Two-Step Press Forming for Side Wall Camber Suppression
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Solution Overview
Problem
Press forming high-strength metal sheets results in significant wall camber due to springback, which is difficult to suppress without causing fractures or increasing tool complexity, and existing methods either lead to yield loss or increased manufacturing costs.
Innovation Solution
A two-step press forming method where the preformed part is initially shaped with a concave, convex, or concavo-convex flange portion to apply tensile and compressive stresses exceeding the yield strength, followed by forming into the target shape to reduce residual stress differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a bead is provided in the flange portion to apply large tensile force to the side wall portion, then wall camber is suppressed, but the side wall portion is extended further and fracture occurs
Solution Approach 1:
The invention changes the geometric parameters of the flange portion by forming it with a specific curvature radius (R1) that is larger than the die shoulder radius (R2). This parameter change allows the flange to apply tensile force to the side wall portion without excessive material flow restriction, thereby suppressing wall camber while preventing fracture by maintaining adequate material ductility during forming.
Solution Approach 2:
The invention applies local quality by creating a specific curved shape in the flange portion with a defined curvature radius. This localized geometric feature concentrates the stress distribution in a controlled manner, applying just enough tensile force to the side wall portion to counteract springback-induced wall camber without over-constraining the material flow that would cause fracture.
2Manufacturing precision
If compressive stress is applied to the side wall portion to reduce stress difference, then wall camber is suppressed, but the tool structure becomes complicated and manufacturing cost increases
Solution Approach 1:
The invention employs self-service by designing the flange portion's geometry itself to generate the necessary compressive stress effect. The curved flange with a specific radius automatically creates a stress distribution that reduces the stress difference between the front and rear of the side wall portion during forming, eliminating the need for additional active compression devices or complex tooling mechanisms.
Solution Approach 2:
The invention applies preliminary action by pre-shaping the flange portion with a specific curvature before the actual forming process. This preliminary geometric configuration ensures that during the forming operation, the stress distribution is already optimized to minimize wall camber, preventing the problem rather than correcting it with complex post-processing or active control mechanisms.
3Strength
If high-strength metal sheet is used for weight reduction and collision safety, then dimensional accuracy deteriorates due to larger springback, but using lower strength material does not achieve weight reduction goals
Solution Approach 1:
The invention applies preliminary anti-action by pre-configuring the flange portion with a specific curved geometry that anticipates and counteracts the springback effect. The flange's curvature radius is designed to generate stresses during forming that pre-compensate for the elastic recovery that will occur after die-release, thereby maintaining dimensional accuracy even with high-strength materials that exhibit larger springback.
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
Suppresses wall camber effectively while maintaining yield and avoiding tool complexity, ensuring precise dimensional accuracy of press-formed products.
Implementation Method 1
a first forming step of press-forming a preformed part including a flange portion (35) having a shape curved in a convex shape or a concave shape in the height direction in the axial direction
Implementation Method 2
springback is generated using the residual stress generated during the press forming as a driving force
Data Source
Figure 1(a)~2(b)
Figure 3~4(b)
Figure 5(a)~6
AI summary
A press forming method according to the present invention is a press forming method for suppressing wall camber of a side wall portion due to springback of a press-formed product 1 having a top portion 3, the side wall portion 5, and a flange portion 7, the press forming method including a first forming step of press-forming a preformed part 31 including a flange portion 35 more largely curved in a concave shape in a height direction than a target shape of the press-formed product 1 to provide a height difference and a second forming step of press-forming the preformed part 31 into the press-formed product 1 having the target shape to reduce the height difference of the flange portion 35 of the preformed part 31.