What is an extrusion?
The word comes from the Latin words for ‘out’ and ‘thrust’. Metal is forced through a die, engineer-speak for a slot like hole, shaped say, in an L; the metal extruded through the L comes out as an aluminium girder or beam with an L shaped cross section. As pure aluminium is so soft it is useless structurally, Lotus produced an alloy using 1 or 2 percent of magnesium and silicon, giving it a maximum pulling strength of 16 tons per square inch. There are different ways of joining Aluminium alloy beams to form a frame. In Audi’s A8 the body frame is plugged together with special cast aluminium joints. Renault’s Spyder uses welding. The Elise chassis is bonded – glued – using epoxy resin. Bonding metal chassis parts together is the engineer’s dream. In a pressed sheet-steel car it is the equivalent of continuously welding every seam instead of spot welding. Try to pull a spot-welding or riveted seam apart and the stress on the seam is concentrated at each spot instead of being spread arou
