Investigation on the accuracy of on-machine feature volume measurements in micro EDM milling

In micro electrical discharge milling it is necessary to calibrate empirically tool wear compensation strategies in order to accurately adjust the tool-workpiece relative position and achieve high precision machining. The measurement of the material removed from both tool and workpiece is of paramount importance, since tool wear compensation and machining simulation rely on this information. On-machine volume measurements enable process parameters optimization based on self-learning procedures as well as the implementation of process monitoring algorithms. Commercially available electrical discharge machines allow the detection of electrical contacts between the tool and the workpiece electrodes by sensing low voltage short-circuits. This capability can be exploited to set the workpiece coordinate system and to perform dimensional measurements of tool and workpiece, using the tool electrode similarly to the touch probe in a coordinate measuring machine. However, accurate and traceable measurements of volumes can be challenging and a metrological validation of the method is missing. In this work an investigation of the accuracy of the on-the-machine volume measurements in a micro electrical discharge milling setup is carried out. An evaluation of the error affecting on-machine measurements is provided, and best practices for the applicability of the method are discussed.