A high-precision constant wire tension control system for improving workpiece surface quality and geometric accuracy in WEDM

In wire electrical discharge machining (WEDM), there are inevitable phenomena of wire deflection and vibration because wire electrode is slender and flexible, and these phenomena are closely related to workpiece surface quality and geometric accuracy. Besides, the phenomena of wire deflection and vibration have a direct relationship with wire tension. In this paper, a high-precision constant wire tension control system is built to restrain wire deflection and vibration so as to improve workpiece surface quality and geometric precision. Firstly, the factors resulting in wire tension fluctuation are briefly introduced. Additionally, the constant wire tension control system is designed on the basis of the structure improvements of wire winding system and closed-loop control. And then, the high-precision transfer function of this control system is deduced by the method of system identification, and three intelligent algorithms are utilized to tune the parameters of PID controller. Next, the wire tension control experiment and cutting experiment are carried out to evaluate the performance of this control system. Experiment data indicate that this control system has good ability of controlling wire tension without obvious overshoot. In addition, it is proved that this control system can obviously improve workpiece surface quality and geometric error, such as surface topography, cutting kerf width, corner error and taper cutting error. This proposed constant wire tension control system is worthy of popularization and application in practical manufacturing field.