, preventing wrinkling while maintaining the desired high wall angles for rigidity
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 allows for the successful formation of a press-formed body with a continuous outward flange across the groove bottom and side wall parts without material yield reduction, enhancing the structural integrity and rigidity of the press-formed body.
Implementation Method 1
binding a part to be formed into a groove bottom part and parts to be formed into ridge line parts in the vicinity of an outward flange at a press-forming material with a ridge line pad having a shape binding the part to be formed into the groove bottom part and the parts to be formed into the ridge line parts while pressing the press-forming material to the punch
Data Source
Figure 1A~1D
Figure 2A~2C
Figure 3A~3D
AI summary
A press-formed body (15) made of a high-tensile strength steel sheet of 390 MPa or more including a groove bottom part (15a), ridge line parts (15b, 15b) continuous to the groove bottom part (15a), and side wall parts (15c, 15c) continuous to the ridge line parts (15b, 15b), and in which an outward flange (16) is formed at an end part in a longitudinal direction is manufactured by a press-forming apparatus including a punch (11), a die (12), and a pad (14) which presses and binds a press-forming material (13) to the punch (11). At a press-forming time, the pad (14) binds a part to be formed into the groove bottom part (15a) and a part having a length of one-third or more of a cross-sectional peripheral length of the ridge line part (15b) starting from a connecting part with the groove bottom part (15a) from among a part to be formed into the ridge line part (15b) in a vicinity of the outward flange (16) at the press-forming material (13). It is thereby possible to surely form the press-formed body (15) without providing cutouts at a ridge line part flange portion of the outward flange, or generating lowering of material yield.