Method and press for producing sheet metal parts that are hardened at least in regions

Abstract

A method for producing a sheet metal part with a press includes the steps of heating a sheet metal blank at least in regions to a above the austenitizing temperature Ac3, inserting the heated sheet metal blank into a forming tool station of the press, hot forming the sheet metal blank to the sheet metal part in the forming tool station, during which the press performs a closing movement, holding the forming tool station closed for a first holding time and cooling the formed sheet metal part during the first holding time, transferring the formed sheet metal part into a second tool station, hardening at least regions of the sheet metal part by cooling in the second tool station within the at least one second holding time, wherein the forming tool station during the closing movement of the press from an upper reversal point to a lower reversal point is moved relative to the press by at least one elastic actuating element so that the hot forming is terminated and the step of holding the forming tool station closed starts before the press reaches the lower reversal point.

What is claimed is: 
     
         1 . A method for producing a sheet metal part which is hardened at least in regions in a press, which has a press table, a press ram and multiple tool stations, comprising the steps of:
 heating at least regions of a sheet metal blank to a temperature above austenitizing temperature Ac3;   inserting the heated sheet metal blank into a first one of the tool stations of the press, said first tool station being configured as forming tool station;   hot forming the sheet metal blank to the sheet metal part in the forming tool station, wherein the press during the hot forming step performs a closing movement from an upper reversal point to a lower reversal point;   holding the forming tool station closed for a first holding time;   cooling the formed sheet metal part during the first holding time;   transferring the formed sheet metal part into a second one of the tool stations tool; and   hardening the sheet metal part at least in regions by cooling the sheet metal part in the second tool station within a second holding time,   wherein the forming tool station during the closing movement of the press is moved relative to the press by at least one elastic actuating element so that the hot forming is terminated and the step of holding the forming tool station closed starts before the press reaches the lower reversal point, wherein the upper die and the lower die have cooling channels through which a coolant is conducted.   
     
     
         2 . The method of  claim 1 , wherein the step of holding the forming tool station closed is terminated by the at least one elastic actuating element during an upward movement of the press after the press has completely passed the lower reversal point. 
     
     
         3 . The method of  claim 1 , further comprising performing a trimming and/or a hole punching in the forming tool station, 
     
     
         4 . The method of  claim 3 , wherein the trimming and/or hole punching is performed before the press is completely closed. 
     
     
         5 . The method of  claim 1 , wherein a second one of the multiple tool stations is moved at least in regions relative to the press during the closing movement of the press by at least one other actuating element, so that a closed state of the second tool station is initiated before the press has reached the lower reversal point. 
     
     
         6 . The method of  claim 5 , wherein the closed state of the second tool station is terminated at least in regions by the at least one other elastic actuating element during an upward movement of the press after the press has completely passed the lower reversal point. 
     
     
         7 . The method of  claim 1 , wherein the forming tool station and preferably also the second tool station are mechanically, hydraulically or pneumatically spring supported by the at least one elastic actuating element. 
     
     
         8 . The method of  claim 1 , further comprising transporting the sheet metal part between two respective ones of the multiple tool stations with a transfer system, in particular with a linearly guided transfer bar with grippers, within a transfer time between 1 to 4 seconds, preferably between 2 to 3 seconds. 
     
     
         9 . The method of  claim 1 , further comprising, in the forming tool station cooling a first section of the sheet metal part to a first cooling temperature that is greater than a martensite start temperature required for transformation of a martensite microstructure, and cooling a second section of the sheet metal part to a second cooling temperature that is smaller than the martensite start temperature, wherein the first cooling temperature is in particular between 540 to 660° C., thereby producing a sheet metal component that is hardened in regions. 
     
     
         10 . The method of  claim 9 , further comprising adjusting a cooling temperature in the second tool station so that at the end of the second holding time a temperature of the first section of the sheet metal part is between 350 to 500° C. and a temperature of the second section of the sheet metal part is smaller than a martensite finishing temperature required for a complete transformation of the martensite microstructure, wherein the second section of the sheet metal part is preferably cooled in the second tool station to below 200° C., in particular to room temperature. 
     
     
         11 . The method of  claim 1 , wherein the first holding time is between 2 and 8 seconds and the second holding time is between 2 and 10 seconds. 
     
     
         12 . The method of  claim 1 , wherein a cycle time of the press to move between the upper reversal point and the lower reversal point is between 3 and 11 seconds. 
     
     
         13 . The method of  claim 1 , wherein the hardening step is terminated in a third tool station, and wherein after the hardening step an entirety of the sheet metal part has a cooling temperature of below 200° C. 
     
     
         14 . The method of  claim 13 , wherein the press comprises a third tool station and wherein a cycle time of the press to move between the upper reversal point and the lower reversal point is between 3 and 9 seconds. 
     
     
         15 . A press for producing a sheet metal part that is hardened at last in regions, in particular for implementing the method of  claim 1 , said press comprising:
 multiple tool stations, at least one of the multiple tool stations being constructed as a forming tool station that is coolable at least in regions and being configured for hot forming of sheet metal blanks, said forming tool station having an upper die and a lower die which in a closed state of the forming tool station form a hollow mold space;   a press ram; and   a press table;   at least one elastic actuating element arranged between the press table and the lower die so that either the lower die is liftable relative to the press table and/or the upper die is impingable with pressure at a distance relative to the press ram to cause the forming tool station to assume the closed state before the press is completely closed, wherein the upper die and the lower die have cooling channels through which a coolant is conductible.   
     
     
         16 . The press of  claim 15 , wherein the at least one elastic actuating element is configured so that a vertical travel of the press is adjustable by the at least one elastic actuating element, said vertical travel being at least 100 mm and smaller than a maximal stroke traveled by the press between the upper and the lower reversal point of the press. 
     
     
         17 . The press of  claim 15 , wherein the at least one elastic actuating element exerts an actuating force, which increases at least over a portion of a travel of the press from the upper reversal point to the lower reversal point of the press, in particular the actuating force is at least 20 percent greater in the closed state of the forming tool station. 
     
     
         18 . The press of  claim 12 , wherein at least the forming tool station is heatable in regions by a heating source so as to effect a reduced cooling rate in a first section of the sheet metal part, wherein unheated regions of the forming tool station have cooling channels for conducting a coolant. 
     
     
         19 . The press of  claim 12 , wherein the press comprises a second tool station following the forming tool station, and wherein the forming tool station and at least the second tool station are heatable at least in regions in particular by a heating source to prevent a complete hardening at least in a first section of the sheet metal part. 
     
     
         20 . The press of  claim 19 , wherein an unheated region of the second tool station has an active cooling source that corresponds at least to a transition section between the first section and the second section of the sheet metal part. 
     
     
         21 . The press of  claim 20 , wherein the first section and the transition section of the sheet metal part are form fittingly fixable at least in the second tool station by fixing elements.