INVESTIGATION OF ELECTRO JET DRILLING (EJD) PROCESS

Abstract

This thesis presents the details of electro jet drilling (EJD) process for drilling micro to small holes. Recent progress made in the field of aviation (cooling holes in jet turbine blades), space, automobile, electronics, computer (printed circuit boards, inkjet printer head), medical (surgical implants), optics, and others has created a need for small and micro size holes to be drilled with high aspect ratio as well as in multiple numbers in extremely hard and brittle materials. Electro jet drilling (EJD) process, one of the variants and special method of electrochemical machining (ECM) process, is on such unconventional process, which possesses all the requisite capabilities in meeting the modern day demands of drilling micro and small holes. The work is divided in three parts as (a) fabrication of electro jet drilling (EJD) setup with horizontal and vertical configuration, (b) design, planning, and conducting experiments, and (c) analysis of the results. The electro jet drilling setup with horizontal and vertical configuration was fabricated. Incoloy 800 is used as work material for the investigation of the process experimentally. The experiments were planned and carried out in three phases as pilot experiments, main experiments and confirmation experiments. Pilot experiments were conducted to fix the stand-off distance, electrolyte temperature, electrolyte concentration, and to know the ranges of voltage, pulse-on time, and pulse-off time which were varied in the main experiments. Main experiments were designed using Box-Behnken approach of response surface methodology (RSM) by varying voltage (325-375 V), pulse-on time (30-70 ps), and pulse-off time (30-70 ps) to study their effects on productivity and quality characteristics of holes drilled by electro jet drilling. Metal removal rate (MRR) is the measure of productivity characteristic and depth averaged radial over cut (DAROC), and hole taper are the measures of quality characteristics. Statistical analyses using ANOVA and development of the regression models for the responses were done using statistical software Design-Expert 7.1.6. Voltage and pulse-on time have been found to be most significant parameters affecting all the three responses. Hole profile analysis was carried out for holes obtained in main experiments. It was observed and approximated that the profile of hole is a combination of frusta of a cone. Optimum combination of the process parameters has been found using the desirability analysis. Confirmation experiments have been conducted to validate the regression models and optimum values of the process