| 摘要 |
PROBLEM TO BE SOLVED: To reduce weight by decreasing the wall thickness of a sliding part without impairing the strength of a flare part in forming a poppet valve by press forming. SOLUTION: In this poppet valve, a sliding part of a stem is formed to be hollow and thin, and the wall thickness of the flare part connected to the sliding part of the stem is formed thicker than the sliding part of the stem. In a press forming method, a metal plate is drawn to form a cup-like material having a cylindrical wall formed with the substantially same diameter as the end diameter of the flare part, and a bottom wall closing one end thereof, and the material is ironed from the bottom wall to the open end of the cylindrical wall by several pairs of ironing dies formed by a punch and a die to reduce the diameter and simultaneously expand in the axial direction, thereby forming a flange part having several steps at the open end of the cylindrical wall. The flange part is clamped by a metal mold to form the flare part.
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