Key Engineering Materials Vols. 364-366

Abstract: In this paper, a novel parallel mechanism (3-RRRS/UPR) used in flexible fixture with configuration composed of two parallel robots (2-RR and 3-RRRS/ UPR) is presented. First, system modeling including the mobility study is conducted. Then a novel methodology is proposed that makes use of screw theory to analyze the deformation and stiffness of the mechanism: firstly we identified the existence of the deformation of the subchain, in terms of the relationship between the effective screw and deformation screw; then we took the deformation as an infinitesimal motion of the mechanism, and the stiffness matrix corresponding to the deformation can be deduced. Finally the global stiffness matrix of the whole mechanism is modeled by assembling different stiffness characters based on the presented methodology.

Abstract: This paper describes the performance of Ni-P and Ni-Mo-P alloy coatings deposited by electroless plating on the aluminum alloy 5052 to evaluate the corrosion resistance, thermal stability and electro-conductivity of coating assemblies. Corrosion behaviors of the obtained deposits in a 0.5M H2SO4 environment were investigated. The crystalline state and morphologies of Ni-P and Ni- Mo-P alloys were examined by field emission scanning electron microscopy (FE-SEM). The experimental results indicate that the Ni-Mo-P coating operated at 70°C and pH 9.0 has a nanocrystalline structure and its corrosion resistance in a 0.5M H2SO4 environment can be enhanced by the co-deposition of Mo as compared to Ni-P films. It has also been found that the Ni-Mo-P ternary alloys reveal good thermal stability after annealing at 400°C. Based on the excellent performance of Ni-Mo-P ternary alloys, these alloys have a potential to be applied to precision mould, optical parts mould, and surface metallization of substrates.

Abstract: As there are always certain defects on the final surface of large-scale lightweight mirrors, which are formed in traditional mechanical polishing process, such as microcracks, lattice disturbances, plastic deformation, and so on, an atmospheric pressure plasma polishing method is a good solution to this problem. As a key component, the design of the capacitance coupling atmospheric pressure radio-frequency plasma torch is introduced. The designed torch uses water cooled coaxial aluminium electrodes with special treatment to avoid arcing between them. In normal machining process, the mixture of reaction gas and plasma gas with optimum ratio is input into the plasma torch. Then, excited by radio-frequency power, reaction gas is ionized in the plasma so as to create high density and energy reactive radicals under atmospheric pressure. The radicals cause chemical reactions with the atoms on the part surface, which performs an effective atomscale removal process. As the machining process is chemical in nature, this method avoids surface/subsurface defects mentioned above. Furthermore, initial experiment data analysis has proved that the atmospheric pressure plasma polishing method is effective and reliable, as well as demonstrates the validity of the designed plasma torch.

Abstract: The influence of surfactant CTAB (cetyl trimethyl ammonium bromide) on electrodeposited nickel layer has been investigated in this research. Our result shows that CTAB added in the electrolysis bath can effectively remove the hydrogen to obtain a smoother nickel layer. The effect of CTAB on the surface roughness is also significant. It may be ascribed to the adsorption of CTAB on the electrode surface which results in a hindering effect in the electrodeposition process. Increasing the concentration of CTAB, the grain size of nickel deposit was reduced and the microhardness of the nickel deposit was therefore improved. The hardness of the metal layer can be promoted to 450 Hv when 300 ppm CTAB is added.

Abstract: The deterministic ultraprecision machining achieves accuracy and repeatability not possible using conventional optical machining techniques, greatly enhances product quality, providing a quantum leap in throughput, productivity, yield, and cost effectiveness. The deterministic ultraprecision machining technology, involving various ultraprecision process from turning, flycutting, grinding and polishing to finishing, is usually referred to the following technologies such as single point diamond turning (SPDT), deterministic microgrinding (DMG), magneto-rheological finishing (MRF),computer controlled polishing (CCP), and computer controlled optical surfacing(CCOS),etc. This paper discusses mainly the current state and development trends of the deterministic ultraprecision machining technologies at home and abroad. In addition, the paper also elaborates on the technical features of the various deterministic machining technologies mentioned.

Abstract: In this study, the SiC particles with a mean diameter of 300nm were used to be codeposited with Ni-P base to produce Ni-P-SiC composite coatings by means of the pulse current electroforming technology. The relationship between the SiC particles and phosphorous contents in the composite coatings has been constructed. The wear behavior of the Ni-P-SiC composite coatings was examined by that measurements data including the wear weight loss, the coefficient of friction, and the temperature increments under the wear tests, in which were correlated to the observation and analysis of the worn surface of the composite coatings. Experimental results show that the wear resistance of Ni-P-SiC composite coatings is superior to Ni-P composite coatings, if they are under the same level of hardness. In addition, the wear weight loss of Ni-P-SiC composite coatings is even about 62% less than that of Ni-P composite coatings, if they are based on the same production conditions. Further more, both the hardness and wear resistance of Ni-P-SiC composite coatings are superior to pure Ni coating, wherein its wear resistance is even up to 10 times better than that of pure Ni coating.

Abstract: A profilometer for micro-surface topography measurement is presented. The instrument is based on the scanning white-light microscopic interferometry (SWLMI). A Linnik type interference microscope is used and the interferograms which present changes of surface profile are recorded by a CCD camera. A developed nano-positioning work stage with integrated optical grating displacement measuring system realizes the precise vertical scanning motion during profile measurement. By white-light phase shifting algorism of arbitrary steps, frames of interferograms are processed by computer to rebuild and evaluate the measured profile. Because of the specialty of SWLMI, the profilometer is suitable for both smooth and rough surface measuring. It also can be used for the measurement of curved surface, dimension of MEMS etc. The vertical resolution of the profilometer is 0.5nm, lateral resolution 0.5+m.

Abstract: We have constructed a novel contact stylus profilometer which is, in a certain sense, a combination of a lever system, an x-y stage, a vertical scanning stage and a Linnik microscope interferometer with a spatially and temporally incoherent light source. The system has large measurement range, high precision and small touch force. Its vertical measuring range is ±5 mm with a resolution below 2 nm, and the horizontal measuring range is ±25 mm in x- and y-range with a resolution of 1.25 μm. This paper describes the system and its performance along with results of measuring some samples.

Abstract: The paper proposes a novel time based brightness compensation circuit for LED back light modules. The brightness of LED decays while running under constant current driven condition. We have designed a suitable controller to compensate the driving currents to maintain the brightness. The compensation data were calculated from the relative luminous efficiency – time curve provided by the LED manufacturer and were stored in the microprocessor. -The embedded system used the running time of the LED in the back light module as an independent variable for tuning the driving current. The experiment results showed that the brightness of different operating times’ LED arrays can be held almost the same as the new ones.

Abstract: This article proposes a rapid prototyping apparatus of selective laser sintering for forming silica ceramic green parts. The main differences between the proposed and other RP processes for forming ceramic part are the slurry material used to obtain fine layer thickness and the capability of constructing support structure to increase the dimensional accuracy of the workpiece having an overhang. The RP apparatus developed by us comprises a laser scanning system, a material paving system, and a computer control system. A CO2 laser is adopted to scan over a mixture made of a silica sol and silica powder. The silica sol acts as a binder to gel the silica powder together, which forms a 3D object using laser gelation method. A series of experiments were carried out to obtain the optimal process parameters. An SEM is employed to analyze the microstructure of the ceramic part. It has been found that the smallest layer is of 100 μm thick. The results show that both the accuracy of the material paving mechanism and the optimal process parameters can fulfill the requirements of the RP processes.