Laser cutting employs a variety of assist gases to aid the cutting process.

The cutting process employed and the material being cut determine the type of assist gas. Either inert or active—that is most suitable for use.

Inert gas cutting (i.e., fusion cutting or inert gas melt shearing), employs chemically inert assist gases. The particular assist gas employed depends on the material’s reactive properties. For example, since molten thermoplastics do not react with nitrogen and oxygen, we can use compressed air as the assist gas when laser cutting such materials. On the other hand, since molten titanium does react with nitrogen and oxygen, argon—or another similarly chemically inert gas. We must use it as the assist gas in laser cutting applications involving this material. When laser cutting stainless steel via the inert gas cutting process, it is typically use the nitrogen as the assist gas. This is because molten stainless steel chemically reacts with oxygen.

When laser cutting material via the reactive melt shearing process.

An active (i.e., chemically reactive) assist gas—typically oxygen—is employed to accelerate the cutting process. In inert gas cutting, only the energy of the laser heats, melts and evaporates the material. In reactive gas cutting the reaction between the assist gas and the material creates additional heat which aids the cutting process. Because of this exothermic reaction, reactive gas cutting typically requires lower laser power levels to cut through a material. Compared to the power level necessary when cutting the same material via the inert gas cutting process.

The cutting pressure of the assist gas employed is determined by the cutting process employed and the properties and thickness of the material being cut. For example, polymers typically require gas jet pressures of 2–6 bar during the inert gas cutting process. While stainless steel requires gas jet pressures of 8–14 bar. Accordingly, thinner materials also generally require lower pressures, and thicker materials generally require greater pressures. In oxidation cutting, the opposite is true: the thicker the material, it requires the lower the pressure and the thinner the material, it requires the higher the pressure.