Hypertherm LH2100 - Manual (Page 31)

1
OPERATION
4-4 LH2125/LH2100 Laser Head Instruction Manual
Piercing
Mild steel
To prevent damage or spatter adhesion to the nozzle, the nozzle-to-workpiece height must be a minimum of 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 diameter. When the
pulse pierce mode is chosen, the nozzle-to-workpiece height needs to be 6 mm for at least 0.5 seconds 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. The focal position cannot deviate from the cutting position by more than 2%
of the focal length or excessive damage to the baffle will occur.
Stainless steel and aluminum
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 to 3 bar (29 to 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.