Process design for drilling of large diameter holes with cutting simulation

In manufacturing of aircraft structures, large diameter holes are machined during the assembly process, and portable self-feeding drill units are used for machining holes. Because torque becomes large in drilling of the large diameter hole, the drilling operations are repeated with increasing the diameter of pilot hole and drill in steps. The diameter of drills, then, should be determined in terms of the torque limit associated with the spindle speed. This paper presents a process design for drilling of the large diameter holes in a plate of titanium alloy. The cutting simulation is conducted to analyze torque for the diameters of drills with changing the pilot hole diameter. In the force model, a chip flow is interpreted as a stack of the orthogonal cutting inclined at a chip flow direction, which includes the cutting and the chip flow direction. The cutting models are given by the orthogonal cutting data acquired in the cutting tests. The force model is validated with the orthogonal cutting data. A sequential process is designed for drilling of the large diameter holes by referring to the torque limit with the maximum torque obtained in the cutting simulation. The diameters of pilot holes and drills to be employed are determined so that torques are below the torque limit for the spindle speeds. In terms of production rate, the diameters are also optimized to minimum the number of tool changes.