Investigation of work coordinate system setting in ultra-precision machining using electrical breakdown for non-conductive materials

The ultra-precision machine tool industry has been consistently improving to the point where machine tools with extreme thermal controls, vibration damping, and command resolutions of 0.1 nm are commercially available. As little research focus has been given to developing peripheral technologies, currently available work coordinate system setting methods are a bottleneck on the achievable accuracy of ultra-precision machine tools. One of the work coordinate system setting methods uses electrical breakdown. The electrical phenomenon occurs when a sufficiently large voltage difference is applied between two conductors. This phenomenon has been observed to have a linear relationship between the breakdown voltage and gap size at short gap sizes. Electrical breakdown is a capable work coordinate system setting with an accuracy of 100 s nm. However, this method is limited to electrically conductive cutting tools and workpiece materials. This study proposes a work coordinate system setting method for ultra-precision machining based on electrical breakdown for non-conductive materials. In this study, a conductive thin film coating is applied to polycrystalline diamond cutting tools to facilitate electrical breakdown work coordinate system setting. With similar motivation, a modification method was tested to enable electrical breakdown work coordinate system setting on non-conductive workpiece materials. The modification method used a 50-nm-thick platinum coating on the workpiece. This study also introduces a method for automatic work coordinate system setting using electrical breakdown and sensors built into the machine tool.