Kinematics and Wear of Novel EDM Tooling

Abstract

Over the last few decades Electrical Discharge Machining (EDM) has become a well established technology that is used throughout the manufacturing sector. In this time, changes in generator technology as well as tool design have brought about a many fold increase in EDM machining rates, particularly in Wire EDM. Yet in Ram-EDM issues with flushing of the inter-electrode gap hinders such improvements to material removal rates. In order to improve the removal rates in Ram-EDM new flushing methodologies are necessary. With this in mind an investigation into novel tooling kinematics, aimed at enhancing inter-electrode gap flushing is presented. Theses novel kinematics are inspired by the Reuleaux Triangle and its ability to machine near sharp comers. This concept is expanded upon in 1)rder to generate tool kinematics, which can machine regular as well as irregular polygons with sharp comers using rotating tools. The curvilinear tooling geometries described in this work are moved along complex orbits which necessitate a 4-axis CNC EDM machining center. Furthermore the slow axis travel speeds on current EDM machining centers presents an obstacle to properly implementing a rapid orbit meant to generating flushing. This problem is obviated in new ED-milling machines, but in the absence of such a machine alternative testing methods were investigated to prove the concept. It is shown that the Reuleaux Triangle inspired tooling machines at constant speed independent of depth, unlike traditional Ram-EDM tools that slow down as greater depths are reached. Thus tr e novel tooling geometries are capable of many fold improvements of machining rates. Ur fortunately these improved removal rates are achieved at the expense of localized tool wear. The novel tooling kinematics result in uneven tool wear patterns that cannot be modded using currently available techniques, thus a new simulation technique is presented. This technique reduces the 3D wear experienced by tools to allow a 2D simulation thereof. A number of examples area shown in order to validate this simulation technique. Due to uneven wear and poor machining rates at low pulse energies, the novel tooling kinematics are deemed unsuitable for finishing operations, but they excel in roughing regimes. It is therefore suggested that the novel tooling be used for the bulk material removal and a conventional Ram-EDM form tool be used to finish the cavity.