CompositesWorld
Issue link: https://cw.epubxp.com/i/891910
NOVEMBER 2017 34 CompositesWorld FEATURE / Reconfigurable Tooling Roundup tolerances during machining and fastening. Designed for a specific aircraft, they are expensive to manufacture, with long lead times (e.g., 24 months) and may account for ≈25% of the total manufac- turing cost. If design changes occur, these fixtures must be rede- signed and remanufactured. One effort to change that equation is the automated flexible fixture tooling demonstrated for the assembly of a hybrid metal/ composite wingbox as part of the EU-funded LOw COst Manu- facturing and Assembly of Composite and Hybrid Structures (LOCOMACHS) project. Led by SAAB Aeronautics (Linköping, Sweden), partners Prodtex (Gothenburg, Sweden and Bristol, UK), Chalmers University (Gothenburg, Sweden), the Manufacturing Technology Center (Coventry, UK) and others achieved project objectives: Manual labor was reduced; geometrical tolerance and variation management were integrated; and the recurring costs of shimming in structural joints — in this case, between the wing cover, leading spar and ribs — were cut by 50%. "e aerospace industry is seeing more variation in products for the future, with shorter development cycles and lower produc- tion volumes," says Prodtex Ltd. director Peter Helgosson. "In these cases, it makes sense to have fewer fixtures that we can easily reconfigure. Right now, each company uses the same basic, heavy steel construction, but with their own methodology. Prodtex set out to make the fixture components very standardized, so it is easier and quicker both to design and to construct." e modular, reusable components Prodtex uses to build recon- figurable fixtures include BoxJoint, Flexapod/Hexapod, ShimBox and TFS Units (Fig. 3, p. 33). Each unit type is manufactured in a set range of sizes and is readily available off the shelf. is reduces cost and fixture lead times to weeks vs. months. BoxJoint beams are used to build the fixture's structural frame without welding. ey may be made from steel, aluminum or composites. ey are joined together using standard plates, bolts and nuts, pulled with high torque to give a rigid friction joint equal in stiffness to a welded joint and can be used to construct myriad configurations. Compared to conventional steel beams, which are formed, heat- treated and then precision-machined per each fixture's specifi- cations, BoxJoint units are less costly. "However, their surface is not precise," explains Helgosson, "so we use ShimBox modules to account for this. We can set the Shim Box in 6DoF and achieve a 0.1-mm tolerance in the fixture. We can handle ±6.0 mm in the frame components." TETRAFIX Flex Support (TFS) units are adjustable, configurable pickups. "Pickups hold the assembled structure to its location points and surface tolerances," explains Helgosson. ey define the fixture's shape. A designer will decide where pickups are needed and how they will hold the assembled structure. "For example, at one location the pickup will hold a component in x, y and z directions," he says, "but at another point, a fixed rotation around each axis may also be required, which means 6 degrees of freedom [6DoF]." "e reason why massive steel frames have been used to hold pickups for the past 70-plus years," says Helgosson, "is because they are stiff and don't move, so that we know where the part is and can ensure proper fit and assembly." However, he contends that with laser trackers and new metrological and computing abilities, "we can very precisely measure where these pickups are, so they can be moved and reconfigured." Given that, Prodtex no longer needed to weld the assembly fixture frame elements. "is then led us to BoxJoint and ShimBox modular elements," Helgosson adds. FIG. 4 CFRP elements for smaller, lighter fixtures The CFRP cradle used in a development assembly fixture for GKN's new STeM composite winglet is an example of Prodtex' Lightweight Structures products. Using CFRP tubes and plates by TETRAFIX, they are smaller, stiffer and lighter than metal alternatives, enabling smaller, faster, more cost-effective robots. Source | GKN Aerospace Source | TETRAFIX