Papers by Keyword: Polishing

Abstract: A novel approach for processing SiC wafers has been developed to grind then polish 150 and 200mm SiC wafers without lapping. The purpose of this work was to optimize the processing of SiC wafers sliced from boules to finished epi-ready wafers by grinding and chemical-mechanical polishing (CMP). Diamond vitrified wheels were used for coarse and fine grinding to correct the irregular shape of SiC wafers before reducing surface roughness by CMP. 4H-SiC wafers were sliced by diamond embedded/slurry wire saw and laser split techniques. Incoming wafer condition was seen to affect coarse grinding wheel performance depending on incoming surface roughness and shape. Wheel characteristics, including abrasive size, abrasive concentration, and bond structure, were adjusted to improve grinding efficiency based on incoming conditions. Coarse grinding wheels were able to reduce wafer total thickness variation to 3-5um and average surface roughness to 20-30nm (Ra). Fine grinding wheels were optimized to reduce total thickness variation (TTV) below 2um and surface roughness to 1-2nm Ra and peak-to-valley height of 20-30nm (Rt). Coarse and fine wafering time was less than 30 minutes total to remove 50 microns on both Si and C-face per wafer. Surface damage from grinding was removed after one hour of polishing each wafer by CMP, achieving surface roughness of 0.4nm Ra and 5-7nm Rt. The benefit of optimizing coarse and fine grinding of 150 and 200mm SiC wafers is demonstrated by producing flat wafers, which reduced overall processing time to prepare an epi-ready condition by CMP.

Abstract: Laser powder bed fusion (PBF-LB) technique can currently offer the lowest surface roughness among all available techniques for metal additive manufacturing. Still the measured values for R_a can easily be over 10 μm depending on the used layer thickness and printing parameters. The current work focuses on improving the surface roughness by utilizing dry electropolishing machine. While suitable for many materials, the material selected for this study is one of the most used in PBF-LB manufacturing, stainless steel 316L. In addition, multistep pre-grinding with the grade of the final finish varied was used to investigate what is the most efficient way to distribute manual preparation work and automated polishing to reach the desired surface roughness. Furthermore, severe shot peening was used before the polishing to study the effect on residual stresses and fatigue life of the material. Laser optical microscopy was used to investigate the surface properties and it was found that dry electropolishing with pre-grinding could be succesfully used to obtain average roughness levels as low as 0.13 μm. The highest reductions in surface roughness were reached with the rougher initial surfaces where it could be reduced by 80% at best. Residual stresses measured after the severe shot peening were preserved after the polishing but did not result in increased fatigue strength.

Abstract: While additive manufacturing of metals has been rapidly growing industry for the past decade, the quality and the fatigue properties of the materials are still not very well known. In this study, we focus on the laser powder bed fusion (PBF-LB) manufactured Ti6Al4V. The as built material was compared to the heat treated counterpart by microstructural analysis, and the mechanical properties, impact toughness and the fatigue strength were determined. Bending fatigue testing was conducted for both as built and polished material to reveal the effect of surface roughness. The results showed that the heat treatment and the resulting microstructural change is crucial for the material properties and the material showed very brittle behaviour without it. According to the results, the surface quality plays also an important role in the fatigue life of the material, especially if no heat treatment is used.

Abstract: Zirconia restorations are usually coated with glazing to provide an aesthetic and reduce wear on opposing teeth. Occlusal adjustments such as grinding and polishing to eliminate occlusal or internal interferences can affect the mechanical properties of zirconia. The purpose of this study was to evaluate the effect of glazing, reglazing, and polishing procedures on the biaxial flexural strength of zirconia ceramic. This experimental study used 20 samples of zirconia discs (12x1,2 mm), which were divided into fourth groups (n=5). The first group was zirconia discs without treatment as control, the second group with glazing treatment, the third group with reglazing treatment, and the fourth group with polishing treatment. Biaxial flexural strength was determined using a piston on three balls technique. The data were analyzed using 1-way ANOVA and t-test. The results of this study showed no statistically significant difference between the group with glazing, reglazing, polishing and the control group (p>0.05). The highest zirconia biaxial flexural strength was found in the polished group but not significant statistically (1913.64 ± 594.28 MPa). The reglazing group with the lowest average biaxial flexural strength was (1413.01 ± 365.66 MPa). It can be concluded that there were no differences in biaxial flexural strength between the polishing, glazing, and reglazing group. The use of polishing can be an alternative technique to improve aesthetics besides glazing and reglazing because it does not impair the biaxial flexural strength of zirconia.

Abstract: The present paper shows a new fixed abrasive bond-grit formulation aimed for best-in-class, low-cost and high-quality finished SiC wafer surfaces. Grinding wheels manufactured with this technology can accomplish ultra-smooth SiC (Ra = 0.55 nm and TTV < 1 μm) surfaces due to their unique bonding structure and their tailored grit size. Additionally, SiC wafers ground with these wheels exhibit reduced sub-surface crystal damage, mirror-like polished surface and improved wafer geometry while both the grinding forces and the wheel wear are kept low.

Abstract: This paper presents the laser surface polishing of titanium alloy (Ti6Al4V) by using a nanosecond pulse laser. Air, nitrogen and argon were employed as a shielding gas in this study, where the areal roughness (Sa) of laser-polished surface was measured and compared. The results showed that argon was the suitable assist gas for improving the metal surface without causing the oxidation. The effect of laser pulse repetition rate and scan speed on the surface roughness was also investigated in this study. The use of high repetition rate together with slow scan speed was able to reduce the surface roughness of titanium alloy. The roughness was found to be reduced by 47% when the pulse repetition rate of 500 kHz and scan speed of 50 mm/s were applied.

Abstract: The research of fluid inclusion thin section is to understand the physical and chemical conditions (such as temperature, pressure, density, pH value, composition, etc.) of minerals, rocks and deposits, and to solve the genesis of rocks and deposits; in the process of production, gas inclusions or liquid inclusions should be produced at low temperature, otherwise the inclusions will be destroyed, especially quartz sandstone, weathered rock, mudstone and other minerals Therefore, when the film is made in a humid temperature environment, it is very easy to be deliquesced, especially for the rocks with developed cleavage and many cracks, after rough grinding after polishing, it is easy to produce warping edge, warping angle, bubbles, etc., thus causing the sample piece to deteriorate after polishing; therefore, a large number of pockmarks and cracks will be produced under the microscope. In this paper, starting from the applicable conditions of materials and technological methods, the practical problems of making materials and technological process in rock slice method are introduced in detail. Keywords Inclusion,Manufacturing, Grinding,Polishing,Filming

Abstract: In recent years, the oil field chemical A-cyanoacrylate mixed adhesive has been used in rock preparation and preparation to a certain extent, and its role has been paid more and more attention due to the solidification of the rock surface in the rock thin section, the early embedding of the rock, and the adhesion of the thin side of the rock to the slide surface, etc. This paper introduces the preparation and application development of a-cyanoacrylate mixed adhesive in geological experiment, and the development of a-cyanoacrylate mixed adhesive in oilfield geological experiment.

Abstract: The surface treatment of tools plays an important role for the operational behaviour of forming processes. Up to now, industrial standard is the manual finishing of tool surfaces, which can lead to a varying quality of the surface finish and therefore influence the tool service life and the forming results. One method to perform the polishing operation automatically is to remelt the top layer of materials by laser polishing. This is accompanied by a considerable change in the material properties in this zone. Therefore, the effect of laser polishing with respect to the local modification of the tool surface is investigated in this study. The results of the investigations reveal that a precise adjustment of the laser parameters is required in order to reduce the roughness of the surface. The heat input also leads to a significant influence on the microstructure of the material. In this study laser polishing remelts the material up to a depth of approximately 20 µm. Furthermore, it can be observed that the heat input during the process results in a heat affected zone of up to a depth of 30 µm. As a contrast to laser polishing, abrasive blasting is investigated as a roughness increasing surface modification.

Abstract: The dimension stone polishing consists of eliminating the surface roughness of the slabs with the use of fickerts. The main tools used for this activity are composed of epoxy resin, derived from petroleum, which contains chemical elements with harmful potential to the environment and human health. To overcome this problem, it is necessary to develop new technologies with the lowest environmental impact in the life cycle, from the raw material acquisition to the waste disposal. This study aims to contribute to the improvement of an ecological fickert developed by the Centre for Mineral Technology (CETEM). The fickerts presented here are composed of castor oil resin, silicon carbide and silica from rice hull ash. Two different compositional formulas were used for the preparation of the pieces that were tested in an industrial polishing machine. The results showed that the formula with higher percentage of fillers showed better performance, expressed by the relation between the loss of mass of the pieces and the increase of gloss on the surface of the slab. Other particularities of the product, as the high abrasion resistance of the matrix that reduced the cutting function, could be solved by choosing a filler with a lower hardness. This fact allows to infer that this line of research presents great potential of applicability in the dimension stones market.