Finishing of non-ferrous internal surfaces using ballizing technique

Tubular parts are important in many industrial applications (e.g., joints, fittings, etc.). The internal surface quality plays a role in part performance. Non-ferrous internal surfaces are difficult-to-finish due to many problems encountered in grinding which is optimum for ferrous metals. Ballizing, as a metal deformation process, is believed to be more suitable since it eliminates sticking, wheel dulling and overheating. In this work, finishing of internal surfaces of aluminum using a ball-headed tool was carried out by holding a tubular specimen on the lathe jaw chuck, rotating it and then pushing an oversized steel ball-shaped tool, clamped to the tool post, into the specimen bore. Specimen rotating speeds of 250, 315, 500 and 800 rpm, tool feed rates of 0.078, 0.098, 0.314 and 0.589 mm/rev; and depths of penetration (interference) of 100, 200, 300 and 400 mm were used. Surface roughness (represented by Ra) proved to be improved by the process to an optimum speed, feed and clearance. Such improvement could be explained at the light of the nature of depth of penetration. Outer surface strains were proportional to the depth of penetration and also optimization was observed for both speed and feed. The process gave a stressed and hardened surfaces which represents an advantage.