Burnishing Process Using Spherical 5-DOF Hybrid-Type Parallel Mechanism with Force Control

Abstract

This paper proposes a novel diamond tip burnishing process to improve the integrity of various free-curved surfaces using a spherical 5-Degree-Of-Freedom (5-DOF), hybrid parallel mechanism. The developed parallel mechanism, which has high rigidity and a large workspace, is composed of a spherical 3-DOF parallel mechanism and an XY stage, and is equipped with a burnishing tool on its output link. Using a three-dimensional force control system, the parallel mechanism can adjust the thrust force in the burnishing process. The surface roughness and profile of the stainless steel (AISI 316) workpiece, burnished by the proposed method, were evaluated. The surface integrity depended on the values of cross-feed and thrust force, which were controlled by the hybrid parallel mechanism. In addition, the surface roughness improved as cross-feed decreased and thrust force increased. The preliminary surface roughness of Ra = 2.5 μm was improved to Ra = 0.25 μm in the burnishing process of the free curved surface, and homogeneous surface integrity was obtained. The results thus suggest that the proposed burnishing method can achieve a high-quality surface finish, even on a free curved surface.