Manufacturing method for hot-stamped parts

Abstract

The present disclosure provides a method of manufacturing hot-stamped parts, the method including: a heating operation of heating a blank; a transferring operation of transferring the heated blank to a press die including a punch; and a forming and piercing operation of hot-forming the transferred blank into a shape of a hot-stamped part and hot-piercing the transferred blank to form a pierced portion in the hot-stamped part.

1 . A method of manufacturing hot-stamped parts, the method comprising:
 heating a blank;   transferring the heated blank to a press die comprising a punch; and   hot-forming the transferred blank into a shape of a hot-stamped part and hot-piercing the transferred blank to form a pierced portion in the hot-stamped part,   wherein a hot piercing delay time in the forming and piercing operation is within a range of 0 second to λ max  from a time point at which the press die reaches a bottom dead point, and   λ max  is derived by the following Equation 1:   
       
         
           
             
               
                 
                   
                     
                       λ 
                       max 
                     
                     = 
                     
                       
                         ( 
                         
                           
                             
                               a 
                               p 
                             
                             ⁢ 
                             T 
                           
                           + 
                           
                             b 
                             p 
                           
                         
                         ) 
                       
                       * 
                       
                         t 
                         
                           c 
                           p 
                         
                       
                     
                   
                 
                 
                   
                     〈 
                     
                       Equation 
                       ⁢ 
                            
                       1 
                     
                     〉 
                   
                 
               
             
           
         
         (wherein the Equation 1, λ max  refers to a maximum delay time (s) of hot piercing, a p  refers to a correction coefficient considering a forming start temperature and hot piercing conditions, T refers to the forming start temperature (° C.), b p  refers to a correction coefficient considering a pressing force of the press die, c p  refers to a correction coefficient considering thickness sensitivity of a material, and t refers to a thickness (mm) of the material). 
       
     
     
         2 . The method of  claim 1 , wherein
 in the Equation 1, a p  has a value greater than 0 and less than or equal to 0.001, b p  has a value greater than 0 and less than or equal to 0.65, and c p  has a value ranging from about 1 to about 1.2.   
     
     
         3 . The method of  claim 1 , wherein
 in the transferring the heated blank, the heated blank is air cooled at room temperature.   
     
     
         4 . The method of  claim 1 , wherein
 the heating the blank comprises:   a multi-stage heating operation in which the blank is heated step by step; and   a soaking operation in which the blank is heated to a temperature of Ac3 to 1,000° C.   
     
     
         5 . The method of  claim 1 , wherein
 the heating the blank is performed in a heating furnace, and   the heating furnace comprises a plurality of zones having different temperature ranges.   
     
     
         6 . The method of  claim 1 , wherein
 in the forming and piercing, the transferred blank is cooled in the press die.   
     
     
         7 . The method of  claim 6 , wherein
 the pierced portion comprises at least two pierced portions.   
     
     
         8 . The method of  claim 1  wherein a p  is expressed as seconds/(° C.×mm). 
     
     
         9 . The method of  claim 1  wherein b p  is expressed as seconds/mm. 
     
     
         10 . The method of  claim 1  wherein a p  has a value greater than 0 and less than or equal to 0.001; b p  has a value greater than 0 and less than or equal to 0.65; and c p  has a value ranging from about 1 to about 1.2. 
     
     
         11 . The method of  claim 10  wherein a p  is expressed as seconds/(° C.×mm) and b p  is expressed as seconds/mm.