Papers by Author: Xing Ai

Abstract: An Al2O3-based composite ceramic cutting tool material reinforced with (W, Ti)C micro-particles and Al2O3 micro-nano-particles was fabricated by using hot-pressing technique, the composite was denoted as AWT. The cutting performance, failure modes and mechanisms of the AWT micro-nano-composite ceramic tool were investigated via continuous turning of hardened AISI 1045 steel in comparison with those of an Al2O3/(W, Ti)C micro-composite ceramic tool SG-4 and a cemented carbide tool YS8. Worn and fractured surfaces of the cutting tools were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results of continuous turning revealed that tool lifetime of the AWT ceramic tool was higher than that of the SG-4 and YS8 tools at all the tested cutting speeds. The longer tool life of the AWT composite ceramic tool was attributed to its synergistic strengthening/toughening mechanisms induced by the (W, Ti)C micro-particles and Al2O3 nano-particles.

Abstract: Two kinds of Cemented carbide tools were used to turn Iron-based superalloy GH2132 at 80m/min-210 m/min under dry cutting condition. Infrared thermometer was used to measure cutting temperature, Tool wear was observed by SEM, and oxygen element distribution of tool surface was analyzed by EDS. Adhesive wear oxidation wear were the main wear mechanisms of the coated cemented carbide tool, Adhesive wear, abrasive were the main wear mechanisms of the carbide tool. Oxidation wear occurs above a certain temperature about 430°C, the higher the temperature the more serious the oxidation wear is. The results might be helpful to guiding the design and selection of tool materials and control of tool wear in high speed machining processes.

Abstract: During the high-speed milling operations of 7050-T7451 aluminum alloy using solid carbide end mills, helical angle, axial and radial depth-of-cut have significant effects on the milling uniformity. A surface roughness predictive model of work-piece was developed by using a full-factorial experimental design and multi-linear regression technology. Genetic algorithm was utilized to optimize the helical angle and cutting parameters by means of a series of operations of selection, crossover and mutation based on genetics. The result shows that it is possible to select optimum axial depth-of-cut, radial depth-of-cut and helical angle for obtaining minimum cutting force and reasonably good metal removal rate.

Abstract: Five-axis milling is widely used in machining of complex surfaces parts. Part quality and productivity are extremely affected by cutting force and tool wear, especially thin-walled complex surface, such as turbine blade. Although extensive research has been conducted on cutting force and tool wear in 3-milling process, very few are on 5-axis milling and bull-nose mills. This paper presents cutting forces with various cutting conditions as well as tool wear patterns in five-axis milling super alloy, which is essential to cutting vibration and defelction analysis of thin-walled complex surfaces parts. The roles of lead angle and tilt angle in five axis milling were investigated, which provide data for NC program edit. In addition, experiments in this research proved that tool wear played affected cutting forces outstandingly.Therefore, tool wear played an very important role in tool change.

Abstract: Ti6Al4V is a difficult to machine alloy with low cutting efficiency and server tool wear. A series of orthogonal milling tests with coated and uncoated carbide insert was carried out. The tool life predictive models based on orthogonal experiment were developed. Finally, the cutting parameters for both tools in Ti6Al4V dry milling were optimized based on tool life-efficiency contour analysis.

Abstract: In the present paper, a dynamic modeling approach is presented to determine the contact stiffness and structural damping between the spindle and the toolholder; and then, the spindle and the toolholder are coupled by some springs and dampers. Finally, the dynamic performances of the HSK-A63 spindle/toolholder interface are analyzed by means of finite element method (FEM). From the simulated results, it can be seen that the natural frequencies of the first two modes increase with the increase of the rotational speed, which make the HSK spindle/toolholder interface appear good dynamic performances and be suitable for high-speed machining.

Abstract: Semi-discretization method is applied to construct stability chart and performance contour in the parametric space for milling processes. The method creates a mapping of the system responses in a finite dimensional state space. Based on the discipline of that, the smaller the largest absolute value (μmax) of the characteristic multipliers of the mapping is, the faster the system converges to zero, minimization of μmax leads to optimal stable limit. The optimal limits are obtained by using stability chart and performance contours. Additional, a novel analytical method for selection of optimal depth of cut (axial depth of cut) is presented. An example of 2-DOF down-milling model is employed to demonstrate the method. It is shown that the spindle speeds corresponding to the optimal depths of cut locate the left side of the resonant spindle speeds, and the optimal cutting parameters pair (spindle speed and depth of cut) can be used to offer high finishing accuracy in precision machining.

Abstract: The granite cutting processing using diamond circular saw blades is the most extensive application processing methods. The cutting force is measured at different cutting depth ap, sawing feed rate vf and linear velocity v when the granite is cut by diamond circular saw blade by orthogonal experimental method. And the sawing force empirical formulas relative to these three variables are educed. We can obtain the experimental results as follows. The radial force Fn is greater than the tangent force Ft when ap is smaller than the circular saw blade diameter. The corresponding Fn and Ft are all smaller as the feed rate is greater at the same circular saw blade diameter. The cutting forces increase obviously as the cutting depth increases at the same circular saw blade diameter and feed rate.

Abstract: A new WC matrix nanocomposite cermet was prepared by hot-press sintering. In the composite, certain amounts of VC is added to the composite as grain growth inhibitors. The consolidation is carried out under pressure 30～35Mpa and sintering temperature 1610°C for soaking 30min sintering. Microstructure of the nanocomposite cermet is scanned by SEM and mechanical properties are measured. It is detected that microstructure and fracture morphology is dissimilar to different particle sizes. Experimental results show that particle size of WC is important to the composite. Results show that relative density and hardness have the similar trend in growth. Meanwhile, the function of Al2O3 addition is also investigated in this paper.

Abstract: A new approach is presented to optimize the tool life of solid carbide end mill in high-speed milling of 7050-T7451 aeronautical aluminum alloy. In view of this, the multi-linear regression model for tool life has been developed in terms of cutting speed and feed per tooth by means of central composite design of experiment and least-square techniques. Variance analyses were applied to check the adequacy of the predictive model and the significances of the independent parameters. Response contours of tool life and metal removal rates were generated by using response surface methodology (RSM). The analysis results show that it is possible to select an optimum combination of cutting speed and feed per tooth that improves metal removal rate without any sacrifice in tool life.