Molding method by forging and molding method for case

Abstract

A material member blanked from metal sheet is subjected to upsetting to form an annular peripheral portion that is thinner than the center part of the material inside the annular portion, and the thicker inside portion is formed into a concavity. The first intermediate product thus formed is drawn to form a cup-shaped case with an internal boss and/or an external boss, and an outside flange. The intermediate product can also be used to make gears and the like.

1 . A method of forming by forging material, characterized in that the method comprises: 
 a first step of preparing sheet material, and    a second step in which a thickness of a circumferential portion of the material is made thinner than a thickness of a center portion of the material.    
     
     
         2 . A method as claimed in  claim 1 , wherein the first step is a step of blanking sheet metal.  
     
     
         3 . A method as claimed in  claim 1 , wherein the second step is a step of simultaneously stamping-forming a concavity in the center portion of the material.  
     
     
         4 . A method as claimed in  claim 1  or  3 , wherein the second step is carried out by upsetting.  
     
     
         5 . A method of forming a case, characterized in that the method comprises: 
 a first step of preparing sheet material, and    a second step in which a thickness of a circumferential portion of the material is made thinner than a thickness of a center portion of the material.    
     
     
         6 . A method as claimed in  claim 5 , wherein the first step is a step of blanking sheet metal.  
     
     
         7 . A method as claimed in  claim 5 , wherein the second step is a step of simultaneously stamping-forming a concavity in the center portion of the material.  
     
     
         8 . A method as claimed in  claim 5 , wherein the second step is a step of forming by forging.  
     
     
         9 . A method as claimed in  claim 5 , wherein the second step is carried out by upsetting.  
     
     
         10 . A method as claimed in  claim 5 , further comprising a third step in which an intermediate product obtained by the second step is forward drawn to simultaneously form the peripheral wall and bottom of the case.  
     
     
         11 . A method as claimed in  claim 10 , wherein, if a is a thickness of the peripheral wall and b is a thickness of the bottom, a<b.  
     
     
         12 . A method as claimed in  claim 5 , wherein an intermediate product obtained by the second step is forward drawn to form a case peripheral wall, and then to form an internal boss.  
     
     
         13 . A method as claimed in  claim 5 , wherein an intermediate product obtained by the second step is forward drawn to simultaneously form the case peripheral wall and the internal boss.  
     
     
         14 . A method as claimed in  claim 5 , wherein an intermediate product obtained by the second step is annealed before being subjected to a subsequent step.  
     
     
         15 . A method as claimed in  claim 7 , wherein the second step is a step of forming by forging.  
     
     
         16 . A method as claimed in  claim 7 , wherein the second step is carried out by upsetting.  
     
     
         17 . A method of forming a cup-shaped case having an internal boss, characterized in that the method comprises: 
 a step of preparing sheet material,    a step of making a thickness of a circumferential portion of the material thinner than a thickness of a center portion of the material and simultaneously stamping-forming a concavity in the center portion of the material, and    a method of forward drawing an intermediate product obtained by the stamping-forming to form a cup-shaped case having a bottom that is thicker than a peripheral wall.