A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word “Laser” is an acronym for Light Amplification by Stimulated Emission of Radiation. But how does light cut through metal?
The laser beam is a column of very high intensity light, of a single wavelength, or color. With a typical CO2 laser, that wavelength is in the Infra-Red part of the light spectrum, so it is invisible to the human eye. The beam is only about 3/4 of an inch in diameter as it travels from the laser resonator, which creates the beam, through the machine’s beam path. It may be bounced in different directions by several mirrors, or beam benders, before it is finally focused onto the sheet metal. The focused laser beam goes through the bore of a nozzle before it hits the sheet metal. Streaming through the nozzle bore is a compressed gas, such as Oxygen or Nitrogen.
The lens is used for focusing the laser beam or by a curved mirror, and this takes place in the laser cutting head. The beam needs to be precisely focused so that the shape of the focus spot and the density of the energy in that spot are perfectly round and consistent, and centered in the nozzle. By focusing the large beam down to a single pinpoint, the heat density at that spot is extreme.
The high-power density results in rapid heating, melting and partial or complete vaporizing of the material. When cutting mild steel, the heat of the laser beam is enough to start a typical “oxy-fuel” burning 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 high-pressure nitrogen is used to blow the molten metal out of the kerf.
Fiber lasers are a type of solid-state laser that is rapidly growing within the metal cutting industry. Unlike CO2, Fiber technology utilizes a solid gain medium, as opposed to a gas or liquid. The “seed laser” produces the laser beam and is then amplified within a glass fiber. With a wavelength of only 1.064 micrometers fiber lasers produce an extremely small spot size (up to 100 times smaller compared to the CO2) making it ideal for cutting reflective metal material. This is one of the main advantages of Fiber compared to CO2.
CNC lasers, the laser cutting head moves over the sheet metal in the shape of the desired part. It then cuts the part out of the metal. A capacitive height control system maintains a very accurate distance between the end of the nozzle and the metal that is being cut. This distance is important, because it determines where the focal point is relative to the surface of the sheet metal. The cut quality can be affected by raising or lowering the focal point from below the surface, above the surface of the plate, and at the surface of the sheet metal.
When controlled properly, laser cutting is a stable, very accurate, and reliable cutting process.
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For more information about proper laser techniques from industry professionals, you can contact Blackstone Advanced Technologies.