TPT November 2010

99 / 124

November 2010 97 ›
Cutting, Sawing & Profiling
Laser cutting
with the right
beam source
CO2 or solid-state laser? Many users ask
this question when they consider doing
cutting work with a laser. “The application
decides which beam source is best to use,”
explained Dr Arnd Szelagowski of Trumpf
Laser und Systemtechnik, Ditzingen/
Germany who recently spoke at the
congress of the German Welding Society
(DVS) in Nuremberg/Germany.
In his presentation – Laser beam cutting
today and tomorrow – current developments
and trends in laser cutting technology, Dr
Szelagowski said, depending on material
and sheet thickness, the CO2 laser is a
better choice for one application, while
the solid-state laser is a better choice
for another.
If users want a flexible way to cut
across all sheet thicknesses and obtain
good cutting quality, the CO2 laser is the
beam source of choice – despite its lower
efficiency compared to the solid-state laser.
If the users focus is on thin sheet cutting,
the solid-state laser has real advantages.
Dr Szelagowski explained the reason
for this by describing the absorption ranges
of both laser beam technologies for iron.
With a wavelength of 1µm, the solid-
state laser produces a very broad, almost
constant absorption level across an angle
of incidence varying from 0 to 60 degrees.
In the range of about 78 degrees, a distinct
level with a subsequently steep drop is
noticeable. With a wavelength of 10µm,
on the other hand, the CO2 laser shows
a significant increase in the absorption
level with an increasingly steeper angle of
incidence (greater than 80 degrees), and
thereby an improved coupling of the laser
output into the material. These effects
directly impact the laser beam fusion
cutting – but not the flame cutting. “In this
case, the laser plays only a subordinate
role. That is why the cutting quality and
speed in flame cutting for mild steel do not
vary between CO2 and solid-state lasers,”
he added.
The situation is different for thin sheet
metal, which is processed at a generally
higher feed rate and develops a flat
cutting front. This favours the solid-state
laser and therefore leads to improved
coupling conditions.
“But with increasing sheet thickness, the
maximum achievable cutting speed drops,
resulting in a steeper cutting front,” explained
Dr Szelagowski. Conversely, this cutting
front feature, in conjunction with the high
melting temperature, produces a constant
high absorption rate in the CO 2 laser beam
in thick sheet metal. The molten material is
homogenously low-viscosity across the sheet
to the bottom edge and – despite its high
volume – it can be driven out of the groove,
improving the cutting quality.
This explains the different areas of
application for these two laser technologies.
“Solid-state lasers show considerable
advantages for stainless steel sheet
thicknesses up to 4mm. Compared to the CO2
laser, they cut faster and are therefore more
efficient and productive with the same high
cutting quality,” concluded Mr Szelagowski.
With the CO2 laser, in contrast, a broad
material and sheet thickness range can be
processed with high quality cutting results.
In order to obtain optimum benefit from
the high productivity of the solid-state laser,
the machine dynamics have to be in line with
the laser’s performance capacity. “On top of
that, users should be aware that a 700 hp
engine does not turn a compact car into a
Formula 1 race car,” said Dr Szelagowski.
The new TruLaser Cell 7040 fibre
provides a system for 3D sheet processing
with a TruDisk disk laser. The TruLaser Cell
7040 fibre with a working range of 4 x 1.5m
is the largest model in the TruLaser Cell
Series 7000.
Trumpf GmbH + Co KG – Germany
Fax: +49 7156 303 936115
Email:
Website:
If users want a flexible way to cut across all sheet thicknesses with very good cutting quality, the CO2 laser is the
beam source of choice, says Dr Szelagowski