Advanced Materials Research Vols. 126-128

Abstract: A novel machining method combined with the irradiation of atmospheric pressure plasma was proposed for the finishing of difficult-to-machine materials. The irradiation of helium-based water vapor plasma efficiently oxidized the surface of single-crystal 4H-SiC (0001), and a ball-on-disc test using an alumina ceramic ball revealed that the wear rate of SiC, the surface of which was modified by the irradiation of water vapor plasma, is 20-fold higher than that of the surface without plasma irradiation. Plasma-assisted polishing using CeO2 abrasives enabled us to improve the surface roughness of SiC without introducing crystallographical subsurface damage, and a scratch-free surface with a roughness of less than 0.3 nm rms was obtained.

Abstract: Chemo-mechanical polishing (CMP) has been a useful method to produce superior brittle wafer surfaces. This paper reviews the CMP of silicon carbide and sapphire wafers, focusing on efficiency of the polishing rate. The effects of slurry type, slurry pH value and mixed abrasives will be discussed in detail.

Abstract: Ultrasonic- magnetorheological combined finishing (UMC) is a new technique for the ultraprecision machining of aspheric surfaces, especially for high quality workpieces with small curvature radius concave surfaces. According to the characteristics of UMC finishing, material removal model has been developed. Several types of tool path planning algorithm have been discussed. Two kinds of polyline dwell time algorithm are presented. Polyline Dwell time algorithm based on two-dimensional discrete convolution is a new dwell time algorithm, and the dwell time on the endpoints which compose the tool path can be solved by the algorithm directly. Every polyline dwell time is the mean value of dwell time of two endpoints, therefore, the polyline dwell time of every type of tool path can be solved efficiently by the algorithm. The simulation of two dwell time algorithms has been conducted with same removal function and original error distribution, and the pv convergence rate is improved from 0.939 to 0.973 by using new algorithm. Figure error PV values reduced to 29.4 nm from 1.67μm after UMC finishing. The efficiency of the polyline dwell algorithm is proved by computer simulation and experimental results.

Abstract: This paper deals with a technique to easily suppress bad odor of water-soluble coolant (working fluid) by using a commercially available ion generator for home use. At the shop floor, water-soluble coolant is in heavy use, where putrid bad odor is apt to be generated from water since over 95% of the coolant component is water, leading to a short life of the coolant. Expecting an effect of suppressing putrid odor of water-soluble coolant, application of ion mixed air using an ion generator for house use was examined. As a result, bubbling with ion mixed air could achieve a drastic suppression of a bad odor generated from putrid water-soluble coolant, compared to a bubbling with air only. In addition, it was confirmed that by discharging ions into a machine emitting a bad odor, the odor level decreases drastically. From these results, a machine having an ion generator built-in can be proposed as an environmentally friendly machine tool.

Abstract: Abrasive flow machining (AFM) is a simple and efficient method to remove recasting layers making by wire electrical discharge machining (WEDM). However, conventional AFM methods have difficulty achieving uniform roughness of an axial distribution in circular hole polishing due to limited unitary axial motion of abrasive media. Therefore, this work develops mechanism designs for different passageways to obtain multiple flowing paths of abrasive medium, whose flowing behavior enhances polishing effectiveness by increasing the abrasive surface area and radial shear forces. The motion of the abrasive medium is studied by utilizing different mold cores, which mold shapes include the circular, hollow and helical passageway. The optimum design of the passageways is then verified using CFD-ACE+ software, numerical results indicate that passageway with six helices performed better in the uniform surface roughness than others’ do. Experimental results show that roughness deviation of six helices passageway of approximately 0.100 m Ra is significantly better than those on a circular passageway of around 0.1760 m Ra. Additionally, the six helices passageway is also superior to circular passageway in reducing roughness improvement rate (RIR) by roughly 87% compared with RIR 67.7% for the circular passageway.

Abstract: Pyramidal structured lapping film, which has minute pyramidal structures formed by abrasive grains and adhesives on polyester films, is newly developed finishing tool[1,2]. It is said that the tool has eminent grinding characteristics, mainly, good finished surface quality because chips generated during grinding process can escape into spaces between pyramidal structures, and high grinding efficiency because new abrasive grains come out from inside of the pyramidal structures during grinding process. However, finishing characteristics of this grinding tool have not yet been fully explained.　In this research, the grinding experiments were conducted, focusing on the efficiency of grinding. The grinding forces were measured to examine the state of the surface of the tool. In addition, to improve the grinding efficiency using this tool, a method for changing the grinding load continuously while processing was used. This method was intended to enhance the effective chip generation and new abrasive grain emergence. As a result, stock removal of the workpiece was increased more than when the grinding load was kept constant. Moreover, using scanning electron microscope, this new grinding tool surface was observed, and its effectiveness was examined.

Abstract: This paper studies the performance assessment of magnetic-assistance electrochemical finishing using an effective design system and magnetic force to the electrolyte to assist the dregs discharge on zinc alloy beyond die casting by electrochemical finishing as a finish process on the freeform surface of castings. An outer shell of toy vehicle is taken for instance in the experiment. A small distance between the two magnets or large magnetic field intensity provides larger magnetic force and discharge ability. A higher current rating with magnetic-assistance can avoid the difficulty of dreg discharge, thus reducing the finish time. Pulsed direct current can slightly promote the finishing effect, but the machining time is increased. Thus the magnetic-assistance electrochemical finishing without pulsed current is recommended for the finish process. It is a great contribution that the magnetic-assistance electrochemical finishing just needs quite short to make the freeform surface of workpiece smooth and bright.

Abstract: This paper is aimed at developing an efficient process, in terms of the material removal rate (MRR), for the lapping of polycrystalline diamond compact (PDC). A carbomer based viscoelastic vehicle with a non-reversible shear-thinning property was first developed for the effective suspension of diamond grits used for lapping. The effects of key process parameters on the MRR such as lapping pressure, speed, vehicle concentration, diamond grit concentration, and vehicle flow rate have been investigated through experiments. To obtain an insight into what happened to the diamond grits during lapping, diamond abrasives were reclaimed and sieved after lapping. The grit size distributions of diamond abrasives before and after the lapping were then compared.

Abstract: In this paper, the with-in-wafer non-uniformity (WIWNU) of the lager quadrate optic in the fast polishing process (FPP) is discussed from the machine side. At the machine side, the non-uniform stress on the wafer surface is the major reason for the non-uniform material removal rate which results in the WIWNU. Stresses arise mainly from two sources, namely the pressure exerted by the polishing pad and shear stress due to the relative motion between the wafer and pad. Based on the special chemical mechanical polishing FPP, the kinematic motion of the wafer is analyzed and the non-uniform stress is analyzed by a 3D axisymmetric quasi-static model. The WIWNU can be reduced by adjusting the stress.

Abstract: In this study, a method is proposed to fabricate the polishing tool with an elastic membrane in thickness of 10 to 120μm, by using the electrophoresis phenomenon. The controllability of the membrane thickness with the applied voltage, processing time and the solution concentration are investigated experimentally. It is found that the thickness can be controlled by the applied voltage and processing time. Moreover, the polishing characteristics with the fabricated tool is examined and compared with the conventional tool. It is found that the polishing tool fabricated with the proposed method achieves the same characteristics as the conventional tool and the tool life is long enough for the practical use.