A composite is a complex material, in which two or more distinct, structurally complementary substances are combined to produce structural or functional properties not present in any of the individual components.
In aerospace composite manufacturing fibers of fibreglass, carbon or Kevlar are combined with resin matrix systems, such as epoxy resins, to form a pre-impregnated material known as "pre-preg". The uncured pre-preg and core is manually applied to shaped molds in a process called "layup". The finished layup is then cured in an autoclave that supplies heat and pressure to produce the composite sandwich panel. Outside excess material is trimmed to the correct shape, and then the parts are inspected, sanded, primed and painted before the final assembly process.
Why Composites?
Composites offer a higher stiffness-to-weight ratio so they can be used to replace higher weight metal components which are typical on today’s commercial jetliners. The lower weight allows for more cargo and passengers to be carried and also helps to reduce fuel consumption, which in turn provides airlines with a more efficient and more competitive product.
Composite Manufacturing
Cloth Cutting
Pre-preg is a primary material required in the manufacturing process. We cut plies, also known as skins, of fibreglass, Kevlar and carbon fibre pre-preg using Computer Numerical Controlled (CNC) cloth cutters. The plies are sorted, collated and then staged for the layup process.
Core
Light weight honeycomb core contributes to the composite panels stiffness and rigidity by separating the face sheets. The core is sliced to the required thickness and then cut and shaped using CNC machining equipment. Some cores require heat forming. Cores are completed by hand work, inspected, and then staged for the layup process.
Layup
Core and pre-preg materials are brought together during the layup process. Layup technicians apply pre-preg skins to a mold of the desired shape. Honeycomb core is then placed on top of the pre-preg skins. Additional pre-preg skins are applied over the honeycomb core. The core is normally chamfered so that the top and bottom plies can come together and create what is known as an edgeband. The edgeband is where holes will be drilled and fasteners will be inserted during assemblys.
Cure
After layup, parts are cured under heat and pressure in an autoclave. The core is now bonded to the cured face sheets and a composite panel is created.
Trim
Parts undergo an edge trim to remove any excess material and give the part a finished edge. Some trimming is done by hand, but the majority is done on CNC trim machines. Often during the trim process, latch and attach holes are also drilled to expedite the assembly process.
Inspection & Non-Destructive Inspection
Inspectors verify that composite panels meet Boeing quality requirements. They confirm that the part’s dimensions meet specification through a series of tests and measurements. Many parts undergo an inspection process in which sound waves are passed through the panels and analyzed to ensure quality and to find possible defects.
Finish & Paint
Painted areas of parts are made smooth via the sand and fill process. A filler compound is applied to each part to fill tiny depressions or imperfections. Parts are sanded to ensure a perfectly smooth surface and good paint adhesion. Parts are then primed and painted. Many parts have a layer of paint that dissipates static buildup.
Assembly
In the final step in the manufacturing process, composite panels are usually joined with frames and other hardware into a sub-assembly.