Atomized dielectric spray-based electric discharge machining (spray-EDM) for sustainable manufacturing
Electrical Discharge Machining is a non-traditional machining process that is widely used in the tool and die-making industry, automotive, and aerospace industries due to its ability to produce complex three-dimensional geometries with good accuracy and surface finish. Despite the aforementioned advantages, the consumption of a large quantity of dielectric (especially hydrocarbon oils) poses a significant health and environmental hazard including respiratory and skin irritation issues. Further, the disposal of waste dielectric that contains a significant amount of metal particulates poses safety concerns. In order to comply with environmental safety standards, extensive filtration and treatment systems capable of handling huge amounts of dielectric waste need to be set up for their safe disposal. This leads to an increased energy consumption and hence higher operating cost for the machining process. Thus, there is a need to reduce the consumption of oil-based dielectrics without compromising their superior machining performance. Several techniques including dry and near-dry EDM have been developed to reduce the consumption of dielectrics. However, they have poor debris flushing capability. This research seeks to develop a technique that minimizes the consumption of dielectrics and also improves the flushing of debris from the inter-electrode gap. A novel method of using atomized dielectric spray in EDM (Spray-EDM) to reduce the consumption of dielectric is developed in this study. The atomized dielectric droplets form a moving dielectric film up on impinging the work surface that penetrates the inter-electrode gap and acts as a single-phase dielectric medium between the electrodes. It also effectively removes the debris particles from the discharge zone. Single-discharge EDM experiments are performed using three different dielectric supply methods, viz., conventional Wet-EDM (electrodes submerged in dielectric medium), Dry-EDM and Spray-EDM in order to compare the processes based on material removal, tool electrode wear and flushing of debris from the inter-electrode gap across a range of discharge energies. It is observed that Spray-EDM produces higher material removal compared to the other two methods for all combinations of discharge parameters used in the study. The tool electrode wear using atomized dielectric is significantly better than Dry-EDM and comparable to that observed in Wet-EDM. The percentage of debris particles deposited within a distance of 100 micro-meters from the center of EDM crater is also significantly reduced using the Spray-EDM technique. In order to understand and improve the debris flushing phenomenon in Spray-EDM, a model based on Computational Fluid Dynamics (CFD) is developed in this research. The debris flushing in Spray-EDM is investigated by developing models for three processes, viz., dielectric spray formation, film formation and debris flushing. The dielectric spray model developed to study droplet atomization and dielectric spray formation is based on the Discrete Phase Modeling (DPM) approach that solves the force-balance equations of the dielectric droplets in a Lagrangian reference frame. The range of spray system parameters including gas pressure and impingement angle that ensure formation of dielectric film on the surface are identified using this model. The film formation model makes use of the Eulerian Wall Film (EWF) approach to facilitate the mass and momentum transfer from the dielectric droplets to the film formed on the machining surface. This model is especially used, to determine the characteristics of the dielectric film including thickness and velocity. The debris flushing model utilizes the DPM approach to predict the trajectory of the EDM debris in the inter-electrode gap. The flushing ability in conventional EDM with stationary dielectric and Spray-EDM processes is investigated. It is observed that the characteristics of the dielectric film, viz., film thickness and velocity play a significant role in removing the debris particles from the machining region.
Electrical Discharge Machining (EDM), debris flushing, atomized spray, modeling spray, modeling film formation, modeling debris flushing, Spray-Electrical Discharge Machining (EDM)
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign