Research on the efficient and stable sinking electrical discharge machining ablation process of Ti-6Al-4V

When machining Ti-6Al-4V, electrical discharge machining ablation (EDMA) using a pure oxygen medium can greatly improve the relatively low machining efficiency in EDM, especially when machining a deep-type blind hole. However, Ti-6Al-4V is prone to an explosive phenomenon in the process of ablation, which makes stable processing unsustainable. In this paper, the relations of this phenomenon to the oxide layer and to oxygen concentration were revealed by analyzing the formation process of the surface oxide layer, the explosion mechanism, and the oxygen diffusion mechanism. The results show that high-concentration oxygen enters the alloy substrate through the broad and deep crack channel on the oxide layer, inducing an explosion phenomenon given the high temperature of the discharge. To reduce the oxygen concentration and the crack width and depth, nitrogen is added to the oxygen medium, which prevents the oxygen from entering the matrix and allows stable processing. Experimental results showed that the crack width and depth increase with the increase of the oxygen concentration. Stable and efficient processing can be achieved when the concentration ratio of oxygen to nitrogen is 5:1, and the machining efficiency is more than 8 times higher than in the air medium. Finally, a deep-type blind hole with a deep diameter ratio of 10 was machined continuously and stably.