Optimization of electrolyte flow field for electrochemical boring of inner cavity in 07Cr16Ni6 high-strength steel

Abstract

Inner cavity structures are a type of functional feature that can reduce the weight and increase the operating speed of spindles. They have been widely used in the aviation, aerospace, and automobile fields. Since these cavities are located deep inside spindles, boring tool bars need to be designed to be sufficiently long, which results in tool chatter. Moreover, this makes the machining accuracy and surface quality difficult to control. Herein, a new method of electrochemical boring is proposed. In this method, the workpiece rotates around its axis, a long-nozzle tool is linearly fed along the diameter direction, and the entire inner cavity is processed in a single tool-feed operation. In this work, a flow-field model for electrochemical boring was established, and the axial flow-field distribution of the nozzle was simulated. To improve the uniformity of the electrolyte flow field, a nozzle structure with a variable cross section is proposed. An optimized nozzle structure was obtained via the golden-section method. Finally, comparative electrochemical boring experiments with constant and variable cross-section tools were conducted for an inner cavity length of 420 mm in 07Cr16Ni6 high-strength steel with 20 wt% NaNO3 solution. The results indicate that the specimen processed by the optimized variable cross-section tool had higher inner-diameter accuracy. The diameter deviation of the final inner cavity was found to be within ± 0.04 mm, the wall-thickness deviation of the specimen was within ± 0.02 mm, and the inner surface roughness was less than Ra = 0.5 µm. These experimental results verify the effectiveness of the flow-field simulations and the optimization of the cathode structure.