Breakthrough detection and servo control for micro‑hole array EDM drilling

• Published in: International journal of advanced manufacturing technology Vol. 119; no. 1-2; pp. 615 - 629
• Main Authors: Liu, Huan, Bai, Jicheng, Zhang, Bo, Cao, Yan, Hou, Shaojie, Zhou, Zimu
• Format: Journal Article
• Language: English
• Published: London Springer London 01.03.2022; Springer Nature B.V
• Subjects: Arrays; CAE) and Design; Computer-Aided Engineering (CAD; Drilling machines (tools); EDM electrodes; Electric discharge machining; Electrodes; Engineering; Flow velocity; Industrial and Production Engineering; Mechanical Engineering; Media Management; Microholes; Original Article; Servocontrol; Three dimensional flow; Three dimensional models; Workpieces; Breakthrough detection; Flow field; Micro-EDM; Micro-hole array; Servo strategy
• ISSN: 0268-3768; 1433-3015
• DOI: 10.1007/s00170-021-08205-w

The micro-hole array machined by micro-electrical discharge machining (micro-EDM) has been widely used in aerospace, electronic communication, and other industrial fields. However, due to the unavoidable electrode wear and the unstable discharge state during the electrode breakthrough, the electrode breakthrough detection is usually inaccurate, and the servo tracking performance is also poor, which has adverse effect on the machining efficiency and quality of micro-hole array. In the present study, a three-dimensional flow field model was established, and the gap flow field before and after electrode breakthrough based on the model was analyzed. Simulation results showed that the flow field pattern of dielectric was changed and the flow velocities in bottom gap increased in general after electrode broke through the workpiece, which enabled to analyze the influence of the variation in flushing mechanism of debris on the discharge state in breakthrough stage to some extent. A scheme was proposed for online detecting the breakthrough by monitoring the variations of the gap voltage and the electrode displacement, and the verification experiment was carried out. The proposed scheme has been shown to guarantee the electrode breakthrough, while in the same time controlling the distance of electrode feeding past the micro-hole outlet not exceeding 25 μm. In addition, a segmented servo strategy was proposed to ensure the machining performance of micro-hole array, and it was experimentally tested. This strategy could reduce the average machining time of micro-hole array by about 36% and ensure the machining quality of micro-hole outlet.