MANUFACTURE OF STEPPED HOLLOW GEAR

PURPOSE:To facilitate the manufacture of a stepped hollow gear by forming the blank stock having a small diameter part, large diameter part and through hollow part by extruding to a mandrel side by a punch and forming a tooth part by the metal of the large diameter part and a boss part by the metal of the small diameter part. CONSTITUTION:The blank stock WIII having large diameter part BIII, small diameter part CIII and through hollow part is formed in advance. This blank stock WIII is then set between the mandrel 28 of a lower die 25 and the punch 38 of an upper die 26 and a knock-out member 29 is freely, slidably and vertically arranged on the mandrel 28, which is taken in two stepped shape at the upper side. When a punch 38 is descended via the upper die 26 to press-form the blank stock WIII, the metal of the small diameter part CIII forms a boss part C by the pressure of the punch 38. On the other hand the metal of the large diameter part BIII forms a tooth part D by the tooth part forming part 37 of a die 35. In case of extrusion forming each part can be formed simultaneously, hence the manufacture is facilitated.