Laser Cutting Theory
LASER CUTTING PROCESS
Due to its high thermal conductivity and high reflectivity to a C02 laser’s wavelength, aluminium requires considerably higher laser energy intensity in order to initiate cutting compared to steel. This means the need for a laser possessing exceptional beam quality and capable of outputting at least 500 watts, in addition to precise focus control. Due to the reduced coupling efficiency, even 1-2 kilowatt lasers are limited to cutting of thicknesses under 3.8mm.
During the cutting process, the assist gas serves primarily to blow the molten material from the cut zone. This helps to produce edge quality that is generally superior to that produced by a bandsaw. However, the melted material tends to flow along the edge and cling to the backside of the cut. While this slag is easily removable, there are intergranular cracks emanating from the cut surface on some alloys. Concern over the presence of this micro-cracking has prevented the use of lasers for manufacturing structural components such as aircraft.
Copper has less ability than aluminium to absorb energy from a CO2 laser. Due to its high reflectance, copper generally cannot be cut. Brass on the other hand can absorb some energy. It essentially behaves like aluminium with slag adhering to the backside of the cut.
Pure titanium responds well to the concentrated heat energy of a focused laser beam. The use of an oxygen assist enhances the cutting speeds but tends to promote a larger oxide layer along the cut edge. Aircraft alloys such 6AL-4V do tend to exhibit some slag that adheres to the bottom side of the cut but is relatively easy to remove.