Ya Zhou Sun

The Prediction Model of Cutting Forces Based on Johnson-Cook’s Flow Stress Model

Thin-walled parts with complex configurations are extensively used in aerospace and precise instrument industry. However, because of low stiffness, cutting forces, clamping forces and residual stresses in cutting have been the main factors influenced on machining accuracy of thin-walled parts. Furthermore, biggish deviation exists between practical finished surface and theoretical value as a result of machining deformation caused by cutting force namely “cutter relieving” phenomenon; besides, direct relation exists between determination of clamping force and generation of machining residual stress and cutting force, so it is necessary to build up accurate cutting force prediction model to improve the machining accuracy of thin-walled parts. Therefore, cutting force prediction model based on Johnson-Cook’s flow stress model and Oxley’s shear angle model has been developed, which takes the property of high strain, high strain ratio in area of cut and high cutting temperature into account fully and determines shear angle more accurately on the basis of force balance principle; with different cutting and tool geometric parameters existing, perform simulation and experiment studies on cutting force prediction model, verify the validity of prediction model and obtain the response rules resulted from cutting force prediction model acting on cutting and tool geometric parameters.

Simulation of Residual Stress in Ultrasonic Vibration Assisted Micro-Milling

The machining-induced residual stresses are strongly dependent on the work-piece material and the chosen process parameters. A 2D finite element (FE) model of ultrasonic vibration assisted micro-milling (UVAMM) is established using ABAQUS. Johnson-Cook’s work-piece material and shear failure principle are used, while friction between tool and work-piece uses modified Coulomb’s law whose sliding friction area is combined with sticking friction. By means of FE analysis, the influence rules of spindle speed, vibration frequency and work-piece material on the surface residual stresses are obtained, which provides a basis for choosing optimal process parameters and improving the longevity and reliability of micro-component.

Simulation on the Wear of Micro Mill Cutter in Micro Milling

In this paper, the prediction model of micro-milling cutters in milling process is established to simulate the wear depth in the software DEFORM-3D, the chips growing up an forming process. The paper studies the wear level during the cutting process of micro milling amount of feed per tooth and spindle speed. In this paper the cutting force, cutting heat flow and the contact situation between cutting tool and workpiece are considered in the simulation model. The paper uses abrasion mathematical model related to contact stress and temperature, etc. and studies the influence of the wear depth of milling cutter through the analysis of milling temperature and metal sliding characteristics. Finally, the FEA micro –soft ware is used to verify the change of amount of feed per tooth and the spindle speed with wear depth. The paper provides reasonable parameters for using the micro milling cutter better.

Factors Effect on Vortex Torque of Aerostatic Bearings

In order to improve the drift accuracy of aerostatic bearings, the air supply pressure and manufacturing errors effect on vortex torque of aerostatic bearings were studied by using the finite element method. This paper analyzed the influence of air supply pressure on vortex torque, in view of elliptical error, incline error of throttle slit and radial eccentricity ratio exist. The quadratic regression orthogonal design was adopted to establish function expression of vortex torque among air supply pressure, elliptical error, incline error of throttle slit and radial eccentricity ratio. In research, the simulation vortex torque values of a certain aerostatic bearing are compared with the experimental values. The predicted characteristics are in good agreement with experimental results and then prove that the finite element model, the method used to solve the problem and the function expression obtained are correct. The research has great significance for predicting performance and choosing the air supply pressure of aerostatic bearings.

Manufacturing Errors Effects on Disturbing Torque of Aerostatic Bearings

In order to improve the drifting accuracy of aerostatic bearings, the manufacturing errors effects on disturbing torque of aerostatic bearings is studied by using the finite element method. The finite element mathematic model of the major influence factors of disturbing torque is established. Then, the finite element equation in the gas film domain is solved and the disturbing torque in the presence of disturbing factors is calculated. The research focuses on elliptical error and prismatic error of journal and incline error of throttle slit. The setting angle of journal, incline position angle of throttle slit and radial eccentricity ratio which affect the disturbing torque is also studied. The results show that roundness error of journal and incline error of throttle slit affect the disturbing torque significantly, that is the greater roundness error of journal and incline error of throttle slit the greater disturbing torque. Disturbing torque is periodic function of setting angle of journal and incline position angle of throttle slit. Radial eccentricity ratio affects the disturbing torque, and there is specific radial eccentricity ratio makes disturbing torque to be extreme point or zero point. In the research, the theoretical disturbing torque value is compared with the experimental value of a certain aerostatic bearing, find that they are on the whole accordant with each other and then prove that the finite element model and the method use to solve the problem is correct. The research is of great significance for designing, manufacturing and assembling aerostatic bearings and for performance prediction of aerostatic bearings.

Machining Simulation and Experimental Research of Complex Surface Parts Based on the PMAC

In order to machine the complex free surface, in this paper, NC interpolation of any complex surface is realized used the recursive reconstruction algorithm. The interpolating errors of this algorithm are controllable, and its applicability is relatively wide. Then, these NC codes of the complex human’s free surface are obtained with data exchange of the manufacturing module in the software UG, and machining simulation is obtained used NC codes. Finally, these NC codes are entered into the NC micro-machine tool, which is controlled by the PMAC and developed by ourselves, and the experimental research of the human’s free surface has been finished on this machine tool. The experimental results show that the NC interpolation accuracy of this recursive reconstruction algorithm is very high, and the machining simulation and machining experiments of the complex human’s surface are completely consistent. The study result shows that the complex surface molding is smooth and continuous, and the machined surface is satisfactory.

Experimental and Modelling of Constitutive Equation of Polycarbonate Material

In this paper, according to the principle of building the constitutive model of polymer material, the one-dimensional structure of the ZWT material constitutive model is added to dashpot element in parallel, and in which strain rate and coefficient of viscosity is introduced and the nonlinear viscoelastic constitutive model of Polycarbonate material is achieved. Additionally, tensile test at low strain rate and Hopkinson test at high strain rate of polycarbonate material are carried out, and the change rule of yield strength of polycarbonate material is obtained both at high strain rate and low strain rate. According to the experimental data, the parameters of the constitutive model have been optimized and fitted using ant colony algorithm, and then the fitted results are compared with experimental results. The comparative results show that the improved ZWT constitutive model can reasonably represent the nonlinear characteristics of polycarbonate material at different strain rate.

Frequency Domain Error Analysis in Ultra-Precision Flycutting

In some special fields such as precision optics, the part surface has strict requirements on the frequency domain errors, besides the conventional spatial domain errors such as surface roughness error. In light of the available works lacking of the frequency domain error analysis in ultra-precision flycutting, this paper therefore presents its frequency domain error analysis. A case study of KDP crystal flycutting is carried out to show its detailed processes, where the processing parameters, tool geometry, motion dynamic error of the machine guideway and tool-work vibration induced dynamic error are considered. A surface profile generation method is put forward. Two cases with different tool-work vibration frequencies are carried out. The spatial frequency spectrum is obtained based on the FFT analysis of the generated profile in the specified direction. After the in-depth analysis, the inherent correlation of the generated spatial frequency components with feed spatial frequency and machine dynamic errors induced spatial frequency under certain machining conditions are found, which is very meaningful for the frequency domain error prediction in the real application. The proposed analysis method can also be applied into other types of surface machining.

Mechanical properties of and critical conditions for crack initiation in electronic glass

In this paper, the mechanical properties of electronic glass are tested using a combination of the Vickers indentation test and a multiple-loading nanoindentation test to obtain the elastic modulus, Poisson’s ratio and hardness values. The basic mechanical property parameters of the electronic glass and its stress–strain curve are found using atomic force microscopy analysis of the indentation morphology. The critical pressure and depth for crack initiation and the corresponding load and depth can be obtained during vertical loading on the electronic glass. When cracks extend to the surface, the results show that the electronic glass is isotropic. Several loading cycles causes a fatigue effect on the surface of the electronic glass, which decreases its elastic–plastic response. While the loadings are increasing, the elastic–plastic response rates are decreasing bur it rends stability finally. These results can provide a reference and guide for micro machining and surface microstructure machining of electronic glass.

Structure Scheme Design of a Large Ultra-Precision Hydrostatic Rotary Table with a High Diameter-Length Ratio

This essay briefly introduces a structure scheme design of a high diameter-length ratio rotary plate. This structure scheme is unique from any well-known schemes. In this scheme, there is only one flat act as the working flat for both main thrust bearing and aux thrust bearing. It minimizes the faces which need lapping. At the same time, this scheme minimizes the number of assembling parts. So, it will be easier for this scheme to achieve high accuracy. This essay includes the process of design: calculation for bearings and schemes compare.