Method and system for using air gaps in hot-stamping tools to form tailor tempered properties

Abstract

A sheet metal blank is hot-stamped between first and second tool surfaces of first and second die tools, respectively, to form a hot-stamped product. That product is then heat treated between the first and second tool surfaces. An actively cooled portion of the tool surfaces quenches part of the hot-stamped product to form a hardened zone. An actively heated portion of the tool surfaces slows heat transfer from the hot-stamped product to the heated portion, which causes the hot-stamped product to have a soft zone. A matrix of insulating gaps is formed in the heated portion to further slow the rate of heat transfer from the hot-stamped product to the heated portion. The insulating gaps may facilitate the use of a lower-temperature heated portion, which may consequently save energy and result in the heated portion having greater wear resistance and longer life.

What is claimed is: 
     
         1 . A hot-stamping method comprising:
 hot-stamping a metal blank between first and second tool surfaces of first and second die tools, respectively, to form a hot-stamped product; and   heat treating the hot-stamped product between the first and second tool surfaces, said heat treating comprises:
 using an actively cooled portion of at least one of the first and second tool surfaces to form a first zone in the hot-stamped product, and 
 using an actively heated portion of at least one of the first and second tool surfaces to form a second zone in the hot-stamped product, wherein the heated portion is heated by a heater that is thermally connected to the heated portion, 
   wherein the heated portion comprises a combination of (1) one or more insulating gaps that cumulatively define a non-contact surface area of the heated portion, wherein the non-contact surface area does not contact the hot-stamped product during the heat treating and (2) one or more contact surfaces that define a contact surface area of the heated portion and contact the hot-stamped product during the heat treating,   wherein the one or more insulating gaps slow heat transfer from the hot-stamped product to the heated portion during said heat treating, and   wherein the heat treating results in a hardness throughout the second zone of less than y Hv, wherein y is 350 Hv.   
     
     
         2 . The method of  claim 1 , wherein a maximum temperature of the heated portion during said hot-stamping and heat treating is at least x° C. cooler than a red hardness temperature of a tool material that forms the heated portion, wherein x is 1. 
     
     
         3 . The method of  claim 2 , wherein x is 25 and y is 220. 
     
     
         4 . The method of  claim 3 , wherein the heat treating results in a hardness in the first zone of at least 350 Hv. 
     
     
         5 . The method of  claim 3 , wherein the heat treating results in a hardness in the first zone of at least 400 Hv. 
     
     
         6 . The method of  claim 3 , wherein:
 the tool material comprises W360; and   the maximum temperature of the heated portion during said hot-stamping is less than 600° C.   
     
     
         7 . The method of  claim 1 , wherein the heat treating results in a hardness in the second zone of less than 220 Hv and a hardness in the first zone of at least 400 Hv. 
     
     
         8 . The method of  claim 1 , wherein a maximum temperature in a core of the first and second die tools during said hot-stamping and heat treating is at least x° C. cooler than a red hardness temperature of a tool material that forms the first and second die tools, wherein x is 1. 
     
     
         9 . The method of  claim 1 , wherein:
 an area of the heated portion is at least 10000 mm 2 ;   the contact surface area occupies less than 50% of the area of the heated portion; and   the contact and non-contact surface area is shaped such that overlaying a circle with a diameter c onto anywhere within the area of the heated portion results in the circle overlaying at least a portion of the contact surface area, wherein c is less than 75 mm.   
     
     
         10 . The method of  claim 1 , wherein the heat treating results in a hardness throughout the second zone of between 180 and 220 Hv. 
     
     
         11 . The method of  claim 10 , wherein the heat treating results in a hardness in the second zone of at least 350 Hv. 
     
     
         12 . The method of  claim 1 , wherein the insulating gaps each comprise air gaps. 
     
     
         13 . The method of  claim 1 , wherein the heated portion comprises a matrix of (1) said one or more insulating gaps or (2) said one or more contact surfaces. 
     
     
         14 . The method of  claim 13 , wherein the matrix comprises a grid of (1) said one or more insulating gaps or (2) said one or more contact surfaces. 
     
     
         15 . The method of  claim 13 , wherein:
 the heated portion comprises first and second heated portions of the first and second tool surfaces, respectively; and   the matrix comprises first and second matrices formed in the first and second heated portions, respectively.   
     
     
         16 . The method of  claim 1 , wherein each of at least 5 of said insulating gaps occupies an area of at least 20 mm 2 . 
     
     
         17 . The method of  claim 1 , wherein each of at least 5 of said insulating gaps are at least 0.1 mm deep. 
     
     
         18 . The method of  claim 1 , wherein each of at least 5 of said insulating gaps have a volume of at least 100 mm 3 . 
     
     
         19 . The method of  claim 1 , wherein, during said heat treating, active heating of the actively heated portion slows a transfer of heat from the hot-stamped product to at least one of the first and second die tools. 
     
     
         20 . A hot-stamping system comprising:
 a first die having a first tool surface;   a second die having a second tool surface, the first and second dies being configured to mate with each other so that the first and second tool surfaces form a die cavity therebetween so as to receive a metal blank therein and hot-stamp the metal blank into a hot-stamped product;   a cooler positioned and configured to cool a cooled portion of at least one of the first and second tool surfaces;   a heater positioned and configured to heat a heated portion of at least one of the first and second tool surfaces; and   the heated portion comprises a matrix of (1) insulating gaps separated by contact surfaces, or (2) contact surfaces separated by insulating gaps,   wherein the insulating gaps are shaped and configured to create a clearance between the hot-stamped product and the heated portion in the area of each of the insulating gaps after the metal blank is hot-stamped,   wherein the contact surfaces are shaped and configured to contact the hot-stamped product after the metal blank is hot-stamped,   wherein the insulating gaps are shaped and configured to slow heat transfer from the hot-stamped product to the heated portion.   
     
     
         21 . The hot-stamping system of  claim 20 , wherein the insulating gaps each comprise air gaps. 
     
     
         22 . The hot-stamping system of  claim 20 , wherein:
 the hot-stamping system is shaped and configured to heat treat the hot-stamped product between the first and second tool surfaces;   the hot-stamping system is shaped and configured to use the cooled portion to form a first zone in the hot-stamped product during the heat treating;   the hot-stamping system is shaped and configured to use the heated portion to form a second zone in the hot-stamped product; and   the first zone is harder than the second zone.   
     
     
         23 . The hot-stamping system of  claim 22 , wherein the heated portion is divided into (1) a non-contact area that is formed by the insulating gaps and is configured not to contact the hot-stamped product during said heat treating, and (2) a contact area that is shaped and configured to contact the hot-stamped product during said heat treating. 
     
     
         24 . The hot-stamping system of  claim 22 , the heater is positioned and configured to slow a transfer of heat from the hot-stamped product to at least one of the first and second die tools during the heat treating. 
     
     
         25 . The hot-stamping system of  claim 20 , wherein the matrix comprises a grid. 
     
     
         26 . The hot-stamping system of  claim 20 , wherein each of at least 5 of said insulating gaps occupies an area of at least 20 mm 2 . 
     
     
         27 . The hot-stamping system of  claim 20 , wherein each of at least 5 of said insulating gaps occupy a volume of at least 100 mm 3 . 
     
     
         28 . The hot-stamping system of  claim 20 , wherein each of at least 5 of said insulating gaps are at least 0.1 mm deep. 
     
     
         29 . The hot-stamping system of  claim 20 , wherein:
 the heated portion comprises first and second heated portions of the first and second tool surfaces, respectively; and   the matrix comprises first and second matrices formed in the first and second heated portions, respectively.