Press-Formed Part Shape Prediction Under Residual Stress Relaxation
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Solution Overview
Problem
Conventional press forming simulations have low accuracy in predicting shape changes of press formed parts with U-shaped or Z-shaped cross-sectional shapes over time, particularly due to stress relaxation after die release, and fail to account for shape changes without external press loads, which are significant in automotive parts manufacturing.
Innovation Solution
A method that includes a shape/residual stress acquisition step, a residual stress relaxation and reduction setting step, and a residual stress relaxation shape analysis step to predict the shape change of press formed parts with U-shaped or Z-shaped cross-sectional shapes by relaxing and reducing residual stresses in specific portions, allowing for accurate simulation of stress relaxation and shape changes over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional press forming simulation is used to predict shape immediately after die release, then springback shape can be predicted, but shape change with lapse of time cannot be accurately predicted
Solution Approach 1:
The patent performs preliminary stress relaxation analysis before final shape prediction. By calculating residual stress distribution immediately after die release and predicting stress relaxation with lapse of time in advance, the method determines the shape change that occurs over time before comparing with actual measurement, thereby resolving the contradiction between predicting immediate springback shape and time-dependent shape changes
Solution Approach 2:
The patent introduces feedback by comparing predicted shape (immediately after die release and after stress relaxation) with actual measured shape of press-formed parts. This feedback loop allows correction and improvement of prediction accuracy for shape changes that occur with lapse of time, addressing the limitation of conventional simulation methods
2Strength
If high-strength metal sheet is used for press forming, then collision safety and weight reduction are achieved, but springback increases and dimensional accuracy decreases
Solution Approach 1:
The patent changes the parameter of residual stress by introducing stress relaxation analysis. By calculating how residual stress decreases with lapse of time and incorporating this stress relaxation into the prediction model, the method accurately predicts shape changes in high-strength metal sheets while maintaining the benefits of using high-strength materials for collision safety and weight reduction
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 enables accurate prediction of shape changes in press formed parts, improving dimensional accuracy and manufacturing efficiency for automotive parts by simulating the twist in the longitudinal direction of press formed parts with U-shaped or Z-shaped cross-sectional shapes after die release and springback.
Implementation Method 1
a shape change in which an end side in a longitudinal direction is twisted due to stress relaxation with the lapse of time after springback
Data Source
AI summary
A shape change prediction method of a press formed part predicts a shape change in which an end side in a longitudinal direction is twisted due to stress relaxation with a lapse of time after springback at a moment of die release from a tool of press forming with respect to the press formed part having a U-shaped cross-sectional shape including a top portion and side wall portions, and includes: acquiring a shape and a residual stress of the press formed part immediately after the springback by a springback analysis of the press formed part; setting a value of stress relaxed and reduced compared to the residual stress immediately after the springback for at least one of the side wall portions; and acquiring a shape with which moment of force is balanced for the press formed part in which the value of the relaxed and reduced stress is set.