A numerical method and a material model were examined because of the precision improvement needed for the prediction of the following : (1) the strain prediction when deformation is concentrated on the local part of workpiece from the half way of the forming process. (2) the spring-back prediction.

The strain prediction technique combines the static implict method with the dynamic explicit method. The square-cup drawing process is numerically analyzed by this method. It was found out that the strain could be predicted within a practical calculation time and precision useing this technique. The most notable feature of this spring-back prediction is that in order to precisely predict the spring-back behavior of the formed sheet, the non-linear property of the sheet material during unloading is taken into consideration. Various results of the present calculation (into which the proposed material model is newly introduced) are compared with the experimental ones, regarding the material strength range, the die shoulder radius, and the blank-holding force. It is confirmed that the proposed method can precisely predict the spring-backed shape.
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