Showing papers on "Surface finishing published in 2011"

Robust surface electronic properties of topological insulators: Bi2Te3 films grown by molecular beam epitaxy

Abstract: The surface electronic properties of the important topological insulator Bi2Te3 are shown to be robust under an extended surface preparation procedure, which includes exposure to atmosphere and subsequent cleaning and recrystallization by an optimized in situ sputter-anneal procedure under ultrahigh vacuum conditions. Clear Dirac-cone features are displayed in high-resolution angle-resolved photoemission spectra from the resulting samples, indicating remarkable insensitivity of the topological surface state to cleaning-induced surface roughness. © 2011 American Institute of Physics. doi:10.1063/1.3595309 Recently, a new class of materials, called the topological insulators TIs, has been predicted theoretically and experimentally observed. 1 TIs are characterized by odd number of Dirac cones that show a linear energy dispersion similar to relativistic particles. Hence, carriers at the surface of TIs form a two-dimensional electron gas with unparalleled properties, such as extremely high mobilities or dissipationless spin-locked transport, which may lead to new applications in the field of spintronics or quantum computing. Bi 2 Te 3 is a narrow gap semiconductor that has been traditionally investigated as a thermoelectric material, however, very recently the TI behavior has been observed at its surface. 2 To date, the

High-Efficiency Large-Area Rear Passivated Silicon Solar Cells With Local Al-BSF and Screen-Printed Contacts

Abstract: This paper describes the cell design and technology on large-area (239 cm2) commercial grade Czochralski Si wafers using industrially feasible oxide/nitride rear passivation and screen-printed local back contacts. A combination of optimized front and back dielectrics, rear surface finish, oxide thickness, fixed oxide charge, and interface quality provided effective surface passivation without parasitic shunting. Increasing the rear oxide thickness from 40 to 90 A in conjunction with reducing the surface roughness from 1.3 to 0.2 μm increased the Voc from 640 mV to 656 mV. Compared with 18.6% full aluminum back surface field (Al-BSF) reference cell, local back-surface field (LBSF) improved the back surface reflectance (BSR) from 65% to 93% and lowered the back surface recombination velocity (BSRV) from 310 to 130 cm/s. Two-dimensional computer simulations were performed to optimize the size, shape, and spacing of LBSF regions to obtain good fill factor (FF). Model calculations show that 20% efficiency cells can be achieved with further optimization of local Al-BSF cell structure and improved screen-printed contacts.

Study on the Effect of Surface Finish on Corrosion of Carbon Steel in CO2 Environment

Abstract: Standard surface finish used in laboratory corrosion testing may not represent the 'as-delivered‟ internal pipe surface condition, which typically varies from 20 μm to 50 μm. Surface roughness is known to affect the hydrodynamic and mass-transfer boundary layer, thus influencing the corrosion mechanism and rate. The objective of this study is to investigate the effect of various grit surface finishes of 60, 240, 400, 600, 800 and 1200 used in laboratory corrosion testing in predicting field corrosion behaviour. The effect of the surface roughness on the corrosion rate is investigated by varying the specimen surface finishing using SiC abrasive paper of 60, 240, 400, 600, 800 and 1200 grit. The specimen used is carbon steel BS 970 (070M20), tested in stagnant and turbulent CO2 environment at pH 5.5 and 3 wt% NaCl. The corrosion rate is measured by the Linear Polarization Resistance (LPR) Long Term and Custom Sweep, Weight Loss and Electrochemical Impedance Spectroscopy (EIS) method. Surface profiles produced by 400, 600 and 800 grit samples fall within the range of 20 μm to 50 μm, which resemble the 'as-delivered‟ internal pipe surface roughness. Corrosion rates in turbulent flow are higher than static condition for all surface finish. For both static condition and turbulent flow, the average corrosion rates of 400, 600 and 800 grit finish samples obtained differ within 18% and 15%, respectively. In conclusion, based on surface profiles and corrosion rate measured, the practice of 400, 600 and 800 grit surface finish in laboratory testing is acceptable to represent the 'as-delivered‟ pipe condition.

Improving surface smoothness of laser-fabricated microchannels for microfluidic application

Abstract: Inexpensive and flexible CO2 laser rapid prototyping of polymer microfluidics is facing challenges due to the rough microchannel surface typically with a roughness Ra in the µm range produced directly through laser ablation. In this study, a wet chemical etching technique was developed and used successfully to carry out smoothing of microchannel surfaces fabricated on a polymethyl methacrylate substrate using CO2 laser direct writing. The microchannel surface roughness of a few µm was significantly reduced through etching in acetone diluted with ethanol in an ultrasonic bath in a short time cycle. The surface roughness Ra of below 10 nm could be achieved through etching in the heated etchant solution while without noted deformation in a microchannel structure. The mechanism to reduce surface roughness by the tunable solubility of a polymer in a liquid through concentration and temperature control is discussed with respect to the effect of the etching parameters: acetone concentration, etching time and the temperature of the etching solution. The results would be attractive for microfluidic chip applications when using laser prototyping.

Surface finishing of flat pieces when submitted to lapping kinematics on abrasive disc dressed under several overlap factors

Abstract: In machining of pieces that require surface finishing levels finer than grinding can offer, it is necessary to use specific finishing processes. However, these processes, which have lapping as the most classic representative, are usually difficult to setup and demand much time in setting the large number of variables. This paper discusses the investigation of an abrasive process for finishing of flat workpieces based on the combination of important grinding and lapping characteristics. Instead of loosing abrasive grains between the workpiece and the lapping plate, a resinoid grinding wheel of hot-pressed silicon carbide is fixed on the plate of a device resembling to a lapping machine. The grinding wheel is dressed with a single-point diamond for maintaining its form flat and mainly for interfering in the workpieces surface finishing by varying of the overlap factor (Ud). It was noticed that the studied process can simplify the setup and make it easier than in lapping, which is a painstaking process. The surface roughness values and flatness deviations showed to be comparable to those achieved in lapping, or even better. The best surface roughness and flatness deviation found were Ra = 0.8 nm and 0.4 μm with Ud = 3, respectively. The workpiece material was made of quenched and tempered SAE 4340 steel, reaching a hardness of 60 HRC. The process was also monitored by acoustic emission (AE), which indicates to be a promising and suitable technique to be used in this process. Compared to lapping, there is an additional advantage of a less contaminated workpiece surface with a shiny appearance.

Comparison of Roller Burnishing Method with Other Hole Surface Finishing Processes Applied on AISI 304 Austenitic Stainless Steel

Abstract: Component surface quality and selection of the optimum material are the main factors determining the performance of components used in machine manufacturing. The level of hole surface quality can be evaluated by the measurements regarding surface roughness, micro-hardness, and cylindricity. In this study, data had been obtained for different hole drilling methods. The characteristics of materials obtained after applications were compared for different hole-finishing processes to identify best hole drilling method. AISI 304 austenitic stainless steel material was used. Surface finishing of holes were performed using drilling, turning, reaming, grinding, honing, and roller burnishing methods. The results of the study show that the roller burnishing method gives the best results for mechanical, metallurgical properties, and hole surface quality of the material. On the other hand, the worst characteristics were obtained in the drilling method.

Smart automation of robotic surface finishing

Abstract: A method and an apparatus for smart automation of robotic surface finishing of a three-dimensional surface of a work piece is described. A three-dimensional motion path is created along the surface of the work piece. A variable contact force profile is specified along the three-dimensional motion path. The three-dimensional motion path is modified based on the specified variable contact force profile. The surface of the work piece is finished using one or more surface finishing tools along the modified three-dimensional motion path. The surface of the work piece includes at least a flat region and a curved region.

Mathematical modeling for finishing tooth surfaces of spiral bevel gears using pulse electrochemical dissolution

Abstract: Gears with a complex curve tooth, such as spiral bevel and hypoid gears, lack an ideal technique for the final finishing process. Pulse electrochemical finishing (PECF) is considered a promising method for surface finishing due to its micro-removal characteristics. A PECF system for spiral bevel gear (SBG) is established according to the generation of SBG tooth surfaces. An SBG (module, 12 mm; number of teeth, 38) is selected as the processing test piece, and mathematical models are developed for analyzing the characteristics of PECF. The influence of the experimental variables, including applied voltage, interelectrode gap, and finishing time, on the total removal thickness and surface roughness is discussed. The calculated values are found to be approximately consistent with the experimental values. The other parameters, including the concentration of electrolyte, tool rotational speed, flow rate of electrolyte, and pulse period, are also studied. Results show that the roughness of the SBG tooth surface is reduced from Rz 7.13 to 4.32 μm. The precision of the SBG is also improved.

Xylogen-inorganic nano composite material and producing process thereof

Abstract: The invention provides a raw material prescription of lignin-inorganic nanometer composite material and the preparation method thereof. The composite material comprises lignin or derivate, inorganic nm material, water soluble lignin surface finishing agent and other types of surface finishing agent. The preparation method comprises the steps as follows: the inorganic nanometer material is pretreated with the water soluble lignin surface finishing agent, the other types of the surface finishing agent are added to finish pretreatment; the inorganic nanometer material is added into the lignin orthe derivate, acid is added for sediment, and is filtered and dried to acquire the lignin-inorganic nm composite material. The invention has simple raw materials prescription, easily-available sources, low cost and simple technique, is favorable for the recirculation and the reuse of biographic resources, and has good product performance, brilliant economical benefit and wide application prospectwithout pollution.

Comparison of Burnishing Process with Other Methods of Hole Surface Finishing Processes Applied on Brass Materials

Abstract: In this article, effects of traditional surface machining processes and a newly used surface finishing process called burnishing process on a brass material are compared on the basis of microstructure, circularity, cylindricity, and surface roughness. For this reason, test samples made of brass material which is a non-ferrous metal were prepared to be widely used in many fields of machining industry as it accurately reveals deformation effects of surface finishing processes, and those samples were subjected to drilling, lathing, reaming, grinding, honing, and burnishing. After these processes, hole surface roughness, cylindricity, and change in microstructure were analyzed. All surface machining processes were performed under constant depth of cut, cutting speed, and feed rate. Data collected after experimental research indicates that the best combination of surface characteristics is obtained by burnishing process, in comparison to all other different methods of finishing. Also the highest hardness and b...

An Investigation into the Use of Industrial Robots for Machining Soft and Low Density Materials with HSM Technique

Abstract: The needs to comply with an increasingly competitive international market lead industries to some innovative solutions, such as the use of robotic arms as machine tools. Although these solutions present some well known drawbacks, there are some advantages and niches of application where success is possible. The present work investigates the use of such pieces of equipment to machine aluminum alloys AA2024 applying high speed machining (HSM) technique, assessing surface finishing as a function of different orientation angles between end mill and machined surface. It also tests the best condition to machine foam for prototyping applications. Results indicate that the directions close to the normal are the best compromises because of dynamic stability of the robot arm structure and roughness as low as 4 µm Ra are possible to be achieved in aluminum alloys. A complex shape such as a semi sphere can be easily machined in foam for rapid and accurate prototype machining. Surface finishing can be very smooth and well suitable for industrial applications in such materials.

Fatigue life and surface integrity measurements of EN S355J2 steel used in hydraulic components

Abstract: This article is aimed at studying the impact of surface integrity - surface roughness, hardness and residual stress - on fatigue performance of EN S355J2 steel. The test specimens were manufactured by turning. A longer fatigue life for the machined components can be obtained by applying such cutting conditions as a low feed rate. The fatigue limit of the specimen with the surface roughness Ra 1,6 μm is approximately 7 % higher than that of the specimen with Ra 3,2 μm. From the residual stress results it can be seen that the cutting conditions used for producing surface finish Ra 1,6 μm will introduce mainly compressive residual stress whereas the cutting conditions used for producing surface finish Ra 3,2 μm will introduce tensile residual stress. The measurements were carried out at Aalto University at the Departments of Engineering Design and Production and Material Science and Engineering in Espoo. The main purpose of the study is to find proper surface finishing techniques and fatigue improvements for hydraulic components.

Inclined-wall regular micro-pillar-arrayed surfaces covered entirely with an alumina nanowire forest and their improved superhydrophobicity

Abstract: This paper reports a multiple-scale hierarchically structured superhydrophobic surface that is composed of inclined-wall regular micro-pillar arrays covered entirely with an alumina nanowire forest (ANF) to improve the surface wettability. The multiple-scaled structures were fabricated stably using a simple batch process based on an anisotropic chemical silicon etching process and a subsequent time-controlled anodic aluminum oxide technique. The surface wetting properties of the mono-roughened surfaces with inclined-wall micro-pillar arrays, which are normally in the Wenzel wetting regime, could be transitioned perfectly to the slippery Cassie mode and enhanced greatly in the Wenzel regime in cases of a high- and low-density of the micro-pillars, respectively, by easily amplifying the intrinsic contact angle through the entire coverage of the ANF on the micro-roughened surfaces. The wettability of the proposed multiple-scaled surfaces could also be predicted using analytic surface models and the experimental results agreed greatly with the wetting trends estimated theoretically due to the geometrical regularity of the base micro-structures.

Surface finishing techniques for SLM manufactured stainless steel 316L components

Abstract: Selective Laser Melting (SLM) is an additive manufacturing (AM) process which builds components through melting layers of powdered material together. The surface finish on these manufactured components typically requires additional manual finishing or post-processing. Traditionally, mechanical polishing techniques utilise semi skilled labour and usually requires significant time input resulting in it being an expensive and inefficient process. This paper considers less labour intensive post processing techniques such as media blasting and tumbling for SLM produced stainless steel 316L components. In particular, the change in the surface profile due to the finishing processes employed was the primary issue for investigation. However, changes in the dimensions, geometric features and overall form were also studied. Parameters of the build process (machine operation) that ultimately impact on the final components surface finish or finishing process required, were noted and discussed. It was found that a range of surface roughness and surface finishes can be achieved using the techniques outlined above. It is possible to achieve a good surface finish using some of these techniques, although, it is obvious that these techniques are not solely sufficient for the post processing of stainless steel 316L components.

Investigation of ultrasonic Pd coated Cu wire wedge bonding on different surface finish

Abstract: In IC, wire bonding is the main technology for electrical connections between chip and leadframe or substrate. Gold wire bonding has the advantages of a fast bonding process, excellent electrical property, and stable chemical property. But, gold prices have risen significantly over the last few years. Many manufactures have been investigating ways to replace the conventional gold wire various new material. Copper wire bonding is an alternative interconnection technology. Compared with gold wire, Cu wire is better than gold with respect to electrical conductivity. The inherent stiffness of the copper wire also makes long wire with small diameters more resistant to wire sweep during molding. There are also some problems with Cu bonding process: (1) Copper easily oxidizes in air. The application of copper wire coated with palladium is a solution to prevent copper oxidation during the bonding process. (2) The higher hardness of wire generally requires higher ultrasonic power and bond force to bond on metal. It also lead to high risk of cratering for ball bonding and tearing for wedge bond. This paper reports a study on the influence of surface finish type, deposition thickness and bonding machine parameter for wedge bonding. In this study, 0.7mil Pd coated Cu wire was bonded on three kinds of surface finish, as electro-plating Nickel and Gold, electro-plating Nickel, palladium & gold, Electroless Nickel, Electroless Palladium and Immersion Gold (ENEPIG). The noncontact optical profiler, microhardness tester and scanning electron microscope (SEM) were used to examine surface finish characteristics. Bonder machine alarm rate, pull strength and failure mode after wire pull test were performed to confirm the quality for Pd coated Cu wire bonded on three kinds of surface finish. Then, wedge bonding mechanism of Pd coated Cu wire was discussed in this paper.

Surface finishing method of silicate reinforced material by using microbial fermentation

Abstract: The invention discloses a surface finishing method of a silicate reinforced material by using microbial fermentation. In the method, bacteria cellulose prepared by bacillus xylinus fermentation is used for surface treatment of the silicate reinforced material; by coating cellulose organic polymers on the surface of a silicate material, the surface modification of the silicate reinforced material is realized and the compatibility of the silicate reinforced material with polymeric matrix resin is increased, thereby achieving the purpose of improving the interface combination of composite materials and forming an environment-friendly surface finishing method of the silicate reinforced material.

The Effect of Different Surface Finishing Procedures on Surface Roughness and Fracture Toughness in All‐Ceramic Restorations

Abstract: The aim of this study was to determine the effect of different surface treatments on the flexural strength of four different ceramic specimens. The four ceramic systems investigated in this study were lithium disilicate reinforced, zirconium oxide reinforced, glass-infiltrated alumina reinforced, and feldspathic ceramic. For the first group, grinding burs, for the second group polishing kit and for the third group glazing procedures were applied for surface treatment. Surface roughness, mean fracture toughness, and a SEM were used to describe surface features. The surface treatments affected the flexural strength and surface roughness of the ceramic systems evaluated.

Study on Internal Magnetic Field Assisted Finishing Process Using a Magnetic Machining Jig for Thick Non-Ferromagnetic Tube

Abstract: This paper describes an internal finishing process for thick non-ferromagnetic tube (10~20 mm in thickness) by the application of a magnetic field-assisted machining process using a magnetic machining jig (permanent magnet tool). In this study, a new automatic inner surface finishing system was developed, and to achieve smooth surface roughness and high form accuracy, a multiple-stage machining which contains of rough machining and precision finishing was carried out. Especially, in order to improve the form accuracy the rough processing time was made longer compared with the research in the past. The experiments were performed for a thick SUS304 stainless steel tube 10 mm in thickness. The results showed that surface-roughness and form accuracy were able to be improved greatly, the initial surface roughness of 4.9μm Ra can be improved to 0.01 μm Ra and the roundness of inside tube can be improved from 206 μm to13μm.

Slip Coefficient in High-Strength Bolt Joints Coated with Corrosion-Resistant Zn/Al Metal Spray Method

Abstract: In high-strength bolted joints, it is known that the corrosion of base material causes the reduction of slip resistance. In this article, tensile tests on slip-critical joints utilizing Zn/Al metal spraying corrosion resistance method, which can prevent corrosion and meet the required mechanical characteristics of bolted joints, were carried out. In addition, slip coefficient and surface roughness were calculated. The key parameters of specimens were surface finishing condition and thickness of coating with the identical geometry in all specimens. It is found from the results that the slip coefficient of the joints with coated finish after sand blast treatment as well as those of noncoated joints with only sand blast treatment were similar or superior to 0.45, which is a specification criteria of slip coefficient in friction-typed joints.

Curved surface finishing processing device

Abstract: The invention relates to a curved surface finishing processing device which is equipment for surface processing, in particular to a processing device using flexible shafts and surface processing tools to finish or smoothen a processed three-dimensional curved surface, belonging to the field of mechanical engineering and aiming at changing the traditional processing way finishing the surface of a plane workpiece by driving the tool by a rigid shaft and providing a solving scheme for the finishing processing of the three-dimensional surface of the workpiece. The curved surface finishing processing device comprises flexible shafts, flexible shaft support mechanisms, the surface processing tools, a support frame, a base and a work table and is characterized in that the flexible shafts (1) areone group or a plurality of groups, each group of flexible shafts (1) are provided with a plurality of the surface processing tools (3), the flexible shafts (1) are arranged on the support frame (4) through a popularity of the flexible shaft support mechanisms (2), and axes of the flexible shafts (1) are passively bent following the surfaces of workpieces (5) to be processed.

Suppressed Superconductivity on the Surface of Superconducting RF Quality Niobium for Particle Accelerating Cavities

Abstract: Significant performance degradation of superconducting RF (radio frequency) niobium cavities in high RF field is strongly associated with the breakdown of superconductivity on localized multi-scale surface defects lying within the 40 nm penetration depth. These defects may be on the nanometer scale, like grain boundaries and dislocations or even at the much larger scale of surface roughness and welding pits. By combining multiple superconducting characterization techniques including magneto-optical (MO) imaging and direct transport measurement with non-contact characterization of the surface topology using scanning confocal microscopy, we were able to show clear evidence of suppression of surface superconductivity at chemically treated RF-quality niobium. We found that pinning of vortices along GBs is weaker than pinning of vortices in the grains, which may indicate suppressed superfluid density on GBs. We also directly measured the local magnetic characteristics of BCP-treated Nb sample surface using a micro-Hall sensor in order to further understanding of the effect of surface topological features on the breakdown of superconducting state in RF mode.

Method for protecing surface using decoration sheet

Abstract: PURPOSE: A surface finishing treatment method using a decoration sheet is provided to hold excellent moldability capable of easily applying to complex shaped products. CONSTITUTION: The surface finishing treatment method using a decoration sheet is as follows. The decoration sheet for surface finish treatment includes a molding and releasing layer(200); an UV hardening resin layer(210); a printing layer(220); an adhesive layer(230); a releasing film layer. The releasing film layer of the decoration sheet is removed, and the adhesive layer is attached to the surface of a molding body. The UV hardening resin layer hardens. The molding and releasing layer is removed.

Study on Thermomechanical Treatment, Mechanical Properties and Fatigue of Nitinol Superelastic Thin Sheet

Abstract: A wide range of different thermomechanical treatments was performed on commercially available superelastic Nitinol thin sheet. The ingot composition in the range of standard superelastic material with about 50.8 at.% Ni, balance Ti, was used to manufacture a series of samples with different thermomechanical conditions. Production parameters such as cold work, heat treatment temperature, and heat treatment time were varied. All finished samples were of the same final thickness of 0.3 mm and received the same industrial surface finishing process to obtain a smooth, defect, and oxide-free, shiny surface. Before carrying out the laser cutting, the material was characterized by tensile testing, DSC, and bend-and-free recovery test. Miniature dogbone specimens were cut from the as-manufactured sheets in both directions, longitudinal as well as transverse to the rolling direction. These samples were surface finished using standard deburring and electropolishing processes. For some specific parameter combinations, there were also samples taken at 45° to the rolling direction. All qualified samples were then exposed to fatigue testing in a bending mode until fracture or run-out. The results showed there is a significant effect on the fatigue performance of the samples from both the applied thermomechanical treatment as well as the sheet anisotropy. It is also obvious that the achieved strain data is on average lower than the data obtained in comparable studies on tube or wire, which can be attributed to the different test setup (bending mode in air at 37 °C) as compared to most other studies as well as the larger surface.

Correlation between Mechanical Strength and Surface Conditions of Laser Assisted Machined Silicon Nitride

Abstract: High power fiber-coupled diode lasers for Laser-Assisted Machining (LAM) of ceramics provides an efficient, cost effective solution for surface finishing of ceramic products. This paper presents experimental evidence of advantages of LAM over the traditional diamond wheel grinding, a standard technique currently utilized in the finishing of ceramic surfaces. LAM, utilizing fiber-coupled diode lasers, also provides advantages over other types of lasers such as CO2 and Nd:YAG lasers. The emphasis of this work is in the evaluation of LAM in the strength of finished products of two different sources of silicon nitride. An optical technique based on evanescent illumination was utilized to measure the Ra of the finished surfaces utilizing LAM, laser glazed, diamond ground, and as-received surface conditions. Four point bending test for specimens of each surface condition were utilized to measure the fracture strength. A correlation was found between the measured Ra and the predicted strengths resulting from Weibull analysis. The correlation shows a decrease of strength with the increase of Ra. The fracture surfaces were observed both optically and with a SEM, and the flaw sizes were measured. The analysis of the fractographs indicated that the flaw sizes are consistent with Fracture Mechanics predictions. Explanations of the correlation between Ra, strength, and flaw sizes require further testing.

Accurate layer thickness control and planarization for multilayer SU-8 structures

Abstract: A technique is developed to enable accurate layer thickness control and planarization in a multilayer SU-8 2000 micromachining process, while maintaining a high quality surface finish. Relying on carefully controlled mechanical lapping and polishing stages, layer thicknesses from 30-400 μm have been routinely achieved to an accuracy of ±3 μm with excellent planarity. High-aspect ratio structures (intended for use in a millimeter-wave engineering application) with up to five layers and of 770-μm thickness have been fabricated using this method. The quality of the resulting surfaces has been investigated and characterized using scanning probe microscopy: a typical rms surface roughness of around 10 nm has been measured. The problem of air-bubble formation and migration encountered during the lapping stage has been documented along with a technique for their elimination. It is also shown that the common problem of the expansion of the lower layers in a multilayer structure due to solvent reabsorption can be effectively eliminated through careful process optimization.