There are several factors that affect the laser cutting process. The laser machine itself, the operator, the surface to be cut — every single element plays an important role in regards to the final result of the cut edge finish quality. That being said, the type of the material and its thickness are the two most crucial factors.
The quality of the cut edge depends equally on the material and on its thickness. The thicker the sheet, the more prominent the formed striations. These striations are formed due to the fact that the molten parts of the metal come in contact with the cold parts and the difference in temperature forms these striations. They affect negatively the finish of the cut edge. The thicker the material, the bolder the striations. For example, the following striations are formed from a CO2 laser machine:
These striations are responsible for the tolerance achievable. For example, in steel sheets less than 1.0mm thick, it’s suggested to offer +/- 0.12mm, in 10mm steel the repeatable tolerance would increase to +/-0.25mm and steel at 20mm thick you should be maintaining +/-0.75mm tolerances.
One way to enhance the quality of the the cut edge and to reduce the formed striations is to use higher powered laser machines. By using lasers with higher power beams we are able to cut thicker metallic sheets easier and faster, having a better quality cut edge.
The latest technology advancements and the progress in fiber lasers have bolstered the competition between the all-so-popular CO2 lasers and the newcomer Fiber Lasers. Fiber lasers offer increased cutting speeds in comparison to CO2 lasers while they maintain a higher quality cut edge in the corners and on the material surface.
Nonetheless, the cut edge quality notably decreases the thicker the material is.
The material type covers the largest spectrum of the different factors that affect the laser cut edge, with the most important one the type of the metal itself. Different metals feature different properties and they react in a different manner when they are being machined by lasers.
The composition and the metal mixture at hand play an important role in the cut edge finish. The levels of of carbon, manganese, silicon, phosphorus and sulphur can all have a bearing on the surface quality provided by laser cutting. For example, the higher the carbon content in mild steel the rougher the cut edge will become.
The quality of the material can affect the laser cut quality drastically. It is advised to only use clean metals without rust or other oils. Low quality metals can be proven quite problematic to be cut with lasers. Impurities of low grade metals may cause laser cutting problems and diminish the quality of the end result.
Hot rolled steel is another type of machined metal that is difficult to be laser cut due to its surface scale. There’s a high chance the surface will melt in with the metal itself causing poor quality laser cut edges. The surface needs to be as smooth as possible, free of imperfections otherwise the laser beam focus can be reflected affecting the cleanness and the quality of the cut.
You should try to find “laser grade” or “laser ready” steel which is specifically machined for laser cutting and engraving purposes.