Punching apparatus and method

Abstract

A punching apparatus includes a plurality of punches for punching a workpiece, a pad, and a single piston supporting the pad. The punches are disposed on a top surface of a portion of the pad. The top surface has a circumference circumscribing circumferences of outermost ones of the punches. A diameter of the piston is larger than a diameter of the portion of the pad.

What is claimed is: 
     
         1 . A punching apparatus comprising:
 a plurality of punches for punching a workpiece;   a pad; and   a driving mechanism for moving the pad and the punches together between an advanced position and a retracted position,   wherein the pad is supported on the driving mechanism and the punches are disposed on a top surface of a portion of the pad, the top surface having a circumference circumscribing circumferences of outermost ones of the punches, and wherein the driving mechanism has a diameter and the portion of the pad has a diameter, the diameter of the driving mechanism being larger than the diameter of the portion of the pad.   
     
     
         2 . The apparatus of  claim 1 , wherein the driving mechanism comprises a single piston having a diameter being the diameter of the driving mechanism. 
     
     
         3 . The apparatus of  claim 1 , wherein the driving mechanism comprises a plurality of pistons including outermost pistons having circumferences inscribed in a circle having a diameter being the diameter of the driving mechanism. 
     
     
         4 . The apparatus of  claim 1 , wherein the driving mechanism comprises a plurality of pistons, the pistons have portions contacting the portion of the pad, and a total cross-sectional area of the portions of the pistons is more than 80% of a cross-sectional area of the portion of the pad. 
     
     
         5 . The apparatus of  claim 4 , wherein the pistons are the same in cross-sectional area. 
     
     
         6 . The apparatus of  claim 1 , wherein the punches are arranged to punch the workpiece for forming plate-shaped elements for a metal belt of a belt-type continuously variable transmission, such that the elements are stacked in a peripheral direction of the belt. 
     
     
         7 . A punching method comprising the steps of:
 (i) providing a metal sheet and a punching apparatus, the punching apparatus comprising:
 a plurality of punches; 
 a pad; and 
 a driving mechanism for moving the pad and the punches together between an advanced position and a retracted position, 
 wherein the driving mechanism supports the pad and the punches are disposed on a top surface of a portion of the pad, the top surface having a circumference circumscribing circumferences of outermost ones of the punches, and wherein the driving mechanism has a diameter and the portion of the pad has a diameter, the diameter of the driving mechanism being larger than the diameter of the portion of the pad; and 
   (ii) activating the punches to punch the sheet for forming elements for a metal belt of a belt-type continuously variable transmission.