Materials Science Forum Vols. 505-507

Abstract: Piezoelectric servo mechanism, with its existing nonlinear response and hysteresis, restricts the precision greatly when applied to manufacturing of non-axisymmetric optic mirror. On the basis of theory analysis and experiments, this paper builds three kinds of feed-forward model of piezoelectric servo cutting system. According to these mathematical models, we make the compensation control to the cutting tool position, which results the maximum displacement error less than 0.04μm. And based on this method, experiments on machining non-axisymmetric optic surface of wave front corrector shows the Zernike relative error is less than 10%. So the compensation control of feed-forward control model of cutting tools position can efficiently counteract the influence of nonlinear response and hysteresis, which improves machining precision of non-axisymmetric optic mirror surface.

Abstract: Five degrees-of-freedom (DOF) motion errors of an ultra precision feed table were measured in this study. The laser interferometer was used to measure the yaw and pitch errors and the reversal method was used for the roll error measurement. The linear motion errors in the vertical and horizontal directions were measured using the sequential two point method. The influence of angular motion errors on the linear motion errors while applying the sequential two point method was compensated with the data from the laser interferometer and the reversal method. Capacitive type sensors and an optical straight edge were used while applying the reversal method and the sequential two point method. To demonstrate the effectiveness of our measuring scheme for the ultra precision feed tables, five DOF motion errors of a hydrostatic table driven by a linear motor were measured and presented. From the measured repeatabilities of 5 DOF error motions, it was estimated that the measuring accuracies were ±0.02 μm for the horizontal and vertical linear motion, ±0.04 arcsec for yaw motion, ±0.05 arcsec for pitch motion and ±0.02 arcsec for roll motion.

Abstract: Electron beam welding (EBW) is currently the most advanced jointed technology because of its superior welding precision and larger depth-width ratio than other conjunctive methods. The high vacuum environment of EBW is favorable for the welding of magnesium alloys to prevent the active metals from oxidation. In this study, a home-made 11mm-thick AZ91D extrusive plate was used. By operating and comparing the changeable welding parameters, the optimum condition has been determined as 113mA, 40kV, 73.3mm/s and focal position at bottom. 82% and 89% of the matrix material strength were obtained by stress and non-stress concentration weldments, respectively. Under other worse parameters, the reduction of the strength of EBW for AZ91D-F resulted from four factors, which were undercuts, heat affected zone (HAZ), hot cracking, and cavities.

Abstract: Due to environmental concerns, biodegradable materials, which are currently used in many medical applications, are being considered as a candidate for replace plastics in the future. One of the most common mass production processes to shape biodegradable materials is injection molding. However, the material manufacturers usually do not provide optimized parameter information. In this research, two biodegradable materials, PLA 3001D and Biomax, are investigated. Experiments are conducted utilizing the Taguchi method to determine optimal injection molding parameters, which include injection speed, injection pressure, holding pressure, and cooling time. Shrinkage was the major index to evaluate the injection results. As a result, the best combinations of parameters were determined.

Abstract: A predictive model is presented for the prediction of shear strength in laser welding AISI304 stainless steel. Welding experiments conducted using a pulsed Nd:YAG laser machine while the laser welding parameters and their levels have been arranged according to design of experiments of Taguchi method. The tensile tests are performed after welding and the measurements of tensile strength are further calculated for shear strength. The data can be analyzed using the principles of Taguchi method for determining the optimal laser welding parameters and for investigating the most significant laser welding parameter on shear strength. Furthermore, the results are treated as the training and recalling patterns for constructing a predictive model using back-propagation neuron network to predict shear strength for the range of laser welding operation tested. It is indicated that welding speed is the most significant affecting parameters on shear strength. In addition, an increase in welding speed causes a decrease in shear strength is found. An average error 5.75％for shear strength can be found by comparing the experimental results obtained from conducting verification tests with the predicting values obtained from the established predictive model. It shows that the predictive model is capable of good predicting behavior of laser welding AISI304 stainless steel.

Abstract: Generally, the light guiding plate is fabricated by injection molding. Polymethyl methacrylate (PMMA) material is used to fabricate the light guiding plate. In order to reduce the space of backlight, the light guiding plate is based on double-side microstructures by using MEMS and hot-embossing technologies. From the experimental results, the minimal illumination is 355 lux and the average illumination is 368.1 lux, the uniformity of illumination is 0.08. The novel integrated light guiding plate is achieved a uniformity of distribution, without any optics sheets. In this paper, non-prism LGPs, micro-prism LGPs, and the double-side hot embossing LGPs are fabricated.

Abstract: In this paper, the machining possibilities of silicon wafers by the EDM process are described. Micro components of silicon wafer were processed by EDM process. A fine tungsten carbide rod was machined as tool electrode for EDM process. Performance was investigated utilizing serious experiments. Micro hole was process with the fine electrode using EDM drilling. Micro slots were also processed on the surface of a silicon plate by a copper section electrode. The surface roughness of the silicon wafers in the EDM process was investigated. Array-micro-hole was machined by a tungsten carbide multi-electrode. Array micro holes on the coaxial circle were processed by a graphite-copper electrode of Dia.0.45mm. Batch production technology for economical EDM machining of micro holes were proposed.

Abstract: Liquid cooling heat sink has excellent heat dissipation ability at the personal computer. It can also produce the similar effect at the notebook when the same heat sink is used. However, under the installing space is limited in notebook, the size and weight of heat sink must be limited too. Therefore a novel liquid cooling heat sink was fabricated herein to understand the heat dissipation efficiency in the notebook. Wire electrical discharge machining (WEDM) uses heat erosion effect to remove material and only produces little cutting force on the working surface. Therefore, WEDM has excellent ability to fabricate the straight micro fins (high 1000 μm, width 250 μm, fin gap 400 μm). The WEDM parameters were used to find the precision micro fins in this experiment. The precision micro fins were made when the cutting path offset was 185 μm in WEDM. WEDM would produce over cutting during long pulse duration and it caused oblique micro fins. The appropriate off time in cutting process would promote the WEDM efficiency. However, a liquid cooling heat sink with uniform micro fins and slits was obtained using WEDM.

Abstract: The purpose of this paper presents the optical properties of microstructure of lightguiding plate for micro injection molding (MIM) and micro injection-compression molding (MICM). The lightguiding plate is applied on LCD of two inch of digital camera. Its radius of microstructure is from 100μm to 300μm by linearity expansion. The material of lightguiding plate uses the PMMA plastic. This paper uses the luminance distribution to make a comparison between MIM and MICM for the optical properties of lightguiding plate. The important parameters of process for optical properties are the mold temperature, melt temperature and packing pressure in micro injection molding. The important parameters of process for optical properties are the compression distance, mold temperature and compression speed in micro injection-compression molding. The process of micro injection-compression molding is better than micro injection molding for optical properties.

Abstract: The wire running system of the tabletop Wire-EDM machine for making intricate micro parts developed in our previous study is improved in the paper. A very simple but novel micro-wire cutting mechanism that allows the use of the thin wire of a diameter as small as 20μm is designed. The vibration of the micro wire is suppressed by implementing a unique tension control principle and vibration absorbers. In actual machining the workpiece is mounted on the spindle having indexing ability. By proper planning the wire moving path, micro gear, micro turbine, micro screw, etc. can be manufactured. In the paper the micro bevel gear, which has special appearance and is very difficult if not impossible to be machined by other micro fabrication technologies, is also manufactured satisfactorily.