Waterjets are widely used to cut and trim composites and techniques have been developed to trepan and pierce materials without causing delamination or fiber break-out on the exit side. However, using waterjets to mill countersunk holes has not been demonstrated before. This project will use a patented waterjet milling process to show that waterjets can successfully mill countersunk holes in composite materials for airframe structures without damaging the material. The proposed process is robust, reliable, inexpensive and very flexible, cutting holes from as small as 0.060 to inches in diameter, without the risk of heat damage to the material. The process is projected to be much faster than mechanical cutting tool methods and the nozzle wear life is in excess of 70,000 holes. Waterjet equipment already at the Fleet Readiness Centers could be used to cut stand-alone parts and tooling can be developed to drill holes in-situ on aircraft. In addition to carbon fiber products, the process can also be used to cut glass and aramid fiber reinforced product and even cut laminated titanium-graphite materials. The process works on inclined holes and laminated structures that include composites over metal framework.
Benefit: Currently fiber reinforced polymer composites are drilled using diamond coated cutters that have a number of limitations; they can cause fiber damage and delamination, they are relatively slow, particularly if they have to drill through composites with metal backing plates and they suffer from high wear rates caused by the abrasive fibers. The proposed technology, waterjet drilling and milling of composites, is a very different approach that can avoid damaging the composites, is very fast and versatile and doesnt suffer from the wear that shortens tool life. Developing and qualifying the technology for this application would provide an additional method of machining composites for airframe manufacturers and repair and overhaul centers for the Navy. The method promises to be fast and hence inexpensive and should be applicable to a wide variety of geometry and composite types.
Keywords: CFRP, CFRP, Milling, drilling, airframe, countersink, Fatigue, Composites, Waterjet
