Aluminium and aluminium alloys – Elena

“Aluminium” is a term used for both pure aluminium and aluminium alloys.

Pure aluminium is soft, and it often alloy with small amounts of magnesium, copper, manganese, silicon or zinc to improve its mechanical strength.

Cutting of aluminium with CO2 lasers might difficult on account of its high refl ectivity and thermal conductivity. Aluminium alloys, however, are usually somewhat easier to cut than pure aluminium and cutting speed is higher.

Anodised aluminium is also easier to cut. Due to enhanced laser light absorption in the thick surface layer of aluminium oxide. High laser power–over 2kW–and a good laser mode help improve the cutting suitability of aluminium.

A small focal length, of about 63mm (2.5 in), is advantageous for thinner sheets due to the higher power density in the focal spot. We can cut the maximum sheet thickness is about 6–8mm (0.24– 0.32 in).

Both oxygen and nitrogen as cutting gases to cut aluminium.

But cutting speed with oxygen is not signifi cantly higher than with nitrogen. This can be attributed to aluminium oxide’s extremely high melting point, which is 2072°C (3762°F). Solid or viscous aluminium oxide forms a seal on the cut front, which prevents oxygen from penetrating into the metal itself. The oxide seal frequently bursts as a result of turbulent melt fl ow, and the oxidation reaction may still proceed, although at a lower rate.

Low-pressure oxygen-cutting – less than 6 bar (85 psi) – frequently we use it for cutting aluminium nevertheless. We should focuse the laser beam on the upper surface of the sheet. Standard oxygen purity (99.5%) is suffi cient, as higher oxygen purity does not improve cutting speed. The drawbacks of low-pressure oxygen-cutting cutting edges with dross and a rather rough cut surface.

Dross-free cuts can obtain by using high-pressure cutting with nitrogen or oxygen. It appears that nitrogen is the better alternative when cutting aluminium alloys, whereas oxygen is better for pure aluminium. When aluminium cuts with high pressure, the laser beam should focuse close to the lower surface of the sheet. Typical parameters for the cutting of AlMg3 are summarised in Table.