Papers by Author: Zhan Qiang Liu

Abstract: This paper presents investigations on turning TC4 alloy with PVD TiAlN coated cemented carbide inserts. The turning test was conducted with variable cutting speeds ranging from 80 to 120 m/min. Wear surfaces of the cutting tools are analyzed to study the wear mechanism of PVD TiAlN coated cemented carbide tools in turning of titanium alloy TC4. Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer( EDS) analyses by wear maps indicated that the wear of coated cemented carbide tools was caused by adhesion, coating delamination and mechanical fatigue. The analysis of EDS indicated no oxidation wear generated during the machining. The excellent chemical stability and oxidation resistance performance of TiAlN coating made contribution to prevent oxidation wear.

Abstract: Spherical chip appears frequently in high speed grinding of metals. It is attributed to the melt or oxidation of the small chips in grinding. Spherical chip in machining of steels is observed when the cutting speed is high enough. To clarify the formation mechanism of spherical chip in metal cutting, high speed machining of AerMet100 at cutting speeds from 40 m/min to 3000m/min was investigated. Spherical chip of AerMet100 was obtained at cutting speed range 2000-3000m/min. Optical and SEM (Scanning Electron Microscope) observations of the spherical chip was carried out. The chemical composition of the spherical ship was analyzed through X-ray energy dispersive spectroscopy (XEDS) analysis. The formation mechanism of the spherical chip was proposed. The results showed that the spherical shape of chip is due to the intense reaction between Fe of workpiece and O2 in the air accompanying which large mount of heat is released to melt the oxide into small spheres. The formation of the spherical chip is highly influenced by cutting speed and the size of the chip (surface-volume ratio).

Abstract: Numerical controlled milling is widely used in the manufacturing industry because of its high productivity and workpiece surface quality. The aim of this work is to establish a methodology to evaluate the rough machining time and to predict optimal values of cutting speed to minimise machining time of circular cavity, during high speed milling. The circular cavity is divided into volumes distributed according to the real radial depth. The obtained results show that the proposed method is consistent with the actual situation.

Abstract: Ti6Al4V is one kind of difficult-to-machine aeronautical materials, which is generally machined by coated cemented carbide tools. A three-dimensional face milling model is developed in this paper with finite element analysis software AdvantEdge to analyze influences of tool materials on tool temperatures, cutting forces and tool stresses. The simulation results have shown that PCBN tools are the most appropriate for machining titanium alloy when it is machined with heavier cutting parameters. Cemented carbide-K tools and PCD tools are suitable for finish machining titanium alloy. The PCD tools are superior to cemented carbides-K under the same machining conditions. Nature diamond cutting tools are incompatibility to machine titanium alloy due to their higher costs and carbonization at high temperature. In the view of cutting forces and distributions of tool stresses, nature diamond tools are optimal and the cemented carbides-K are the poorest in machinability rate at the same cutting conditions, while super-hard tools gets longer tool life.

Abstract: Turbine blade plays an important role in aero engine and power generation equipment. As thin-walled and free-form surface component, deflection in spiral milling of turbine blade is common, which result in bad dimensional precision. In this paper, a five-axis milling experiment was firstly conducted to get the cutting force components. Then, deflections were studied at different positions. The results show that compensation can be made based on the FEM analysis.

Abstract: Magnesium (Mg) components can significantly reduce energy use due to their low densities compared to the majority alloys. Mg alloys are often machined to fit individual cases. However, process mechanics by high-speed dry cutting of Mg alloys are poorly understood. This study focuses on machining ability of biomedical magnesium-calcium (Mg-Ca) alloys. First, it presents a modeling approach of mechanical behavior of Mg-Ca0.8 (wt %) alloy under cutting regimes using the internal state variable (ISV) plasticity model. Then, the ISV plasticity model is implemented to simulate high speed dry cutting of Mg-Ca0.8 alloy by finite element method. Last, machining performance in the context of sustainability is discussed. Excellent surface finish can be achieved in the range of high cutting speeds. Continuous chip formation predicted by the finite element simulation is verified by high speed dry cutting of Mg-Ca0.8 using polycrystalline diamond (PCD) inserts. Chip ignition as the most hazardous aspect in machining Mg alloys does not occur for in high-speed dry cutting with sharp PCD tools. The predicted temperature distribution well explains the reason for the absence of chip ignition in high speed dry cutting of Mg-Ca0.8 alloy. A mechanism of built-up layer (BUL) formation is proposed.

Abstract: In high speed machining, temperature distribution in workpiece is the main factor which directly affects the surface integrity and dimensional accuracy of machined workpiece. In this paper, the machined workpiece temperature in high speed peripheral milling is analyzed through using moving heat source method and inverse method. Firstly, the workpiece to be machined is considered as a semi-infinite solid to model the transient surface temperature using arc-shaped moving heat source. Inverse method is then applied for the calculating of heat flux. Peripheral milling experiments of 1045 steel is performed with coated carbide insert The machined surface temperatures were measured during experiments. The measured results were found to be in agreement with the predicted ones by transient models for machined surface temperatures. These results confirm the conclusion that the transient workpiece temperature will decline when the cutting speed increases to a critical value.

Abstract: The downscaling of the cutting process into micro dimensions poses some new problems compared to machining in macro dimensions, which is called size effect. In this paper, a mathematical model of ideal turning surface roughness and a turning surface roughness experiment was done, trying to find out whether the theory roughness equals to the real roughness by the influence of size effect.

Abstract: Residual stresses generated in milling process affect the performance of machined components. Milling residual stresses correlate closely with the cutting parameters. In this paper, the generation and distribution of surface residual stresses in milling of aluminum alloy 7050-T7451 was investigated. The cutting speed changes from 300m/min to 3000m/min. In the experiments, the residual stresses on the surface of specimen are detected by X-ray diffraction technique. The result shows that compressive residual stresses are generated when cutting speed is under 500 m/min. In feed and its orthogonal direction, the effect of cutting speed and feed rate on residual stresses is similar. The formation of the residual stresses can be explained by thermo-mechanical coupling effects.

Abstract: Tool selection is one of the most significant process considerations when deciding how a machined product will be manufactured. The tool selection activity is rooted in feature geometry but it also has a direct impact on machinability and machine tool performance. This paper presents a computer-based intelligent system for the automatic selection of cutting processes and tools. The main objective of the research work was to develop a procedure for the selection of cutting tools and cutting parameters. This will help the designers and manufacturing planners to select an optimal set of cutting tools and cutting conditions for different material properties and to give users alternatives on how to reduce cost and time.