CENTER HOLE FORMING METHOD AND FORGING DEVICE

PROBLEM TO BE SOLVED: To provide a technique in which a workpiece inserted into a mold hole is shaft-extruded, and, thereafter, a center hole is certainly formed at a small diameter side end surface as the axis direction end surface of the small diameter side of the workpiece without pulling out the workpiece from the mold hole.SOLUTION: A center hole forming method, in which a workpiece 2 inserted into a mold hole is shaft-extruded, and, thereafter, an axis part center hole 3b (center hole) is formed at an axis part end surface 3a (small diameter side end surface) as the small diameter side axis direction end surface of the workpiece 2 without pulling out the workpiece 2 from the mold hole, is implemented as follows. Namely, a load toward the axis part end surface 3a is applied in advance to a head part end surface 4a (larger diameter side end surface) as the large diameter side axis direction end surface of the workpiece 2 so that the workpiece 2 is not moved in the mold hole by pressing a counter punch 15 before forming the axis part center hole 3b at the axis part end surface 3a by pressing the counter punch 15 to the axis part end surface 3a. 【課題】型孔内に挿入した加工対象物を軸絞りし、その後、加工対象物を型孔内から抜き出すことなく、加工対象物の小径側の軸方向端面としての小径側端面にセンター孔を確実に形成する技術を提供する。【解決手段】型孔内に挿入した加工対象物２を軸絞りし、その後、加工対象物２を型孔内から抜き出すことなく、加工対象物２の小径側の軸方向端面としての軸部端面３ａ（小径側端面）に軸部センター孔３ｂ（センター孔）を形成する、センター孔形成方法は、以下のように行われる。即ち、軸部端面３ａにカウンターパンチ１５を押し当てることで軸部端面３ａに軸部センター孔３ｂを形成する前に、カウンターパンチ１５の押し当てによって加工対象物２が型孔内で動かないように、加工対象物２の大径側の軸方向端面としての頭部端面４ａ（大径側端面）に対して、軸部端面３ａに向う荷重を予め掛けておく。【選択図】図５