Parker Balston - High Quality Nitrogen for Laser Applications
High-pressure nitrogen or oxide-free, assist-gas cutting has, in recent years,
won favor from job shops and OEMs
because of the cut quality achieved when inert gas is used in the laser cutting
process. Parts processed using high-pressure nitrogen are produced virtually
burr-free and do not need secondary grinding operations. Because there is no
oxide layer, the resultant edge is a bright, milled quality that makes for
As laser cutting system capabilities grow, applications for high-pressure
nitrogen cutting also expand. Once considered most suitable for stainless steel
and aluminum, high-pressure nitrogen cutting is now being applied to light gage
mild steel in applications where an oxide layer presents a concern and part
quality is important. In
this overview, we will examine:
1. The high-pressure assist-gas
2. The advantages of
high-pressure laser cutting with nitrogen in stainless steel and mild steel
3. The costs of using nitrogen
as an assist gas.
MAKE THE MOST OF LASER TECHNOLOGY
As more reliable and efficient high-powered lasers are introduced, high-pressure
assist-gas cutting is becoming an economical option for mild-steel processing,
and continues to provide high part quality and burr-free cutting in stainless
steel and aluminum applications
THE CUTTING PROCESS
Nitrogen is the most commonly used inert gas. Other inert gases used in laser
cutting can include argon and helium. Because of nitrogen's stability, it is
commonly used as a high-pressure assist gas, while argon and helium are used for
more specialized material-specific applications. Benefits
oxygen-assist cutting, an inert gas does not contribute to the burning or
cutting process but, rather, shields the cutting front of the material being
processed. During cutting, the inert gas "floods" the area being cut and
essentially starves it of oxygen so that oxide cannot attach to the cut edge,
producing a bright, oxide-free edge.
absence of an oxide layer also makes the nitrogen processed part weld-ready. In
contrast, stainless steel parts cut using oxygen-assist gas must be ground to
remove the oxide layer before welding. If the oxide layer is not removed, the
resulting weld will be structurally inferior due to porosity.
gas will blow molten metal through the underside of the material, preventing
Another advantage to welding parts processed with nitrogen is that the resultant
part edge will have little or no bevel or taper. This is particularly true of
stainless steel in thicknesses from 6.4 to 13 mm. If processed with oxygen, the
edges will have a considerable bevel or taper which will result in a poor fit
during fixturing for welding.
cutting with nitrogen, the inert gas flows into the kerf (The space between the
two cut edges or cutting “trough”) at a very high rate, quickly ejecting the
molten material. The high speed at which this is accomplished does not allow
time for molten material to attach to the part and form a burr (Rough or random
edges). Typical pressures and flow rates in stainless steel from 6.4 to 13 mm
range from 21bar – 26bar (300 to 375 psi) at between 34 to 45 m3/hr.
nitrogen also helps cool the part, minimizing heat penetration or the heat
affected zone (HAZ) size. This is particularly apparent in thick stainless steel
from 4.7 to 13 mm, where the HAZ is most often measured in tens of thousandths
of an inch, as opposed to cutting with oxygen assist, where the HAZ may be as
much as 10% of the material's thickness.
technique employed when high-pressure assist cutting with nitrogen is different
from cutting with oxygen-assist gas. When high-pressure cutting is employed, the
laser's focal point setting must be adjusted into the bottom 10 to 15% of the
material. When cutting with oxygen, the focal point is set at the part's
surface. Driving the focus deeper into the part makes the resultant kerf wider
and allows for optimum ejection of molten material. The wider kerf also allows
for higher gas volume to be pushed into the kerf, creating an optimum shield for
the edge. Nitrogen shields cut edges from oxygen, so an additional process to
remove an oxide is not required. In
addition, high-pressure inert gas cutting requires using a larger nozzle
orifice, 1.5 to 2.5 times larger than nozzles used for oxygen-assist cutting.
This allows maximizing the assist gas column's pressure and volume. The nozzle's
internal geometry is specially designed to allow the assist gas column to attain
a higher velocity.
Nitrogen as an assist Gas for High Pressure Nitrogen Cutting
high-pressure nitrogen cutting usually requires additional specialized operator
training. However, this laser cutting technique offers a cost-effective
alternative for processing stainless steel
parts in thicknesses of 6.4 or 9.5 mm. In the past, thick stainless steel could
only be processed using more labor-intensive and time-consuming processes, such
as milling or EDM.
addition to its cosmetic appeal, a part cut using high-pressure nitrogen gas can
move directly from the laser system to welding operations without additional
nitrogen-cut parts have considerably less taper than parts processed using
oxygen, welding operations are minimized, less fixturing is required, and parts
generally have better a fit. Improved welds also translate to less time spent
polishing parts. One large OEM manufacturer of stainless steel parts reports a
20 to 35% reduction in finishing time and fixturing operations.