Press-Formed Part Shape Prediction Using Residual Stress Relaxation
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Solution Overview
Problem
Current press forming simulations have low accuracy in predicting shape changes of press formed parts after springback, especially over time, due to the lack of consideration for stress relaxation phenomena and creep effects, which are not adequately addressed in conventional analysis methods.
Innovation Solution
A shape change prediction method that includes a shape/residual stress acquisition step, a residual stress relaxation/reduction setting step, and a shape analysis step to simulate stress relaxation and predict shape changes over time, by reducing residual stresses based on their ratio to the tensile strength of the metal sheet and balancing moments of force in the press formed part.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a high-strength metal sheet is used for press forming, then weight reduction and collision safety are improved, but dimensional accuracy deteriorates due to increased springback
Solution Approach 1:
The patent applies preliminary action by performing a press forming simulation before actual manufacturing to predict springback shape changes. The simulation results are used to determine corrective amounts that are applied in advance to the die shape or forming parameters, compensating for the expected springback and ensuring dimensional accuracy in the final pressed part.
2Productivity
If conventional press forming simulation is used to predict shape change, then prediction speed is maintained, but prediction accuracy decreases for certain press formed parts
Solution Approach 1:
The patent implements feedback by measuring the actual shape of pressed parts and comparing it with simulation results. The difference (correction amount) is fed back to improve the simulation model, creating a closed-loop system that continuously enhances prediction accuracy while maintaining computational efficiency.
Solution Approach 2:
The patent applies parameter changes by adjusting simulation parameters such as material properties, boundary conditions, or geometric parameters based on the comparison between simulated and actual measurements. This allows the simulation model to adapt to specific part characteristics and improve accuracy without requiring complete remodelling.
3Strength
If the metal sheet has higher strength, then the residual stress generated by press forming becomes larger, but the shape change due to springback becomes more difficult to control
Solution Approach 1:
The patent uses preliminary simulation to predict the magnitude and distribution of residual stress and springback in high-strength materials. Based on these predictions, corrective measures are planned in advance, such as modifying die geometry or applying pre-stress, to compensate for the larger expected springback in high-strength metal sheets.
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 allows for accurate simulation and prediction of shape changes in press formed parts after springback, improving prediction accuracy by accounting for stress relaxation and creep effects, leading to better dimensional control and reduced shape deviation from the target form.
Implementation Method 1
a shape change generated in a press formed part to which a press load is not applied from the outside in a manner illustrated in FIG. 5 has not been known until now
Implementation Method 2
such a shape change of the press formed part with the lapse of time units seems to be similar to a phenomenon in which a structural member that keeps receiving a high press load from the outside gradually deforms, such as a creep phenomenon
Data Source
AI summary
A shape change prediction method for a press formed part for predicting a shape change of the press formed part with a lapse of time units after springback at a moment of a release from a die includes: a shape/residual stress immediately after springback acquisition step of 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; a residual stress relaxation/reduction setting step of setting a value of a residual stress relaxed and reduced from the acquired residual stress to the press formed part immediately after the springback; and a shape analysis step of determining a shape, in which moments of force are balanced, for the press formed part to which the value of the relaxed and reduced residual stress is set.