Papers by Keyword: Polycrystalline Diamond (PCD)

Abstract: Polycrystalline diamond (PCD) is an ideal tool material for machining high-pressure laminated (HPL) flooring with ceramics overlay. In this paper, the finite element (FE) model of PCD cutter was built firstly, then stress distribution of PCD cutter for machining wear resistance layer embedded with Al2O3 particles was analyzed. The analysis results showed that the stress distribution was variable in rake and flank face of tool, which leads to the final uneven wear profile. Moreover, the test of cutting load was carried out. From the analysis and test, it was shown that PCD cutter was suffering from the fatigue loading of high cycling while machining. At last, a series machining experiments was conducted and the wear characteristics were examined. The analysis results were verified by the wear characteristics of PCD tool. Machining experiments also revealed that the typical micro crack in wear region had great effects on the wear of tool.

Abstract: As its hardness and wear resistance being approximate to that of natural diamond, polycrystalline diamond (PCD) is a kind of perfect tool material for cutting Si-Al alloy pistons. In the turning process of Si-Al alloy pistons, the normal wear of PCD tools is a continuous and gradual process, which mainly is hard grain wear, as well as adhesion wear, diffusion wear, and chemical wear. The breakages of PCD tools include collapse, crash and flake etc, which occur mainly in discontinuous turning process. Experimental results and production statistic indicate that about 40~55% of PCD tools failure is breakage in discontinuous turning process of Si-Al alloy pistons. Reducing impact load is the main method to avoid tool breakage.

Abstract: In this work we present an equipotential surface map with a resolution higher than 100 nm, resulting from conductive atomic force microscopy (AFM). The images, obtained in polycrystalline MPCVD (Microwave Plasma Assisted Chemical Vapor Deposition) diamond devices, are clearly structure dependent. Diamond and non-diamond phases were identified by micro-Raman spectroscopy and correlated with the electrical conduction map. The application of the non-homogeneous contact theory lead to the extraction of two Schottky Barrier Heights (SBH), one close to 0.6 V with dispersion ~ 0.1 V, attributed to the diamond / metal interface, and the other close to 0.4 V with dispersion ~ 0.04 V, due to the non-diamond phases / metal interface. The diamond / non-diamond phase ratio is about 85:15, taken from the micro-Raman spectra. Combining these results with the electrical conduction map, a general model to predict the macroscopic electrical behavior of polycrystalline diamond based devices is proposed.

Abstract: PCD tools, especially curve edge PCD compound tools are used widely in machining nonferrous and non-metal materials with high efficiency and precision because of their excellent cutting properties. But high quality grinding of PCD tools is the uppermost obstacle in application because there are great difficulties to profile and sharpen edge in grinding, especially for milling cutter and drill with curve edge. This paper studied technology of wire EDG curve edge PCD compound tools by wire electrical discharge grinding machine with five-axis CNC system. The grinding quality was evaluated by scanning electron microscope (SEM) and roughometer. Three steps processing technique (roughing, finishing and fine finishing) and optimal process parameters of wire EDG PCD tools were recommended after considering synthetically the surface quality, precision and machining efficiency. The results met the requirement of high surface quality, precision and efficiency. This paper also applied successfully the optimal technology to grind a PCD milling cutter with outer and inner blade by electrical discharge grinding machine with five-axis CNC system. By the optimal parameters, the process yielded high precision of ±4.3µm and low roughness of 0.30µm. Experiment results have great practical significance to the high precise and efficient wire EDG of PCD tools.

Abstract: Polycrystalline diamond (PCD) composite sheet is a kind of material for cutter blank, which is formed by uniformly mixing micron diamond particles and metal binder powder such as Co and Ni, then sintered on WC under high pressure and high temperature. PCD tools have broad application and very high commercial value. However, compared with other materials, PCD tools’ service life relies greatly on blade sharpening quality. This paper just experimented on preparing precision blade of CTB002 PCD composite sheet on grinding machine of high precision diamond tools and with different performance parameters of TYROLIT diamond grinding wheel. Rotational speed of grinding wheel, grain size of grinding wheel and grinding pressure were researched in the orthogonal test method, which have the largest influence on grinding process, and influencing rules and the best combination of the three parameters are obtained.

Abstract: The structural and electrical properties of as grown multicrystalline (mc) solar silicon have been characterized with special emphasis on the ingot's edge regions. For this purpose a vertical cross section of an mc-Si Bridgman ingot was investigated by Fourier transform infrared spectroscopy (FTIR), laser scattering tomography (LST), lateral photovoltage scanning (LPS), infrared microscopy and microwave detected photoconductivity decay (&PCD). Images of the distribution of dislocations, grain boundaries, precipitates, impurities (O, N, C) and the minority charge carrier lifetime were obtained, partly differentiating the defects by their electrical activity. In particular the LPS method displays dopant striations indicating the shape of the phase boundary. Deviations of the phase boundary from a slightly convex shape in the middle of the ingot to a concave one in the vicinity of the side walls could be observed. The existence of an horizontal temperature gradient deduced from this shape is the reason for convection in the melt. The influence on the concentration profiles of interstitial oxygen and the correlation with the minority charge carrier lifetime are discussed.

Abstract: Molybdenum silicides were obtained by the self-propagating synthesis (SHS) method. Diamond composites containing 30 mass% of MoSi2 or Mo5Si3 bonding phase had been prepared using HT-HP Bridgman type apparatus. Sintering of the diamond composites were carried out at 2073±50 K and 8±0.2 GPa. The interactions in diamond-silicide composites were studied by means of X-ray diffractometry and transmission electron microscopy (TEM). Results of both mechanical properties and thermal resistance measurements are reported. Hardness HV1 for the composite with the predominantly MoSi2 bonding phase was found to be around 42 GPa. After heat treatment in 1200 °C for 30 min. in vacuum HV1 decreases to 29 GPa. In the second composite containing the Mo5Si3 bonding phase the HV1 of 28.0 GPa after thermal exposure changes to 21.0 GPa.

Abstract: This paper presents the tests of electrical discharge grinding (EDG) of polycrystalline diamond (PCD) on electrical discharge machine tool with high speed rotating device. The effects of wheel speed, open circuit voltage, peak current, pulse on time, and pulse off time of EDG on the material removal rate (MRR), wheel wear rate (WWR) and surface roughness (SR) are investigated respectively. The tests indicate that it is possible to shape PCD blank with EDG. The wheel speed makes the MRR increase dramatically. The higher the open circuit voltage, the larger is the MRR. The effect of peak current on the MRR, WWR and the SR is similar with that of open circuit voltage. However, the influence of the peak current is much larger than that of the open circuit voltage. Moreover, the peak current should be smaller than 32A. There is a best ratio between the pulse on time and pulse off time. If a ratio is larger or smaller than that value, there may be adverse effect on the SR and the MRR. Large pulse on time makes the MRR increase and the WWR decrease. However, all the parameters investigated have little influence on the SR of PCD. The SR is determined mainly by the grain size of PCD.