Nippon Steel Corporation

Ryusuke Nakano

Kenji Tamura

Junichi Okubo

Kunihiro Yoshida

Masao Hori

Samsoo Hwang

Sam Soo Hwang

Yukihiro Ota

Provided is a production method, including a first preforming process for obtaining a first preform from a billet, a second preforming process for obtaining a final preform from the first preform, and a finish forging process for forming the final preform into a finishing dimension of a forged crankshaft. In the first preforming process, a plurality of flat parts are formed by pressing pin-corresponding parts and journal-corresponding parts in a direction perpendicular to an axial direction of the billet. The second preforming process includes: a process of pressing regions to be a plurality of journals with a width direction of the flat part as a pressing direction by using a pair of first dies; and a process of, after starting pressing by the first dies, decentering regions to be a plurality of pins with the width direction of the flat part as a decentering direction by using second dies.

Method for producing forged crankshaft

Provided is a production method, including a first preforming process, a second preforming process, and a finish forging process. In the first preforming process, while a plurality of flat parts are formed, a region to be a second pin is decentered. The second preforming process includes: a process of pressing each region to be a plurality of journals in a pressing direction corresponding to a width direction of the flat part by using a pair of second dies; and a process of, after starting the pressing by the second dies, decentering a region to be a first pin and to be disposed in a first position and a region to be a third pin and to be disposed in a third position from each other in opposite directions with a width direction of the flat part being as a decentering direction by using third dies.

A production method includes a preforming process, a forming process and a finish forging process. In the preforming process, an intermediate preform is formed from a billet. In the forming process, while each of a plurality of rough journals of the intermediate preform is held and pressed vertically by a pair of holding dies, rough pins are decentered in directions perpendicular to the pressing direction by the holding dies and an axial direction of the intermediate preform, and the intermediate preform is pressed in the axial direction of the intermediate preform. In the finish forging process, a final preform is placed such that the directions in which the rough pins are decentered are parallel to a horizontal direction, and the thus placed final preform is pressed vertically by a pair of pressing dies. The production method reduces the risk of occurrence of seams on a forged crankshaft.

A forged crankshaft production method includes a first preforming step, a second preforming step, and a final preforming step. The first pair of dies includes web processing parts to come into contact with portions to be formed into arms and portions to be formed into weights integrated with the arms. Each of the web processing parts includes an arm processing part and a weight processing part. The arm processing part and the weight processing part form a recessed portion, and the width of the open side of the weight processing part becomes greater with increasing distance from the bottom of the recessed portion. Accordingly, in the blank, volume can be distributed between a portion to be formed into an arm and a portion to be formed into a weight integrated with the arm, and the material yield rate can be improved.

A forged crankshaft production method includes a first preforming step, a second preforming step, and a final preforming step. In the first preforming step, sectional areas of portions to be formed into pins and sectional areas of portions to be formed into journals are decreased, whereby flat portions are formed, and the portion to be formed into the pin located at a second position is decentered. In the second preforming step, a portion to be formed into the pin located at a first position is decentered, and a portion to be formed into the pin located at a third position is decentered to a side opposite to the portion to be formed into the pin located at the first position. In a blank obtained thereby, portions to be formed into pins have been reduced and decentered, and the material yield rate can be improved.

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Tokyo, Japan

Ryusuke Nakano