Sorbo, N. and Dionne, J., "Dry Drilling of Stackup Composite: Benefits of CO2 Cooling," SAE Int. J. Aerosp. 7(1):156-163, 2014, doi:10.4271/2014-01-2234.
The use of composite materials and composite stackups (CO-Ti or CO-Al) in aerospace and automotive applications has been and will continue to grow at a very high rate due to the high strength and low weight of the materials. One key problem manufacturers have using this material is the ability to efficiently drill holes through the layers to install fasteners and other components. This is especially true in stackups of CFRP and titanium due to the desire of drilling dry for the CFRP layer and the need for cooling when drilling the high strength Ti layer.By using CO2 through tool cooling, it is possible to protect both layers. Through work supported by the National Science Foundation (NSF) and Department of Energy (DOE) it is shown that CO2 through tool cooling productivity can be significantly increased while maintaining required hole tolerances in both the composite and Ti layers. Improvements in tool life have been demonstrated when compared to either emulsion or dry drilling. By providing dry CO2 cooling through the tip of the drill, resin binders in the CFRP don't soften, and cool Ti chips don't degrade the composite at either exit or mid-levels. The summary of this paper is that when drilling stackups of composite material, oil-free, CO2 through tool cooling provides significant benefits over other types of cooling or lubrication.