Servo Control Strategies for Vibration-Control in Robotic Wire EDM Machining

Abstract

Exotic materials play a key role in high-end applications. Thus, Wire Electric Discharge Machining (WEDM) stands out due to superior surface roughness and high precision. Currently, WEDM is found in rigid bed-based CNC machines constraining the workpieces in geometry and size. Parallelly, the stochastic nature of WEDM and the lack of complete mathematical models make it complex to control. As a result, whenever the servo feed becomes faster than the material removal rate, short circuits and wire break occur. On the other hand, traditional machining using six-axis industrial robots (IR) have been extensively investigated for cost efficiency, improved envelope and virtually unlimited axis combination. However, the IR design offers low stiffness, facing severe vibrations in machining hard-to-cut materials, resulting in low accuracy, poor finishing, and lack of repeatability. Thus, IRs are not comparable to CNC. The present research reviews the ideal servo control strategies for a synergistic combination of a novel machining technic of WEDM working with an IR as the servo. Employing a theoretical analysis followed by a series of simulations, it is demonstrated how the combination can be successfully controlled by frequency modulation, delivering a robotic process able to machine any hard-to-cut conductive material yet free of vibration.