MULTI-STAGE STAMPING OF HIGH STRENGTH STEEL WHEEL DISK

High strength steel blank with less blank thickness was employed in the multi-stage stamping of a wheel disk to obtain a reduction in weight. The increase in thickness at the inner corner of the high strength steel disk becomes small if compared to the mild steel disk for similar forming conditions. The small increase in thickness is mainly due to the decrease in blank thickness. Since the fatigue strength of the disk sharply decreases even for a small decrease in thickness at the inner corner, a tailor blank with local thickening at the portion equivalent to the inner corner formed by stamping was employed in the multi-stage stamping to improve the increase in thickness at the inner corner. A tailor blank with an average increase in thickness of 8.2% at the equivalent portion was formed, and the wall thickness at the inner corner of the stamped disk was successfully increased by 14.5%.