Automated workpiece setting operation by on-machine measurement for efficient ultraprecision cutting of micro-shapes

Ultraprecision cutting used for creating highly precise components and particularly micro-shapes requires ultraprecision machine tools. However, these machine tools are operated under restricted cutting conditions such as feed rate and depth of cut, resulting in low productivity. Therefore, this study deals with this problem by devising a novel ultraprecision cutting system with automation of the workpiece setting operation. In the devised system, the workpiece is roughly machined by an ordinary machine tool. After that, an industrial robot transfers the workpiece to an ultraprecision machine tool to complete the rest of the machining process. The proposed machining system overcomes two types of errors. The first is the shape error due to rough machining on the ordinary machine tool. It is practically difficult to create the expected shape exactly in rough machining, and therefore the shape error of the roughly machined workpiece is affecting the finish machining directly. The other is the setting errors due to the transfer of the workpiece to the ultraprecision machine tool from the ordinary machine tool. The differences from the ideal workpiece position and orientation are detected to identify the setting errors. Thus, the roughly machined workpiece is scanned to derive an error map by on-machine measurement. Additional tool paths are generated for semi-finish machining, and the error map helps to eliminate the form errors induced by rough machining. The NC program for finish machining is modified to compensate the identified workpiece setting errors. Finally, finish machining can be conducted on the roughly machined workpiece. Hence, the removal volume in finish machining on an ultraprecision machine tool is reduced, and the time required for the whole machining process is expected to be shorter. The experimental results confirm that the developed ultraprecision cutting system contributes to the automated workpiece setting operation to create micro-shapes with high accuracy.