| 摘要 |
PURPOSE:To obtain a gear excellent in dimensional accuracy and quality, by forming a mandrel for extrusion-forming a gear into a shape having a straight axial part and a round tip-part tapered and continuing to the straight part. CONSTITUTION:When a mandrel 22 is lowered to the position of blanks 42, 43, there causes no stepped-part at the inner diametral parts of the blanks 42, 43 because the mandrel 22 is formed to have a tapered round-tip-part 22b. When a bolster 23 is further lowered, the tip of the mandrel 22 reaches an inner diametral part of a blank 41, but no stepped-part is produced. When the bolster 23 is further lowered, the blank 41 formed into a tooth-shape is extruded, and falls downward through a hollow part of a lower pressure-receiving member 35. Still more, marks are hardly produced at the inner diametral part of the blank 41 formed into a tooth-shape, in a case when the mandrel 22 is moved upward by lifting the bolster 23. |
