Study on the Movement Rule of Discharge Products in Large Area Titanium Alloy Machining by Electrical Discharge Machining

In a large area titanium alloy machining by electrical discharge machining, the discharge products are easily to gather together and not easily cooling. It will generate concentrated discharge, arc discharge, short circuit phenomenon, and even burn the surface of the work piece. In order to achieve sustained and stable normal spark discharge, the location of the discharge point in the process must be evenly distributed. Bubble and debris produced by the discharge is a key factor influencing the distribution uniformity of discharge point. Therefore, the law of bubble motion is analyzed by computational fluid dynamics software Fluent, and then its reliability is verified by observing the EDM gap phenomena through a transparent electrode from the direction normal to the machining surface using a high-speed video camera. The result shows that the bubble motion in the gap goes through the process of expansion, contraction and rupture. The diameter distribution and quantity of processed debris generated by the pulse discharge are studied through experiments, and a reasonable assumption about the scatters mechanism of debris particles in the discharge moment is made. The three-dimensional model of gas-liquid-solid mixed phase in the inter-electrode gap flow field is established, and then the influence of the bubble on the debris movement is analyzed by simulation. The study finds that the bubble in the initial stages promotes the motion of the debris and the debris gradually are far from the discharge location while the bubble expanding. Velocity of the debris fall rapidly after through the boundary of the bubble into the working liquid, and the debris gradually are close to the discharge location while the bubble contracting. Therefore, the size of the bubble and the distribution of debris particles could be controlled by changing the processing parameters, which can effectively avoid the concentration of discharge and finally improve the uniformity of the discharge. © 2017 Journal of Mechanical Engineering.