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Experimental study on ECM with a grid cathode composed of circular cells

In order to resolve the problem of single machining object existing in traditional electrochemical machining (ECM) with unitary cathode, a grid cathode composed of circular cells is used to produce the workpieces with different shapes. Three types of circular cells, ??1.5 mm, ??2.0 mm, and ??2.5 mm, are utilized to construct the plane, slant, and blade cathode. The material of the cathode and the anode is CrNi₁₈Ti₉, and the ingredient of electrolyte is 15% NaCl and 15% NaNO₃. The machining balance current and the balance time are acquired and analyzed, the machining process and the workpiece quality are compared between using the grid cathode and the unitary cathode. Moreover, the machining errors and the error reasons of workpiece surface are analyzed. Research shows that the grid cathode can be used to manufacture workpieces with a complex shape, and the workpiece quality is better if the circular cell is smaller. If the circular cell is small enough the workpiece quality is almost equal to it machined by the unitary cathode.     

Characteristics of A356/SiCp and A390/SiCp composites

Aluminum alloy matrix composites reinforced with SiC particles (AMC) are potential materials applicable to weight reduction of friction materials. We developed two AMC: A356/SiC and A390/SiC. 30 ??m and 60 ??m SiC particles with volume fraction of 20% were dispersed in the matrix of A356 and A390 alloys. When the temperature of the liquid alloy was higher than that of the melting point, SIC particles floated up to the surface because of the low viscosity, high surface tension and interfacial energy. To mix the ceramic particles, the aluminum alloy was in the mushy state near the solidus temperature, 610°C for A356 and 645°C for A390. Metallurgical, mechanical and tribological characteristics of the manufactured composites were evaluated.     

Investigation of laser-welded titanium and stainless steel specimens using digital radiography methods

Specimens of ??titanium-titanium?? and ??titanium-12X18H10T steel?? welded joints that were obtained using laser radiation were investigated. When ??titanium-12X18H10T steel?? welded joints were formed, a copper plate was used as the intermediate insert. The digital computer radiography method using phosphorous image plates was used to study specimens; images were read out from image plates using an HD-CR 35 laser reader produced by Durr NDT. Fuji SR and Kodak SO-170 image plates were used in the experiments. The relative contrast sensitivity of X-ray images of specimens that was obtained experimentally was 1?C1.5% at exposures that were two to three times lower than for conventional radiography on an X-ray film. Defects with openings of > 0.1 mm were detected.     

Residual stresses in aluminium alloy friction stir welds

Residual stresses are detrimental to the fatigue, fracture and corrosion resistance of welds. The literature on residual stress measurements in aluminium alloy friction stir welds is reviewed. The results of a large number of longitudinal residual stress measurements performed by the slitting method on friction stir welds in 2024-T3, 6082-T6 and 5754-H111 aluminium alloys are compared and their origin discussed. From the current investigation, it can be derived that the type of machine used for welding has only little influence on the residual stress profile. The influence of alloy type and welding parameters on the magnitude of the residual stresses and the shape of their distribution across the weld is investigated. Their magnitude is far below the room temperature yield strength of the base material. A distribution with an ??M-shape?? is always found on age hardenable structural alloys (albeit more pronounced in 6082-T6 alloy than in 2024-T3 alloy), while a ??plateau?? is found in the case of the strain hardenable 5754 H111 alloy. The low magnitude and the differences in distribution of the longitudinal residual stress are attributed mainly to the microstructural changes in the weld centre and are discussed based on the hardness profiles performed across the welds. The paper also discusses the reasons why those results are in disagreement with a number of numerical simulations from the literature that do not account for the influence of the welding thermomechanical history on the material microstructure and properties.     

Three-dimension surface characterization of grinding wheel using white light interferometer

Wyko NT9300 white light interferometer was employed to measure the surface topography of 60# and 120# alumina grinding wheels. The correlation of wheel topography and its performance was characterized through the employment of three-dimensional (3D) surface characterization parameters. Eight parameters from the ??Birmingham set?? were used to characterize the performance of grinding wheels, in items of grit density, grit sharpness and chip space. The effect of sampling interval on the 3D surface parameters was analyzed and the optimal sampling interval was selected to calculate the 3D surface parameters of grinding wheels.     

Vibrational-shock surface cleaning

Formulas are presented for the stress arising in a vibrational-shock tool and at the surface of the treated object (a pipe, say), the coefficient of impact-energy transfer to the object, the depth of residual plastic deformation at the object??s surface, and the stress in the deposit at the object??s inner surface. A sample calculation is outlined.     

Development of a press-forming technology of the pressboard for a 154 kV transformer

A pressboard consisting of an angle ring and a cap is installed at the primary and secondary coil windings of a transformer. This pressboard is related to transformer durability. Since transformer capacities are increasing, it is necessary to develop a pressboard of high voltage grade (above 150 kV). In this study, a press-forming technology was developed for the pressboard of a 154 kV transformer. To determine the optimum shape of the pressboard, the press-forming factors were experimentally evaluated through the mechanical tensile strength and AC withstand voltage tests under wet conditions. From the results, the optimum size and shape of the pressboard was found to be R15??R20 mm under a forming pressure of 10 MPa. When the relative humidity (RH) was less than 50%, the moisture absorption rate in oil decreased by 25??40% compared to that in air. However, when RH exceeded 50%, the difference in the moisture absorption rate between the cases of oil and air was just 8??10%. The AC withstand voltage of the pressboard was weak against moisture. The average AC withstand voltage at 40°C and RH of less than 50% decreased by about 15% compared to the dried condition, and the maximum value decreased by 30% at 40°C and RH of more than 50%.