Abstract
The influence of the central hole-edge condition on the hole expansion ratio (HER) of four automotive-grade steel sheets is experimentally investigated in this work. The punched hole shows inferior HER for all selected automotive-grade steel sheets than the wire-electrical discharge machined (WEDM) hole. The finite element simulation approach is used to determine the influence of the coefficient of friction and spring-back on HER. With an increased coefficient of friction, the punch force increases. Material near the inner edge of the central hole comes out in the direction of the sliding punch in the presence of friction. Spring-back has a small effect on HER, and its importance increases for lesser HER materials.
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