Multi-Objective Optimization of PMEDM Process of 90CrSi Alloy Steel for Minimum Electrode Wear Rate and Maximum Material Removal Rate with Silicon Carbide Powder

This study aims to minimize electrode wear (EW) and maximize material removal rate (MRR) in powder mixed electrical discharge machining (PMEDM) process of 9CrSi alloy steel with silicon carbide powder. To achieve these objectives, Taguchi method and Grey Relational Analysis (GRA) are applied to optimize one two-level and four three-level PMEDM process parameters, including Ton, Toff, CP, IP and SV in eighteen experiments based on an orthogonal array L18 (21 and 43). Results have provided a set of optimal PMEDM process parameters in which Ton has the strongest effect on SW and MRR while that of CP is insignificant. The obtained minimum EW and maximum MRR have been verified and proven by a PMEDM experiment using optimal process parameters. The proposed method can be further applied to optimize other PMEDM process parameters for different objectives.

Complex elements of aerospace equipment from reaction silicon carbide ceramics

The results of studying the process of obtaining complex-profile elements of the substrate of mirrors of optical telescopes from reaction-sintered silicon carbide ceramics are presented. It is shown that the strength of silicon carbide ceramics depends on the dispersion of the silicon carbide powder and on the temperature of reaction sintering. An increase in the sintering temperature from 1500 to 1650 °C leads to an increase in strength by 60 MPa, and to 1800 °C – to a decrease in strength by 40 MPa. An increase in strength is explained by a decrease in free silicon and an increase in the content of secondary silicon carbide, a decrease in strength is explained by an increase in the size of carbide grains. The study of the influence of the modes of soldering of hexagonal elements to obtain a complex-profile element of the substrate of the mirror of an optical telescope on the strength of the soldered seam showed that the introduction of silicon carbide powder 7 μm in size and amorphous boron in an amount of 6 % into the solder composition based on silicon carbide has a positive effect on the strength of the soldered seam. Tests of the brazed specimens at three-point bending showed that fracture occurs along the body of the specimens being brazed, and not the brazed seam. The structure of the brazed joint depends on the composition of the braze alloy and the gap between the samples to be brazed.

Applications of Membrane Hydrocyclone Recovery of Silicon Carbide Powder

This work investigated the possibility of using membrane hydrocyclone as a separator to recover the silicon carbide powder. The weight percentage of silicon carbide powder is 62.9%. Classifying these powders by a 2.5 cm-diameter hydrocyclone that equips membrane tube in the center position, overflow and underflow are obtained. The results of the primary separation show that the overflow and underflow are about half of the proportion of solid, but silicon carbide powder content in the overflow is higher. Therefore, it is necessary to consider the recovery of silicon carbide powder contained in the overflow.