Servo control for super-high-thickness cutting in high-speed wire electrical discharge machining

Severe uneven wire tension occurs during super-high-thickness (more than 1000 mm) cutting in high-speed wire electrical discharge machining, resulting in different discharge regularities between electrodes when the wire electrode is in the positive and negative traveling directions. Regarding the specific performance, a certain proportion of no-load pulses will appear between electrodes when the wire electrode is in the positive traveling direction, resulting in the feeding of the machine tool; when the wire electrode is in a negative traveling direction after feeding, a large number of short-circuit pulses will be formed, which seriously affect the continuous and stable feeding and the cutting speed. According to these different regularities, this work proposes the use of different reference objects as the basis of servo feeding in the positive and negative traveling directions. A pulse probability detection servo control method based on the discharge peak current is designed, and different control objects for the positive and negative traveling direction are used as the target probabilities of the proportional integral derivative algorithm. The results of experiments demonstrate that the proposed servo control method can significantly improve the cutting stability and cutting speed for super-high-thickness cutting. When cutting a workpiece with a thickness of 1000 mm, the surface machined by the average voltage detection-based servo method with the fixed threshold and the conventional pulse probability-based servo control method was found to exhibit obvious streaks, and the cutting speed was respectively 53.75 mm²/min and 63.6 mm²/min. Finally, the surface machined by the proposed servo control method was even, and the cutting speed was 77.78 mm²/min, thereby exhibiting an improvement of 44.71% as compared to that of the average voltage detection method with a fixed threshold, and the surface evenness was greatly improved. Thus, the proposed servo control method for super-high- thickness cutting was found to achieve a faster cutting speed and higher surface quality.