Laser cutting of steels is divided in three groups: Reactive Fusion Cutting, Fusion Cutting and Vaporization Cutting. These processes differ from each other for needed laser power, gas pressure and process gas. Main principle of laser cutting: Focused laser beam melts material and melted material is removed by blowing it away with gas pressure.
Reactive fusion cutting/Oxygen cutting/Laser flame cutting
Reactive fusion cutting is done with using oxygen as the cutting gas. Oxygen gives additional energy to the cutting with exothermal reaction of the material when heated to above its ignition point. Reactive fusion cutting enables using high cutting speeds and/or thick materials. Cut edge is covered with an oxide layer, this layer must be removed before next work phase.
Fusion cutting
Focused laser beam melts a part of work piece that is about to be cut. Gas blows the material out towards the bottom of it at high pressure. Cutting speeds are much lower than reactive fusion cutting, but quality of cutting is much better. Nitrogen and argon is used as the cutting gas because these gases are inert. Cut edges are oxygen free and don’t need further treatment.
Vaporization Cutting
In vaporization laser cutting the focused beam heats up locally material to boiling point. Only small amount of material melts because the rapid heating to vaporization point. Needed laser power is much higher in this process than other cutting processes. Vaporization cutting is the method with lowest speed, but it is suitable for precise, complex cut geometries in thin pieces.
Acceptable materials for laser cutting
Almost every material that has the properties listed below are acceptable to laser cutting:
• The energy of the laser beam has to be capable of absorption in material, material that in highly reflective or transmissive for the wavelength of the laser beam cannot be cut.
• The energy which has been absorbed to material must be so high that it can melt or boil the material, or keep up the oxygen reaction in reactive fusion cutting.
Mainly four different laser types are used for laser cutting. CO2 – laser and Nd: YAG- laser represents the ”old-school” technique. These lasers are commonly used in manufacturing industry. Nd:YAG is used for accurate cutting in low power range and more robust cutting in power level above 500W. Fiber- and disc lasers are newer laser types and they aren’t yet commonly used in manufacturing industry.
Main characteristics of laser cutting
• Simple to cut different kinds of shapes
• Overall heat input is small
• Good kerf quality can be achieved
• Cutting speed at thin materials are huge
• Kerf is very narrow
Position cutting of pipe