Abstract:Viscous pressure forming (VPF),is suitable for forming difficult- to-form sheet metal parts. An investigation in the effect of blank holder pressure (BHP) on VPF aluminum alloy ladder parts was conducted.Based on experimental and numerical simulation results of the effect of BHP on dimensional accuracy, wall-thick ness reduction,forming pressure, material flow and defects (such as wrinkling and fracture) of specimens,the effect patterns of BHP load path on VPF ladder parts were explained.The limits of BHP corresponding to specimens with no defect and with wrinkling or fracture defect were determined.In the limits of formable BHP,the variable load path of BHP was beneficial to drawing blank into the die and decreasing wall-thickness reduction of specimens.The experimental results show that the ladder parts of good surface fineness and high dimensional accuracy can be obtained by variable load paths of BHP.

Key words: viscous pressure forming; ladder parts;blank holder pressure; aluminum alloy