Drilling of composites and resulting surface integrity

In aircraft manufacturing there is an ongoing demand for the use of lightweight materials. This is motivated by the ecological requirements for minimized fuel consumption as well as for economic reasons like low operating costs, long maintenance cycles, and large ranges of the aircraft with high passenger numbers (reduction of life-cycle-cost). These requirements are demanding light weight construction materials, and as a result are leading to the need of new manufacturing methods and advanced machining technologies. In this paper results are presented and discussed regarding the thermal and mechanical influence of orbital drilling and conventional drilling processes on the borehole surface layer in aluminum, CFRP (carbon fiber reinforced plastic), and titanium materials (multi-layer materials). Different process parameters were investigated and compared regarding their influence on surface integrity of the borehole. This was accomplished by measuring the cutting temperatures and forces as well as by analyzing micrographs in cross-sectional areas. As an example the investigations reveal that the use of high cutting speeds leads to increasing borehole surface layer damage in the CFRP material.