Effects of Surface Treatments for Wear of Tools Used in High-Precision Form-Rolling Processes

Abstract

Various finishing treatments on the surfaces of tabular shaped tools have been carried out. The tools are employed in the mass production of wristwatch parts called “winding stems” in a form-rolling process. The winding stems, which are long and thin, possess a complicated shape with grooves, steps and threads. The treatments' effects on the lifetime of these tools have been investigated. In form rolling, it is possible to reduce the wear on tools by applying a TiCN coating to their surface rather than a DLC coating and to even further decrease wear depth by applying cementation and plasma nitriding to the tools. Tools subjected to multi stage surface treatments, such as coating with TiCN after plasma nitriding, show markedly reduced wear. Employing these multi stage surface-treated tools in the form-rolling process makes it possible to minimize dimensional changes in the form-rolled products and to manufacture form-rolled products in large volumes that exceed 2.5×10⁵ pieces.