Process parameters optimization in micromilling of watch mechanism features

The micro machining technology is a widespread process in several industrial sectors, such as the electronics, the moulds fabrication, the biomedical field and the horology. The main advantages of micro-milling are the low material scrap, the high accuracy and repeatability, the possibility to manufacture small size features and the respect of the geometrical and dimensional tolerances. For these reasons, micro-milling is suitable to manufacture precision components in watchmaking industry. In the high-end horology field, high geometrical precision and elevated surfaces quality are key requirements. An optimal process parameters set should be identified to comply the very strict quality standards. This paper reports the results of an optimization performed to define how to make high-quality main-plates and bridges of wristwatch movement. The dimensions, the geometry and the surface finishing of holes, pins and pockets are the optimized wristwatch features. During the optimization, cutting speed, feed rate and depth of cut were varied and measurements of geometrical errors and roughness were performed to understand how the process parameters affect the final product quality. The experimental tests were conducted on “Nickel Silver” (CuNi18Zn20) samples by using an ultraprecision 5-axis milling center located in controlled environment. The surface roughness, the burrs extension and the geometrical errors were measured by using a multifocal 3D microscope, a coordinate measuring machines and an autofocus 3D laser probe. This study allowed to manufacture a wristwatch movement in conformity with the required technical characteristics.