Self-tuning breakthrough detection for EDM drilling micro holes

In electrical discharge machining (EDM), accurate and timely detection of the breakthrough of the tool electrode is rather intricate when drilling though-holes due to considerable longitudinal tool wear. This paper proposes a novel method for detecting the completion of the drilling process using the cumulative sum (CUSUM) control chart. In this method, variations in the amount of normal discharge pulses per unit time are monitored for detecting the completion of the drilling process. The actual process conditions are sensed at the start of the drilling process and the control limit for detecting the hole completion is accordingly self-tuned. The robustness of the detection method to different process conditions is supported by a design of experiments study. Experimental validation has been carried out by drilling through micro holes at relative angles between the tool and workpiece of 30°, 45°, and 60°. The proposed method has been shown to guarantee the hole completion, while in the same time avoiding machining a surface situated 1 mm below the outlet of the drilled hole. This is critical for EDM drilling applications in the aerospace and automotive sectors.