SUMMARY

In the aerospace industry, burr removal is an important part of the manufacturing process. Sections of an aircraft are assembled and drilled by hand. Due to extensive burr formation the sheets must be destacked and burrs removed, then the stacks are reassembled and fastened together. If the burrs are minimized in the drilling process, this would reduce the necessity for the sheets to be destacked and deburred. One approach to minimizing burrs is to lower the thrust force in drilling through modification of the drill geometry such as the use of a step drill. Although prior researchers have analyzed different drill geometries and their effect on burr formation in the drilling process through experimentation, no work has been reported on modeling and analysis of the relationship between step drilling forces and burr formation as a function of the geometry. Consequently, this thesis focuses on the modeling of the thrust force and torque for step drills and analyzes their relationship with burr size as a function of the step drill geometry parameters. First, a mechanistic model for thrust and torque in drilling is implemented for a standard twist drill. This model is then adapted to predict the thrust and torque for a step drill. Subsequently, experiments are performed to validate the mechanistic model and to evaluate burr formation with standard and step drills. The influence of thrust and torque on burr formation is analyzed for step drill geometries and experimental feeds and speeds. The results show that the predicted thrust and torque values for both drill geometries are in agreement with measured values. In addition, a reduction in the predicted thrust force for a step drill relative to the standard twist drill is found to correlate well with a reduction in the burr size. However, further reduction in the thrust force by varying the step angle and diameter ratio does not correlate well with the burr size. Likely reasons for this are presented in the thesis.