Papers by Author: Xing Ai

Abstract: In this study, orthogonal turning experiments are performed to analyze the machinability of Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17), a β-rich, α+β type alloy. PVD TiAlN coated carbide tool inserts are applied, because they are used widely for machining this material. The cutting forces and cutting temperatures are examined under different cutting conditions, which the cutting speeds are varied from 44m/min to 123m/min, the feed rates are 0.06mm/r, 0.08mm/r, 0.10mm/r and 0.12mm/r,respectively.There are some different varying trends of both the cutting force and the thrust force with the change of cutting speed. The cutting temperatures are found to increase with cutting speeds as well as feed rates.

Abstract: Ti6Al4V is a difficult to machine alloy with low cutting efficiency and server tool wear. A series of orthogonal turning tests with coated carbide in higher speed scale was carried out on a CA6140 lathe. The experiential functions of tool life based on orthogonal experiment were developed. The tool wear morphologies were examined by scanning electron microscope (SEM) and energy disperse spectroscopy (EDS), adhesion, diffusion and micro-chipping were the major wear mechanisms of coated carbide tool. Finally, the cutting parameters of coated carbide tool in Ti6Al4V dry turning were optimized based on tool life-efficiency contour analysis, in same cutting efficiency, the lower cutting speed and larger depth of cut are the better selection in Ti6Al4V turning for coated carbide tool.

Abstract: This paper deals with an experimental research on the wear mechanism of coated carbide tools in dry boring of the titanium alloys TC11 which are commonly used for aero-engines. The wear mechanism of coated tool inserts was investigated at various combinations of cutting speed, feed rate, and depth of cut. Analysis carried out with the SEM suggests that adhesive wear and coating delamination are the dominant wear mechanisms under low speed and feed rate and depth of cut; while chipping and breakage are the dominant wear mechanisms for the combinations of high cutting speed, feed rate, and depth of cut. There was no observation of oxygen existing based on the analysis of SEM which indicated no oxidation wear generated during the boring machining. The excellent chemical stability of TiAlN coating and oxidation resistance performance made contribution to prevent oxidation wear. Another reason was that boring temperature was lower than oxidation temperature.

Abstract: The grain growth in the sintering process of ceramic materials has an important impact on the ceramic materials performance. In this paper, a grain growth simulation model considering the requirement of heat and space is established. The Al2O3-based ceramic materials are preparation, and the model is verified by the Al2O3-based ceramic materials. The simulated results of the grain growth by the model are very close to the grain growth of Al2O3-based ceramic materials. The model can be used in the study of grain growth in ceramic materials sintering process.

Abstract: The efficiency of the high-speed milling process is often limited by the occurrence of chatter. In order to predict the occurrence of chatter, accurate models are necessary. With the speed increasing, gyroscopic effect plays an important pole on the system behavior, including dynamic characteristic and rotating behavior. Considering the influence of gyroscopic effect on rotating behavior, an updated model for the milling process is presented which features as model of the equivalent profile of tool. In combination with this model, a nonlinear instantaneous cutting force model is proposed. The use of this updated equivalent profile of tool results in significant differences in the static uncut thickness compared to the traditional model.

Abstract: Powder metallurgy (PM) nickel-based superalloy is regarded as one of the most important aerospace industry materials, which has been widely used for engine components. As the demands of the service performance increase, the surface characteristics are becoming more and more important. However, the machined surface of PM nickel-based superalloy is easily damaged due to its poor machinability. A series of milling experiments in a wide range of speeds were carried out to investigate the effects of dry milling parameters on the surface characteristics of PM nickel-based superalloy. The machined surface is evaluated in terms of surface roughness and work hardening. The results show that, milled surface characteristics of PM nickel-based superalloy are sensitivity to the cutting speeds. The machined surface roughness increases with increase of the cutting speed, but with further increase of cutting speed between 70 to 90 m/min and 150 to 170 m/min two decreases in surface roughness appear. For work hardening, it can be seen that the machined workpiece surface hardens seriously.

Abstract: A difficult-to-machining material, cast supper alloy K24 has been cut with two different methods, milling and abrasive waterjet (AWJ). It is shown that milling is characterized by high tool cost, low efficiency, and good surface roughness while abrasive waterjet brings high efficiency and worse surface quality. The results have proven that the combination use of AWJ and milling is an efficient way in cutting K24.

Abstract: This paper deals with an experimental research on wear properties and mechanisms of coated carbide tools in dry turning of 300M steel which are widely used to manufacture the central spindle, wheel gear, aerofoil fastener and so on. Based on Makarow’s theory, the minimum surface wear rate hs = 2.88 μm and the optimal cutting speed v = 200 m/mim were attained under the condition of the feed rate f = 0.1 mm/r and the depth of cut ap = 0.15 mm. Analysis carried out with the SEM suggests that adhesion of workpiece material and chipping are dominant wear mechanisms. There was no observation of oxygen existing based on the analysis of EDS which indicated no oxidation wear generated during the turning machining.

Abstract: The strong demand for increasing productivity and workpiece quality in milling process makes the machine-tool system operate close to the limit of its dynamic stability. Milling cutters with variable pitch angles can be very effective in improving stability against chatter for certain speed ranges, which will be predicted by the model presented here. The present paper deals with the design of structural geometry of variable pitch end mills in detail. Based on the analysis of tooth engagement factor, which is expressed and extended in the paper, an approach is proposed to design variable pitch end mill with high milling stability. The certain speed ranges with high milling stability are given.

Abstract: Vibration frequencies during high-speed milling processes are investigated. Based on the resonant theory and three critical stats of phase position of successive two cutter teeth, six kinds of spindle speeds are shown, which divide the stable region in stability limit diagram into four parts. Furthermore, using optimal control theory, a novel stable region is proposed, which divides the region into three parts (unconditional stable, optimal stable, and conditional stable region).