Manabu Iwai

Material Removal Mechanism in Dynamic Friction Polishing of Diamond

The Dynamic Friction Polishing Method enables highly efficient abr asive-free polishing of single crystal diamond and polycrystalline diamond (PCD) by simply pressing them against a stainless steel (SUS304) disc rotating at a high peripheral spee d utilizing the thermochemical reaction occurring as a result of dynamic friction between them in the atm osphere. In this paper, the polishing mechanism involved in this method is discussed based on the polishing effic iency and the X-ray diffraction analysis of the machined swarf and the metal disc sur face of SUS304 used for polishing the surface of a single crystal diamond in various polishing atmospher es. The material removal mechanism is estimated to be due to the diffusion of carbon from the di amond into the disc and its subsequent evaporation by oxidization. Introduction The authors have been conducting a study of the “Dynamic Friction Polishi ng Method” utilizing thermochemical reaction induced by dynamic friction between a diamond w rkpiece and a metal disc tool rotating at a high peripheral speed in the atmosphere. This met hod has made possible highly efficient polishing of single crystal diamond and polycrystalline di amond (PCD) simply by pressing them against a rotating stainless steel (SUS304) disc with low carbon content and low thermal conductivity [1,2]. It has been thought that the material removal mecha nism involve diffusion of carbon from diamond into the disc tool by thermochemical reaction. In our previous study, high efficiency polishing was found to be especially associated with SU S304 disc in which carbon content is rather low and the iron element (Fe) exists as a phase (an austenitic structure). Moreover it was observed that the carbon content increased on the disc tool surface afte r polishing. Considering that the polishing operation is carried out in the atmosphere, carbonization of diamond followed by evaporation by oxidization may occur. In this paper, the polishing mechanism in this method is investigated ba s on polishing efficiency and X-ray diffraction analysis of the machined swarf, the metal disc s urface and the diamond surface when a single crystal diamond is polished with an SUS304 disc under vari ous polishing atmospheres. Background According to the previous similar research works, three main points be low have been stated on the material removal mechanism in polishing of diamond due to thermochemica l rea tion under friction with iron based material [3~6]. (1) Diffusion of carbon from diamond into steel. (2) Conversion of carbon structure from diamond to graphite or amorphous structure. (3) Oxidation of converted carbon under heat and in an oxygen atmosphere, res ulting in forming of CO or CO2 gas and evaporation. In our research work on diamond polishing, a high polishing efficiency was achieved by intelligent use of the thermochemical reaction. The result achieved until now are a s follows: Key Engineering Materials Online: 2003-04-15 ISSN: 1662-9795, Vols. 238-239, pp 235-240 doi:10.4028/www.scientific.net/KEM.238-239.235

A New Application of PCD as a Very Low Wear Electrode Material for EDM

Electrically conductive CVD diamond having a high thermal diffusivity, when used as an electrode for micro EDM, revealed very low wear compared to copper and Cu-W electrodes in the case of finish EDM condition, where the short pulse duration is adopted. In this research work polycrystalline diamond (PCD), which has a thermal conductivity similar to that of the electrically conductive CVD diamond, is introduced as a new composite electrode material for EDM. Various properties of PCD with respect to EDM of die-steel (SKD11) and tungsten carbide (G5) have been studied and compared with those of the electrically conductive CVD diamond, copper and copper-tungsten electrode materials. It is found that electrode wear and material removal rate decreased with an increase in thermal conductivity depending on the type of the PCD material when very short pulse duration of te=1µs is applied. Extremely low wear, 1/20~1/50 times of the Cu-W electrode in the case of EDM of tungsten carbide workpiece at short pulse duration and zero wear in the case of EDM at short and long pulse duration of SKD11 can be realized.

A Micro Ultrasonic Grinding Device with Very High Frequency and its Application

This paper deals with the development of an extremely high frequency ultrasonic transducer of magnetostrictive type with vibration frequency of up to 400kHz, and its application to ultrasonic grinding. This transducer provides longitudinal, torsional and complex modes of vibration. The application of this transducer to grinding or boring on glass, ferrite and alumina ceramic workpieces, resulted in stable grinding force and reduced chipping, especially in the complex mode of vibration. The vibration amplitude of the transducer is controlled to a step of 0.2μm, thus a depth of cut of 0.2μm is realized in grinding on a normal NC machine.

A New Complex Grinding Method for Ceramic Materials Combined with Ultrasonic Vibration and Electrodischarge Machining

A new complex grinding method named Ultrasonic Electrodischarging Grinding Method (US-ED-G in short) is described. In the US-ED-G, ultrasonic grinding and ED grinding are simultaneously carried out on an electrically conductive workpiece with a metal bond grinding wheel. When compared with other complex grinding methods, the US-ED-G is remarkably effective in reducing grinding force a great deal and maintaining grinding ability of a wheel for a long time in efficient grinding of extremely hard-to-grind ceramic materials like TiB2. A stock removal rate of 200mm3/min and a grinding ratio of 110 have been attained by selecting appropriate conditions in US-ED-G of TiB2. A compact and rigid ultrasonic attachment is also described, which was developed as a removable tool for carrying out US grinding and US-ED-grinding on a machining center or a grinding center.

Low-wear diamond electrode for micro-EDM of die-steel

The reduction of electrode wear is very important for high-finish and high-accuracy machining in micro-electrical discharge machining. Electrically conductive CVD diamond has shown almost zero electrode wear, even at short pulse duration of 3 µs. Zero electrode wear is extremely important for maintaining the desired shape. This research involves the investigation into the effect of various EDM parameters on the EDM of die-steel using electrically conductive CVD diamond with respect to electrode wear, efficiency and EDMed surface property. The effect of joule heating due to the high electrical resistivity of electrically conductive CVD diamond was also studied. The results indicate that there is no deterioration of the workpiece surface due to joule heating when EDM is performed using the electrically conductive CVD diamond electrode. An investigation into the factors responsible for the low wear of the CVD diamond electrode leads us to deduce that an accelerated deposition of heat-resolved carbon along with the high thermal stability of the diamond are mainly responsible.

A New Longitudinal Mode Ultrasonic Transducer with an Eccentric Horn for Micro Machining

A compact eccentric horn shape transducer body with longitudinal vibration sensor bolted to it has been developed. The device can produce an angular vibration of the or der of 40 kHz at the cutting tip attached to the end of the horn. The vibrating tip was to be used for precision machining of straight micro-grooves, which are difficult to achieve using exist ing precision machine tools, on which the processing was at a slow speed of the order of 4m/min. The vibration features such as vibration angle and amplitude of the horn at the tool tip, observed by a CCD camera at the magnification of 1500x, were 30°and 6μm P-V, respectively. An ultrasonic vi bration frequency of 57.4 kHz was achieved. The R-shaped micro-groove machining was successful ly carried out on the cold rolled steel SKS93 and Hv209 in two stages, a roughing cut at a dept h of cut of 20μm, and a finishing cut of 3μm, 6μm, and 10μm, for the feed rates of 1.5 and 2.0m/min, re spectively. The length was 125mm. The appearance of the machined surface is excellent compa red with the torn surface obtained in conventional groove machining. Introduction Many advanced technology products used by consumers need machining of straig ht precise micro grooves at a high speed, however the existing machine tools cannot provide the accuracy/precision required due to their inherent limitation. In fact most precision ma chine tools are slow cutting with a speed of about 4m/min. In order to overcome this problem of slow cutting i .e. low speed, low feed rate and depth of cut, it is thought that the introduction of an ultrasonic vibration right to the cutting point can improve the machining efficiency, including a highly increased pparent machining speed, the surface finish and profile accuracy/precision. Piezoelectric ultrasonic vibration transducer is utilized for fabricating a tool body to hold a standard throwaway cutti ng ip that will finally receive the desired ultrasonic vibration [1]. This eccentric horn was made from aluminum for an initial test, which was quite large in size in order to get large amplitude. Moreover, the vibrati on f equency was limited to 28kHz. Smaller size can provide higher frequency of vibrati on. As a next step it was decided to use this method for precision machining of groove by developing a more compact eccentric horn made of steel. In order to do this, it was essential to develop a trans ducer body that can provide high vibration frequency and function efficiently for the precision groove machining. Thus further attempts are made as will be discussed in this paper to d velop a suitable transducer body by using CAE. This paper presents the sequence of this development w ork using 3-D modeling and FEM analysis [2]. Development of a New Transducer Body for Precision Groove Machining Eccentric horn ultrasonic vibration device with high frequency The first attempt was made by constructing an eccentric horn ultr asonic vibration transducer device as shown in Fig. 1. An ultrasonic vibration frequency of nearly 60kHz corresponding to 190V of t he Key Engineering Materials Online: 2003-04-15 ISSN: 1662-9795, Vols. 238-239, pp 147-152 doi:10.4028/www.scientific.net/KEM.238-239.147

Forming Fine V-Grooves on a Tungsten Carbide Workpiece with a PCD Electrode by EDM

Polycrystalline diamond (PCD) exhibits a thermal conductivity similar to that of the electrically conductive chemical vapor deposition diamond (EC-CVD diamond) found to function as zero-wear electrodes at short pulse duration. In this study, PCD was used as electrodes applied to EDM on tungsten carbide. Two kinds of PCD (CTB-010 and CTH-025) with a flat surface were used. The wear of the PCD electrodes was about 1.5% for very short pulse duration such as te=1μs, but it was zero wear at te=30μs, though the wear of a Cu-W electrode was 10% even on the machine recommended conditions for the low wear. EDM experiment using a V-shaped PCD electrode with an included angle of 45° was also carried out and the performance was compared with the case using a V-shaped Cu-W electrode. Under the conditions of a no load voltage of 60V, a set peak current of 2A, and a medium pulse duration of te=15μs, there was no wear on PCD electrodes when observed under the SEM, whereas a 50μm-deep wear on the Cu-W electrodes even under the machine recommended condition for the low wear was observed.

Prediction of Surface Roughness by 3D-CAD Model in Helical Scan Grinding and Groove Grinding

This paper deals with prediction of improvement in surface roughness in helical scan grinding by simulation of virtual ground surface with a 3D-CAD model. It has been found that, by choosing the value of parameters of four grit conditions such as grit arrangement, protrusion height, apex angle and inclination angle randomly to a real wheel, the maximum unevenness of the virtual ground surface and tendency of its change with feed angle nearly coincide with the surface roughness in the experiment of helical scan grinding. Furthermore, it is demonstrated that this analyzing method can be applied to R-shaped groove grinding and suggested that helical scan grinding is effective in grinding bearing grooves.

Development of New PCD Made Up of Boron Doped Diamond Particles and its Machinability by EDM

This paper deals with a new PCD named EC-PCD which is made up of boron doped diamond particles and its properties related to EDM machinability. For the purpose of improving various properties of standard PCD including resistance to heat, wear and reactivity, a new PCD (EC-PCD) was manufactured on a trial basis using electrically conductive diamond particle as a basic ingredient. Grain size, resistivity and thermal conductivity of the boron doped diamond used are 10μm, 5~37×10Ω•m and 440~580W/m•K. In this report, machinability of newly developed PCD (EC-PCD) by wire EDM was investigated in comparison with that of standard PCD. In wire cutting of 2 types of PCD in water under the condition of open gap voltage: ue=80V, set peak current: iP=0.8A and pulse condition: te/to=20/20μs, it was found that roughness of the first cut surface of standard PCD was approximately 8μm Rz, while that of EC-PCD was far better such as 3μm. Also in finish cut (7th cut), the latter achieved the value of Rz=1.7μm while the former achieved only the value of Rz=2.7μm. Expecting better performance, EC-PCD was tested also in oil. As a result, the best achieved roughness was improved to Rz=0.4μm with no chipping on the edge. To explore a reason for such a good roughness obtained, the cut samples were observed on the SEM, which revealed that the diamond particles in EC-PCD were flattened by electro discharge.

A New Diamond Wheel Containing Boron Doped Diamond Abrasives Enabling Electrically Conductive Cutting Edge and High Thermal Stability

Electrically conductive cutting edges diamond grinding wheels (EC-cutting edges D wheels) have properties such as, 1) convenient precise forming by EDM, 2) realization of high cutting edge density, 3) sufficiently large chip pockets along with fine cutting edges on large diamond grits, 4) contact sensing of the cutting edges with workpiece due to electrical conductivity, 5) expected application to the grinding of various types of steels due to high thermal resistance. Until now, the grinding ability of the sharp edges generated on the electrically conductive CVD diamond thick film wheel by electrodischarge trueing (ED trueing) was confirmed by grinding experiments using a small diameter lapping wheel and a small diameter disk wheel. In this research work, metal bonded diamond wheels containing boron doped electrically conductive diamond (EC diamond) grits, which possess high oxidation temperature, were trial manufactured. From the results of grinding test for an optical glass (BK7), it was found that the wear and grinding force for the EC diamond grits wheel were significantly low compared to a conventional diamond grits wheel. Furthermore, from the results of the investigation on ED trueing performance, a high trueing efficiency along with the possibility of cutting edge tip formation was confirmed.