Analysis and Strategies for Five-Axis Near-Dry EDM Milling.

Abstract

Strategies for precision five-axis near-dry electric discharge machining (EDM) milling are investigated. By understanding the material removal process behind near-dry EDM milling, its performance can further be improved using a machine with five degrees of freedom. Three major research areas are investigated: (1) effect of electrode orientation in five-axis milling, (2) the trajectory planning for five-axis near-dry EDM milling, and (3) a new gap control strategy for five-axis near-dry EDM process. Computational fluid dynamics (CFD) model is developed to predict the dielectric fluid flow rate for various electrode inclinations and qualitatively compared with the experimentally measured material removal rate. The study shows that the material removal rate is linearly proportional to the mass flow rate of air and kerosene mixture, the tool electrode wear ratio is inversely related to the mass flow rate of the air and kerosene mixture, and the average surface roughness is not correlated with the flow rate of the mixture. Using the results from the electrode orientation investigation, a tool path planning strategy that maximizes the material removal rate in roughing process is developed. The strategy includes methods to engage into the workpiece, machining of workpiece edge, minimum lead angle for curved surface, and minimum and maximum path interval. Experimental verifications of the proposed path planning strategy yielded higher material removal rate compared with that of standard path planning. A new gap control strategy for five-axis near-dry EDM is proposed and experimentally investigated. The new gap controller retracts the electrode in the direction of electrode orientation. The performance of the new gap controller in term of material removal rate, tool electrode wear ratio and surface roughness is compared with that of a conventional controller. The experimental verification yielded 30% increase in material removal rate while not affecting the tool electrode wear ratio and surface roughness.