Improvement of Surface Quality for Titanium Alloys During Counter-Rotating Electrochemical Machining Using an Auxiliary Cathode

Abstract

Counter-rotating electrochemical machining (CRECM) is an innovative ECM method that can be used to manufacture revolving parts, especially titanium alloy casings. Because titanium alloys are easily passivated metals, sufficient electrical quantity is required to achieve the transition from pitting to smoothing with a lower speed. However, a low rotational speed means more material is removed in a machining cycle, which is not conducive to wall thickness control. Therefore, achieving fast smoothing at a relatively high rotational speed for titanium alloys is focused. In this paper, the proposed methodology applies an auxiliary cathode to accelerate the transition from pitting corrosion to smoothness of titanium alloys at a relatively high rotational speed. Experimental results show that titanium alloy can be smoothed regardless of rotational speed with an auxiliary cathode. The auxiliary cathode can weaken the off-current density region and accelerate the breakdown of the oxide layer, and the layer-by-layer dissolution of micron-thick materials is achieved at a relatively high rotational speed. The grid-like convex structure is produced at a relatively high rotational speed with an auxiliary cathode, and the surface roughness is 1.808 μm. This fully demonstrates the reliability of the auxiliary cathode for achieving the smoothness of titanium alloys.