Research on the efficient self-adaptive servo-control strategy in micro-EDM milling

Abstract

As an important fabricating technology, micro-EDM is always confined by the rather low efficiency in practical applications. To solve this problem, a self-adaptive servo-control strategy is proposed in this study. Firstly, a self-determination technique is developed to define the threshold voltages of different discharge conditions. Then, the least square method is applied to predict the discharge condition of the next sampling period. After that, a detailed servo-control strategy considering both discharge condition and velocity is put forward to adjust the feed speed to match up with the actual material removal rate. Finally, a comparative experiment is undertaken to verify the effects of the proposed self-adaptive strategy. The results demonstrated that the material removal rate and ratio of spark pulse to the whole discharge pulses are significantly improved in comparison with the traditional constant speed strategy. The surface texture and tool wear generated by the two strategies are also compared. The results indicated that the proposed self-adaptive strategy enhances the efficiency without bringing extra disadvantages to the surface precision or tool wear. Moreover, retraction of the electrode is significantly decreased and the feed speed can steadily keep close to the material removal rate under the proposed strategy. Thus, the dynamic performance of the machine tool was better and the microelectrode was prevented from crashing into the workpiece. The idea of the proposed strategy can also be applied to other micro-EDM techniques such as drilling and die sinking.