Laser Cutting Machine
Sinrad Laser summarize the factors that affect the quality of
cutting: cutting speed, focus position, auxiliary gas, laser output power and
workpiece characteristics! We will give you one by one to analyze:
1. The
effect of cutting speed on cutting quality
For a given laser power density and material, the cutting speed
is in accordance with an empirical formula. As long as the threshold is above
the threshold, the cutting speed of the material is proportional to the laser
power density, that is, increasing the power density can increase the cutting
speed. The power density referred to here is related not only to the laser
output power but also to the beam quality mode. In addition, the
characteristics of the beam focusing system, that is, after focusing the spot
size also has a great impact on laser cutting.
The cutting speed is inversely proportional to the density
(specific gravity) and thickness of the material being cut. (Such as from
high-order mode to low-order mode up to TEM00); reduce the focus spot size (in
the range of 500 to 2 000 W) Such as plastic, plexiglass, etc.); cutting
low-density materials (such as white pine, etc.); cutting thin materials.
In particular, for metal materials, the laser cutting speed can
have a relative adjustment range while maintaining a satisfactory cutting
quality when the other process variables remain constant. This adjustment range
appears to be slightly smaller than that of the thicker width. Sometimes, the
slow cutting speed will lead to the excretion of hot melt material surface, so
that the surface is very rough.
2. The
effect of focus position adjustment on cutting quality
Since the laser power density has a great influence on the
cutting speed, the choice of lens focal length is an important problem. After
focusing the laser beam, the spot size is proportional to the focal length of
the lens. After the beam is focused by the short focal length lens, the spot
size is very small and the power density at the focal point is very high, which
is advantageous for cutting the material; but its disadvantage is that the
depth of focus is very short, Small, generally more suitable for high-speed
cutting thin materials. As the telephoto lens has a wide focal length, as long
as there is sufficient power density, more suitable for cutting thick
workpiece.
The relative position of the focus and the workpiece surface is
particularly important to ensure the quality of the cutting after determining
which lens to use. Due to the high power density at the focal point, in most
cases, the focus position at the time of cutting is just at the surface of the
workpiece, or slightly below the surface. Throughout the cutting process,
ensuring that the relative position of the focus and the workpiece is constant
is an important condition for obtaining a stable cutting quality. Sometimes,
the lens work due to poor cooling and heat caused by changes in focus, which
requires timely adjustment of the focus position.
When the focus is in a better position, the slot is smaller,
more efficient, better cutting speed can get better cutting results.
In most applications, the beam focus is adjusted to just under
the nozzle. Nozzle and the workpiece surface spacing is generally about 1.5mm.
3.
Effect of auxiliary gas pressure on cutting quality
In general, material cutting requires the use of auxiliary gas,
the problem is mainly related to the type and pressure of auxiliary gas.
Typically, the auxiliary gas is coaxial with the laser beam to protect the lens
from contamination and blow away the bottom slag of the cutting zone. For
non-metallic materials and parts of metal materials, the use of compressed air
or inert gas, the treatment of melting and evaporation materials, while
inhibiting excessive cutting of the cutting area.
For most metal laser cutting is the use of active gas (as long
as O2), the formation of hot metal and the formation of exothermic reaction,
this part of the additional heat can increase the cutting speed of 1/3 ~ 1/2.
In the premise of ensuring the auxiliary gas, the gas pressure
is a very important factor. When high-speed cutting of thin materials, the need
for higher gas pressure to prevent the incision on the back of sticky slag (hot
sticky slag to the workpiece will damage the trimming). When the material
thickness increases or the cutting speed is slow, the gas pressure should be
appropriately reduced. In order to prevent the plastic cutting and frosting, it
is also cut with a lower gas pressure.
Laser cutting practice shows that when the auxiliary gas is
oxygen, its purity has a significant effect on the cutting quality. A reduction
in oxygen purity of 2% reduces the cutting speed by 50% and results in a
significant deterioration in the quality of the incision.
4.
Effect of laser output power on cutting quality
For the continuous wave output of the laser, the laser power
size and mode will have an important impact on the cutting. In practice, often
set the higher power to obtain a higher cutting speed, or to cut thick
materials. However, the beam pattern (the distribution of beam energy in the
cross section) is sometimes more important, and the pattern often changes
slightly when the output power is increased. It is often found that a higher
power density is obtained at a focal point that is less than a high power
condition and a better cutting quality is obtained. During the full active life
of the laser, the pattern is not consistent. The condition of the optical
element, the fine change of the laser working mixture, and the fluctuation of
the flow rate all affect the mode mechanism.
In summary, although the factors affecting the laser cutting is
more complex, but the cutting speed, focal position, auxiliary gas pressure and
laser power and mode structure is four very important variables. In the cutting
process, if found that the quality of cutting significantly worse, we must
first check the factors discussed above and timely control.
Sinrad Tech
