Page 173 - Industrial Cutting of Textile Materials

160 Industrial Cutting of Textile Materials

materials, such as silk and light cotton (10–30 W). The most part of textile materials
may be processed with 60–100 W lasers. However, there are some textiles, for exam-
ple, Aramid (Kevlar), that are processed with 400 W lasers.
To achieve high accuracy on complex shapes, the cutting speed has to be reduced;
thus, laser power also should be reduced. If too much heat is applied to the material,
the sides of the cutlines can burn out increasing a cut kerf. However, there is no direct
relation between high laser power and high cutting quality. Most part of textiles are not
processed with maximal power at minimum speed, but the right proportion of both, in
order to create an accurate edge. Optimization of the material edge melting is always
a serious challenge.

10.4.2 Cutting speed

The cutting speed must be matched to the laser power, the shape of the cut compo-
nents, and thickness, absorption properties, and microsurface of the cut material. For
many applications, the higher the laser power, the higher the cutting speed should be.
Dense materials are processed in higher speed by a higher power laser and vice versa –
in low speed by a lower power laser. When processing thicker materials with the same
laser power, cutting speed has to be reduced. The complex geometry lines have to be
cut in reduced cutting speed to ensure high cutting accuracy.
The cutting speed also depends on processing requirements – the priority for high
speed or high accuracy and desired effects of the cut edges.

10.4.3 Cutting gas pressure
As the cutting gas ensures cleaning of the cutting gap, its pressure has to be precisely
matched to certain cutting process. If the pressure is not sufficient, the gases being
generated during the laser cutting process are not blown out of the cutting gap com-
pletely. This can lead to an increased build-up of smoke deposits. Too high pressure
can generate turbulence that can also result in poor cutting quality. If the pressure is
appropriate, gases being generated in cutting process are flushed out of the cutting gap
keeping it clean and ensuring high cutting quality.

10.4.4 Focal/focus position
The beam focus is the point where the beam diameter is smallest. It provides highest
1
intensity of the laser beam for material treatment. Above and below the focus, the
intensity of the laser beam drops. An acute angle with which the focus is set keeps the
focus very thin in longer distance and vice versa. It can be important in processing
thick materials. The laser beam focused in the acute angle creates thinner kerfs, thus
reducing vaporized material part on the cut edges.

1 The intensity of a laser beam is equal to its power divided by the area over which the power is concen-
trated. The high-intensity laser beam heats up the material rapidly so that little time is available for heat
to dissipate into the surrounding material resulting in highest cutting quality. The laser beam with higher
intensity can be reached by increasing laser power or using a focusing lens with a shorter focal length.