Understanding Blank Holder Effect on Formability of Sheet Metal Stampings

Blank holder design, set-up and maintenance are crucial for successful stamping of sheet metal parts. Educated spotting as well as adjustment of the appropriate levels of blank holder forces at the different contact areas is a complex process involving the interaction of die design, die making, prototyping and set-up.

The response of the part to a blank holder set-up depends on the type of press and the source of blank holder action. A finite difference based microcomputer program CUPDRW will be used to illustrate the effect of the type of blank holder and its set-up on the formability of circular drawn shells. A methodology is also presented in this work for the design of blankholders and its set-up for complex parts formed under drawing conditions.

It has been recognized by the industry that control of process and material windows is a prerequisite to the production of quality parts. The paper concludes by examining the effect of material gauge variability and blank holder positioning repeatability on part formability. It is shown that parts drawn in double-action mechanical presses are more sensitive to gauge variability as compared to parts formed with air and hydraulic cushions.