Papers by Author: Zhi Jun Wu

Abstract: In this study the influence of tool inclination angle on deformation of thin wall cantilever shape part has been analyzed using finite element numerical simulations. Polycrystalline diamond, PCD tool has been chosen as a tool material in this study because PCD tool has given better results in terms of surface roughness, tool life and productivity in end milling of titanium alloy Ti-6Al-4V. Firstly, in this study, the effect of tool inclination angle on tool contact geometry, cutting speed and cutting forces has been discussed. Then, finite element numerical simulations (FEM) have been carried out in AdvantEdge® for the prediction of cutting forces with PCD tool at four different tilt angles viz. 70°, 75°, 80° and 85° and the results have been compared to the coated carbide tool. Then the maximum magnitude of the forces which occurred in tangential direction (F_Y) were input in the Abaqus® software as a load acting on the thin long cantilever part and deformation results were analyzed. Results show that PCD tool due to its high hardness, strength and better wear resistance produce lower cutting forces at all angles studied and at an angle near the perpendicular to the surface being machined both tools have lower values of the deformation. The FEM simulation results match well with the theoretical study as theoretical analysis also shows that at angles nearer to perpendicular to the surface being machined, the tool will have lower effective cutting speed & forces and hence proved as the key to achieving better accuracies for long thin wall parts.

Abstract: Finite element simulation is an effective method to study the thermal characteristics of high-speed motorized spindle, how to improve the simulation accuracy has become the key point of this research field. This paper presents a FEA method using ANSYS to precisely predict the thermal characteristics of high-speed spindle. Firstly, the heating and cooling characteristics of high-speed spindle are analyzed, main heating source, convective heat transfer coefficient, and thermal contact resistance are calculated. Secondly, FEA model of the machine center is built, the temperature field and thermal deformation of the spindle system are simulated. Thirdly, an experimental system to test thermal characteristics is designed, simulation results are compared with the experimental results. The result shows that the simulation errors are controlled in a relative low range, the FE modelling method can precisely predict the thermal characteristics of the motorized spindle.

Abstract: To improve the vibration isolation performanceof an air spring system,the characteristics of the dynamic stiffness and damping of adual chamber air springwere first analyzed. A theoretical model ofa four dual chamber air springs system wasthen constructed,and through experimental verification,the theoretical and experimental curves showedthe same change trend.Based on the theoretical models, anobjective function used to optimize the structural parameters of an air springwas constructed. It was demonstrated that the vibration isolation performance of the air spring system was improved with the optimized parameters.

Abstract: Aiming at the problem of the influence of joints on machine structure static performance, this paper presents a method of modeling and experiment on static characteristic of BT tool holder-spindle interface. A FEA model of tool holder-spindle interface is established by setting several equivalent springs, whose parameters are identified through experiment. The effectiveness of the proposed method is tested and verified by building finite element model and applying the spring parameters to it. The comparison between the emulational result and experimental result shows that the simulation accuracy has improved tremendously, which the relative error reduces to less than 10% under different axial forces.

Abstract: This paper analyzed the dynamic performances of vertical machining center and investigated the problems of dynamiccharacteristics. The modal analysis in both experiment and simulation wascarried out to obtain the modal parameters. The vibrations of the machine spindle were tested to obtain the vibration spectrum under different spindle speeds. It synthesized and compared with the vibration and modal characteristic in order to investigatethe weak parts of the structure. It is concluded that modal characteristic has something to do with the vibration, and there is eccentric between the active rotor and driven rotor. This comprehensive comparison method for dynamic analysis is very effective.

Abstract: Stiffness analysis plays an important role in the optimization of the machine tool. By analyzing the static stiffness, dynamic stiffness and natural frequency of the key components, we discussed how to improve static and dynamic performance of the whole machine. Through the finite element analysis method, weak parts of the vertical machining center are firstly identified based on static stiffness analysis. Due to the purposes of increasing the stroke in Y-direction, improving the whole machine stiffness and without increasing the whole machine weight, optimal designs are carried out mainly on the structures of the spindle box and the column. And the performance of the parts and the whole machine before and after optimization is compared by testing whether the stiffness is improved or not. We also conducted experiments, and the results are consistent with the results of finite element analysis.

Abstract: The plastic-coated slideways have been widely used for form-generating movement in machine tools. Its dynamic behavior plays an important role in the vibration properties of the whole machine. In this work, according to the situation that researches on this subject were rather insufficient, a theoretical research was analyzed concerning the stiffness and damping characteristics of rectangle-shaped plastic-coated slideways. The mathematical model was firstly suggested especially based on the assembly of the saddle and worktable. Both stiffness and damping characteristics on vertical and horizontal directions were theoretically determined. To derive the governing motion equation of the slideway system, the carriage and rail were considered as rigid bodies and connected with a series of spring and damping elements at the joint face. Moreover, through the Lagrange’s approach, the frequencies of the carriage at vertical, pitching, yawing and rolling vibration mode were identified.

Abstract: With increasing spindle speed the cutting will be easy to enter into micro-feed cutting region. In the paper, the chip thickness and shape of high-speed and micro-feed cutting was researched in orthogonal milling. The cutting times in different fz was analyzed. We calculate the effective rake angle, friction angle and shear angle Furthermore, we measure cutting edge arc wear and tool flank wear of micro-feed cutting. Shown as the research results, the phenomenon of empty cutting and pure extrusion is very obvious as the feed rate per tooth is lower than 0.011mm/z. As the feed rate per tooth is lower than 0.005mm/z, the tool wear form is mainly cutting edge arc wear. As fz achieves 0.015mm/z, tool wear will decrease obviously and the tool appears the self-sharpening phenomenon.

Abstract: Tool geometric parameters, which are key factors to be considered in tool design, have a direct effect on tool cutting performance. Based on the diversity and complexity of geometric parameters and technological goals, we select cutting force and temperature as initial input conditions to build a comprehensive dimensionless tool geometric parameters evaluation method. According to the multilevel weight relationships between the technological goals and the basic cutting characteristics, the evaluation factors for cutting force and temperature are determined. The comprehensive evaluation method (CEM) is then applied to analyze and optimize the key parameters of a saw milling tool. As shown by the research results, the parameters obtained by the CEM prove that some tool parameters from actual production were reasonable, while others had re-optimized space. The CEM is shown to be effective and feasible. Also, the analysis results have an explicit guiding function for production practice.

Abstract: Warpage deformation is an inevitable phenomenon as a cantilever sheet part is machined by combined saw milling tool. This problem affects machining quality obviously. In order to find the formation mechanism and a suitable solution, the paper carried out a qualitative analysis of the warpage causations, clarified the relationships of many factors and carried out quantitative analysis through the combined method of AdvantEdge FEM and Ansys. Furthermore, experiments of residual stress release and warpage solution were carried out in order to verify the correctness of theory analysis results. As is shown by the research results, warpage has already formed during residual stress formation. The causation of warpage is the unreasonable cutting path and the residual stress imbalance of the up and down sheet plane. The solution can control the warpage deformation well. The research results have an explicit guiding function to the actual production.