Study of the effect of machining parameters on the machining characteristics in electrical discharge machining of tungsten carbide

摘要

Electrical discharge machining (EDM) is a process for shaping hard metals and forming deep and complex-shaped holes by arc erosion in all kinds of electro-conductive materials. The objective of this research is to study the influence of operating parameters of EDM of tungsten carbide on the machining characteristics. The effectiveness of the EDM process with tungsten carbide is evaluated in terms of the material removal rate, the relative wear ratio and the surface finish quality of the workpiece produced. It is observed that copper tungsten is most suitable for use as the tool electrode in EDM of tungsten carbide. Better machining performance is obtained generally with the electrode as the cathode and the workpiece as the anode. Tools with negative polarity give higher material removal rate, lower tool wear and better surface finish. High open-circuit voltage is necessary for tungsten carbide due to its high melting point and high hardness value. Dielectric flushing pressure is found to be optimal at 50 kPa. High material removal rate, low relative wear ratio and good surface finish are conflicting goals, which cannot be achieved simultaneously with a particular combination of control settings. To achieve the best machining results, the goals have to be taken separately in different phases of work with different emphasis. In rough EDM of tungsten carbide, material removal rate is of primary importance. Thus, the higher the discharge current, the faster is the machining time. Material removal rate and the surface roughness of the workpiece are directly proportional to the discharge current intensity. When approaching the finishing stage, an optimum control setting is required for attaining the best surface finish and precision machining. For precision machining of tungsten carbide, the optimum condition of relative wear ratio and surface roughness takes place at a gap voltage of 120 V, discharge current of 24 A, pulse duration of 12.8 #mu#s, pulse interval of 100 #mu#s, dielectric flushing pressure of 50 kPa and copper tungsten (CuW) as the tool electrode materials with negative polarity. This study confirms that there exists an optimum condition for precision machining of tungsten carbide although the condition may vary with the composition of the material, the accuracy of the machine and other external factors.