How Does Laser Cutting Work?

An Introduction To Laser Cutting Technique

What Is Laser Cutting?

It is the process of cutting materials using a laser beam. Based on the requirement, laser beam can help trim down the material or cut the material into complex shapes that conventional drills would otherwise struggle with. A laser cutting machine can also be used for drilling and engraving materials. Laser cutting technique is considered very versatile as it can cut a vast range of materials with varying thicknesses.

Why Lasers Are Used For Cutting

Lasers are used for many purposes. One way they are used is for cutting metal plates. On mild steel, stainless steel, and aluminum plate, the laser cutting process is highly accurate, yields excellent cut quality, has a small kerf width and small heat affect zone, and makes it possible to cut very intricate shapes and small holes.

Most people already know that the word “LASER” is an acronym for Light Amplification by Stimulated Emission of Radiation. But how does light cut through a steel plate?

How Does Laser Cutting Work?

Beam Generation

The laser beam is a column of very high-intensity light, of a single wavelength, or color. In the case of 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 plate. The focused laser beam goes through the bore of a nozzle right before it hits the plate. Also flowing through that nozzle bore is a compressed gas, such as Oxygen or Nitrogen.

Beam Focusing

Focusing the laser beam can be done by a special lens, or by a curved mirror, and this takes place in the laser cutting head. The beam has to be precisely focused so that the shape of the focus spot and the density of the energy in that spot is 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. Think about using a magnifying glass to focus the sun’s rays onto a leaf, and how that can start a fire. Now think about focusing 6 KWatts of energy into a single spot, and you can imagine how hot that spot will get.

Localized Heating

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.

Beam Movement

On a CNC laser cutter, the laser cutting head is moved over the metal plate in the shape of the desired part, thus cutting the part out of the plate. A capacitive height control system maintains an exactly accurate distance between the end of the nozzle and the plate that is being cut. This distance is important because it determines where the focal point is relative to the surface of the plate. Cut quality can be affected by raising or lowering the focal point from just above the surface of the plate, at the surface, or just below the surface.

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