Two-Stage Press Forming for Curved Flange Springback Control
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Solution Overview
Problem
In press forming of products with flange portions curved in a convex or concave manner, springback due to residual stress occurs, leading to inaccurate flange angles and potential tool damage during trimming processes, as existing methods either change flange angles or fail to effectively reduce residual stress without altering the angle.
Innovation Solution
A two-process press forming method where the first process forms the top and side wall portions with a side wall height greater than the target shape, and the second process adjusts the side wall height to the target shape, reducing stress in the flange portion by controlling strain and stress distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the flange angle is changed in the forming processes to reduce residual stress, then springback is suppressed, but stress at the distal edge portion markedly changes causing potential tool damage during trimming
Solution Approach 1:
The forming process is divided into two distinct stages: a first forming process that forms the basic shape, and a second forming process that specifically targets the flange portion. This segmentation allows stress control without concentrating excessive stress at the distal edge during trimming, as the flange is formed at the target angle in the second process rather than changing the angle to control stress.
Solution Approach 2:
The first forming process performs preliminary forming of the flange portion at a preliminary forming angle, creating an intermediate state that prepares the material for the final forming. This preliminary action distributes stress more evenly throughout the flange portion, preventing marked stress concentration at the distal edge while still achieving springback suppression through the two-stage approach.
2Reliability
If the flange angle is changed to reduce residual stress, then springback is controlled, but the target flange angle accuracy cannot be maintained
Solution Approach 1:
The forming process is divided into two distinct stages: a first forming process that forms the basic shape, and a second forming process that specifically targets the flange portion. This segmentation allows stress control without concentrating excessive stress at the distal edge during trimming, as the flange is formed at the target angle in the second process rather than changing the angle to control stress.
Solution Approach 2:
The invention changes the forming angle parameter between the two processes: the first process uses a preliminary forming angle, and the second process uses the target flange angle. This parameter change allows the final flange to be formed at the precise target angle while the intermediate preliminary forming controls stress distribution, thereby achieving both springback control and angle accuracy.
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 significantly reduces springback and maintains the target flange angle without altering the flange angle during forming, effectively addressing the issue of residual stress in press-formed products.
Implementation Method 1
the top and side wall portions are formed by plastic deformation
Implementation Method 2
springback caused by residual stress in the flange portion generated in a process of forming occurs after die release
Data Source
Figure 1(a)~1(c)
Figure 2~3
Figure 4(a)~4(b)
AI summary
A press forming method according to the invention forms a press-formed product 1 that has a top portion 3, a side wall portion 5 continuing from the top portion 3, and a flange portion 7 continuing from the side wall portion 5, and is curved in a convex or concave manner in a height direction. The press forming method includes: a first forming process that forms the top portion 3 having the same shape as a target shape of the press-formed product 1 and forms the side wall portion 5 and the flange portion 7 such that a side wall height is larger than the target shape; and a second forming process that reforms a flange side ridge 11 between the side wall portion 5 and the flange portion 7 such that the side wall portion 5 formed by the first forming process has the side wall height of the target shape. The side wall height of the side wall portion 5 formed by the first forming process is set to be larger by addition of a value half or less of a radius of curvature of the flange side ridge 11 in a longitudinal direction vertical cross section of the target shape.