Laser Cutting Steel Quality
In this article, we describe edge quality and cut tolerances for steel laser-cut parts from 1/8" to 3/4" thick A36 steel (generic low-carbon "mild steel.")
In general, the edge quality on laser-cut steel parts depends on laser power, assist gas, and laser type (i.e. CO2 or fiber). Our laser is a 3 kW Trumpf Trudisk laser (basically, a fiber laser). The results we show here will give you a good idea what you can expect to see from our laser-cutting machine, but may not represent what all fiber lasers will do, or how all fiber lasers compare to older CO2 lasers.
Note that all of these parts were laser-cut using oxygen assist gas. Nitrogen produces a better surface finish and faster cutting speeds on steel up to 1/4" thick. Thicknesses greater than 1/4" thick require oxygen. You can learn more about the differences between oxygen and nitrogen cuts on our laser cutting with oxygen vs. nitrogen article.
The machine itself has a rated position tolerance of 0.005" over the entire 5' x 10' bed. Neglecting other factors that may affect accuracy (like kerf) the end-to-end length of a part can be expected to fall somewhere within that range. Smaller parts tend to be much better, as will be shown. The laser-cutting head may be off by as much as 0.005" over ten feet, but over a handful of inches, it does a much better job.
All of the test parts shown in this article were 2" x 5". Only the cutting tolerance measurements for the 2" dimension are shown, but at 5" the performance was identical.
Because the beam tends to expand as it passes through the metal, you can expect the part width to be smaller on the bottom of the part, compared to the top. The effect is usually minimal, within one or two thousandths of an inch. At 3/4" thick steel, the effect becomes much larger, as discussed below.
Laser Cutting Edge Quality on 1/8" Thick Steel
Our fiber laser really shines when cutting eighth-inch mild steel. Cutting speeds are high, and usually the edge is pristine. The reflective, glassy edge shown below is the product of an oxygen cut. Some people prefer that finish, but it is less suitable for painting and other finishing operations - the shiny scale may need to be removed before paint will adhere.
Laser Cutting Edge Quality on 1/4" Thick Steel
Laser Cutting Edge Quality on 1/2" Thick Steel
Laser Cutting Edge Quality on 3/4" Thick Steel