The principle of laser cutting

Lasers serve many purposes. One way they are used is to cut sheet metal. On mild steel, stainless steel and aluminum plates, the laser cutting process has high precision, excellent cutting quality, very small kerf width, small heat-affected zone, and can cut very complex shapes and small holes. Most people already know that the word "LASER" is actually an acronym for Light Amplification by Stimulated Emission of Emission. But how does light penetrate the steel plate?

A laser beam is a train of very high intensity light with a single wavelength or color. In the case of typical CO2 lasers, this wavelength is in the infrared part of the spectrum and therefore invisible to the human eye. As the beam travels through the machine‘s beam path from the laser resonator that generates the beam, the beam is only about 3/4 inch in diameter. It may be reflected in different directions by many mirrors or "beam benders" before it is finally focused on the board. A focused laser beam passes through the nozzle‘s hole before hitting the plate. Also flowing through the nozzle hole is a compressed gas such as oxygen or nitrogen.

Focusing of the laser beam can be done with a special lens or curved mirror, which takes place in the laser cutting head. The beam must be precisely focused so that the shape of the focused spot and the energy density in that spot are perfectly circular and consistent, and centered in the nozzle. By focusing a large beam of light onto a single precise point, the heat density at that point is very high. Consider using a magnifying glass to focus the sun‘s rays onto leaves, and how this can start a fire. Now consider 6 kilowatts of energy concentrated into one spot, and you can imagine how hot that spot would get.

The high power density results in rapid heating, melting and partial or complete vaporization of the material. When cutting mild steel, the laser beam is hot enough to start the typical "oxy-fuel" combustion process, and the laser cutting gas will be pure oxygen, just like an oxy-fuel torch. When cutting stainless steel or aluminum, the laser beam simply melts the material and then uses high-pressure nitrogen to blow the molten metal out of the cut.

On a CNC laser cutting machine, the part is cut from the plate by moving the laser cutting head over the metal plate in the shape of the desired part. A capacitive height control system maintains a very precise distance between the end of the nozzle and the board being cut. This distance is important because it determines the position of the focal point relative to the surface of the board. Cut quality can be affected by raising or lowering the focal point from just above, at the surface, or just below the surface of the board.

There are many other parameters that affect cut quality, but when all are properly controlled, laser cutting is a stable, reliable and very precise cutting process.