Method and fixture for local softening of hot stamped member

Abstract

A method and fixture for local softening of a hot stamped member is provided. A local region to be softened of a hot stamping blank is covered by a heat-insulating layer, and the heat-insulating layer is covered by a heating layer. After the hot stamping blank is fed into a heating furnace, a local temperature difference is generated, thereby forming a soft region. Then, the hot stamping blank having soft and hard regions is fed into a thermoforming machine so as to be machined into a hot stamped member. A hot stamping blank is subjected to local temperature control during heating to form a hot stamping blank having soft and hard regions, so that a hot stamped member that is locally softened can be formed in one step without the need for tailor welding. Therefore, die costs can be reduced, and the dimensional precision of obtained parts is high.

1 . A method for local softening of a hot stamped member, comprising the following steps:
 laying flat a first heat-absorbing plate;   providing a first heat-insulating blanket on an upper surface of the first heat-absorbing plate;   placing a hot stamping blank on the first heat-insulating blanket, so that a region to be softened thereof faces the first heat-insulating blanket, and a region to be hardened thereof is exposed out of the first heat-insulating blanket;   placing a second heat-insulating blanket on an upper surface of the region to be softened of the hot stamping blank, the position of the second heat-insulating blanket corresponding to that of the first heat-insulating blanket;   providing a second heat-absorbing plate on an upper surface of the second heat-insulating blanket;   feeding, into a heating furnace, a whole member formed by stacking the first heat-absorbing plate, the first heat-insulating blanket, the hot stamping blank, the second heat-insulating blanket, and the second heat-absorbing plate, so as to heat the same, the heating temperature reaching to above the austenization temperature of the hot stamping blank;   maintaining the temperature for several minutes, and taking out the whole member from the heating furnace;   sequentially removing the second heat-absorbing plate, the second heat-insulating blanket, the first heat-insulating blanket, and the first heat-absorbing plate to obtain a hot stamping blank having soft and hard regions; and   feeding the hot stamping blank having the soft and hard regions into a thermoforming machine to machine the hot stamping blank, and rapidly cooling the hot stamping blank to form a hot stamped member.   
     
     
         2 . The method for local softening of a hot stamped member according to  claim 1 , wherein an average heating rate of the heating furnace is 115 to 546° C./min. 
     
     
         3 . The method for local softening of a hot stamped member according to  claim 1 , wherein a heat preservation time during the step of maintaining the temperature in the furnace is determined according to the thickness of the hot stamping blank and performance requirements of the region to be softened, and the heat preservation time is 100 s to 475 s. 
     
     
         4 . The method for local softening of a hot stamped member according to  claim 1 , wherein all of the steps are performed on a conveyor belt, and the first heat-absorbing plate is laid flat on the conveyor belt. 
     
     
         5 . The method for local softening of a hot stamped member according to  claim 1 , wherein the step of laying flat the first heat-absorbing plate to the step of providing the second heat-absorbing plate on the upper surface of the second heat-insulating blanket, and the step of sequentially removing the second heat-absorbing plate, the second heat-insulating blanket, the first heat-insulating blanket, and the first heat-absorbing plate, are all implemented by a manipulator. 
     
     
         6 . The method for local softening of a hot stamped member according to  claim 1 , wherein the region to be softened remains lower than the austenization temperature of the region to be hardened of the hot stamping blank. 
     
     
         7 . The method for local softening of a hot stamped member according to  claim 1 , wherein martensite is not formed in the region to the softened of the hot stamping blank during the step of rapidly cooling the hot stamping blank. 
     
     
         8 . The method for local softening of a hot stamped member according to  claim 7 , wherein martensite is formed in the region to be hardened of the hot stamping blank during the step of rapidly cooling the hot stamping blank. 
     
     
         9 . The method for local softening of a hot stamped member according to  claim 1 , wherein the step of rapidly cooling includes cooling the hot stamping blank to a temperature below 200° C. 
     
     
         10 . The method for local softening of a hot stamped member according to  claim 1 , wherein a manipulator lays flat the first heat-absorbing plate on a conveyor belt, the manipulator places the first heat-insulating blank on the first heat-absorbing plate, the manipulator places the hot stamping blank on the first heat-insulating blanket, the manipulator places the second heat-insulating blank on the upper surface of the region to be softened of the hot stamping blank, and the manipulator placing the second heat-absorbing plant on the upper surface of the second heat-insulating blanket. 
     
     
         11 . The method for local softening of a hot stamped member according to  claim 10 , wherein at least one of the first heat-absorbing plate and the second heat-absorbing plate are made of metal or a metal alloy. 
     
     
         12 . The method for local softening of a hot stamped member according to  claim 10 , wherein at least one of the first heat-insulating blanket and the second heat-insulating blanket are made of ceramic fibers. 
     
     
         13 . The method for local softening of a hot stamped member according to  claim 10 , wherein a conveyor belt feeds the whole member into the heating furnace. 
     
     
         14 . The method for local softening of a hot stamped member according to  claim 13 , wherein after the whole member is removed from the heating furnace, the manipulator sequentially removing the second heat-absorbing plate, the second heat-insulating blanket, the first heat-insulating blanket, and the first heat-absorbing plate from the hot stamping blank. 
     
     
         15 . The method of  claim 14 , wherein, the conveyor belt feeds the hot stamping blank into the thermoforming machine. 
     
     
         16 . A fixture for local softening of a hot stamped member, said fixture comprising a hot stamping blank to be stamped and wherein a first heat-insulating blanket and a first heat-absorbing plate are sequentially stacked below a region to be softened of the hot stamping blank, and a second heat-insulating blanket and a second heat-absorbing plate are sequentially stacked thereabove. 
     
     
         17 . The fixture for local softening of a hot stamped member according to  claim 16 , wherein the thickness of the first heat-insulating blanket or the second heat-insulating blanket is 0.4 to 10 mm. 
     
     
         18 . The fixture for local softening of a hot stamped member according to  claim 16 , wherein the thickness of the first heat-absorbing plate or the second heat-absorbing plate is 0.4 to 10 mm. 
     
     
         19 . The fixture for local softening of a hot stamped member according to  claim 16 , wherein the material of the first heat-insulating blanket or the second heat-insulating blanket comprises, but is not limited to, one or a mixture of ceramic and quartz fibers. 
     
     
         20 . The fixture for local softening of a hot stamped member according to  claim 16 , wherein the material of the first heat-absorbing plate or the second heat-absorbing plate comprises, but is not limited to, one or a mixture of metal and alloy plates.