Surface quality improvement of multistage forged microparts for wristwatches

The trial of a new production technique using multistage forging of watch parts called the “crown” has been investigated. In the conventional forging process, the flaws on the shearing surface of the mother wire remain in the final products. These surface defects present the most important problem in the manufacturing process of decorative watch parts. An analysis of the deformation behavior of the flaws during multistage forging using a finite-element (FE) simulation and experiments has been performed, and a new manufacturing process that yields better products is suggested. In the conventional process, small amounts of metal flow and plastic strain near the center of the sample during multistage forging were observed by FE simulation, and as a result, the flaws on the shearing surface of the mother wire remained on the surface of final products. The simulation results are compared and are in good agreement with experimental results on metal flow of the flaws. Carrying out additional forging with a conical punch in the conventional manufacturing process in order to accelerate the metal flow at the center of the sample is effective for obtaining improved final products.