Tetsutaro Uematsu

On-machine trueing/dressing of metal bond grinding wheels by electro-discharge machining

Summary This paper describes a newly proposed method for carrying out effective and precise trueing and dressing of metal bond grinding wheels on an NC grinding machine or a machining center by utilizing wire or die sinking electro-discharge machining(EDM). The main feature of this method is that a staple ED unit is mounted on the NC table of the grinding machine. Thereby trueing for eliminating the eccentricity of wheels and for generating or correcting profiled wheels is carried out by the help of NC movement of the table, keeping the grinding wheel on a machine spindle. In order to prevent the influence of wear of a block electrode in die sinking EDM, another new method is proposed for shaping or correcting the form of the electrode with a cutting tool on the grinding machine by the help of NC movement of the table. The superior effects of the proposed methods have been confirmed in the case of grinding of ceramic material with cast iron fiber bond diamond wheels.

Highly Efficient Grinding of Ceramics and Hard Metals on Grinding Center

Summary A machining center provided with necessary counterplans as a grinding center was used with a newly developed cast iron bonded diamond wheel in grinding of ceramics and hard metals. Highly efficient three dimensional form grinding was found to be possible by utilizing the rigidity and numerical control function of the machining center and the high toughness and grinding ratio of the grinding wheel. The maximum stock removal rate of 42000mm 3 /min in deep grinding of alumina and that of 2000mm 3 /mm/min in high feedrate grinding of silicon nitride were obtained. Decrease of grinding force and increase of stock removal rate were attained by inprocess dressing in creep feed grinding. Specially devised, numerically controlled tool paths for improving the grinding ability were proposed and the helical scan grinding among them was found to improve surface roughness.

A New Grinding Method for Ceramics Using a Biaxially Vibrated Nonrotational Ultrasonic Tool

Summary A new method for grinding ceramics and hard materials by using a non-rotational tool has been developed. In the method a fixed abrasive type grinding tool is vibrated by a complex ultrasonic transducer longitudinally and torsionally at the same time. Experiments showed that the complex ultrasonic vibration keeps grinding force low and stable for a long time in grinding hard ceramics even without rotating the tool. When a diamond grinding tool with a square or triangular bottom is used, this method has a great effect on producing cavities with sharp inner corners of almost zero radius on various hard-to-machine materials.

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

Development of a Simplified Electrochemical Dressing Method with Twin Electrodes

Summary The paper deals with a newly developed method for electrochemical dressing of metal bonded superabrasive wheels. In this method, alternating current derived from a wall outlet via an inexpensive transformer is supplied to a wheel through twin electrodes, hence a troublesome brush and an expensive DC power source are unnecessary. The preprocess dressing of a wheel (d 3 = 200 mm) was accomplished within a few minutes. Inprocess dressing of a wheel resulted in lower grinding force, longer wheel life and higher grinding efficiency in grinding of ceramic materials and hard metals.

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.

Effect of Inorganic Polyphosphate on Periodontal Regeneration

We designed a new bio-material using sodium polyphosphate [poly(P)] that can be used for acceleration of periodontal regeneration. The effects of poly(P) on cell calcification and periodontal regeneration, including alveolar bone regeneration, were investigated in vitro and in vivo. Expressions of osteopontin (OPN) and osteocalcin (OC) mRNAs were induced by poly(P) treatment of MC3T3-E1cells. Alkaline phosphatase (ALPase) activity was also enhanced by poly(P), and the cells treated with poly(P) were strongly stained by alizarin red. As an in vivo experiment, artificial periodontal pockets were made in the buccal alveolar bone of mandibular first and second molars of each rat. Poly(P) was injected into the artificial pockets over a period of 1 to 3 weeks, and the regeneration of alveolar bone was evaluated histologically. At 1 week after the start of poly(P) treatment, remarkable regeneration of periodontal tissues, including alveolar bone, was observed in the poly(P)-treated group, whereas little regeneration was observed in the control group. The average area of regeneration in the poly(P)-treated group (after 2-weeks treatment) was more than 2-fold larger than that in the control group, suggesting that poly(P) positively stimulates alveolar bone formation. In addition, inflammation of the defected area was diminished and tissue repair was also accelerated in the poly(P)-treated group. Since poly(P) has antibacterial activity against P. gingivalis and S. mutans and since poly(P) stimulates the growth of fibroblasts by stabilizing fibroblast growth factors (FGFs), poly(P) could be effective for periodontal regeneration.

Surface generation mechanism in helical scan grinding: an analytical study

Abstract Helical scan grinding has been found to improve the ground surface roughness and decreases the value of roughness to one seventh of that by plunge grinding (K. Suzuki et al, Proceedings of the International Conference On Machining of Advanced Materials, NIST, Gaithersburg, USA, 1993, pp. 12–20). In the present work an analytical model of ground surface texture was proposed for helical scan grinding, and the results of the analysis were compared with experimental results. Both experiment and analysis show that the ground surface roughness decreases with helical angle and reaches a limiting surface-roughness value at a critical helical angle, which latter is dependent on the speed ratio. Increasing the speed ratio increases the critical helical angle and then decreases the limiting surface roughness. The theoretical model also shows that the critical helical angle is dependent on the wheel diameter and the abrasive size of the wheels. The helical scan grinding method is more effective in improving ground surface roughness, for large and/or coarse wheels than for small and/or fine wheels.

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.