Key Engineering Materials Vols. 447-448

Abstract: Electro-magneto-rheological (EMR) fluids, which exhibit Newtonian behavior in the absence of a magnetic field, are abruptly transformed within milliseconds into a Bingham plastic under an applied magnetic field, called the EMR effect. Based on this effect, the particle-dispersed EMR fluid is used as a special instantaneous bond to cohere abrasive particles and magnetic particles together so as to form a dynamical, flexible tiny-grinding wheel to machine micro-groove on the surface of optical glass. Experiments were conducted to reveal the effects of process parameters, such as the feed rate of the horizontal worktable, feeding of the Z axis, machining time and machining gap, on material removal rate of glass. The results indicate that the feed rate of the worktable at horizontal direction has less effect on material removal rate, which shows a fluctuation phenomenon within a certain range. The feed rate of the Z axis directly influences the machining gap and leads to a remarkable change on material removal rate. Larger material removal rate can be obtained when the feeding frequency of Z direction is one time per processing. With the increase of rotation speed of the tool, material removal rate increases firstly and decreases afterwards, and it gets the maximum value with the rotation speed of 4800 rev/min. The machining time is directly proportional to material removal amount, but inversely proportional to material removal rate. Furthermore, material removal rate decreases with the increase of the machining gap between the tool and the workpiece. On the basis of above, the machining mode with the tiny-grinding wheel based on the EMR effect is presented.

Abstract: Aiming at micro machining of 3D microstructure of brittle materials with a novel tiny-grinding wheel based on the electro-magneto-rheological (EMR) effect, five conical tools with different cone angles are designed to reveal the effect of the cone angle on the machining characteristics. The distribution of the magnetic and electric fields in the polishing area is simulated using the finite element analysis software, and the machining experiments of micro groove were conducted to confirm the simulation results. Experimental results indicate that the material removal rate increases first and decreases afterwards with the increase of the cone angle, and the section width of micro groove increases but the section depth of micro groove shows a fluctuation phenomenon within a certain range. The intensities of the electric and magnetic fields on the tip of the conical tool with the 45° cone angle are at a larger level in the five tools, which is helpful to form a stable tiny-grinding wheel based on the EMR effect and obtain a better machining effect, so the tool with the 45° cone angle is an effective and ideal machining tool for the machining of 3D microstructure.

Abstract: This paper describes the laser hardening of micro-cutting edges using an on-machine heat treatment system with a YAG laser. Various laser conditions were evaluated to perform laser quenching on a machine tool without melting at the edges. We also investigated the influence of the motion accuracy of the machining center on the quenching characteristic of micro-cutting edges after laser irradiation. We clarified that we could quench both the straight and curved corner parts by arranging proper laser irradiation conditions considering the motion accuracy of the machining center.

Abstract: Numerically controlled local wet etching (NC-LWE) is a novel technique to fabricate the ultraprecision optical components and/or finishing the functional materials. In this technique, a figuring is performed by controlling the dwelling time of the combination nozzle, which consists of a supply and a suction part of an etchant, on the workpiece. In this paper, we proposed fabrication process of millimeter-thick elliptical neutron focusing mirror substrate by applying NC-LWE figuring involving CeO2 slurry polishing. We fabricated a millimeter-thick elliptical neutron focusing mirror substrate with a figure error of less than 0.2 μm and obtained a surface roughness of less than 0.15 nm rms.

Abstract: In the X-ray fluorescence analysis on sub-micron particle, application of the doubly curved crystal (DCC) spectrometer with Johansson-type geometry is effective to improve the lowest limit of detection because DCC makes it possible to focus and monochromatize an X-ray beam simultaneously. A strain-free crystal is essential for the high-performance focusing crystal spectrometer. We propose the application of the open-air type numerically controlled plasma chemical vaporization machining (NC-PCVM), which utilizes neutral reactive species generated by atmospheric pressure plasma, to fabricate the DCC substrate. By applying NC-PCVM technique, a curvature radius error of 0.08% was obtained, and there was no degradation of the crystallinity of the Si (111) substrate.

Abstract: Quartz resonator is a very important device to generate a clock frequency for information and telecommunication system. Improvement of the productivity of the quartz resonator is always required because huge amounts of resonator are demanded to install to various electronic devices. Resonance frequency of the quartz resonator is determined by the thickness of the quartz crystal wafer. Therefore it is essential to uniform the thickness distribution of the quartz crystal wafer with nanometric level. We propose the improvement process of the thickness distribution of the quartz crystal wafer by numerically controlled correction using atmospheric pressure plasma which is noncontact and chemical removal technique. We have already succeeded in obtaining a thickness uniformity of 33.1nm within 2 min in the thickness correction of an AT-cut quartz crystal wafer with an area of 24 mm × 24 mm. However, increase of removal rate and improvement of correction accuracy are required for industrial manufacturing. Heating effects of the quartz crystal wafer in the removal rate and the correction accuracy were investigated. The heating of the substrate and compensate of the scanning speed of the worktable in accordance with the variation of the surface temperature enabled an increase of 50% in removal rate and 10-nanometric-level accuracy in correction of the thickness distribution of the quartz crystal wafer.

Abstract: A system of ultrasonic combined with grinding has been designed, and one novel connective method of straight screw combined with taper surface has been applied in spindle, so compact size and high revolving accuracy can be achieved. Modal analysis of ultrasonic vibration system has been implemented by FEM (Finite Element Method), and its optimal dimension has been calculated to find out optimal vibration estate. Full-bridge converter has been applied in driving circuit of ultrasonic vibrator, and auto-frequency tracking has been designed in order that ultrasonic vibration works on resonant or quasi-resonant frequency. Finally, machining experiments have been fulfilled about ultrasonic combined with grinding, and its machining effect has been distinctly improved comparing ordinary grinding machining.

Abstract: In order to resolve the problem of connecting rod notches machining, a new process of WEDM (Wire Electric Discharge Machine) has been presented, and it is greatly possible that expensive laser process can be replaced by WEDM in virtue of its unique advantages. Firstly, process parameters of notch have been analyzed, and project of machining notch using WEDM has been introduced, including measures to achieve good-quality notch. The relationship between cutting speed and power supply parameters has been investigated, and it is discovered that micro-crackle on bottom of notch are greatly effect to fracture splitting process, also new idea of active controlling micro-crackle has been presented. Finally, fracture splitting machining has been carried out. The cost and entrance standard of fracture splitting process are greatly dropped owing to new breakthrough of machining notch using WEDM.

Abstract: The silicon carbide particle reinforced aluminium matrix composite (SiCp/Al) which is acknowledged as one of the most competitive metal matrix composites is now widely applied in aviation, aerospace and military fields, and its application is extending gradually. As a result of the hard and brittle SiC particles contained, mechanical machining of the material is difficult, but the method of electric discharge machining (EDM) has certain prominent advantages. In this paper, SiCp/Al was machined using micro-EDM. First, a Ф40μm × 4.1mm micro tool electrode of which the aspect ratio is up to 100 was made; and then, through experiment, the impact of open-circuit voltage and electrode material on processing speed and electrode wear was analyzed; finally, 28μm wide micro slits, micro square platform of 34μm long on each side and other micro three-dimensional structure were machined. Research and experimental results show that the use of appropriate micro-machining parameters and reasonable processing methods can improve processing performance to better achieve the micro-EDM of SiCp /Al.

Abstract: The wire electrodischarge grinding (WEDG), which is one of the electrical discharge machining (EDM) methods, of submicron-diameter zinc micropins was attempted using a relaxation-type pulse generator. Tungsten wire of 30 µm diameter was employed as the tool electrode. The open-circuit voltage was set at lower than or equal to 15 V in the finish machining step. The electrostatic capacitance of the pulse generator was its stray capacitance only. As a result, a micropin of 0.3 µm diameter was processed. They are the smallest-diameter micropins fabricated by EDM, to the best of our knowledge.