Papers by Author: Li Qiang Xu

Abstract: Based on finite element software DEFORM-3D, a three-dimensional oblique cutting model for aerospace aluminum alloy was built. The material’s flow stress behavior was described with Johnson-Cook constitutive equation. The separation of the chips with the workpiece was realized by the combination of adaptive remeshing technique and separation criterion. The material’s failure was defined by adopting Cockcroft & Latham fracture criterion. The tool-chip friction model was the combination of a Coulomb friction model and shear (sticking) friction model. To validate the finite element model, cutting tests were conducted. The effects of tool geometrical parameters such as flank wear, cutting edge inclination and corner radius on cutting forces were analyzed by three-dimensional oblique finite element model.

Abstract: The wear and breakage features of TP1000 multi-coated tool were investigated through a series of cutting experiments. These experiments were performed for turning hardened 45 and T10A steel by orthogonal experimental method. SEM and XRD analysis were conducted on cutting tools. The results show that both wear and breakage occur when turning hardened 45 steel. The major wear mechanism is abrasion and oxidation, and the major breakage mechanism is surface spall. When turning hardened T10A steel, the main disability is breakage, and the major breakage mechanism include surface crack, spall and tipping.

Abstract: In order to theoretically simulate the welding process of complex structure with large quantities of welding spots, a simplified method for analyzing a single spot welding should be developed firstly. In this paper, a 2D axisymmetric model of thermoelectric Finite Element Method (FEM) is developed to analyze the transient thermal behavior of Resistance Spot Welding (RSW) process using ANSYS. The determination of the contact resistance at the faying surface is moderately simplified to reduce the calculating time, while the temperature dependent material properties, phase change and convectional boundary conditions are taken into account for the improvement of the calculated accuracy. The thermal history of the whole process and temperature distributions for any position in the weldment is obtained through the analysis. The model can also predict the weld nugget size and the width of the Heat Affected Zone (HAZ).

Abstract: When machining aerospace monolithic components, a severe deformation can be observed due to the release and redistribution of the original residual stresses, together with the action of cutting loads and clamping force. In this paper, a finite element model predicting machining deformation was developed considering the above mentioned multi-factors coupling effects. Based on the model, the effect of process routing on machining deformation for multi-frame double sided monolithic components was studied. To validate the FE model, true frame components were machined and deformations were measured on a Coordinate Measuring Machine. The result revealed that the prediction model is credible. At last the paper puts forwards optimal process routing based on minimizing the machining deformation.

Abstract: The friction coefficient on rake face was calculated through the cutting forces tested in a series of cutting experiments. These experiments were performed for turning two kinds of hardened steel with four types of coating tool by orthogonal experimental method. The curves of the friction coefficient changing with the cutting process and its dependence on the cutting parameters were analyzed in detail. The results show that the friction coefficient on rake face decreases rapidly during the cutting progress and comes to a steady value, which could be an indication of the self-organization when turning hardened steel with coating tool.

Abstract: Advanced Ti(C, N) matrix cermet tool materials with higher mechanical properties are successfully developed by dispersing nano-scale Al2O3 powder into the micro-scale Ti(C, N) matrix and Ni-Mo bonding phases powder. The effect of the content of nano-scale alumina on the microstructure and mechanical properties of micro-scale Ti(C, N) matrix cermet tool materials are investigated. The research results show that a type of Ti(C, N) matrix cermet tool material has the most optimal flexural strength of 900MPa, Vickers hardness of 17.4GPa and fracture toughness of 9.95MPa.m1/2 when the content of nano-scale alumina is 12% in term of mass. It is found from the microstructure analysis that the main reason of the mechanical properties improvement is the grain fining effect caused by nano-scale Al2O3.

Abstract: The effect of sintering temperature on mechanical properties and microstructure of rare earth oxides toughened Ti(C,N) ceramic cutting tool materials was investigated. The results showed that the mechanical properties of Ti(C,N) based ceramics were greatly influenced by sintering temperature. As a result, both of the density and mechanical properties of the materials sintered at 1350
and 1400
are worse than those sintered at 1450
and 1500
. Low sintering temperature results in low density and degraded mechanical properties, but too high sintering temperature results in the precipitation of bond metal and thus reduces its fracture toughness. Intergranular fracture mode of the material is mainly observed.

Abstract: The employment of ceramic material simulation design methods can eliminate the disadvantage of traditional ceramic material developing methods of being time-consuming, laborious and high cost. Three simulation methods of artificial neural network, regression analysis and pattern recognition, and their application to ceramic material simulation design were presented in this paper. The problems existing in ceramic material simulation were proposed finally.

Abstract: Ti(C, N) based ceramic tool materials in the Ti (C0.7N0.3)-(Ni-Co)-Cr3C2-VC system have been made by hot-pressing technology, their mechanical properties and fracture morphologies have been studied under three different fabrication conditions. The results show that the mechanical properties are significantly influenced by fabrication conditions, and the main fracture mode is intergranular fracture.