Improvement in machining speed with working gap control in EDM milling

•A notch filter that effectively removes the frequency of the electrode rotation.•Feed-forward compensation removes the offset and improves the machining speed.•The feed-forward value is derived with the weighted least-squares method.•The new controller improved speeds that are 2-6 times higher in a straight line.•This method is useful for other fast machining methods such as microhole EDM.

High-speed electrical discharge machining (EDM) milling is investigated with working gap control. EDM milling has a merit that does not need complex electrode fabrication; however, it is necessary to improve the removal rate in EDM milling. Rotation of the electrode improves the removal rate, but this rotation causes a periodic change in the working voltage. As a consequence, the periodic change causes a disturbance that decreases the control performance. EDM milling realizes a high machining precision by the scanning method. A small working area allows for fast scanning. If the working gap is appropriate, it becomes longer because the machined surface of the workpiece is removed. Therefore, the conventional controller remains at the steady offset and lowers the machining efficiency. The proposed controller introduces a notch filter, which eliminates the frequency component due to rotation of the electrode. It also has a feed-forward compensator to eliminate the steady offset. The controller for each machining condition is derived from a coordinate transformation and the least-squares approximation. It is confirmed that the proposed controller achieves machining speeds that are 2-6 times faster in a straight line and greater than 30% higher in the profile machining than in the conventional one.