EFFECT OF WIRE-EDM CUTTING ON FATIGUE STRENGTH OF AZ61 MAGNESIUM ALLOY
Effect of wire electrical discharge machining (wire-EDM) cutting on fatigue strength of an extruded AZ61 magnesium alloy at room temperature was investigated. The surface condition of the samples after the wire-EDM cutting process is compared to the samples which have undergone careful polishing on their surfaces. A series of high cycle fatigue tests are performed on both the wireEDM as-cut and polished samples with constant amplitude stress at the frequency of 10 Hz. Fractographic analyses were conducted on the tested samples to identify the mechanism of fatigue fracture. The finding show that the fatigue limit of wireEDM as-cut specimen is 20 MPa lower as compared to smoothly polished specimens. Fatigue cracks are found to initiate and propagate to final failure from a cutting pit on the wire-EDM as-cut specimens.
Experimental investigation on effects of machining parameters on the performance of Ti-6Al-4V micro rotary parts fabricated by LS-WEDT
Abstract The low speed wire electrical discharge turning (LS-WEDT) is firstly proposed to fabricate the Ti-6Al-4V micro rotary workpiece in this study. The surface quality, sub-surface damages and machining efficiency of LS-WEDT process are discussed. The single factor experiments and orthogonal experiments are respectively conducted to analyze effects of speed parameters and peak current on surface roughness (Ra), material removal rate (MRR), surface morphology and the white layer of the TC4 micro rotary workpiece machined by LS-WEDT. Experimental results indicated that the most important factors affecting the Ra and MRR in LS-WEDT respectively are the peak current and feeding speed, and the rotating speed and feeding speed have significant interactive effect on Ra and MRR. Besides, the low feeding speed can cause surface burning and the high rotating speed will elongate craters. Furthermore, the surface oxidation of TC4 workpiece machined by LS-WEDT is far more serious than the surface alloying and Ti 3 O and Ti 6 O can be detected on the machined surface. Moreover, the serrated white layer can be observed and gradually becomes continuous and thin with the decrease of peak current. Finally, large amounts of oxygen and less copper elements can be detected on the top of the white layer and longitudinal cracks.
Numerical and experimental investigation on air distributor design of fluidized bed reactor of sawdust pyrolysis
Abstract An improved biomass conversion in a lab-scale fluidized bed reactor (FBR) is achieved by optimizing the air distributor orifice size and number. Two approaches for introducing air were numerically and experimentally examined. These included perforated plate and downward orifice sparger. 3 mm and 5 mm orifice diameters, and 7, 9 and 13 holes were simulated at flow velocities of 2, 4, 6, and 8 times the minimum fluidization velocity, Umf. The simulation results revealed that increasing the orifice number has a positive effect on gas holdup, particularly for the perforated plate, which showed a uniform distribution of bubbles. The sparger configuration produced larger bubbles sizes, which could lead to better recirculation of solid flux, while stagnant particle zones were observed at the lower section of both distributors. A pyrolysis unit is also inserted at the top of freeboard of the FBR. For perforated plate with 6Umf, the pyrolysis process achieved thermal and cold gas efficiencies of 82.91% and 52.03%, respectively, while combustible gases with 41.6%mol CO, 8.7%mol CH 4 and 2.17%mol HC, were obtained. For sparger pipe and 6U mf _sp, 35.33 ppm NOx and 111 ppm SO 2 were measured in flue gas from combustion process at bed region.