Key Engineering Materials Vols. 389-390

Abstract: The measurement principle where in a high-NA (Numerical Aperture) surface, for which the degree of the angle of surface inclination exceeds π/3 radians, could be evaluated with high precision and high speed is proposed. This is based on the stitching method, where aspherical surface measurement becomes possible by dividing the surface of the sample into a range so that measurements can be made with an interferometer and finally combined. We examine the method of applying an interferometer to the condition in which the sample is rotated on an air spindle at a constant speed. It is not necessary in this method to make the sample static. Therefore, the vibration of the servo motor and any location errors can be eliminated. Moreover, the measurement time does not depend on the number of divided areas which are necessary for the stitching method, allowing for high-speed measurement. The principle behind this technique is expanded first, and an experiment system based on it was constructed. The principle proposed was evaluated, and its effectiveness was confirmed.

Abstract: Surface geometries of grinding wheels vary due to the wear in grinding process. Since the wheel wear patterns are affected by the grinding process, measuring and investigating these patterns quantitatively, grinding process can be evaluated whether appropriate or not. Utilizing a three-dimensional measuring device for wheel surfaces developed so far, this study aims to evaluate wheel wear patterns quantitatively. As the results, applying developed device, it is clarified that wheel wear pattern can be classified and evaluated quantitatively.

Abstract: During the last decades, heat generation in grinding is one of the top concerns because high temperature under fabrication leads to less dimensional accuracy of a workpiece. Several studies with regard to grinding heat have been carried out, focused on micro phenomena of abrasive grains or macro phenomena of thermal deformation in grinding machines. However, these researches have been extensive, schematized information such as thermal deformation, and grinding temperature is indispensable for practical applications. In this study, we combined the simulation model of the plunge grinding process and the numerical analysis method with the differencing technique for the non-steady heat conduction problem, and have constructed the simulation technique for analyzing the heat problem in the workpiece. The simulation results provided information of the heat conduction, and the thermal deformation of the workpiece.

Abstract: This paper presents a comprehensive model for predicting surface roughness due to grinding. Fuzzy rules are provided, to estimate roughness for any practical combination of (1) wheel hardness grade, (2) abrasive grain size, (3) dressing condition, (4) table speed, (5) wheel depth of cut, and (6) coolant application. The rule-base can be adapted to account for the effect of (7) different workpiece material hardness, (8) wheel rotational speed, and (9) equivalent wheel diameter. The 86 rules are intuitive, and are particularly useful for production and/or embedded control applications.

Abstract: Estimation of mechanism of surface finish improvement in helical scan grinding, a method in which a good surface finish is obtained besides keeping a high grinding efficiency, is performed based on the virtual grinding trace using a 3D-CAD model. In three grit models, (a) a single grit on a wheel, (b) plural grits arrangement on a helical line on the wheel circumference, and (c) multiple grit arrangement in a triangular pattern, virtual grinding traces and their unevenness or surface roughness are investigated. The virtual grinding trace in helical scan grinding is made by interference of grit trajectories, and the results of the analysis are very similar to experimental results.

Abstract: Diamond tools wear easily under cutting tungsten carbide. To clarify the wear mechanism, the authors composed a temperature-measurement system of a cutting point using a dual-colorinfrared pyrometer and performed planing experiments. Infrared rays, emitted from the contact point between a mono-crystal-diamond tool and a cobalt-free tungsten carbide, are transmitted though the diamond tool and an optical fiber and then they are detected by the pyrometer. Before the planing experiments, rubbing experiments were performed using a mono-crystal-diamond stick and a tungsten-carbide disk. The effects of gas environments and rubbing conditions on contact-point temperature, friction coefficient, and diamond wear were experimentally investigated. Planing experiments of the tungsten carbide using mono-crystal-diamond tool, were performed. The effects of planing conditions and gas environments on cutting-point temperature and tool wear were investigated. Through the experiments the following results were obtained. Rubbing and cutting point temperature is the highest in Argon gas followed by Nitrogen gas and is the lowest in Air. Diamond-tool wear is the greatest in Argon gas, less in Nitrogen gas, and the least in Air. The reason for this is that a chemically or physically absorbed layer of oxygen or nitrogen on tungsten carbide acts as a lubricant at the contact point. Cutting-point temperature was in proportion to cutting speed. The temperature under cutting speed at 90m/min and cutting depth at 1.0μm in Air was approximately 170degrees Celsius.

Abstract: In this paper, turning with actively driven rotary tool was investigated. The influence of machining conditions such as tool rotational speed and inclination angle on the cutting edge temperature is examined experimentally. The temperature was measured by a thermocouple of constantan wire and work material. Experimental results show that the cutting temperature decreases with increasing tool rotational speed to a minimum value at a certain tool rotational speed and then increase. Next, the minimum temperature recorded by tool rotation was approximately 150oC lower than that the cutting with a non-rotating tool. Finally, the cutting temperature also decreases with the increase of inclination angle to a minimum value at an inclination angle.

Abstract: The service life of a diamond tool in cutting single-crystal silicon is normally very short because of severe tool wear. Therefore, it is important to use a proper coolant in order to restrain tool wear. In this paper, the performances of oil-based and water-based coolants were compared in silicon machining by investigating cutting forces and tool wear geometries. The water-based coolant was found to restrain flank wear more effectively than the oil-based one. The effective tool life using the water-based one was averagely three times longer than that using the oil-based one. The tool wear mechanism might be related to microplasma generated between silicon and diamond during cutting.

Abstract: Reaction-bonded silicon carbide (RB-SiC) is a recently developed ceramic material with many merits such as low manufacturing temperature, dense structure, high purity and low cost. In the present paper, the precision machinability of RB-SiC was studied by microindentation and single-point diamond turning (SPDT) tests. The influence of depth of cut and tool feed rate on surface roughness and cutting force was investigated. Results showed that there was no clear ductile-brittle transition in machining behavior. The material removal mechanism involves falling of the SiC grains and intergranular microfractures of the bonding silicon, which prevents from large-scale cleavage fractures. The minimum surface roughness depends on the initial material microstructure in terms of sizes of the SiC grains and micro pores. This work preliminarily indicates that SPDT can be used as a high-efficiency machining process for RB-SiC.

Abstract: When cutting titanium alloy, the temperature of a cutting tool edge is easy to rise and the tool edge is tend to be worn away quickly because the titanium alloy has the characteristics of low thermal conductivity and high chemical activity. Therefore, it is difficult to achieve a balance between the productivity and the tool life in cutting the titanium alloy, namely, low-speed cutting must be carried out at present. To examine the possibility of the improvement in the cutting efficiency, a PCD (polycrystalline diamond) tool having high thermal conductivity was adopted to the cutting of titanium alloy and its cutting performance was investigated. The PCD tool was found to have excellent flank wear resistance compared with conventional cemented carbide tools. It was also revealed that unprecedented high speed cutting become possible by use of PCD tool with an application of high pressure coolant.