CompositesWorld

JAN 2018

CompositesWorld

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JANUARY 2018 32 CompositesWorld PLANT TOUR Moving on, Bausek points out a full DART 450 wing spar struc- ture (two C-spars) in a bonding fixture (Fig. 4, p. 31). e spar is part of a "wet" wing, meaning that aircraft fuel will be stored inside the wing structure, in addition to other onboard fuel tanks. Following this, CW watches as one of Diamond's in-house-built Automated Laminating Machines (ALM, Fig. 5, top left) applies Hexion liquid epoxy to 60-inch-/1.52m-wide carbon fiber lami- nates, which are then cut and immediately applied by a team of technicians that is working on — and in — a large DA62 half-fuse- lage mold. When the technicians are done with layup, the mold will be bagged for pre-cure in a heating room at temperatures around 45°C. Bausek says it takes about 6 hours to lay up one half of a DA62 fuselage. As noted, the manufacturing process Diamond Aircraft employs depends on the part's structural requirements. With vacuum bagging of the laminate material, says Bausek, parts porosity is about 2.4%. More void-free molding processes are used for spars, spar caps and radomes. "Everywhere that we need very low porosity and high quality," Bausek explains, infusion or medium- heated pressure chambers are used, which provides 0.2% porosity or less. After cure, structures are adhesively bonded together. e only bonding paste Diamond Aircraft uses is a modified form of Hexion's legacy epoxy resin. Bausek says this is applied primarily by hand and only occasionally via automated methods. e company, he says, would like to move toward more automated paste application, but that would require a material that has more consistent viscosity characteristics, which is something Hexion is working on. All mating surfaces of all structures, Bausek says, must be easily accessible for external interrogation and assess- ment, which is performed with a BondMaster ultrasonic bond FIG. 5 Automated wet-pregging One of the unique aspects of Diamond Aircraft's composites fabrication opera- tions is the use of this in-house developed Automated Laminating Machine (ALM), which produces wet-preg plies for layup. Although the use of wet-preg limits fabric out time, it reportedly enables production of high-quality, low- porosity structures. Source | CW / Photo | Jeff Sloan FIG. 6 Seven axes of post-mold forming freedom CNC machining at Diamond Aircraft is performed with an HG Grimme SysTech GmbH (Wiedergeltingen, Germany) rotary cutter. It offers 5 axes of freedom at the spindle, with another 2 axes available through manipulation of the part itself. Source | CW / Photo | Jeff Sloan e longest mold in the room is for the main wing C-spar for a DART 450 (Fig. 3, p. 31). It is one of the few resin-infused parts at Diamond Aircraft. Bagged and under preparation for infusion, its process employs a Membrane Tube Infusion (MTI) resin flow promoter (manufactured by DD | Compound, Ibbenbüren, Germany). Bausek says this C-spar represents the company's most complex and labor-intensive layup. "e know-how here is the injection point," Bausek says, "to manage resin flow." FIG. 7 Pre-fit, postcure, paint and final assembly In pre-assembly, composite structures — wings, fuselages, nose sections, tails, horizontal structures, are first fitted together and then postcured. Next steps? Painting and final assembly. Source | CW / Photo | Jeff Sloan

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