Laser processing is more sensitive to material quality than are other processes.
The surface finish can dramatically affect the quality of cutting. In most cases, steel
must be clean, pickled, and oil-free. Impurities on low-grade steel are highly reactive to
the thermal process, especially when oxygen is used as a processing gas. Hot rolled
steel presents serious quality problems in cutting because of the surface scale. The
surface tends to melt in with the metal, creating an undesirable finish. If the material
surface is not smooth, the assist gas and laser focus can be altered, affecting the
quality of the cut [34].
Laser cutting can leave a recast layer on the surface. Because lasers melt and
burn some of the metal, remelted materials are deposited on the side of the cut edges
and on the bottom of the cut. This layer of deposited materials is highly stressed and
may crack, especially if it is an oxide. Although these cracks are small, they can
propagate into the material, creating larger cracks. This is especially true of inside
corners with small radii, where stresses are higher [34].