Flushing Velocity Observations and Analysis during EDM Drilling

Insufficient flushing is the greatest limitation factor for material removal rate (MRR) in electrical discharge machining (EDM). In order to increase the flushing efficiency during erosion and thus to increase MRR, better understanding of the dielectric distributions and flow directions is required. Additionally the discharge development and its influence to the fluid flow and flushing efficiency must be taken into account. The dielectric flow trajectory can be tracked by high speed imaging with an auxiliary magnification lens. Consequently, flow velocity vectors, bubble development and movement can be analyzed. The flushing behavior is observed with particle tracking velocimetry (PTV), the corresponding data from the measurements are used to compare and validate the computational fluid dynamics (CFD) simulations. This paper describes a setup for high speed imaging in micro meter scale of a common EDM drilling process using electrode with multi-hole flushing. The analysis of the erosion process is performed within two conditions: first, the initial contact of the electrode with the material surface and second, erosion inside a predrilled hole. It is concluded that those two described conditions have a high influence to the flushing and therefore to the MRR, whereas the flushing efficiency drops by an increase of the drilling depth.