Hot press forming method

Abstract

A steel plate is heated so that an average temperature becomes Ac3 point or higher, a press forming is performed on the steel plate by use of a mold, and the steel plate is cooled during press forming. A formed product is removed from the mold, and the formed product is cooled further. In the hot press forming method, although a quantity of change in shape of the formed product decreases as a removal temperature of the formed product decreases. When the removal temperature of the formed product is lower than 322° C., no more improvement on an accuracy of the formed product can be realized, and a time during which the mold is occupied exclusively to cool the formed product becomes long. When the removal temperature of the formed product is 510° C. or lower, the rate of change of the quantity of change in shape with change in temperature is increased drastically, whereby an increase in accuracy of the formed product can be realized. Consequently, the removal temperature of the formed product is set to a temperature range from 322° C. or higher to 510° C. or lower.

1 . A hot press forming method comprising:
 heating a steel plate so that an average temperature of the steel plate becomes Ac3 point or higher;   executing a press forming on the steel plate whose average temperature is so set by use of a mold;   cooling the steel plate during press forming;   removing a formed product from the mold, while the average temperature of the formed product stays within a temperature range from 322° C. or higher to 510° C. or lower; and   cooling the formed product further.   
     
     
         2 . The method according to  claim 1 , further comprising:
 setting the average temperature of the steel plate to 366° C. or higher, when the steel plate is removed from the mold.   
     
     
         3 . The method according to  claim 1 , further comprising:
 setting the average temperature of the steel plate to 451° C. or lower, when the steel plate is removed from the mold.   
     
     
         4 . The method according to  claim 1 , further comprising:
 setting the average temperature of the steel plate to 451° C. or lower, when the steel plate is removed from the mold.