Key Engineering Materials Vols. 291-292

Abstract: The high-strength reaction-sintered silicon carbide (RS-SiC) developed by TOSHIBA is one of the most excellent materials for large-scale space-borne optics. The bending strength of the high-strength RS-SiC is two times higher than other SiC ceramics. The purpose of this study is to investigate the ELID grinding properties of the high strength RS-SiC. Two types of metal bond diamond wheels (cup type and straight type) were used to grinding tests. The ground surface properties, such as roughness, subsurface damage and micro-step were made clear by measurement or observation. It was confirmed that, both the surface roughness and the depth of micro-step produced by cup-wheel were lower than those produced by straight-wheel. When a #20000 grit sized cup-wheel was used, a considerably high quality mirror surface (Ra<0.8nm) can be achived.

Abstract: In the present study, natural granites were ELID ground with metal-resin bonded diamond wheels on a lap-grinding machine to achieve smooth surface. The surface roughness during the grinding process and final glossiness were examined to describe the formation of finely finished granite surfaces. According to the detailed micro-observation of ground surfaces, it can be concluded that natural granite surface on the main mineral components can be smoothly finished with ELID lap grinding. However, the appearance of natural defects and residual fracture on the ground surface lead to the scattered surface roughness, and restrict the improvement of surface glossiness.

Abstract: It is a cost-effective technology to obtain aspheric optics made from optical glass and other brittle materials using pressing mould. The optical quality of molded optics is determined mostly by the surface quality of the mould, which means poor mould surface with lots of cutter marks will result in adhesion phenomena and error replication between the optics and mould. [1] In this article, a chatter model about parallel grinding system was presented, and the reasons of chatter induced by velocity feed back was analyzed and simulated. By using parallel grinding system integrated ELID technology, and wheel with greater cross-section radius in rough grinding and constant grinding velocity in fine grinding, the amplitude of cutter marks in the surface of mould was minimized and the quality of the mould surface was improved.

Abstract: For the purpose of investigating the effect of cutting edge truncation on ground surface morphology, several kinds of hard and brittle materials used for optical devices, borosilicate glass, glass quartz, crystal quartz and sapphire, are plunge ground with a SD600 metal-bonded grinding wheel, the cutting edges of which are truncated so as to be aligned with the height level of the grinding wheel working surface, after electrocontact discharge truing and dressing. It is found that an improvement of roughness can be obtained for every material investigated, although the degree of roughness improvement depends on the kind of material. Ductile-mode grinding is most likely to be realized in the case of crystal quartz.

Abstract: The precise face grinding and lapping technology with abrasive or abrasive tool has been widely used in the field of the precise manufacture and ultraprecise manufacture. It has become an essential technology in the manufacture of many components. The planetary lapping machine is typical equipment for face grinding or lapping process. And the relative motions between the workpieces and grinding wheel will affect the formation of wear profiles of the tools, furthermore, the work result will be affected directly by the cutting path of this relative motions. In this paper, the kinematic principle of face grinding process on lapping machines has been analyzed. By means of the concept of pitch point and pitch circles, the complicated grinding process has been converted into two kinds of rotations with the fixed center distance. Two kinds of path curves, i.e. workpiece against grinding wheel and grinding wheel against workpiece, and their relations are analyzed. The geometrical analyses and the manufacture quality of the workpiece are linked with the aid of the cutting velocity, the range of the rotational angle of the cutting traces and the rate of the change of the rotational angle with time. The optimal path curve and kinematic parameters are achieved, and these results are corresponding to the experimental results.

Abstract: Along with the recent developments in the optical communication industry, the demand for optical communication components has increased. Ferrule is a significant element that determines transmission efficiency and quality of information in the optical communication area. Most ferrule machining entails grinding and this requires high processing precision. Therefore, the ultra precision centerless grinding machine for ferrule grinding was designed. The centerless grinding machine is composed of a high damping bed, grinding wheel spindle unit, regulating wheel spindle unit, feeding table and dressing unit. Reliability prediction is very important for the high quality design. In this study, reliability of the centerless grinding machine was predicted.

Abstract: Grinding machining quality contains machining precision and grinding surface integrality. The factors influencing grinding machining quality have fuzzy characteristics. For example, the magnitude and measure methods of grinding surface roughness have fuzzy uncertainties. The grades of the machining quality are vague, and there is no definite boundary between “good” and “bad” machining quality. Analytical Hierarchy Process (AHP) combined with the fuzzy comprehensive evaluation technique is used to evaluate the grade condition of the quality in this paper. Considering the fuzziness of the factors, a two-stage fuzzy comprehensive evaluation model is proposed to evaluate the grinding machining quality. In light of different reliable degrees of different kinds of fuzzy operator models, the weighted average method is used. The membership degrees of the evaluation factors are determined by experts’ knowledge and experiences. The factor weights are calculated via the AHP method. Certain synthetic importance of each stage evaluation is presented through weighted sum of the relative important degree. Examples of conventional external grinding machining illustrate the effectiveness of the proposed model.

Abstract: In this study, the crankshaft pin grinding mechanism, which is carried out with wheel head oscillating type CNC crankshaft pin grinder, is theoretically analyzed. In order to maintain grinding process, the pin rotates and also rocks along wheel working surface, because the wheel head oscillates with journal rotation. Then, it is made clear that cylindrical plunge grinding process progresses in the pin grinding process for the first time. Therefore, grinding speed ratio, which is defined as ratio of substantial pin surface speed to wheel surface speed, is firstly formulated. Secondly, undeformed chip size generated by a grain is estimated with the grinding velocity ratio. Finally, the grinding performance is predicted with experimental equations, which obtained previous study. By this simulation, it is made clear that dimensional accuracy and also surface roughness vary on whole of the pin surface with constant journal rotation grinding method. On the contrary, deviations of both the dimensional accuracy and the surface roughness are reduced with controlled speed ratio grinding method, in which journal rotation speed is adequately controlled.

Abstract: During wafer rotation grinding, the wafer is centered on a porous ceramic vacuum chuck and so; the dressing shape of vacuum chuck becomes a critical factor affecting the flatness of ground wafers. In this paper, a theoretical model of the dressing shape of vacuum chuck in wafer rotation grinding is developed. From the model, the relationship between the dressing shape and the affecting factors is given. The dressing shape is predicted by computer simulations based on theoretic model and the vacuum chuck dressing experiments are conducted to verify the theoretical model. It is shown that the theoretical analysis matches the experimental measuring results very well. The study results provide a theoretical basis for analysis of the relationship between the dressing shape and the flatness of ground wafer, for improving the flatness of ground wafer and for selecting the proper parameters of grinding process.

Abstract: A study of the energy-mode adjustment and application was presented to investigate the effects of adjustable methods on energy mode. Three methods of energy-mode adjustment were used: by circular profile itself, by an optical scanning expander and deformable mirror. The circular profile naturally modifies energy density with the changes of incident angle. The optical scanning expander was used to turn a Gaussian beam into a uniform beam. Also a novel technique of deformable mirror was designed to obtain a more controllable energy mode for laser selective processing. Moreover, the models describing energy modes were developed to improve laser-processing performance. An experiment was arranged to simulate single-tip diamond truing and produced a result, as shown in the SEM photo, quite similar to a fine thread. The results were discussed to reveal the mechanism of laser processing.