Key Engineering Materials Vols. 304-305

Abstract: As the common materials of making cutting tool, the cemented carbide has been widelyused in all kinds of mechanical machining. Based on the manufacturing craft of the brazing welded cemented carbide cutting tools, according to the theory of engineering mechanics and fracture mechanics, the main factors are analyzed and studied which influence surface cracks of cutting tool from prefabricated stress σc, brazing stress σq, removable stress σw at heat preservation and extra stress σf several aspects in this paper. Then the author founded the math-mechanics model of forming the surface cracks and deduced the critical condition generated surface cracks in brazing welded cemented carbide cutting tools and puts forward several kinds of technology, crafts and methods restraining or minishing surface cracks of the cemented carbide cutting tools.

Abstract: A novel polishing technique based on the two-dimension vibration of fluid is put forward to obtain ultra-smooth surface without damage. In operation, the polishing pad is replaced by fluid where fine abrasive particles are mixed, and the impact and grinding effect can be produced by means of the vibration of fluid and the relative motion of workpiece. It can achieve the ultra-precise polishing for all kinds of planes and curved surfaces. A finite element method is employed to analyze the dynamic behaviors, including vibration mode and harmonic response under the action of the exciter, and the fluid field based on two-dimension vibration is simulated.

Abstract: A novel lapping mode is developed on the base of present eccentric v-grooves lapping mode for precise balls. The kinematics analysis shows that the ball spin axis can wiggle up to 180° under the developed mode, so the lapping trace will be dispersed onto the whole surface of the ball. The effect of offsetting and groove radius on the lapping uniformity in the developed eccentric v-grooves, the present eccentric v-grooves and the traditional v-grooves lapping mode are compared, and the advantage of the developed mode is that the impact offsetting is less while the groove radius has no impact.

Abstract: In this paper, three kinds of granite were lapped and polished by loose abrasives. Glossiness and surface roughness of the lapped and polished granites were measured and the surface morphologies were observed. The experimental results revealed that the readings of roughness were very discrete. High glossiness can be achieved only when the surface roughness is decreased to a certain level. The average surface roughness of the three kinds of granite after being finely polished can reach 0.02～0.04um. Further reducing of roughness has little effect on the glossiness because the existence of the defects, which prohibits the further increase of the glossiness.

Abstract: In this paper, the scratching processes by a diamond indentor under the loads linearly increased from zero were studied to assess the mechanical behavior of LiTaO3 crystal wafer. Material removal mechanism of LiTaO3 crystal by mechanical loads was analyzed based on the measured acoustic signals in the scratching processes and the observation on the scratched surfaces of LiTaO3 wafers. The chemical mechanical polishing (CMP) processes of LiTaO3 wafers were analyzed in detail according to the observation and measurement of the polished surfaces of LiTaO3 wafers with SEM and XRD. The research results show that there exist four regimes along the scratched groove with the increasing of down force in a scratching process of LiTaO3 crystal wafer, and the critical load for each regime is affected by the loading speed and final load, etc. When H2O2 and KOH are added into the polishing slurry, the material of LiTaO3 wafer is removed by chemical reaction and mechanical action sequentially in the CMP processes, and the material removal rate increases while the surface roughness is improved.

Abstract: The wear mechanism of several kinds of diamond circular saw blades was studied in the different sawing parameters during dry cutting of cement concrete, ferroconcrete and steel fiber reinforced concrete. Seven wear forms of diamond grits were obtained in the sawing experiments. The cobalt based bond shown the best wear resistance. It showed that the damage of blade body was caused by thermal damage and the scratching action of concrete chips. The result indicates that the wear of diamond saw blades arises mostly from the difficult chips removing, high cutting temperature and drastic impacting in dry sawing.

Abstract: In non-abrasive cryogenic polishing, ice disk is used as polishing tool .The effects of ice disk characteristics by different water quality on surface roughness of machined parts are investigated. Non-abrasive cryogenic polishing is a plastic transfiguration process based on brittle-plastic transition theory. During machining, higher micro peaks become lower and the number of micro peaks increases which results in lower roughness. Experiments are done to attest to the process.

Abstract: Bonnet tool polishing is a novel aspherical polishing method. This paper describes a method to obtain the local removal rate for the polishing process using bulbous flexible membrane covered with a polishing pad and pressurized by an internal fluid. According to the principle of bonnet polishing and Preston equation, the local removal rate model was established. It is confirmed by the experiments that the local removal depth has a linear relation with the dwell time. Preston coefficient can be calculated from the experimental data. Finally the expression of the local removal rate in bonnet tool polishing is acquired semi-empirically.