It used to be a costly, time-consuming operation: drilling holes and driving rivets to attach nameplates to the cast aluminum housings of commercial electric motors. There was always the danger of chips getting into the motors, and drill bits would invariably break off in a casting.
Raytheon Aircraft of Wichita, KS, has added 2 more Viper FPS-3000 CNC fiber placement systems from Cincinnati Machine. The company will also add 2 more systems in 2001. The Viper machines automate production of the industry-first composite fuselages for the new Raytheon Premier I and Hawker Horizon business jets. The Raytheon fuselages are the largest CNC fiber-placed structures in the world, with over 80 miles of composite fiber tow in each fuselage.
According to Hansel Tookes, CEO of Raytheon Aircraft, the automated fiber placement systems "allow us to build complete fuselages in a fraction of the time required for similar metal structures, along with vastly reduced part counts, simplified assembly, reduced maintenance, and compelling size and performance advantages."
Fiber placement was one of the enabling technologies Raytheon used to reduce total parts on the Premier I by more than half -- from 16,000 parts to 6,000 -- compared to conventional construction, say Raytheon officials.
The new Viper systems are 90 ft long and accommodate longer mandrels for the spacious Hawker Horizon, which will seat 8-13 passengers. The Premier I fuselage is formed in 2 composite sections that are then bonded together, while the larger Hawker Horizon will be assembled from 3 fuselage sections. The mandrels are mounted in line for sequential lay-up, enabling one ship set to be produced per cycle.
It takes just 4 people less than one week to produce both sections for a Premier I fuselage on a Viper FPS. Each mandrel (mold) provides the basic shape of a fuselage section. The mandrels are mounted horizontally in the Viper FPS and rotated. The FPS places 24 tows of 1/8 in. wide carbon fiber preimpregnated with epoxy over a rotating mandrel in multiple plies to first form the interior wall. This is covered with a layer of Nomex honeycomb core, then the Viper lays the exterior skin. The final ply on the outer surface is a hybrid fabric of carbon fiber and fine metallic wires to provide lightning strike protection.
Plies for the interior and exterior layers are laid at various angles to the previous one to maximize strength. The Viper FPS automatically maintains tow placement accuracy to less than 0.1 in. while performing laydown at speeds up to 1,200 ipm. Automated fiber placement allows the creation of tapered geometries, concave and convex surfaces, and small radii and cylinder shapes. Start/stop tow control creates precision openings and edges, minimizing the need for subsequent trimming and hand finishing.
The near-net-shape parts greatly minimize scrap and subsequent machining. With CNC fiber placement, only 5% of the carbon fiber materials is lost as scrap, according to Raytheon. By comparison, it experienced scrap rates of 50% and greater -- on material costing 10 times more per pound than aluminum -- with hand lay-up methods used on a first-generation carbon fiber aircraft.