Improvement in formability by control of temperature in hot stamping of ultra-high strength steel parts

The formability in hot stamping of an ultra-high strength steel part was improved by preventing a temperature drop of the flange increasing resistance to drawing. The temperature drop was reduced by high speed forming using a servo press and by less contact with a die and blankholder using spacers thicker than the sheet. In addition, hardening of the flange was prevented by slow cooling for the less contact using the spacers to facilitate trimming of the hot-stamped part. From a hot deep drawing experiment with a hemispherical punch, the effectiveness of the present approaches of temperature control was demonstrated.