Study of the Effect of Tool Wear on Hole Quality in Drilling CFRP to Select a Suitable Drill for Multi-Criteria Hole Quality

In recent years the use of carbon fiber composites in aerospace industries has been on the rise due to their unique properties like high specific strength, high stiffness, and fatigue characteristics. The machining behavior of these materials differs from machining homogenous metals because the drill bit encounters fiber and matrix alternatively which have widely different properties. Among the various machining operations, drilling is very common to facilitate assembly using fasteners to others parts in the structure. Rapid wear of the tool due to the abrasive carbon fibers is an important reason for damage occurrence. This results in frequent drill changes affecting the production cycle and increasing the final cost. Drill geometry is an important factor which decides the quality of the drilled hole. Hole quality is decided by a number of parameters like fiber pullout, delamination, surface finish, etc., among others. It is therefore necessary to evaluate the performance of the different drills available based on the quality of the holes they produce and drill life time. Three tool geometries are evaluated for thrust force, tool wear, surface roughness, fiber pullout, hole oversize, and eccentricity. Recommendations are given to aid in the selection of appropriate drill for the desired hole quality parameter.