Lasers are used for many purposes. One way to use it is to cut metal plates. Laser cutting of low-carbon steel, stainless steel and aluminum sheet is extremely accurate, provides excellent cutting quality, has a very small cutting width and a small area of thermal impact, which allows you to cut very complex shapes and small holes.
Most people already know that the word “LASER” actually means amplification of light due to forced radiation. But how does light cut a sheet of steel?
How a laser cutter works – click to enlarge
A laser beam is a column of very high intensity light with one wavelength or color. In the case of a conventional CO2 laser, this wavelength is in the infrared part of the light spectrum, so it is invisible to the human eye. The beam is only about 3/4 inch in diameter as it passes through the machine beam from the laser resonator that generates the beam. It can be reflected in different directions by a series of mirrors or rays before finally focusing on the plate. The focused laser beam passes through the nozzle hole just before it hits the plate. Compressed gas, such as oxygen or nitrogen, also passes through the nozzle orifice.
Focusing of a laser beam can be carried out by means of a special lens or the bent mirror, and it occurs in a laser cutting head. The beam must be fully focused so that the shape of the focus and the energy density at this point are perfectly round, aligned and centered in the nozzle. By focusing a large beam at one point, the heat intensity at that point becomes very high. Think about using a magnifying glass to focus the sun’s rays on the sheet and how it can cause a fire. Now think about concentrating 6 kW of energy in one place, and you can imagine how hot this spot will become.
High specific power causes rapid heating, melting and partial or complete evaporation of the material. When cutting black steel, the heat from the laser beam is sufficient to initiate the typical process of “oxygen-fuel” combustion, and the gas for laser cutting will be pure oxygen, as in an oxygen-fuel burner. When cutting stainless steel or aluminum, the laser beam simply melts the material, and nitrogen under high pressure is used to blow molten metal out of the cut.
In a CNC laser cutting machine, the laser cutting head is moved by a metal plate in the shape of the desired part, and this part is cut from the plate. The capacitive height control system provides a very precise distance between the nozzle tip and the cutting insert. This distance is important because it determines where the focus is relative to the surface of the plate. Cutting quality can be affected by raising or lowering the focus point above the sheet surface, the surface, or slightly below the surface.
There are many other parameters that affect the quality of cutting, but with proper control, laser cutting becomes a stable, reliable and very accurate cutting process.