Design of Borer-Rib Type Electrode in Electrochemical Smoothing of Large Holes

This study discusses the electrochemical smoothing and electrobrightening of medium or large holes beyond traditional drilling, boring, turning, or extruding using both inserted and feeding electrodes of borer-rib type for several common die materials. High electrical current is not required when the electrode of borer-rib type is employed to reduce the engaged area for large holes. Traditionally, the hole polishing of a die requires a sequence of complicated premachining or some manual skill. In the current experiment, six types of electrode are completely inserted and connected to both continuous and pulsed direct current, while another six types of electrode are fed into holes using continuous direct current. The design features of the electrodes are of major interest for effective electrochemical smoothing of holes. The controlled factors include the diameter of the electrode as well as the chemical composition and concentration of the electrolyte. The experimental parameters are current density, current rating, electrode design, die material, rotational speed, and feed rate of electrode. For the inserted electrodes, the single-plate electrode performs better than the double-plate electrode, and the single-plate electrode with half borer gives the best polishing effect. Pulsed direct current can slightly improve the polishing effect but at the expense of increased machining time and cost. For the feeding electrodes, the electrode of one-side borer tip with half borer performs the best polishing. It was also found that the electrobrightening after precise boring takes only a short time to make the hole bright, while the electrochemical smoothing saves the need for reaming, making the total processing time less than that required for electrobrightening.