Abstract:Smart hot stamping processes of ultra-high strength steel parts have been developed to overcome difficulties in the present hot stamping process. Using rapid resistance heating, the stamping equipment became considerably simpler than that using furnace heating. The formability was improved by high speed hot stamping using a mechanical servo press in comparison with the conventional process using a hydraulic press. Parts having a different distribution of strength were produced by tailored die quenching using local bypass resistance heating. Die-quenched steel parts and ultra-high strength steel sheets were sheared by reducing the flow stress in the shearing zone using local resistance heating. An ultra-high strength steel gear drum was produced by hot spline forming using resistance heating of side wall of a cup. V-shaped hot forming using sealed air was developed to produce ultra-high strength hollow axle beams used for suspensions of automobiles. A one shot hot stamping process consisting of resistance heating, forming, shearing and die quenching was applicable to comparatively small high strength steel parts.

Key words: hot stamping; ultra-high strength steel; die quenching; tailored die quenching; spline forming; tube forming; one shot forming