At the start stage of MPF process, only less pins touch the
sheet. These pins endure big forming force which can bring
plastic deformation in a small region around each pin. It is
called dimple. Placing an elastic pad between the pins and sheet
metal, utilizing the deformation of elastic pad to fill the clearance
between pins so as to turn the concentrated load to dispersive
load, can effectively eliminate dimples. Due to the increased
restriction area by elastic pad, wrinkles can be restrained effectively.
Eight nodes solid element is adopted as the element model
for the elastic pad [7].