Since the invention of wire electrical discharge machining (WEDM), WEDM technology has developed rapidly and become indispensable in precision die and mold manufacturing. In accordance with recent developments in computer systems and instrumentation equipment, WEDM performance has improved rapidly. Although new findings and knowledge based on fundamental studies have promoted WEDM technology, WEDM related research is still stagnant and difficult because of complicated physical processes and current machine tool architecture.
Generally, WEDM related technology is based on conventional EDM technology in basic machining process attributes. Major WEDM specific technological concerns are maintaining the stable discharge machining status and precision machining. These needs are mainly caused by wire rupture or deflection during machining process, but it is not easy to access the WEDM system directly because of complicated system architecture. Hence, many researchers have proceeded indirectly to WEDM systems by add-on monitoring and control equipment for original WEDM CNC. This approach has some limitations since overall control strategy should be managed under consideration of all machine resources and is affected by individual sub-control function.
So, this paper deals with the design and implementation of an open architecture CNC system for Wire-EDM, with a consideration of the differences between Wire-EDM and NC cutting machines. Recent open architecture controller (OAC) related research results could be applied to directly access WEDM systems at the CNC level. However, previous research about OAC is mostly aimed at NC cutting machines such as milling or lathes, and hence these results are inadequate to apply to WEDM. In contradiction to NC cutting machines, WEDM operates relatively slow feed rates and should handle more discrete events. Moreover, the WEDM system is based on a feedback control loop to the machining process in discharge control.
To close the gap between previous general research on OAC and Wire-EDM specific needs, an open architecture NC model for Wire-EDM composed of a synchronization kernel and a NC functional module is proposed. Based on control information flow and Wire-EDM specific machining process, the conceptual CNC model and the detailed implementation model for Wire-EDM is suggested. The prototype CNC system based on the proposed model is developed as a test-bed and applied to the existing commercial Wire-EDM by retrofit method.
Precision NURBS interpolator appropriate for WEDM was suggested and tested as a system implementation case study.
Computer simulations and experimental cutting was conducted.