Composites 101 - An Overview
Dictionary.com defines a composite as complex material, in which two or more distinct, structurally complementary substances combine to produce structural or functional properties not present in any individual component.
In aerospace composite manufacturing, fibreglass, carbon fibre and Kevlar fibre are combined with matrix systems, such as epoxy resins, to form a pre-impregnated material. Parts undergo an autoclave curing process under heat and pressure to produce the solid laminate "sandwich" panel. Parts are trimmed, inspected, sanded and painted before the final assembly process.
Why Composites?
Passengers want to arrive sooner and business wants cargo delivered now. Composites are helping airlines to achieve these goals. Composites offer a higher stiffness to weight ratio, and where cost effective, can be used to replace aluminum, steel and titanium on today's aircraft.
Composite Manufacturing in a Nutshell
Cloth Cutting
Cloth is the primary material required in the manufacturing process. We cut plies, also known as skins, of fibreglass, Kevlar and carbon fibre pre-preg using CNC cloth cutters. The plies are sorted and collated by product and staged for the layup process.
Core
Honeycomb core gives composite panels stiffness and rigidity. We slice core to the required thickness and shape it using six-axis CNC core carvers and finish by hand.
Layup
Core and pre-preg are joined during the layup process. Layup Technicians apply cloth skins to a tool known as a layup mandrel, which is an inverse of the part. Multiple skins are applied to the tool side. Core is then placed on top. Additional skins are applied over the core, much like a "sandwich". Technicians use plastic tools called sweeps to ensure each pre-preg ply adheres perfectly to the next ply, to the core and so that all plies conform to the tool's shape.
Cure
After layup, parts are cured under heat and pressure in a process known as an autoclave cure. During this process cloth plies bond together with the core to become a composite panel.
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 drilled to expedite the assembly process.
Inspection & Non-Destructive Inspection
Inspectors verify composite panels meet Boeing quality requirements. They confirm the part's dimensions meet specification through a series of tests and measurements. Certain parts undergo an ultrasonic non-destructive inspection process.
Finish & Paint
To ensure optimum aerodynamics and esthetics, parts are made smooth through the sand and fill process. A filler compound is applied to each part to fill tiny depressions or imperfections. Excess material is sanded away to ensure a perfectly smooth, aerodynamic finish. Parts are then primed and painted.
Assembly
In the final step in the manufacturing process, composite panels are joined to its substructure to build up the sub-assembly.