Failure and forming quality study of metallic foil blanking with different punch-die clearances

As an important forming parameter, the influence of punch-die clearance on thick plate blanking has been extensively discussed. In contrast, the analysis and prediction of metallic foil blanking are more difficult due to the size effect caused by thickness reduction. To explore the clearance effects at a meso-scale, a series of blanking tests of 304 stainless steel foils with 100 μm thickness were carried out at 5, 10, and 15 μm punch-die clearances. Corresponding working conditions were also numerical simulated, where the damage mechanism was described using an extended Gurson-Tvergaard-Needleman model while the size effect was characterized using a mechanism-based strain gradient (MSG) theory. The results indicated that damage was observed to evolve as a function of the machining process. Furthermore, shear damage was underestimated without considering the size effect, resulting in inaccurate failure punch penetration prediction. In terms of forming quality, a decrease in the clearance resulted in a proximate damage value on the punch and die side materials along with a decrease in the shear band width. The change in clearance is negatively correlated to the rollover and burnish lengths, and positively correlated to the fracture length. The introduction of the MSG theory made the simulation results more consistent with the scanning electron microscope (SEM) observations of the sheared edges. Overall, this study presented an advanced simulation method and contributes to optimal clearance selection with respect to forming quality prediction for foil blanking.