Key Engineering Materials Vols. 589-590

Abstract: The aim of this paper is to compare the predicting ability of the orthogonal cutting models developed by three commonly used finite element softwares, namely commercial explicit dynamic code Abaqus/explicit, Thirdwave AdvantEdge and implicit finite element codes Deform 2D. In all proposed models, the chip formation was simulated through adaptive remeshing and plastic flow of work material around the round edge of the cutting tool. Therefore, there was no need for a chip separation criterion which made the physical process simulation more realistically. Predicted cutting, feed force and shear angle were compared with experimental results. In addition, the effect of friction coefficient on the chip morphology was investigated as well.

Abstract: Work-hardening of machined surface plays an important role in the evaluation of surface quality and performance of wear resistance in the process of machining components. In this study work-hardening of machined surface during milling 7050-T7451 aluminum alloy is investigated using micro-hardness experiments under different cutting conditions. Moreover, the wear resistance of machined surface including wear quantity and friction coefficient are obtained and studied by means of high speed ring-block friction-wear tester. The work-hardening and wear resistance are particularly sensitive to cutting speed. Friction coefficient has marked drop trends and the tendency of wear quantity is ascend in first and descend at last as work-hardening increases. The comparison of wear resistance under different cutting conditions shows that the wear resistance of machined surface can be directly affected by work-hardening and machined surface obtained by high speed milling with higher micro-hardness have more superior in wear resistance performance.

Abstract: A 3D finite element model (FEM) of metal cutting was constructed based on the thermal-mechanical coupling theory. The cutting process of Sialon ceramic tools turning Inconel 718 was simulated and experimented. The effect of cutting speed, feed rate and depth of cut on the cutting force was analyzed. According to the correlation characteristics between the data points, the fractal characteristics of cutting forces in the cutting process were also investigated. The results showed that the cutting speed had a great effect on the fractal dimension of cutting force. The simulation results were in good agreement with the experimental findings. It was concluded that the minimum fractal dimension of cutting force was obtained at v=230 m/min under these experiment conditions. The fractal analysis is a simple and powerful tool for quantifying the stability of cutting process. The finding of this research is valuable for future practical implementation.

Abstract: Cutting temperature always highly reaches over to 1000°C when high speed machining with PCBN tools. Diffusion of tool material element may have important influence on tool wear at such high temperature; the diffusion wear and oxidation wear have become the major wear mechanism. In this paper, the rules of diffusion wear and oxidation wear for PCBN cutting tools are proposed and analyzed based on thermodynamics theory. Dissolution concentrations in typical normal workpiece materials of PCBN tool material at different temperature are then calculated. Diffusion reaction rules in high temperature are developed and analyzed using Gibbs free energy criterion. The machining tests were conducted using the PCBN tools at different cutting speeds of 50, 95,100 and 180 m/min, feed of 0.1, 0.2 and depth of cut of 0.1, 0.8, 1, and 1.5 mm respectively on PUMA300LM numerically-controlled lathe. It was found that the theoretical results were uniform with the experimental data; the results will provide useful references for tool material design and selection.

Abstract: A method for building the constitutive relationship based on the J-C model and hardness is presented through considering the influence of hardness on the yield strength and the tensile strength. A constitutive relationship of hardened AISI 1045 is built by this method and the adiabatic shear critical cutting conditions of three kinds of hardness AISI 1045 steel are prediction through a model building by the linear pertubation analysis which considering the influence of compression stress of the primary shear zone, the cutting conditions and the constitutive relationship. For proving the prediction results, some orthogonal cutting experiments are performed to get the critical cutting conditions of adiabatic shear. The comparison shows that the prediction results are consistent with that of experiments.

Abstract: Studying the dynamic properties of a material are an important method to understand the dynamic processes and deformation mechanism of material at different working conditions, particularly at high strain rate. The constitutive equation of a material has the highest significance to represent the mechanical properties, and is the principal research basis for the numerical simulation. In this paper, an important titanium alloy TC11 was studied through the quasi-static tensile test and the split Hopkinson pressure bar (SHPB) tests. Dynamic compressive behavior of TC11 alloy was discussed. Moreover, this paper gave the constitutive model of TC11 alloy and established the Johnson-Cook (J-C) constitutive equation.

Abstract: This article takes common material Cr12MoV for automobile panel die as research object, aiming at difficulties when tool cutting in workpiece which are caused by high material hardness in maching, based on simulation software DEFORM-3D, a high precision simulation model of cut-in process in hard milling die steel is established, and the accuracy of the model is verified by tests, the milling force cut-in process in hard milling die steel is studied, the influence law of different cutting parameters and cut-in angles on milling force in milling cutter cutting in workpiece is analyzed, and the optimized cut-in angles are obtained, this study provides a reference for further optimization of cut-in conditions, reducing tool early damage and improving processing efficiency.

Abstract: The metal machining 3D finite element model was established on the basis of the thermal-elastic-plastic finite element theory. And the machined surface residual stress simulation in different cutting parameters was obtained through the finite element analysis. It is concluded that the residual stress distribution variation is spoon-shaped curve. When the feed increased, the slope of the curves is smaller, however the speed increased, the slope of the curves is higher and the stress tends to negative values quicker. Finally, the experiments are carried out. The result was basically consistent with the simulation.

Abstract: The changes of drilling forces during bone drilling provide a useful index for evaluating the risk of potential damage to the bone. The aim of the work is that an elastic-plastic dynamic finite element model is used to simulate the process of a drill bit drilling through the bone. The finite element model was set up in the Abaqus6.11; the prediction model of the drilling force was gotten by using the regression orthogonal experiment and data processing software Matlab7.0. Diverse values of drilling speed, feed rate and drill diameter are important factors which will lead to changes in the drilling forces. By controlling the drilling parameters can obtain the optimal drilling force. The results show that the diameter has the greatest influence on the drilling force, the drilling speed the second, the feed rate the last.

Abstract: Both aluminum alloy and titanium alloy have been widely used in aerospace, aviation, military and automotive industries. This research presents a study of modified drills for drilling aluminum alloy and titanium alloy. The modified drills can be expected to reduce the cutting forces and torque. A set of experiment was carried on to investigate the performance of the modified drills. A method to quantitative assess of the reduction of the thrust force and torque was given below, and the calculation shows that the modified drills can reduce the thrust force and the torque by as high as 21.16% and 90.48%, respectively, as compared to the conventional drills under the same conditions.