Hypertherm LR2075 - Manual (Page 29)

OPERATION
4-4 LR 2075 Laser Head Instruction Manual
Piercing
Mild steel
To prevent damage to the FAST laser nozzle from molten metal, the nozzle-to-workpiece height must be at least 6 mm
(.24") and the cutting gas pressure must be 1.4 bars (20 psi) or higher. For continuous wave piercing, most pierce times
are less than 2 seconds and create a hole that is approximately 1.5 times larger than the nozzle orifice. When the pulse-
pierce mode is chosen, the nozzle-to-workpiece height must be 6 mm for at least 0.5 sec. to allow the formation of a
small pit in the material surface. This prevents damage to the baffle from the laser beam reflections from the workpiece.
After the formation of a pit, the nozzle-to-workpiece height can be lowered to 4 mm and the focal position can shift to
the workpiece surface. If the focal position deviates from the cutting position by more than 2% of the focal length
excessive damage to the baffle will occur.
Stainless steel and aluminum
FAST laser nozzles are not intended to be used for cutting stainless steel or aluminum with an inert assist gas. Cutting
gas pressures for piercing stainless steel are typically lower than pressures used during cutting to prevent the formation
of a plasma cloud, which will interrupt cutting. 2 - 3 bar (29 - 43 psi) is a typical pressure for piercing stainless.
Additionally, the lead-in for thicker stainless material must be slow until the kerf is well established or a plasma cloud will
form.
Highly reflective material can present a problem during piercing. If inert gas is used, the material will not oxidize and can
remain highly reflective. See caution below.
CAUTION
Highly reflective material can cause the beam to be reflected back through the beam delivery system
when the focus is near the surface of the workpiece, causing a significant increase in laser power
that can cause catastrophic failure of components.