Papers by Author: Xing Ai

Abstract: This paper studies the application of CBR (case-based reasoning) in stone equipments variant design. As the actual design process and CBR process have collateral corresponding relation, CBR accords with the actual design process of deviser. The basic resolution model of variant design is established, and the instance of products variant design is presented. With the application of variant design principle, the design intensity will be lightened, and the design time will be shortened. Therefore the variant design accommodates the requirement of products diversification and client orientation.

Abstract: High-speed machining is investigated in a new viewpoint, thermodynamic theory. Many phenomena in cutting, such as heat conduction, chemical reaction, diffusion and so on, can be studied with thermodynamic theory. In this paper, entropy generation and entropy flow in cutting system are revealed as well as the interaction of sub processes. As a case study, the oxidation of cemented carbide tool was studied in thermodynamic theory and experiments. The results show that thermodynamic theory is effective.

Abstract: The friction and wear behavior of cutting tool materials keeps an issue. In this study, an high temperature tribometre (UMT-2) was used to investigated the tribology properties and mechanism of two kinds of typical cutting tool materials. Commonly used cemented carbide (ZU5) and ceramic (AT) were chosen. The characteristics as to wear rate, friction coefficient and worn surface were studied. From the results, we found that the ceramic had better wear resistance than the cemented carbide. The friction coefficient of cemented carbide decreased with the increase of ambient temperature while the ceramic exhibited an inverse tendency. Finally, the probable wear mechanism was discussed.

Abstract: ZrTiN hard coatings were deposited by multi-arc ion plating on tungsten carbide substrates, using separated Ti and Zr targets in nitrogen and argon atmosphere, combined with ion bombardment of samples surface. The films exhibited a dense and fine grained structure with no columnar growth structure. ZrTiN coatings deposited reveal a (111) preferred crystal orientation. For the coatings, solid solutions were formed. The coatings possessed a higher microhardness value (approx. 2700 Hv_0.05) than their binary counterparts. The increased microhardness was probably due to a solid solution strengthening mechanism while depositing. The thickness of the coatings were between 2.0 and 2.3 μm. The adhesive strength of the coating-substrate system was up to more than 70N.

Abstract: CrN and CrAlN coating tools were heated and heat-preserved in electric stove to make oxidation experiment. The results were obtained through SEM, EDX and XRD. The results are as follows: The oxidation of CrN and CrAlN coating is induced by the micro-holes which were formed by the diffusion of nitrogen atoms and chromium ions towards the coating surface under sufficient thermal energy. With the incorporation of Al, CrAlN coating showed stronger oxidation resistance as compared to CrN. The dense mixture of Cr₂O₃ and Al₂O₃ makes oxygen diffusion through the film difficult and then oxidation and decomposing are alleviated effectively, therefore CrAlN coating can remain high oxidation resistance and high hardness after high temperature which make this coating tool be competent for high speed machining of the hardworking materials. In addition, the failure of the coating is primary induced by oxidation and the different expansion coefficients between coating and substrate.

Abstract: The present paper is an experimental investigation on the machinability of powder metallurgy (PM) nickel-based superalloy during drilling using high-speed steel (M42) drills. The effect of machining parameters on the cutting force, cutting temperature and tool wear were investigated during the experimentation. The effect of machining parameters on the tool wear was examined through SEM micrographs. The research work findings will also provide useful economic machining solution by utilizing economical high-speed steel drills during drilling processing of powder metallurgy nickel-based superalloy, which is otherwise usually machined by costly coated carbide tools or CBN tools. The present approach and results will be helpful for understanding the machinability of powder metallurgy nickel-based superalloy during drilling for the manufacturing engineers.

Abstract: Powder metallurgy (PM) nickel-based superalloy is regarded as one of the most important aerospace industry materials. A series of turning tests in a wide range of speeds with different inserts were carried out to select the proper tool material. Then, the effect of cutting parameters on the cutting force, cutting temperature and tool wear was investigated for the selected insert. The effect of cutting parameters on the tool wear was examined through SEM and TEM micrographs. The experiential functions of tool life, cutting force and cutting temperature were developed. Finally, the cutting parameters in PM nickel-based superalloy dry turning were optimized based on tool life-efficiency contour analysis. The present approach and results will be helpful for understanding the machinability of PM nickel-based superalloy during dry turning for the manufacturing engineers.

Abstract: Cemented carbide has relatively good mechanical properties, so it is widely used as cutting tools. In this paper, a sliding wear test at high ambient temperature between cemented carbide tool material and ceramic was carried out using a ball-on-disc wear-test machine. The characteristics as to wear rate and friction coefficient were investigated. The special wear rate increased with an increase in operating temperature. The cemented carbide material with addition of TiC phase gave better wear resistance than cemented tungsten carbides at elevated temperature. SEM technology was adopted to observe the worn surfaces of specimens and wear mechanism were simultaneously discussed.

Abstract: An experimental investigation was carried out to understand the behavior of a powder metallurgy nickel-based superalloy when machined with sialon ceramic insert tools. Turning experiments were carried out at different cutting speeds and feed rates while depth of cut was kept constant. Cutting tool performance was evaluated with respect to temperature and cutting forces generated during turning, and tool wear. The sialon ceramic cutting tool showed high performance when increasing cutting speed, the machining experiments showed that sialon ceramic tools performed better at cutting speed up to 80 m/min. Abrasion and adhesion was the dominant wear mechanisms. Chipping on the tool rake and flank faces, as well as catastrophic failure under thermal shock and mechanical loading, was also observed in experiments. As cutting temperature was very high when turning powder metallurgy nickel-based superalloy, good high-temperature strength and thermal shock resistance were indispensable to the cutting tools for machinging this kind of material.

Abstract: The thermal stresses generated in ZrTiN coating deposited on HSS and tungsten carbide substrates are investigated by finite element analysis and calculated by mathematics model. FEM analysis provides detailed information about all stress components. The influence of deposition temperature, substrate materials, coating thickness and interlayers on the generation is analyzed. The thermal stress of coatings has a linear relationship with deposition temperature, and an inverse relationship with the coating thickness. The results of simulated thermal stress are in accordance with the analytical method. The highest shear stress found at the interface between the coating and substrate indicates that the interface is the critical location which is learned from the failure point of view. Results also show that the insertion of TiZr interlayer between the coating and substrate can reduce the stress components especially the shear stress. The interlayer thickness has a great effect on stress reduction.