Papers by Keyword: Electrically Conductive Diamond

Abstract: In this study, a polycrystalline composite diamond (PCD) was adopted instead of a single crystal diamond as a burnishing tool. At first, EDM machinability was compared between two kinds of PCDs (10μm grain size), i.e. standard PCD (S-PCD) and electrically conductive PCD (EC-PCD (which was made of boron doped diamond particles). EDM machining time to make a hemispherical shape was 17 minutes for EC-PCD and 37 minutes for S-PCD. Further experiments were conducted with EC-PCD of different grain sizes such as 2μm and 5μm. As a result, the smaller the grain size of EC-PCD the higher the machining efficiency was. Surface roughness values of the EC-PCD after finish EDM were Rz=1.7μm for EC-PCD010, Rz=1.4μm for EC-PCD005, and Rz=1.2μm for EC-PCD002. As a result of burnishing a carbon steel bar (S45C, φ30mm) with the EC-PCD tool, the surface roughness value after machining was improved from 10μm to 1μm.

Abstract: In order to cope with various problems associated with machining of PCD, development of a new PCD possessing excellent tool properties and good machinability at the same time has been demanded. From this point of view, the authors have developed a new PCD, “EC-PCD (Electrically Conductive PCD)”, composed of boron doped diamond particles in place of the standard non-conductive diamond. In this research, investigation into material properties of the newly developed EC-PCD is made. Through the tests, it was found that the boron doped diamond particles (the source material of the new PCD) had an electrical resistivity of 1.6×10^-4Ω·m and the thermal conductivity after sintering was lower than that of the standard PCD. In addition, it was confirmed that the electrical conductivity of the source diamond particles of the EC-PCD had not been lost even under the condition of high temperature and high pressure during the manufacture. As a result of the heat test, EC-PCD’s high resistance to oxidation at high temperatures was confirmed showing no changes in the surface condition even at 675oC while the surface of the S-PCD was largely changed at the same temperature. One of the reasons for this is guessed to be that EC-PCD is hard to react with the cobalt contained as a catalyst metal. Further, it was found in the friction tests using a steel ball that the friction coefficient of the EC-PCD was 50% higher than that of S-PCD at the room temperature though it dropped by 10-30% at the temperature of 80oC.

Abstract: This paper deals with a new surface finishing method of electrically conductive diamond materials by making efficient use of an electrically conductive nature of the workpiece material, instead of conventional methods such as grinding, lapping and polishing using diamond abrasives. The authors focused on the electrolytic machining method and not on the electro discharge machining method for the two advantageous features of the electrolytic machining in addition to the general view that a better surface roughness could be obtained. One of those features is that no higher heat is generated at the machining point. This can eliminate a risk of the film delamination in the case where a workpiece is the CVD diamond coated tool. The other is that a wider machining gap is available between an electrode and a workpiece. This was thought to allow the electrolytic machining to be applied to a tool with a complex shape such as a drill and an endmill. Based on these concepts, electrolytic machining experiments were conducted on the electrically conductive diamond materials. From the results, it was found that the surface of the electrically conductive diamond could be smoothened enough by electrolytic machining though relatively long period of time was required.

Abstract: Electrically conductive polycrystalline composite diamond (EC-PCD), which consists of electrically conductive diamond particles manufactured by doping boron atoms, has recently been developed for the purpose of providing material with both excellent tool properties and good machinability. This paper deals with an investigation into the machinability of EC-PCD by EDM with a copper electrode. As a result, it was found that the material removal rate of EC-PCD made up of diamond particles of 10 and 25 µm in diameter respectively was far higher than that of the conventional PCD. Furthermore, it was confirmed in the single pulse EDM experiment with a needle electrode that the EC diamond region in the EC-PCD was removed together with the cobalt region whereas only the cobalt region of C-PCD was removed when the electrode was set at plus polarity.

Abstract: Polycrystalline Composite Diamond (PCD) is excellent in chipping resistance despite its very high hardness. However, it is not easy to EDM or grind PCD. To realize high efficiency and high quality processing of PCD simply and at low cost, the authors devised new PCD (EC-PCD) by using electrically conductive diamond particles and applied a complex electrodischarge grinding method. In this study, investigation is made on effective grinding condition to realize high efficiency, low and stable grinding force and low wheel wear in complex electrodischarge grinding. As a result, superior grinding property was obtained when the grinding wheel was set at minus polarity, and set peak current of i_P = 4 and 6 A was applied. Furthermore it also became clear that additional conventional grinding process followed after complex electrodischarge grinding improved the surface condition.

Abstract: A new PCD (electrically conductive PCD: EC-PCD) consisting of electrically conductive diamond particles has recently been developed. The authors have proposed a complex grinding assisted with electrical discharge machining (EDM) where discharge machining and grinding are used in combination during material removal to realize high efficiency, low and stable grinding force and low wheel wear for the EC-PCD. In this study, the effect of constant-force grinding in a complex grinding assisted with electrical discharge machining of EC-PCD was investigated. As a result, it was found that higher material removal rate, higher grinding ratio and better surface condition were obtained on EC-PCD compared with standard PCD (S-PCD) in the constant-force grinding.

Abstract: Electrically conductive polycrystalline composite diamond (EC-PCD) material, which consists of electrically conductive diamond grits, has recently been developed for the purpose of providing the material with both excellent tool property and machinability. This paper deals with the material property and the wear characteristics of EC-PCD. The result shows that the EC-PCD is superior in heat resistance compared with the conventional PCD. And the EC-PCD shows low frictional wear at high temperature in sliding test against stainless steel disk. Furthermore, in a cutting test of aluminum alloy, the EC-PCD cutting tool shows the same wear characteristics as the conventional PCD tool.

Abstract: A new PCD material named EC-PCD (Electrically conductive polycrystalline composite diamond), which consists of electrically conductive diamond grits, has recently been developed. This paper deals with an investigation of a complex grinding assisted with electrical discharge machining (EDM) to realize high efficiency, low and stable grinding force and low wheel wear for the new EC-PCD. The effect of complex grinding assisted with EDM is compared experimentally with the standard PCD (S-PCD). The result shows that, in the complex grinding, lower and more stable grinding force is realized thanks to the material removal action in EDM and that lower wheel wear and better surface finish are attained, just when the EC-PCD is selected as a workpiece.

Abstract: Electrically conductive polycrystalline composite diamond (EC-PCD), which consists of electrically conductive diamond grits, has recently been developed for the purpose of providing the material with both excellent tool property and good machinability. This paper deals with an investigation of machinability of EC-PCD by EDM with a copper (Cu) electrode. As a result, it was found that the EDM speed (Material removal rate) for EC-PCD was higher than that of the standard PCD. Although the surface roughness of the standard PCD was 13µm Rzjis at set current ip=3A, the surface roughness of the EC-PCD was 5µm Rzjis at the same current condition. Furthermore, it was observed that the EC diamond particle in EC-PCD was machined by single discharge EDM. Moreover, it was confirmed that EC-PCD was able to be applied a fine discharge profiling or a making fine holes using a rotating electrode.

Abstract: This paper proposes a new dynamic friction polishing method which utilizes resistance heating for solving a problem of too high pressure on a workpiece in the previous dynamic friction polishing method proposed by the authors. In the new method, an electrically conductive diamond workpiece (which has proper electric resistance) is heated by an electrical current flowing from a stainless steel disc tool to the diamond workpiece during the dynamic friction polishing and the polishing efficiency increases remarkably even at a very low pressure on the workpiece. For example, polishing efficiencies of 233 and 800 µm/min are attained at low pressures of 2 and 5 MPa, respectively, at a disc sliding speed of 2500 m/min.