Laser cutting
In laser cutting, we principally distinguish between laser cutting with oxygen and laser cutting with a non-reactive gas like e.g. nitrogen or argon. Cutting quality is exceptionally high here (so-called “laser quality”): precise contours, parallel cutting edges, little roughness of cutting surface, no adhesions (burrs), no caving, etc.
Laser sublimation cutting tends to be used more on non-metals.
Similar to oxy-fuel cutting, in laser cutting the workpiece is heated to ignition temperature directly by the laser beam and then burned in an oxygen jet, see Figure 20. High cutting speeds on sheet metal with thickness between 1mm (0.040 in.) to over 25 mm (1in.) are attained as a result of the exothermic reaction and the additional generation of energy. Laser cutting with oxygen is primarily used for unalloyed and low-alloyed steels. The purity of the cutting oxygen used is reflected directly in the attainable cutting speed.
The energy needed to melt the workpiece must be provided fully by the laser beam in laser cutting with nitrogen, with the non-reactive gas jet merely serving to blow out the melt, see Figure 20. Cutting stainless steel in the thickness range of less than 1 mm (0.040 in.) to almost 20 mm (4/5 in.) and the cutting of other high-alloy steels and nonferrous metals constitute the main field of application. Here, stainless steels are cut with high-purity nitrogen which maintains the corrosion resistance of the material. Certain nitride forming materials like titanium and zirconium can only be cut with argon in argon atmosphere. Mild steel is also cut with nitrogen occasionally if the oxide layer which forms during cutting with oxygen must be avoided e.g. for a subsequent painting or powder coating procedure.
Figure 20: The principle difference between laser cutting with oxygen and laser cutting with nitrogen
Cutting of nonmetals with air has been around for a long time. It has not found many applications with regards to cutting of metals. Main reasons are that, first of all, cut quality is generally inferior to the quality achieved with oxygen and nitrogen, especially when cutting material thicker than 1.5 mm (0.060 in.). Secondly, the lifetime of the focusing lens is generally shortened due to contaminants (oil, moisture, particles) which are always present in shop air. Last but not least, changing air quality would result in frequent parameter adjustments, which are generally disregarded especially if the machine is supposed to run unattended or in a light-out cycle. However, in some cases cutting with air can meet the required cut quality. Nevertheless, thorough calculations should include compressed air (electricity, maintenance, spare parts for the compressor), optics, system shut-down and production failure rate.
The material is vaporized spontaneously in laser sublimation cutting. This method is used e.g. for cutting wood or fabrics. In metal processing, very high intensities, that could only be provided using super-pulse operation, would be needed. The method is only used in special cases due to the low feed rate it is associated with.