What Is Laser Cutting

LASER = Light Amplification by Stimulated Emission of Radiation

The original laser, based on stimulating a ruby crystal, was low power. Despite such humble beginnings, laser technology has seen spectacular developments that enable parts to be created that even in 1990 were not easy to make using traditional means.

A laser beam is characterised as being coherent radiation of a single wavelength (also know as monochromatic light). The advantage of monochromatic light is that it will not dissipate its energy as quickly as conventional light beams. It is these characteristics that make a laser beam suitable for the energy transfer needed to cut metals.

Modern industrial cutting lasers are primarily carbon dioxide lasers where carbon dioxide gas is the stimulated medium (as opposed to the original ruby laser), emitting radiation with a wave length of 10.6 micrometre. This is infra-red radiation, which cannot be seen with the naked eye but is a safety hazard to an unprotected eye.

Lasers are adapted to cutting by the process of polarising and focusing a beam of high power laser light onto a work piece. This melts or burns the material along the cut line. To clear the cut and prevent rejoining, a cut assist gas aligned concentrically with the laser beam expels melted materials clean from the cut area. Cut assist gases in common use are oxygen, nitrogen and air. Oxygen is typically used for mild steel cutting. Nitrogen (an inert gas in this process) is used for stainless steel cutting, where it acts to shield the hot stainless steel from oxygen, much like argon is used in welding processes. Both air and nitrogen can be used for aluminium cutting.

The laser beam is directed to the cutting head by specialised water cooled mirrors, where it is focused using a special lens made of zinc selenide. The beam diameter before the lens is about 25mm or 7 watts per square mm. This is reduced to 0.25 mm, or 71,000 watts per square mm, at the focal point where cutting occurs.

The cutting head is coupled to a conventional CNC system which directs the cutting head position according to the computer program controlling the job. A part is created in a computer aided design (CAD) system on a PC, programmed to be run on the CNC.

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