Enhancement of machinability of titanium alloy in the Eductor based PMEDM process

In this study, an attempt has been made in PMEDM process to sustain the homogeneity in the powder-dielectric mixture irrespective of the nature of the powders, their particle size, concentration etc., The traditional way of powder mixing system in Powder Mixing Electric Discharge Machining (PMEDM) has been refurbished with a novel Eductor based system along with a metering devise to ensure uniform mixing of the powers with the dielectric. Additionally sintered crucible filtration test on the sample of powder-dielectric mixture ensured the presence of known quantity of powders in the dielectric. The experiments are conducted on Titanium alloy with Gap current, Duty factor, Delivery pressure, powder types (Alumina, Silica, and copper) and concentration of these powders as variable process parameters. The output responses, namely material removal rate, tool wear index and surface finish obtained during the machining process have been optimized using AHP-TOPSIS method. The confirmation test indicated that the closeness co-efficient value for the TOPSIS analysis improved by 2.37% compared with the predicted value.

A Theoretical Formula for the Validity Limits of the Dipole Approximation for a Dielectric Mixture

A newly criterion for the validity limits of the dipole approximation for a dielectric mixture was presented, based on the comparison between the dipole approximation and the numerical solutions by the finite-element method (FEM). In terms of this criterion and the dipole-enhanced model, a simple theoretical formula for the validity limits was derived. This formula includes three variables: the dielectric mismatch, the volume fraction of particles and the precision. Its calculated results have a good agreement with the limits determined by the empirical method in the range of our interest, which indicates the theoretical formula is creditable. Using this formula, we can approximate the precision of the dipole approximation for an arbitrary dielectric mixture. And we found that the dipole approximation is acceptable with the precision equal to 30% when the dielectric mismatch is less than 2.3 (εi/ εe2.3) for the almost touching spheres.

Differential Dielectric Sensor Model and its Applications for Water and Oil Flow

As a composition measurement tool, Differential Dielectric Sensor (DDS) developed by Chevron, has been investigated by several authors both theoretically and experimentally since 1989. The previous generation of DDS was based on empirical models which are produced time-consuming and labor-intensive. Uncertainty and repeatability are always issues limiting the application of empirical models. If parameters such as sensor geometries or properties of materials are modified in order to improve and/or optimize, the whole development process of the empirical model has to be repeated. In this paper, measurement model of DDS is developed with integrating 2 sub-models: dielectric mixture model and DD sensor model. The dielectric mixture model, taken from literature, outputs the effective dielectric permittivity of a two-component mixture. The development of DD sensor model is the main focus of this paper. Given effective permittivity provided by dielectric mixture model, DD sensor model predicts attenuation and phase shift of the transmission signal from transmitter to receiver. The measurement model is validated by experimental data and good agreement is observed.