Eliminating spikes by optimizing machining parameters in electrochemical drilling

Abstract

Electrochemical drilling (ECD) is an important method for producing small holes in difficult-to-machine materials such as titanium alloys and nickel-based alloys. However, the hollow tube shape often generates spikes at the hole bottoms, and these significantly influence the flow uniformity, machining accuracy, and process stability. This paper considers the hole bottom to be spiked, flat, or pitted depending on the equilibrium gap, which can be controlled with the machining parameters of applied voltage and electrode feed rate. Consequently, the spikes can be eliminated with a suitable choice of machining parameters. An electric-field model of ECD is established and the dynamic shaping of holes is simulated. This reveals that the machining parameters affect the equilibrium gap, whereupon the hole bottom shape is determined. Experiments verify the simulation results, and the relationships between the machining parameters (applied voltage and electrode feed rate) and (i) the equilibrium gap and (ii) the bottom shape are plotted. It is found that a low voltage with a high feed rate generates a small gap and a spiked bottom, whereas a high voltage with a low feed rate produces a large gap and a flat or pitted bottom. Finally, three typical parameter groups are selected with which to drill through holes. The machining-current signals at the moment of hole punching and the tool durability indicate that the ECD stability without a spike is better than that with a spike. Optimal parameters are beneficial for eliminating spikes and enhancing the ECD process performance.