Method and device for producing hardened steel components

Abstract

The invention relates to a method for press hardening sheet steel components in which a blank is detached from a sheet steel band composed of a hardenable steel alloy and the blank is then austenitized, in that it is heated to a temperature greater than Ac3 and is then inserted into a forming tool and formed in the forming tool, and during the forming, is cooled at a speed greater than the critical hardening speed, characterized in that in order to inhibit microcracks of the second type from being produced during the forming and hardening process in the sheet metal blanks that are to be formed, oxygen is supplied adjacent to the positive radii and/or drawing edges; the invention also relates to a device for performing this method.

1 . A method for press hardening sheet steel components in which a blank is detached from a sheet steel band composed of a hardenable steel alloy and the blank is then austenitized, the method comprising: heating the blank to a temperature greater than Ac 3 ; inserting the blank into a forming tool having a mold cavity; and forming the blank in the forming tool, wherein during the forming, the blank is cooled at a speed greater than the critical hardening speed, characterized in that in order to avoid microcracks of second type from forming in the sheet metal blanks to be formed during the forming and a subsequent hardening, an oxygen-containing fluid reservoir is present
 adjacent to positive radii and/or drawing edge and/or   in other contact regions outside of the positive radii and/or drawing edges.   
     
     
         2 . The method according to  claim 1 , characterized in that entry of oxygen takes place by means of at least one recess provided in the forming tool adjacent to the drawing edges and/or positive radii, which are dimensioned so that deep drawing is not negatively affected and the recess forms a reservoir for oxygen-containing fluids or else oxygen-containing fluids can be supplied via this recess. 
     
     
         3 . The method according to  claim 2 , characterized in that the entry of oxygen-containing fluid is ensured by means of the air that is present in the recess. 
     
     
         4 . The method according to  claim 2 , characterized in that the recess is supplied with fluids or oxygen or oxygen-containing fluids from the forming tool side, or the recess or mold cavity is supplied with fluids, in particular oxygen or an oxygen-containing fluid, between two forming procedures. 
     
     
         5 . The method according to  claim 2 , characterized in that vacuum is applied to the recess. 
     
     
         6 . The method according to  claim 1 , characterized in that oxygen-containing fluid is supplied continuously. 
     
     
         7 . A device for performing the method according to  claim 1 , having two faulting tool halves; the two forming tool halves cooperate in order to deep-draw a blank and are embodied so that they can move toward and away from each other; depending on a desired forming contour, at least one positive radius ( 1 ) or one drawing edge region ( 1 ) is provided with a drawing edge ( 2 ), wherein a recess ( 5 ) is provided
 in a surface ( 4 ) that is situated after the drawing edge ( 2 ) or the positive radius ( 1 ) in the drawing direction and/or   in other contact regions outside of the positive radii ( 1 ) and/or drawing edge ( 2 ).   
     
     
         8 . The device according to  claim 7 , characterized in that the recess ( 5 ) is dimensioned so that the remaining thickness of the drawing edge ( 2 ) between a surface, which adjoins the drawing edge ( 2 ), and the recess ( 5 ) corresponds approximately to its radius. 
     
     
         9 . The device according to  claim 7 , characterized in that the recess ( 5 ) between the drawing edge ( 2 ) and a forming tool surface ( 4 ) has a height, which corresponds to approximately 25 to 35 mm at a depth of 5 to 9 mm or is embodied as a groove ( 6 ), which has a height between the surface ( 4 ) and the drawing edge ( 2 ), which totals approximately 8 to 12 mm, with a depth of 5 to 9 mm or in the region of the wall ( 4 ) adjacent to the drawing edge ( 2 ), a plurality of recesses in the form of grooves ( 7 ) extending in the drawing direction; and the grooves ( 7 ) or slots ( 7 ) have a slot width of 4 to 8 mm and a slot spacing of 7 to 11 mm so that remaining bridge pieces have a width of 1 to 5 mm. 
     
     
         10 . The device according to  claim 9 , characterized in that the recesses ( 5 ), the grooves ( 6 ), or the slot ( 7 ) are supplied from the rear, i.e. from the tool side, with an oxygen-containing fluid by means of supply openings and correspondingly drilled lines.