Study of wire tension control system based on closed loop PID control in HS-WEDM

Abstract

Wire electrical discharge machining (WEDM) is widely used in mould and die manufacturing, but the low machining accuracy limits its further developments, especially for high-speed wire electrical discharge machining (HS-WEDM) because of its non-even wire tension. A constant tension can restrain the high-frequency vibration of wire electrode effectively, which can improve the accuracy of workpiece surface. In this paper, a wire tension control system is designed to reduce the wire tension fluctuation, according to the process characteristic of HS-WEDM. Wire tension control system adopts a closed-loop control strategy. A mathematical model of control system is built based on DC servo motor, linear motion platform, and tension sensor. Meanwhile, a simulation model of transfer function is built to calculate proportion integration differentiation (PID) control parameters. Simulation results show that the calculated PID control parameters can satisfy the requirements of the control system. A series of experiments are designed to test the stability and reliability of wire tension control system and its workability. The value of wire tension fluctuation has been down by almost half with wire tension control system. The surface roughness of workpiece with wire tension control system is almost 0.6 μm lower than that without wire tension control system, which implies that this control system can improve the quality of parts manufacturing for HS-WEDM.