Investigation of Dry and Near-Dry Electrical Discharge Milling Processes.

The dry and near-dry electrical discharge machining (EDM) processes are investigated in this research. Dry EDM uses gas to replace the liquid dielectric fluid in conventional EDM. Near-dry EDM applies liquid-gas mixture as the dielectric fluid. The EDM milling configuration is used to supply the dielectric fluid through a rotary tubular tool electrode. The process is capable to achieve both high material removal rate (MRR) and fine surface finish. Experimental investigation is conducted to achieve high MRR for rough machining. Effect of process parameters, including electrode material, dielectric fluid and discharge parameters are investigated. The oxygen-assisted dry EDM is proved capable to provide high MRR (39 mm3/min) and low tool wear. The mechanism of the enhanced MRR is attributed to the rapid exothermic oxidation stimulated by the oxygen environment and high discharge energy density. The dry and near-dry EDM milling is exploited for the finishing process. The effects of different dielectric fluids, electrode materials and discharge parameters are investigated. Efforts are made to realize a mirror-like surface finish (0.09 µm Ra). Key factors and observations during the ultra fine finishing EDM are discussed. Process planning is conducted to integrate the oxygen-assisted dry EDM roughing and near-dry EDM finishing processes. A model is built for the EDM finishing process to simulate the discharge crater formation on the anode workpiece. A computational fluid dynamics (CFD) package, FLUENT, is used to model the crater formation process. Realistic crater and debris geometry is simulated by the model. Experiments are conducted to validate the simulation. The model supports the experimental findings that the near-dry EDM and low discharge energy is beneficial for better surface finish.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/60725/1/tjstorm_1.pd