Patent ID: 8201434

Claim:
A method of forming a cam lobe, the cam lobe including: a cam base ( 9 , 109 ) having a semicircular outer circumference about a shaft center (X 5 , X 105 ); a cam top ( 8 , 108 ) having a shape that further projects outward from the outer circumference of the semicircular cam base ( 9 , 109 ) on a side opposed to the semicircular cam base ( 9 , 109 ) in relation to the shaft center (X 5 , X 105 ); and a cam-lobe hole ( 10 , 110 ) that is axially pierced concentrically with the shaft center (X 5 , X 105 ); the method comprising: a first step in which a primary intermediate formed article (W 1 , W 101 ) is formed into a substantially columnar shape; a second step in which a secondary intermediate formed article (W 2 , W 102 ) is obtained by piercing a preliminary hole ( 3 , 103 ) through the primary intermediate formed article (W 1 , W 101 ) in an axial direction of the primary intermediate formed article (W 1 , W 101 ) such that a radial thickness of a prospective cam top part ( 6 , 106 ) to become a cam top ( 8 , 108 ) is larger than a radial thickness of a prospective cam base part ( 7 , 107 ) to become a cam base ( 9 , 109 ), and by forming a positioning part ( 5 , 105 ) on an outer circumference on a side of the prospective cam top part, the positioning part ( 5 , 105 ) projecting radially outward from an outer circumference of the prospective cam base part ( 7 , 107 ); a third step in which a tertiary intermediate forged article (W 3 , W 103 ) including a cam top ( 8 , 108 ), a cam base ( 9 , 109 ), and a deformed hole ( 4 , 104 ) that is deformed from the preliminary hole ( 3 , 103 ) is obtained by, under a state in which the positioning part ( 5 , 105 ) of the secondary intermediate formed article (W 2 , W 102 ) is positioned by bringing the positioning part ( 5 , 105 ) into contact with a tertiary-intermediate-forged-article forging die ( 36 ) for forging a tertiary intermediate forged article (W 3 , W 103 ), axially pressing and forging the secondary intermediate formed article (W 2 , W 102 ) with the use of the tertiary-intermediate-forged-article forging die ( 36 ); and a fourth step in which a finished cam lobe (W 5 , W 105 ) is obtained by piercing, in an area including the deformed hole ( 4 , 104 ), a cam-lobe hole ( 10 , 110 ) that is larger than the deformed hole ( 4 , 104 ).