Unified plastic limit analysis of the cap periphery formation in orbital drilling of titanium alloy

The cap geometry and formation mechanism play a key role in influencing the hole-making quality on the bore exit side and must be the focus of research in orbital drilling of aeronautical metal materials. For a “bowl shape” cap geometry formed in orbital drilling process, the corresponding undeformed cap periphery geometry, generated by the cap periphery cutting edges, is simulated and given the parametric description. Especially, the cap periphery is simplified as a simply supported annular plate under uniform load with arbitrary loading radius based on the characteristics of the cap periphery shape and mechanical analysis of processing. Then its unified plastic limit analysis is developed. The ultimate load, stress field, and plastic deformation at the periphery of the cap are derived from the unified strength theory. Furthermore, the numerical solutions are obtained in terms of the Tresca yield, Huber–von Mises, and twin-shear yield criteria. The conclusions enabled an in-depth understanding of the cap periphery formation mechanism in the orbital drilling of holes from the unified plastic limit analysis perspective.