Strain Path Effects on the Modified FLD Caused by Variable Blank Holder Force 950695
The objective in this research is to investigate the effects of variable blank holder force (VBHF) on the material formability, due to its effect on the strain path. It is found in a recent study  that VBHF does not significantly affect the overall trend of the strain path. This strain path in deep drawing process is linear for the materials in the flange and under punch face, and is roughly bi-linear for the material around the punch nose. The second segment of the strain path in the punch nose region is plane-strain. VBHF, however, affects the strain ratio ρ1 = ε2/ε1 of the first segment of the bi-linear strain path. These effects, especially ρ1, on limit strain were studied using M-K method. A strain path dependent modified forming limit diagram (MFLD) was calculated based on the actual strain path. It is found that the MFLD is strongly dependent on ρ1. The effects of various loading conditions on formability (i.e. on the shape of MFLD) were discussed through their effects on ρ1. It is shown that a suitable VBHF can improve the formability of material in deep drawing process. A calibration diagram that gives modification value due to the effect of strain path was suggested. The modified FLD can be obtained by adding the modification value to the conventional FLD.
In order to verify model predictions, experiments are being carried out, using a recently-built apparatus and the results will be published later.