Method of predicting die lives

Abstract

Disclosed is a method of predicting lives of dies for plastic processing of metals, typically, forging dies, to enable improved die design by predicting an important factor, low cycle fatigue life FL (shot number possible until the die lives end). The method is characterized in that the low cycle damage value “Dc” defined by the formula: Dc=σ eq /(YS×softening rate), wherein, σ eq is Von Misese's equivalent stress, YS is yield stress (including both of those at tension and compression), and that the following formula is introduced: FL=C 1 ×exp(C 2 ×Dc C3 ), wherein, FL is shot number until the die fracture, and C 1 , C 2 and C 3 are constants depending on the material used, so as to presume the possible shot number of the die.

1 . A method of predicting die lives enabling design of improved dies by predicting low cycle fatigue life of dies, which give important influence to die lives, characterized in that the low cycle damage value “Dc” defined by the formula below is calculated:  
         Dc=σ   eq /( YS× softening rate)  
     wherein, σ eq  is Von Misese's equivalent stress, YS is yield stress (including both of those at tension and compression), and that the following formula expressing the low cycle fatigue life “FL” is introduced:  
         FL=C   1 ×exp( C   2   ×Dc   C3 )  
     wherein, FL is shot number until the die fracture, and C 1 , C 2  and C 3  are constants depending on the material used, so as to presume the possible shot number of the die.  
   
   
       2 . A method of predicting die lives enabling design of improved dies by predicting low cycle fatigue life of dies, which give important influence to die lives, characterized in that low cycle life tests under “tension-tension” and “tension-compression” are carried out at respective die materials so as to comprehend the relation between the cycle and the stress amplitude, and using the results, the low cycle damage value “Dc” defined by the formula:  
     
       
         
           
             
               Dc 
               fatigue 
             
             = 
             
               
                 { 
                 
                   
                     maximum 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     tensile 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     stress 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ( 
                       
                         σ 
                         damage 
                       
                       ) 
                     
                   
                   + 
                   
                     ?? 
                     ⁢ 
                     
                       × 
                       
                           
                       
                       ⁢ 
                       maximum 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       compressive 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       stress 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                          
                         
                           σ 
                           damage 
                         
                          
                       
                     
                   
                 
                 } 
               
               / 
               
                 ( 
                 
                   YS 
                   × 
                   softening 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   rate 
                 
                 ) 
               
             
           
         
       
       wherein, “σ damage ” is damage stress defined as below, “?” is a constant depending on the material, and “YS” is as mentioned above:  
         σ damage =σ eq (σ 1max −σ 1min ≧0)  σ damage =−σ eq (σ 1max −σ 1min −0)  
       wherein, σ eq  is the above-mentioned Von Misese's equivalent stress, σ 1max  is maximum main stress, and σ 1min  is minimum main stress;  
       and that, on this basis, the following formula expressing the low cycle fatigue life “FL” is introduced:  
           FL=C   1 ×exp( C   2   ×Dc   C3 )  
       wherein, FL is the shot number until the fracture, and C 1 , C 2  and C 3  are constants depending on the material used, so as to presume the possible shot number of the die.