ap-4-12.dvi


Acta Polytechnica Vol. 52 No. 4/2012

Laser Cutting of Materials of Various Thicknesses

Martin Grepl1, Marek Pagáč1, Jana Petr̊u1

1
VŠB – Technical University of Ostrava, Faculty of Mechanical Engineering, Department of Machining and Assembly,
17. listopadu 15/2172, 708 33 Ostrava, Czech Republic

Correspondence to: martin.grepl.st@vsb.cz

Abstract

Thise paper deals with the application of laser technology and optimizing the parameters for cutting nickel alloy. The

theoretical part of the paper describes various types of lasers, their principles and usage. The experimental part focuses

on optimizing the section parameteres of Haynes 718 alloy using a CO2 gas laser. This alloy is employed in the production

of components for the aircraft industry. The experiment was performed on the Wibro Delta laser system designed for

sizable parts. The actual section is measured with respect to its quality and any accompanying side effects that occur

during the process. In this case, laser output and cutting speed were the parameters with most influence on the final

cut. The summary explains the results achieved in a metallographic laboratory.

Keywords: laser, cutting, thickness.

1 Introduction

Lasers have found wide application in scientific work
in astronomy and in optics, in the investigation of
material characteristics and other basic research ar-
eas. Other practical applications include optical
equipment for eye surgery, use in geodesy and seis-
mography, in welding miniature parts from hard-to-
melt materials, in chemistry and metallography dur-
ing spectral microanalyses, etc.

Laser Cutting

Laser cutting can be:
• Sublimating — the material is removed primar-
ily by evaporation due to the high intensity of
the laser radiation in the cut area;

• Melting — the material is melted by a laser
beam in the cut area and blown away by an
auxiliary gas. Mainly metallic materials are cut
using this process;

• Burning — a laser beam heats the material to its
ignition temperature, so it can then burn in an
exothermic reaction with the reactive gas (e.g.,
oxygen), and the slag is removed from the cut-
ting area by an auxiliary gas. Titanium, low
carbon and corrosion resistant steels can be cut
this way.
Laser cutting, the most established laser material

processing technology, is a method for shaping and
separating a workpiece into segments of desired ge-
ometry. The cutting process is executed by moving a
focused laser beam along the surface of the workpiece
at a constant distance, thereby generating a narrow

cut kerf. This kerf fully penetrates the material along
the desired cut contour.

The absorbed energy heats and transforms the
prospective kerf volume into a state (molten, va-
porized, or chemically changed) which is volatile or
which can be removed easily. Normally, removal of
the material is supported by a gas jet that, impinges
coaxially to the laser beam. This cutting gas acceler-
ates the transformed material and ejects it from the
kerf.

This process is successful only if the melt zone
completely penetrates the workpiece. Laser metal
cutting is therfore generally restricted to thin sec-
tions. While cutting has been reported through
100 mm sections of steel, the process is more typi-
cally used on metal sheets 6 mm or less in thickness.

Figure 1: Principle of laser cutting

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Acta Polytechnica Vol. 52 No. 4/2012

Table 1: Chemical composition of Haynes 718 alloy

Elements Ni Co Fe Cr Cb + Ta Mo Mn Si Ti Al C B Cu

Weight [%] 52 1* 19 18 5 3 0.35* 0.35* 0.9 0.5 0.05 0.009 0.1*

* Maximum

2 Experimental cutting of

materials

The goal of this experiment was to find suitable cut-
ting parameters when cutting 2.5 mm and 3.2 mm
metal sheets of this type of alloy using the Winbro
Delta laser system. The Winbro Delta manufacturer
recommends using this machine for cutting material
with a maximum thickness of 6 mm. We also in-
vestigated the influence of cutting parameters on the
resulting cutting structure from the point of view of
shape deformations of the cutting gap and the cre-
ation of a recast layer, which is an undesirable ac-
companying effect of laser cutting.

2.1 Material

Test samples were made from the Haynes 718 high
strength alloy, which belongs to the nickel alloy
group. These alloys are suitable for operations un-
der extremely demanding conditions. They are ma-
terials that are primarily resistant to high tempera-
tures. These alloys are used in the construction of
land gas and aircraft engine turbines, and also for
industrial furnaces, combustion chambers, etc. The
alloy features outstanding resistance to temperatures
from −253 ◦C to +705 ◦C, and also excellent resis-
tance against oxidation up to 980 ◦C.

2.2 Laser system

The experiment was performed on the Winbro Delta
laser system designed for sizable parts up to 1 900 mm
in diameter, 500 mm in height, and up to 500 kg in
weight. The Delta system can be configured with
up to four different types of laser sources in order to
meet the requirements for specific applications of op-
erational laser technology (e.g., cutting, drilling, or
welding) (see Figure 2).

The laser system has been supplemented by the
Rofin DC 020 source, and is equipped with the Hei-
denhain iTNC 530 control system. It is a gas CO2
laser that operates in continuous regime.

2.3 Cutting parameters

Samples were made from sheet metal 2.5 mm and
3.2 mm in thickness. The laser cutting speed was set
to 500 mm·min−1 based on experimental experience,

the distance of the jet from the surface was 0.9 mm,
exciting frequency 2 000 Hz, filling 75 %.

The laser source output was changed by 10 % for
each cut, see Tables 2 and 3.

The cut length was 10 mm. The placement or dis-
tances of the cuts were empirically selected so that
the gaps between them would be sufficient from the
point of view of possible temperature effects on the
neighboring cuts.

Figure 2: Wibro Delta laser system with the Heiden-
hain iTNC 530 control system

Table 2: Power of laser (2.5 mm thickness)

Number of cut Power of laser 2 kW [%]

Cut 1 90

Cut 2 80

Cut 3 70

Cut 4 60

Cut 5 50

Cut 6 55

Table 3: Power of laser (3.2 mm thickness)

Number of cut Power of laser 2kW [%]

Cut 7 90

Cut 8 80

Cut 9 70

Cut 4 60

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Acta Polytechnica Vol. 52 No. 4/2012

Figure 3: The sample — sheet metal 2.5 mm in thickness (Haynes 718): a) upper side of the sample, b) underside
of the sample

3 Realization of the
experiment

Cuts nos. 1 to 5 were formed according to the pro-
posed cutting parameters. It was demonstrated that
the metal was not completely cut through with the
parameters set for no. 5. The output for the cut no.
6 was therefore set to 55 %, i.e. for the average value
between cuts no. 4 and 5. However, 55 % power was
again not sufficient for cutting the metal. The lowest
power useful for this material thickness is 60 % of the
maximum source output, which corresponds to laser
source output of 1 200 W.

Figure 3a) shows cuts nos. 1 to 6. Cuts nos. 1
to 4 went through the whole thickness of the metal.
The reason why the last two cuts were unsuccessful
was insufficient laser source power.

Figure 3b) shows the apparent temperature influ-
enced cutting area, which decreases with increasing
output. Burnt-on slag forms on the bottom part of
the cut. This can be considered as an accompanying
phenomenon of the cutting process that can be influ-
enced by setting the cut parameters. It can generally
be stated that the height of slag that forms does not
exceed the thickness of the cut metal, is brittle and
breaks.

We then we investigated a suitable cutting speed
using the cuts marked by nos. 4a to 4f, in order to
increase the cut quality. The source parameters were
set to the values for cut no. 4, and the cutting speed
was the only variable. For each cut we increased the
cutting speed by 100 mm · min−1.

Cuts nos. 4c and 4d were evaluated as the
best from the point of view of cutting quality.
These cuts correspond to a cutting speed interval of
〈700; 800〉 mm · min−1. In order to make the cutting
speed value more exact, we performed cut no. 4f with
a cutting speed of 750 mm · min−1.

Table 4: Laser cutting velocities with 60 % power

Number of cut Laser cutting velocities

[mm · min−1]
Cut 4a 500

Cut 4b 600

Cut 4c 700

Cut 4d 800

Cut 4e 900

Cut 4f 750

Figure 4: The cuts of variable cutting velocity with
constant power 60 %

Figure 5: The sample — sheet metal 3.2 mm in thickness (Haynes 718): a) upper side of the sample, b) underside
of the sample

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Acta Polytechnica Vol. 52 No. 4/2012

Table 5: Laser cutting velocities with 80 % power

Number of cut Velocities of laser cutting

[mm · min−1]
Cut 8a 500

Cut 8b 600

Cut 8c 400

Cut 8d 300

Cut 8e 450

Figure 6: The cuts of variable cutting velocity with
constant power 80 %

Cuts nos. 7 to 10 were formed according to the
proposed cutting parameters. It was demonstrated

that the metal was not completely cut through with
the parameters set for no. 10. The lowest power use-
ful for this material thickness is 70 % of the maximum
source output, which corresponds to laser source out-
put of 1 400 W.

Then we investigated a suitable cutting speed, us-
ing the cuts marked by nos. 8a to 8e, in order to in-
crease the cut quality. The source parameters were
set to the values of cut no. 8, and the cutting speed
was the only variable. For each cut we changed the
cutting speed, see Table 5.

Cuts nos. 8a and 8c were evaluated as the
best from the point of view of cutting quality.
These cuts correspond to a cutting speed interval of
〈400; 500〉 mm · min−1. In order to make the cutting
speed value more exact we performed cut no. 8e with
a cutting speed of 450 mm · min−1.

4 Metallographic evaluation

We made metallographic sections in the metallo-
graphic laboratory, and compared the cuts. Figure 7
is a photograph showing a comprehensive view of
cut no. 1 (magnified 10 and 50 times, etching agent
Vilella), with no recast layer observable, except for
an imperceptible layer on the cut walls that proba-
bly occurs always. The cut profile is symmetrical,
without major shape deformations.

Figure 7: Detail of cut no. 1 (power 90 %, cutting velocity 500 mm · min−1, magnified 10× and 50×)

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Acta Polytechnica Vol. 52 No. 4/2012

Figure 8: Detail of cut no. 4 (power 60 %, cutting velocity 500 mm · min−1, magnified 10× and 50×)

Figure 9: Detail of cut no. 6 (power 55 %, cutting velocity 500 mm · min−1, magnified 10× and 50×)

We can see the originating asymmetrical distri-
bution of the recast layer at the bottom of the cut.
This layer is caused by the barrier that originates due
to the melt concentrated in the bottom part of the
cut. The melt after solidification manifests itself as
a burr on the bottom edge of the cut. Burrs are not
acceptable, and must be removed by milling. Due to
this, the heat that originates during cutting, and does
not have a chance to dissipate from the surrounding
of the cut, accumulates in this location. As a con-
sequence there is local overheating, a change in the
shape of the cut, and an increase in the volume of
the recast layer.

Cut no. 4 was selected as the best in quality after
visual control. It can be seen that it appears satis-

factory, even from the point of view of the size of the
recast layer.

Figure 9 shows at photograph of cut no. 6, in
which the metal was not completely cut through.
This is an unacceptable situation, caused by insuf-
ficient output of the laser.

5 Conclusion

On the basis of experiments, we have found that suit-
able parameters for cutting Haynes 718 alloy and
metal thickness of 2.5 mm are 60 % (1 200 W) of
the laser output and 750 mm · min−1 cutting speed,
according to cut no. 4f.

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Acta Polytechnica Vol. 52 No. 4/2012

For metal thickness of 3.2 mm, the optimal pa-
rameters are 80 % (1 600 W) of the laser output and
450 mm·min−1 cutting speed, according to cut no. 8e.

To avoid any influence of the surrounding atmo-
sphere on the cut, it is suitable to measure the re-
cast layer using a microprobe, and then to perform
a microchemical analysis. We recommend that in-
creased attention be paid to a study of the recast
layer and its increased dependence on cutting pa-
rameters. It would be suitable to perform the micro-
hardness measurement at the melting boundary of
the original material and more importantly, on the
recast layer itself. Our paper has contributed a com-
prehensive view on the influence of the process pa-
rameters on a narrow group of materials used in the
aerospace industry.

Acknowledgement

This paper was prepared within the project: In-
creasing of Professional Skills by Practical Acquire-
ments and Knowledge, no. CZ.1.07/2.4.00/17.0082,

supported by the Education for Competitiveness
Operational Programme financed by the European
Union Structural Funds and with support from the
state budget of the Czech Republic.

References

[1] Gavrilov, P., Jeĺınková, H., Vrbová, M.: Introduc-
tion to Laser Technology. Praha : ČVUT, 1994.
235 p. Faculty of Nuclear Sciences and Physical
Engineering. ISBN 80-01-01108-9.

[2] Grepl, M.: Laser Cutting Materials with Variable
thickness: master thesis. Ostrava : VŠB – Techni-
cal University of Ostrava, Faculty of Mechanical
Engineering, Department of Machining and As-
sembly, 2010, p. 75.

[3] Ready, J. F.: LIA Handbook of Laser Materials
Processing. Laser Institute of America, Orlando,
FL : Magnolia Publishing, Inc., 2001. Laser Cut-
ting, p. 425–470. ISBN 0-912035-15-3.

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