| 摘要 |
PROBLEM TO BE SOLVED: To provide a sheet metal forming method capable of forming a boss having a small diameter, high height, and ensured strength.SOLUTION: A sheet metal forming method includes an extruding step, an intermediate drawing step, and a finish drawing step. In the extruding step, while a sheet metal work-piece 10 is supported by a primary die having a receiving hole having an internal diameter larger than a finished diameter of a boss 13, and a part 20 to be formed is subjected to extruding processing by a first punch to form a primary projection part having a primary hollow recessed part therein. In the intermediate drawing step, while a secondary punch is pressed to the bottom of the primary hollow recessed part, the primary projection part is pushed into a receiving hole of a secondary die having an internal diameter smaller than that of the primary die to reduce the diameter of the primary projection part and increase the height thereof as drawing processing, so that a secondary projection part is formed and a pocket-shaped holding recessed part is formed at the opening side of the secondary hollow recessed part inside the secondary projection part. In the finish drawing step, while a tertiary punch is abutted on the holding recessed part, the secondary projection part is pushed into a receiving hole of a tertiary die having an internal diameter smaller than that of the secondary die to reduce the diameter so as to fill the secondary hollow recessed part and increase the height thereof as drawing processing, so that a desired boss 13 is obtained. |
