Development of an Automatic Wire Feeding System for Wire-cut Electric Discharge Machining

The time consuming and tedious wire threading in Wire Electrical Discharge Machining (WEDM) before the start of the operation is always needed. In addition, wire breaking is inevitable during the machining process, and the chance to re-thread the wire is encountered from time to time. Hence the automatic wire feeder (AWF) is an essential unit closely related to machining efficiency and automation in WEDM. Despite various existing foreign and local patents, a new-type AWF based on modular design is developed in this thesis. Several units including wire receiving motor unit, wire cutting and shaping mechanism, motor positioning unit, etc. which have patent potential are proposed. The incorporation of special design cutter with electrical discharging for wire disconnecting while at the same time applying an appropriate tension on the wire during the wire disconnecting process results in very satisfactory profile wire. Besides, the disconnection point along the wire can be precisely controlled. The problem of too long and fine wire at the tip by using the heating and pulling strategy is prevented. The FEM is applied to simulate the fluid flow field and velocity within the pipe so that the proper shape of the wire guiding pipe can be determined. The developed system has less mechanical parts as compared to those of the existing systems. Hence, it is expected to be cost effective and easy for maintenance. In addition, the developed system is flexible, and it can be implemented on various wire-cut electrical discharge machine (Wire-cut EDM). The programmable logic controller (PLC) is taken for sequence control of the threading process. The associated software is written by the use of assembly language. Experiments are conducted to verify the threading performance of the developed system. It is found that the success rate is 84% ~ 96% for the 50~100 mm thickness workpiece having a 1mm in diameter initial hole. It is 79% ~ 91% when wire threading is carried out at the position of wire breaking. It is reduced to 76% ~ 86% when there is no workpiece in between the upper and lower wire guides. This performance is more or less comparable to the existing AWF. In conclusion, the AWF is successfully developed, and contribution to local EDM industry is expected.