| 摘要 |
A method of forming a collar-shaped protrusion on thin plate material by relatively bringing a forming punch having the outer diameter varying stepwise into the forming hole of a forming die and during forming, punching a small diameter hole by means of a punch-through punch incorporated in said forming die. During the remainder of forming, ironing and burring are performed on the protrusion to form a collar for heat exchanger fins. The die set shaped for carrying out the steps is also included. Since these steps can be performed as a single continuous series of steps, heat exchanger fins of high accuracy can be manufactured with fewer tools, and at less cost and in less time than heretofore. |
