CompositesWorld
Issue link: https://cw.epubxp.com/i/919214
TRENDS JANUARY 2018 18 CompositesWorld Israel Aerospace Industries (IAI, Tel Aviv, Israel) has produced crashworthy seat struc- tures for aircraft since 1978. Providing design, certification and manufacturing, it has earned a reputation for lightweight seating using composites and also has developed efficient production via RTM. Now it is augmenting both with intelligent automation. "The idea was to implement 'one-shot' technology, manufacturing a part in a single, automated process," explains IAI development program manager Hary Rosenfeld. IAI already had acquired exper- tise in resin transfer molding (RTM) during development of the 2.8m-long, one-piece composite rudder it now produces for the Gulfstream G250 business jet (see endnote). "We know how to design parts for RTM," says Rosenfeld, "but now we wanted to automate the preforming as well." For a test case, IAI selected an in-process composite helicopter cockpit. Designed using autoclave- cured prepreg, the original enabled comparison of part weight and cost vs. the consolidated design using auto- mated preforming and RTM. Design allowables were defined for the two laminates used: a satin weave glass fiber fabric and a satin weave carbon fiber fabric from Hexcel (Stamford, CT, US), impregnated with Prism EP2400 epoxy resin from Solvay Composite Materials (Alpharetta, GA, US), which meets aircraft/rotorcraft flame, smoke and toxicity (FST) require- ments. "The epoxy resin is cured at 180°C to meet strength requirements," Rosenfeld notes, adding, "There are resins that can cure at lower temperatures, such as 130°C, but these have a longer cycle time." A key partner in IAI's development was composites automation specialist Techni-Modul Engineering (TME, Coudes, France). IAI had been working with RTM equipment supplier Isojet (Corbas, France), which then recommended TME for making the RTM tools. Isojet and TME are part of Composite Alliance Corp. (CAC, Dallas, TX, US), which provides composites manufacturing solutions that range from single tooling and equipment to automated workcells and complete turnkey systems (see endnote). After completing the RTM tooling, IAI decided to keep working with TME. "They helped us to define the design and require- ments for the production line and suggested automation possibilities," adds Rosenfeld. In the solution developed by IAI and TME, an automated cutting table and single robot are synchronized via a central control unit. Rosenfeld explains: "The robot picks up plies in a predefined sequence per the design: Two glass fabric plies (face-up and face-down) and two carbon fabric AEROSPACE Automated preforming and RTM cell cuts helicopter seat cost and weight plies (face-up and face-down), which achieve a symmetric laminate." The synchronized system changes the rolls of fabric automatically, as needed, to keep the production line running. Cuts are nested to maximize material usage and minimize waste. The fabric also is coated with thermoplastic powder to aid preform consolidation. The robot then places the cut plies onto a heated mold to achieve a 3D shape. "We have developed specialized end-effectors that oper- ate like hands," explains Marc-Ruddy Thimon, director of sales for CAC. "This allows 2D materials to be folded and formed into complex-shaped areas, like corners." A reusable membrane and vacuum helps to consolidate the thermoplas- tic-coated fabrics into a high-quality preform. The single workcell robot, with end-effector — now changed to trimming head — is then used to trim the preform to achieve a net-shape part. The trimmed preform is manually transferred to the bottom mold in the RTM press. "We apply vacuum and begin resin injection, using the Isojet injection machine," says Rosenfeld. "Both temperature and pressure are increased in the mold, reaching 180°C and a pressure of 6 bar, during a 2-hour molding cycle." Then the mold is cooled to 50°C, opened and the finished part is removed. The overall cycle time, including injection and mold cleaning, is about 7 hours. The resulting seat reduces cost by 30% vs. its prepreg predecessor while maintaining critical strength and crash performance and shaving weight by 7%. The latter, says Rosenfeld, is due to very accurate plies. "We optimized the part design for RTM, so there is not as much overlap in ply location and less material wasted. You also don't have to factor in manual layup errors, so this reduces extra material as well." Source | Israel Aerospace Industries and Techni-Modul Engineering