Key Engineering Materials Vols. 364-366

Abstract: The accuracy and surface roughness of a machined component is strongly dominated by the dynamic characteristics of the machine tool while the most important factor related to precision machining is the dynamic behaviors during cutting processes. The main objective of this study is to develop a thermo-elastic-plastic coupling dynamic cutting model under large deformation for precision machining and so that the model can be used to predict several variations of cutting mechanics variables. The flow stress in the model is considered as a function of strain, strain rate and temperature and the critical value of the strain energy density of the workpiece is utilized as a chip separation criterion. A powerful FEM software is adopted to create a complete numerical solution for this model. During the analysis, the cutting tool is incrementally advanced forward in a step-by-step manner, from an incipient stage of tool-workpiece engagement to a steady state of chip formation. Three different dynamic cutting processes are introduced in this study, i.e., wave cutting, wave removing and wave on wave cutting. Various levels of frequencies, of amplitudes and of phase angle associated with different kinds of sinusoidal surface waviness are arranged during each simulation case. A whole simulation of dynamic cutting process is undertaken and the fluctuations of the dynamic cutting force during each dynamic cutting process are determined.

Abstract: Electrochemical polishing is a well-known method in finishing of complex shapes with high surface quality. Inner surface polishing of complex parts with high precision can also be easily done by this method. In this research, barrel chamber’s surface, with numerous serial surface angles, is analyzed so that, according to the various set ups, the optimized polishing parameters are obtained. The comparison between electrochemical polishing and conventional methods from this point of view, shows good advantages of this method, so that, the machining time is more than thirty times less and produces very high surface quality. Besides, the dimensional accuracy of the workpiece repeatability process in this polishing method is noticeable.

Abstract: A procedure for fabricating a periodic structure on a metal at submicron order using holographic interferometry and molding processes is described. First, holographic interference using a He-Cd (325nm) laser is used to create the master of the periodic line structure on an i-line sub-micron positive photoresist film. A 200nm nickel thin film is then sputtered onto the positive photoresist. Pattern is then transferred to a metal using Nickel-Cobalt electroforming. Initial results show the technique can accurately control the grating’s period and depth.

Abstract: Fractal and wavelet methods have been used in this study to analyze the KDP surfaces machined by accurate milling and SPDT (Single Point Diamond Turning) method respectively. Through the 2D wavelet method, the 3D origin machined surfaces were separated into the 3D overlaying roughness surfaces and 3D material structure surfaces. The overlaying roughness surfaces were composed of a large number of length scales superimposed roughness surfaces that are generated from the various vibrations in the machining process. The wavelet method can analyze the information of spatial frequency (vibrations in the machining process) and fractal method can reveal the intrinsic properties of roughness topography. Compared with the conventional methods, the integration of wavelet and fractal is more suitable to characterize the machined crystal KDP surface.

Abstract: In this study, the parametric effects of the EMM process were studied by both numerical simulation and experimental tests. The numerical simulation was performed using commercial software, FEMLAB, to establish a multi-physics model which consists of electrical field, convection and diffusion phenomena to simulate the parametric effects of pulse rate, pulse duty, electrode gap and inflow velocity. From the simulated results, the relationship between parameters and the distribution of metal removal could be established. Proper process variables were also chosen to conduct the EMM experiments. After the experiments, the profile of the processed rectangular slot was measured by a Keyence digital microscope. Comparing profile of the processed rectangular slot with the profile of the cathode, the machining accuracy of EMM process could be determined. It could also verify the goodness of the multi-physics model for predicting machining accuracy. From this study, the effects of parameters such as pulse rate, pulse duty, electrode gap and inflow velocity are better understood. The simulation model could be employed as a predictive tool to provide optimal parameters for better machining accuracy and process stability of the EMM process.

Abstract: In the ultra-precision machining of KDP crystal, there are many factors affecting the surface quality[1-3]. The experiments show that the rake angle and back angle of the tool have significant effects on machined surface roughness. Therefore, an efficient way to improve the surface roughness is to select a proper negative rake angle. In this study, the ANSYS static analysis method was employed to analyze the stress field distribution within the whole cutting region. A finite element simulation model was set up to calculate the residual stresses variation with tool’s angles, which can be considered to select optimal rake and back angles in the ultra-precision machining of KDP crystal. Results show that the optimal tool rake angle and back angle are -49° and 7°, respectively. Finally, by using different tool angles to process KDP crystal and utilizing AFM to analyze the surface roughness, it can be found that the measurement results agree well with what are deduced from theoretical calculation.

Abstract: In Laser Beam (L.B.) and Electron Beam (E.B.) drilling, the energy distribution significantly affects both the penetrating efficiency and working performance, both of which are usually estimated by numerical skill or experimental measure. Through the application of a stimulation model, an unstable solution with the finite difference method will result near the solidliquid interface unless much finer grid sizes are set up. To improve on the above defect, nonuniform grids are therefore utilized; this will complicate the built-up of the program and also easily causes the simulated energy distribution to be divergent in the iteration process. In this study, an estimated small Peclet number and observed narrow-deep cavity made the convective and radial diffusion terms small enough to be neglected in the governing equation. From these assumptions, the model was then used to investigate the drilling efficiency where two-phase flow convection could be simplified further into one dimension and thus the analytical solution becomes possible by transferring the penetration velocity into the logarithmic form. When compared with the experiment made by Allmen [1] , the present model shows good agreement in higher energy density and relative errors are no more than 10%.

Abstract: Laser patterning technology of indium tin oxide thin films has been studied in this research. ITO thin films, which usually coat on the glass and the plastic substrate, have been adopted in the flat panel displays (FPDs) and the plasma display planes. The conventional method of the ITO patterning usually uses the wet chemical etching processing. However, the wet etching processing is not adopted in the plastic materials because the chemical fluid usually damages the plastic substrate. The laser direct writing processing has been developed and replaces the wet etching processing. This investigation is interested in the laser patterning used the third-harmonic Nd:YAG laser (355 nm) to ablate the ITO films of glass substrate. The scanning electron microscope (SEM) measures the characterization of the ablated grooves used the different parameters, including the laser energy, the repetition rate and the feeding speed of the table. Finally, the effect parameters of laser ablating ITO film will be presented in this paper.

Abstract: An advanced conditioning technique was developed to precisely and effectively condition the nickel electroplated mono-layer coarse-grained diamond grinding wheel of 46m and 91m grain size with an aim to fabricate Diamond Micro Tool Arrays (DMTA), to meet the high demands of form accuracy, surface quality and low subsurface damage in ductile machining of silicon carbide (SiC). The precision machining experiments on SiC were carried out on a precision grinder to determine the applicability of these fabricated diamond micro tool array (DMTA). The experimental result indicates that the newly developed DMTA is applicable and feasible to realize ductile machining on SiC with high efficiency and low diamond tool wear rate, which shows a good prospect to apply this new concept diamond tool type in precision machining of SiC, as well as the other brittle and hard-to-machine materials.