Papers by Author: Xing Ai

Abstract: A method for predicting the stability of thin-walled workpiece milling process is described. The proposed approach takes into account the dynamic characteristics of workpiece changing with tool positions. A dedicated thin-walled workpiece representative of a typical industrial application is designed and modeled by finite element method (FEM). The workpiece frequency response function (FRF) depending on tool positions is obtained. A specific 3D stability chart (SC) for different spindle speeds and different tool positions is then elaborated by scanning the dynamic properties of workpiece along the machined direction throughout the machining process. The dynamic optimization of cutting parameters for increasing the chatter free material removal rate and surface finish is presented through considering the chatter vibration and forced vibration. The investigations are compared and verified by high speed milling experiments with flexible workpiece.

Abstract: Ti6Al4V is a difficult to machine alloy with low cutting efficiency and server tool wear. A series of orthogonal turning tests with CBN (Cubic Boron Nitride) 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 CBN tool. Finally, the cutting parameters of CBN tool in Ti6Al4V dry turning were optimized based on tool life-efficiency contour analysis, in same cutting efficiency, the higher cutting speed and small depth of cut are the better selection, it means that utilization of CBN tool enables the high cutting speed turning of Ti6Al4V.

Abstract: A new dynamics model for multi-degree of freedom high-speed milling system is proposed, which takes account of regenerative effects and the effects of the relative vibration of spindle axis in milling process. Based on the mode synthesis theory and the zeroth-order approximation of the Fourier series, an integrated stability analytical method for multiple frequencies is presented, which involves multiple orders modal characteristics and higher order excitations in high-speed milling process. The chatter stability lobes are predicted in the frequency domain using the proposed stability analytical method, and verified by milling experiments. It is shown that stability regions involving multiple natural modes are reduced contrary to the case of single natural mode.

Abstract: Surface roughness in a turning operation is affected by a great number of factors. Two of the most important factors are feed rate and the size of the corner radius. Surface roughness can be roughly determined to increase with the square of the feed rate and decrease with increased size of the corner radius. However, wiper insert geometries changed this relationship with the capability to generate good surface roughness at relatively higher feeds by transferring small part of the round insert edges into the straight cutting edges of the pointed insert. The principle of how wiper inserts behave different from conventional inserts as to the effects on the surface roughness is explored in this paper. Experimental study of the surface roughness produced in the turning of hardened mild steels using coated carbide tools with both conventional and wiper inserts is conducted. The test results prove the effectiveness of the wiper inserts in providing excellent surface roughness. The results also suggest that the use of the wiper insert is an effective way that significantly increases cutting efficiency without changing the machined surface roughness in high feed turning operations.

Abstract: The present work puts forward a generalized simulation model to evaluate the topography of ball-end milled surfaces by considering both the tool deflection and the tool runout. Firstly, a solid ball-end mill with S-shaped cutting edges is modeled as the basis. Then the tool tip trajectory is derived from the tool runout as well as the cutting forces induced tool deflection. And consequently the topography and scallop height of the machined surface are estimated by the numerical calculations of the matrix equations. With good expandibility, the proposed model can incorporate more machining information such as the movements of rotatory axes and tool wear, and hence, can be used to optimize the cutting conditions and parameters in 5-axis ball-end milling process.

Abstract: This paper introduced the machinability and the state-of-art of Ti6Al4V machining. Turning test with thee different tungsten carbide tool have be done at cutting speed 40, 80, 120, 160 m/min, the relationship between cutting force and cutting speed, cutting distance was analyzed, the influence of working cutting edge angle on the tool wear and cutting force was investigated as well. Finally, the tool wear and wear mechanics was analyzed.

Abstract: In this paper, the transient heat conduction and transient thermal stresses in an infinite plate with double-sided functionally graded coatings (FGM coatings) under the convective boundary condition are investigated. The thermo-physical properties of the two symmetrical FGM coatings are assumed to have distributions of power forms along the thickness direction of the plate, the effects of which on the thermal shock resistance of the FGM coated plate are analyzed via numerical calculations. And consequently some design rules for the double-sided FGM coatings are put forward, which provide a guidance for the development of FGM coated cutting tools.

Abstract: The Al2O3/(W, Ti)C nanocomposite was fabricated by hot pressing technique at 1650-1700°C under 30MPa for 10min. The fracture toughness remarkably increased by adding nano-scale Al2O3 (11vol %) particles into Al2O3 matrix. The flexural strength, fracture toughness and Vickers hardness are 840 MPa, 6.55 MPa•m1/ 2 and 20.1 GPa, respectively. The microstructure of the nanocomposite is homogenous skeleton structure. Nano particles could refine matrix grains and lead to the crack deflection as well as branching and bridging. The coexistence of nano-scale Al2O3, micro-scale Al2O3 and (W, Ti)C can reduce the sintering temperature and sintering time as well as the grain size, and improve the densification and mechanical properties of materials.

Abstract: When machining aerospace monolithic components, most of materials could be removed, resulting in severe deformation of the parts due to the release and redistribution of the blank’s original residual stress, together with the action of cutting loads and clamping force. A finite element model (FEM) is built for predicting the deformation caused by those factors mentioned above. In this model, some key techniques such as material properties, initial residual stress model, and application of dynamic cutting loads and transformation of boundary condition are discussed in details. The proposed model predicts the machining deformation for multi-frame monolithic components. Particular attention is paid to the influence of the bulkhead processing sequence on part deformation. At last the paper puts forwards optimal bulkhead processing sequence based on minimizing the machining deformation.

Abstract: In this paper, multi-linear regression and artificial neural network (ANN) models have been developed to predict surface roughness in high-speed milling of 7050-T7451 aluminum alloy. Surface roughness is taken as the response variable, while cutting speed, feed per tooth, radial depth of cut and slenderness ratio are taken as independent input parameters. An orthogonal experiment design is developed to conduct experiments. The measured values of surface roughness are used to find the regression coefficients and train the neural network for prediction of surface roughness. Predicted values of surface roughness by both models are compared with the measured values.