This paper presents an experimental investigation of the machining characteristics of Polycrystalline Diamond (PCD) in micro wire electrical discharge machining (μ-WEDM). The Taguchi method was adopted to obtain the optimum conditions of parameter settings for cutting width and material removal rate (MRR). The ANOVA analysis has been used to predict the significant machining parameters according to L18 orthogonal array and signal/noise (S/N) ratio. The experimental results reveal that the intensity of open circuit voltage (UHP) affects significantly on the amount of cutting width as well as MRR. Additionally, the cutting width is also directly reduced by higher wire tension and lower flushing pressure. The MRR was increased at greater UHP and peak current (I). Finally, the confirmation experiments show that the cutting width and MRR also depends on the grain size of PCD (1.6µm ~7µm) by the optimum machining conditions.

        Keywords:μ-WEDM, Polycrystalline diamond (PCD), Material removal rate (MRR), Cutting width, Taguchi method.

       Polycrystalline diamond (PCD) is a synthetic composite cutting tool material produced by sintering together carefully selected diamond particles under condition of high temperature and high pressure. The interstitial spaces in the diamond matrix are predominantly filled with cobalt, which is used as a solvent catalyst in the synthesis process. Because of its mechanical properties typical of diamond, PCD is an excellent material on components subjected to high stress loads. The great wear resistance of PCD is due to its extreme hardness and high transverse rupture strength – an unusual combination for ultra-hard materials. However, because of these very properties it is difficult to machine this material economically using conventional techniques such as grinding and lapping. For this reason, shortly after its introduction, industry began to search for alternative methods for machining PCD blanks.

    Since PCD unlike single crystal diamond, is generally sufficiently electrically conductive to enable wire EDM methods to be used, this technique, which can be applied virtually irrespective of the hardness and strength of the material, has offered a solution to the problem of how to machine PCD. Today, electrical discharge machining with a wire electrode (Wire EDM) and electrical discharge grinding (rotary EDM) are widely used to machine PCD. In addition, with EDM the kerf is very narrow, thus minimizing waste and increasing economic efficiency [1]. Ahmet and Ulas [2] have reported an experimental investigation of the machining characteristics of AISI D5 tool steel in WEDM process to determine parameters such as open circuit voltage, pulse duration, wire speed and dielectric fluid pressure were changed to explore their effect on the surface roughness and metallurgical structure.

    Saurav Datta et al. [3] performed an experimentalstudy to determine the variation of the machining parameters on the material removal rate (MRR), gap width and surface roughness. In their work, the experiments have conducted with six process parameters: discharge current, pulse duration, pulse frequency, wire speed, wire tension and dielectric flow rate; to be varied in three different levels. Data related to the process responses such as MRR, roughness value of the worked surface and kerf have been measured for each of the experimental runs; which correspond to randomly chosen different combinations of factor setting.

     There is a large volume of published studies describing the effect of WEDM machining parameters on cutting width and MRR [4-7]. However, for the micro-WEDM, there is rare published work studying the effect of machining parameters on PCD statistically. The variation of kerf and MRR with machining parameters and optimization of machining settings for minimum kerf and maximum MRR should be investigated experimentally and the obtained results should be interpreted and modeled statistically to understand closely the behavior of machining rate and accuracy in micro-WEDM.

     This paper seeks to explain the basic relationships in the micro-WEDM cutting of PCD between the parameter settings and the PCD properties but also to determine effect of machining parameters namely, flushing pressure, grain size, wire speed, peak current, open circuit voltage, servo voltage, pulse on duration and wire tension on material removal rate and cutting width of PCD in the fine grades 1.7 μm, 4 μm and 6 μm, respectively, used in manufacturing cutting tools by micro-WEDM process.

Detail 

The machining characteristics of polycrystalline diamond (PCD) by micro-WEDM F. C. Hsua,b, T. Y. Taib , V. N. Vob , S. Y. Chenb , Y. H. Chena a Micro/Meso Mechanical Manufacturing R&D Department, Metal Industries Research & Development Centre (MIRDC), Kaohsiung, Taiwan b Department of Mechanical Engineering, Southern Taiwan University of Science and Technology (STUST), Tainan