Blank holder force (BHF) control in viscous pressure forming (VPF) of sheet metal

An eight-point BHF control system with a flexible blank holder is designed and built as part of an experimental viscous pressure forming (VPF) machine. This paper describes results of VPF experiments, and addresses several blank holding issues specific to the VPF process. FEM simulations of hydroforming with a multi-point BHF control and an elastic blank holder are conducted to fine-tune the control system as well as to predict the forming loads. The FEM results are compared with experimental VPF results. The viscous medium “blow through” phenomenon between the blank holder and the sheet during VPF is described and quantified.