Types of cutting processes

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An almost parallel laser beam, which is usually invisible, generate in the laser source and directe to the cutting head by mirrors. Where it is concentrated (focused) by a lens to a small spot (Fig. 1). Depending on the process, we place the spot on the surface of the workpiece or on the material. (Fig. 1, also see the Laser Basics brochure).

The intense light beam quickly heats up the workpiece and melts the material. The assist gas (also called: cutting gas) is applied to protect and cool the focusing lens. And to remove the molten metal from the cut kerf at the same time. There are two cutting processes, depending on the type of assist gas used:

gas

When cutting with oxygen, the material is burned and vaporised after being heated up to ignition temperature by the laser beam. The reaction between the oxygen and the metal actually creates additional energy in the form of heat. Which supports the cutting process. These exothermic reactions are the reason why oxygen enables penetration of thick and reflective materials when we use it as a cutting gas.

When cutting with non-reactive (inert) gases such as nitrogen or argon. The material is melted solely by the laser power and blown out of the cut kerf by the kinetic energy of the gas jet. As non-reactive gases do not react with the molten metal, and no additional heat generate. The laser power required is usually much higher than in oxygen cutting of the same thickness. Cutting with nonreactive gases often referres to as clean cutting or high-pressure cutting.

Vaporisation cutting is another cutting process.

In vaporized cutting, solid materials can directly convertes into steam without passing through the liquid phase. We can use gases to support the process, remove vapour and shield the cutting optics.

In “cold” cutting, the energy of the laser beam breaks the chemical bonds of the material, thereby producing powdery residues. Laser beam energy and chemical bond energy must match, and they often need cutting gas.

Lasers for laser cutting

We can use many lasers for laser cutting, provided their beam can be focused on a small spot with sufficient intensity to melt the material. And the material absorbes their specific wavelength. CO2 and excimer gas lasers as well as solid-state lasers. Such as Nd:YAG and Yt:YAG lasers, we the most commonly use them in the field of materials processing. Diode lasers, as another example of solid-state lasers. Do not provide similar beam quality and intensity and we also use it for the cutting of non-metallic materials.