Hypertherm HyIntensity Fiber Laser Rev.3 - Manual (Page 147)

setup and OperatiOn
HyIntensity Fiber Laser Instruction Manual – 807090 Revision 3 3-39
Mild steel – air and nitrogen assisted
Cutting mild steel with nitrogen as the assist gas is similar to cutting stainless with nitrogen as the assist gas (refer
to the section below). Air cutting of mild steel can be utilized on thin material [<1 mm (.04 in)]. The air pressures are
typically between those used for oxygen and nitrogen cutting and the resulting cut edge is a little rougher than either
oxygen or nitrogen cutting.
Stainless steel – nitrogen assisted
Stainless steel is most commonly cut with high pressure nitrogen as the assist gas to leave a cut edge that is free of
oxides which would promote corrosion. Typical parameters for cutting stainless steel with a laser place the focus at a
point between the midpoint and the bottom of the plate. Assist gas pressures are usually quite high, ranging from
10 bar (150 psi) for thin material, up to about 18 bar (260 psi) for thicker material. The most common cutting defects
when cutting stainless steel are the formation of plasma which leads to a failure of the cut and well adhered dross on
the part and the skeleton. Because the fiber laser beam can achieve a smaller focus than most industrial CO
2
lasers, the
kerf needs to be wide enough to provide a sufficient assist gas flow to allow the molten material to be expelled. The cut
charts in the CNC can provide a good starting point for optimization of the cutting process.
Piercing stainless steel is quite simple using a method similar to the blast method of mild steel. However, since an inert
gas is used, there is no over-burning of the surrounding material and the material temperature does not impact the
cutting process. The assist gas pressure for piercing is usually lower than the cutting pressure to help prevent plasma
formation during the pierce. After the pierce is complete, a creep process is usually required to establish the cutting kerf
geometry, otherwise the cut can be unstable or lost.
Aluminum – nitrogen assisted
The process of laser cutting aluminum is very similar to stainless steel with a few minor differences. Since the thermal
conductivity of aluminum is higher, cut speeds will be lower for the same thickness material. Also, dross is usually
harder to eliminate by adjusting the cutting process parameters. Luckily it easily removed from aluminum because of the
material softness so minor deburring may be utilized. Assist gas pressures and focal positions are similar to those of
stainless cutting.