Method of forming through-hole and through-hole forming machine

A method of oppositely forming through-holes in a circular wall of a cylindrical part of a work piece,

• comprising the steps of:
• boring a guide through-hole, whose diameter is smaller than that of a first through-hole to be bored, at a first prescribed position, at which the first through-hole will be bored, from an outer face of the cylindrical part;
• setting the work piece to a die;
• inserting a punch, which is provided to a rod-shaped metal core, into the cylindrical part until reaching the first prescribed position;
• pressing and moving a press pin toward the die together with the punch so as to drive the punch into an inner face of the circular wall and bore the first through-hole, wherein the press pin is inserted in the cylindrical part via the guide through-hole, which is located on the opposite side of the first prescribed position, and contacts a surface of the metal core, which is located on the opposite side of the punch;
• resetting the work piece in the die;
• inserting the punch, which is provided to the rod-shaped metal core, into the cylindrical part until reaching a second prescribed position, which is located on the opposite side of the first prescribed position and at which a second through-hole will be bored;
• pressing and moving the press pin toward the die together with the punch so as to drive the punch into the inner face of the circular wall and bore the second through-hole including the guide through-hole, wherein the press pin is inserted in the cylindrical part via the first through-hole and contacts the surface of the metal core, which is located on the opposite side of the punch.

A through-hole forming machine for forming a through-hole in a circular wall of a cylindrical part of a work piece,

• comprising:
• a die for holding the work piece, the die contacting an outer face of the circular wall of the cylindrical part at a prescribed position corresponding to the through-hole to be bored;
• a punch for boring the through-hole with the die, the punch being provided to a front end of a rod-shaped metal core and being inserted into the cylindrical part;
• a press pin being inserted in the cylindrical part via a guide through-hole, which is formed in the circular wall of the work piece and which is located on the opposite side of the prescribed position, the press pin contacting a surface of the metal core, which is located on the opposite side of the punch;
• and
• a mechanism for relatively pressing and moving the press pin and the punch toward the die so as to drive the punch into an inner face of the circular wall and bore the through-hole.

A through-hole forming machine for oppositely forming through-holes in a circular wall of a cylindrical part of a work piece,

• comprising:
• a first boring unit including a punch for boring a guide through-hole, whose diameter is smaller than that of a first through-hole to be bored, at a first prescribed position, at which the first through-hole will be bored, from an outer face of the cylindrical part;
• and
• a second boring unit including:
• a die for holding the work piece, the die contacting an outer face of the circular wall of the cylindrical part at prescribed positions corresponding to the first and second through-holes to be bored;
• a punch for boring the through-holes with the die, the punch being provided to a front end of a rod-shaped metal core and being inserted into the cylindrical part;
• a press pin being inserted in the cylindrical part via the guide through-hole and the first through-hole, the press pin contacting a surface of the metal core, which is located on the opposite side of the punch;
• and
• a mechanism for relatively pressing and moving the press pin and the punch toward the die so as to drive the punch into an inner face of the circular wall and bore the through-holes.