Surface Integrity of Holes Machined by Orbital Drilling of Composites with Single Layer Diamond Tools

Orbital drilling of composites was investigated to observe hole surface integrity in terms of surface roughness, delamination, surface burning, and geometric accuracy. Experiments were conducted with a brazed single layer diamond tool of ball-end geometry to drill 220 holes. Cutting forces and temperatures were measured. Micro-observations were made of the hole surface. The results showed that the forces increased sharply during drilling of the first 44 holes followed by a gradual rise. Part temperatures varied between 98-184°C. Surface roughness Ra varied from 13-17 μm. Almost 99% of the holes were drilled without exit delamination; however, 2.3% of the holes showed entrance delamination.