Punch

Abstract

A punch for use in molding a workpiece with lubricating oil interposed between the punch and the workpiece includes a straight portion at its end and a diameter-increasing portion. The straight portion includes an end face at its end and a side face. The straight portion extends in an axial direction. The end surface extends in a radial direction perpendicular to the axial direction. The side surface is connected to the end surface. The diameter-increasing portion is connected to the straight portion. The diameter-increasing portion includes a width in the radial direction, which is identical to that of the straight portion, at a junction between the straight portion and the diameter-increasing portion. The width of the diameter-increasing portion in the radial direction increases with distance from the straight portion. At least one of the end surface and the side surface of the straight portion is formed with a pit.

1 . A punch for use in molding a workpiece with lubricating oil interposed between the punch and the workpiece, the punch comprising: 
 a straight portion at an end of the punch, the straight portion extending in an axial direction, the straight portion comprising: 
 an end surface at an end thereof, the end surface extending in a radial direction perpendicular to the axial direction; and  
 a side surface connected to the end surface; and  
   a diameter-increasing portion connected to the straight portion, the diameter-increasing portion comprising a width in the radial direction, which is identical to that of the straight portion, at a junction between the straight portion and the diameter-increasing portion, the width of the diameter-increasing portion in the radial direction increasing with distance from the straight portion, wherein:    at least one of the end surface and the side surface of the straight portion is formed with a pit.    
   
   
       2 . The punch according to  claim 1 , wherein the diameter-increasing portion further comprises a side surface, which is not formed with any pit.  
   
   
       3 . The punch according to  claim 1 , wherein the side surface of the straight portion is formed with a plurality of the pits.  
   
   
       4 . The punch according to  claim 1 , wherein the end surface of the straight portion is formed with a plurality of the pits.  
   
   
       5 . The punch according to  claim 3 , wherein a ratio of a total of areas of bottom surfaces of the pits to a surface area of the straight portion is in a range of 20% to 80%.  
   
   
       6 . The punch according to  claim 1  wherein: 
 the end surface of the straight portion is formed with a plurality of the pits,    the side surface of the straight portion is formed with a plurality of the pits, and    the end surface of the straight portion is higher in distribution density of the pits than the side surface of the straight portion.    
   
   
       7 . The punch according to  claim 1 , further comprising: 
 a base material, wherein:    a coating film is formed on a surface of the base material, and    the coating film has at least one of (i) friction coefficient lower than that of the base material and (ii) hardness larger than that of the base material.    
   
   
       8 . The punch according to  claim 7 , wherein the coating film comprises a surface layer comprising a DLC coating film.  
   
   
       9 . The punch according to  claim 8 , wherein the coating film further comprises an intermediate layer, which comprises one of a chromium coating film and a tungsten coating film, between the DLC coating film and the base material.  
   
   
       10 . The punch according to  claim 9 , wherein the intermediate layer comprises: 
 a metal layer consisting essentially of one of chromium and tungsten, the metal layer formed on the base material; and    a gradient composition layer of chromium and carbon or of tungsten and carbon formed on the metal layer.    
   
   
       11 . The punch according to  claim 8 , wherein the pit has a depth so as not to pass through the DLC coating film.  
   
   
       12 . The punch according to  claim 1 , wherein: 
 the base material comprises hard metal comprising carbide containing at least one selected from the group consisting of tungsten carbide, vanadium carbide, titanium carbide and tantalum carbide, and    a mean particle size of the carbide of the hard metal is equal to or larger than 0.05 μm and is less than 0.3 μm.    
   
   
       13 . A punch for use in molding a workpiece with lubricating oil interposed between the punch and the workpiece, the punch comprising: 
 a diameter-increasing portion at an end of the punch, the diameter-increasing portion comprising an end surface extending in a radial direction perpendicular to an axial direction of the punch, the width of the diameter-increasing portion increasing with distance from the end surface, wherein:    the end surface of the diameter-increasing portion is formed with a pit.    
   
   
       14 . The punch according to  claim 13 , wherein the diameter-increasing portion further comprises a side surface, which is not formed with any pit.  
   
   
       15 . The punch according to  claim 13 , wherein the end surface of the diameter-increasing portion is formed with a plurality of the pits.  
   
   
       16 . The punch according to  claim 13 , further comprising: 
 a base material, wherein:    a coating film is formed on a surface of the base material, and    the coating film has at least one of (i) friction coefficient lower than that of the base material and (ii) hardness larger than that of the base material.    
   
   
       17 . The punch according to  claim 16 , wherein the coating film comprises a surface layer comprising a DLC coating film.  
   
   
       18 . The punch according to  claim 17 , wherein the coating film further comprises an intermediate layer, which comprises one of a chromium coating film and a tungsten coating film, between the DLC coating film and the base material.  
   
   
       19 . The punch according to  claim 18 , wherein the intermediate layer comprises: 
 a metal layer consisting essentially of one of chromium and tungsten, the metal layer formed on the base material; and    a gradient composition layer of chromium and carbon or of tungsten and carbon formed on the metal layer.    
   
   
       20 . The punch according to  claim 17 , wherein the pit has a depth so as not to pass through the DLC coating film.  
   
   
       21 . The punch according to  claim 13 , wherein: 
 the base material comprises hard metal comprising carbide containing at least one selected from the group consisting of tungsten carbide, vanadium carbide, titanium carbide and tantalum carbide, and    a mean particle size of the carbide of the hard metal is equal to or larger than 0.05 μm and is less than 0.3 μm.