Poliker won’t reveal details of the proprietary material, but does say it can take the 177☌ autoclave cure temperatures: “It simulates a matched-die tool.” He adds that the mandrel tools are reconditioned in-house, as needed. Made with a carbon fiber composite, the caul exhibits a rough surface finish. The HDF can shape as many as 50 stacked plies, says Poliker, with no intermediate debulking steps: “We were looking to eliminate process complexity, so we form the layups in one shot.” After the prepreg is heated and consolidated in the HDF, a caul is placed over the entire layup, prior to bagging. Made byElectroTherm Industry (Migdal HaEmek, Israel), the static machine (the company also makes moveable versions on carts) is a custom-made, vacuum-forming system, equipped with infrared heating elements and a silicone rubber membrane to heat and compress the composite layups on the tools, prior to cure. The cleanroom is dominated by a hot drape former (HDF). (After forming, the Kapton films are discarded.)įBM’s hot drape forming machine, supplied by Israeli company Electrotherm Industry, deletes intermediate debulking steps, shaping as many as 50 unidirectional plies in one shot, and is credited with accelerating FBM’s layup process prior to cure. This C-forming process is achieved very slowly over a period of 20 minutes. Pressure then will be gently applied to form the laminate, constrained by the two diaphragms over a lightweight tool that accurately represents the inside surface of the spar. This ensures that even the material at the center of the thickest section at the root end is warmed uniformly to the same temperature. The space between the films will be evacuated and then infrared heating will be applied from above the part to raise the temperature to 60☌/140☏ over a period of one hour. To facilitate pulling a vacuum, the layup will be sandwiched between two diaphragms made from Kapton polyimide film, supplied by DuPont Electronic Technologies (Circleville, Ohio). To form the C-section, the preform will be moved from the tape layer to a hot drape former provided by equipment manufacturer Aeroform Ltd. The ATL is able to lay the complex preforms in their developed shapes from unidirectional prepreg, using a 977-2 carbon fiber/toughened epoxy uni tape supplied by Cytec Engineered Materials Ltd. To automate the process, GKN Aerospace has invested in a large ATL with a 20m/63-ft bed, manufactured by MTorres (Navarra, Spain). Grainger emphasizes that these are achievable average rates over a shift, on real parts. At this point, layup rates of 25 kg/hr (50 lb/hr) will be achievable. However, during serial production, the part will be layed up flat, using an automated tape layer (ATL) and subsequently hot drape formed into the C-section shape. Phil Grainger, GKN Aerospace’s technical director and chief technologist, explains that building such a large part manually, as was done on early A400M spars, is slow, with typically a 0.75kg/hr (1.5 lb/hr) lay down rate. Glass-coated magnetic microwires for nondestructive composites monitoring
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