Investigation of the polymer material perforation time: comparison between two fiber laser wavelengths

Abstract

This study investigated the perforation time of polyamide 6.6 using fiber lasers at two different wavelengths: 1070 and 1943 nm. The novelty of this research lies in the comparison of perforation times at equivalent laser irradiances on the polymer sample with two different colors of polyamide 6.6: natural and black. The results revealed that, at comparable irradiance levels and beam diameters, the 1943 nm laser source perforated the polyamide 6.6 sample faster than the 1070 nm laser source. The difference in perforation time was found to be significantly higher for natural-colored polyamide 6.6 compared to black-colored polyamide 6.6. These findings suggest that, for material processing of polyamide 6.6, especially in terms of perforation, the use of 2 μm laser sources should be privileged over 1 μm laser sources.

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Vol.:(0123456789)
Journal of Polymer Research (2024) 31:51
https://doi.org/10.1007/s10965-024-03885-w
ORIGINAL PAPER
Investigation ofthepolymer material perforation time: comparison
betweentwo fiber laser wavelengths
ClémentRomano1 · GunnarRitt1 · MichaelHenrichsen1 · MarcEichhorn1,2· ChristelleKieleck1
Received: 2 October 2023 / Accepted: 10 January 2024
© The Author(s) 2024
Abstract
This study investigated the perforation time of polyamide 6.6 using fiber lasers at two different wavelengths: 1070 and
1943nm. The novelty of this research lies in the comparison of perforation times at equivalent laser irradiances on the poly-
mer sample with two different colors of polyamide 6.6: natural and black. The results revealed that, at comparable irradiance
levels and beam diameters, the 1943nm laser source perforated the polyamide 6.6 sample faster than the 1070nm laser
source. The difference in perforation time was found to be significantly higher for natural-colored polyamide 6.6 compared
to black-colored polyamide 6.6. These findings suggest that, for material processing of polyamide 6.6, especially in terms
of perforation, the use of 2μm laser sources should be privileged over 1μm laser sources.
Keywords Polymer· Perforation· Laser
Introduction
Fiber lasers are efficient light sources that are used in many
applications, including material processing. Their use is
motivated by mechanical stability and vibration resistance,
high beam quality and irradiance, and long lifetime. In par-
ticular, fiber lasers can be used to process various polymer
materials to perform machining [1], polymer consolidation
[2], transmission welding [3], perforation [4], or surface
treatment [5]. These processes are performed at different
laser wavelengths, mostly around 1 and 2μm. The choice of
wavelength is motivated by the availability of high-power
and efficient fiber laser sources with high beam quality and
the absorption of these materials at these wavelengths.
Fiber lasers emitting at 1μm rely on ytterbium-doped fiber
lasers (YDFL). At present, these are the most efficient fiber
lasers sources with > 80% optical-to-optical efficiencies,
multi-kW output power, and a single-mode output [6]. The
wavelength of 2μm, on the other hand, relies on thulium-
doped fiber lasers (TDFL). TDFLs are the second type of
source that can deliver more than 1kW of output power in
a single-mode operation [7]; they can also operate with an
optical-to-optical efficiency close to 60% [8].
When considering the material processing of polymers,
the question of choice between 1 and 2 μm fiber lasers
arises. The absorption of natural-colored plastic materials
in the 2 μm region has been shown to be higher than in the
1 μm region [9, 12]. While 1 μm fiber lasers offer higher
output power and greater efficiency, 2 μm lasers have the
advantage of being more effectively absorbed by natural-
colored polymer materials. There is a tendency in exper-
imental studies to use 2 μm fiber lasers over 1 μm fiber
lasers based on the natural absorption measurement made on
polymers [10]. However, there is currently a lack of studies
that directly compare the performance of these two laser
wavelengths in material processing applications. Therefore,
the objective of this research paper is to provide valuable
insight into the performance of 1 and 2 μm fiber lasers in the
context of polymer material processing. However, provid-
ing an experimental answer to this broad question would be
tedious as there are too many parameters to consider, such
as multiple wavelengths available from a YDFL or a TDFL,
different operation modes (CW or pulsed), or irradiance
levels on the polymer sample. In addition, there is a wide
variety of polymer materials or processes. Thus, to perform a
* Clément Romano
clement.romano@iosb.fraunhofer.de
1 Fraunhofer IOSB (Institute ofOptronics, System
Technologies andImage Exploitation), Gutleuthausstraße 1,
76275Ettlingen, Germany
2 Institute ofControl Systems (IRS), Karlsruhe Institute
ofTechnology, Fritz-Haber-Weg 1, 76131Karlsruhe,
Germany

Journal of Polymer Research (2024) 31:51 51 Page 2 of 6
first study we had to narrow down the number of parameters.
Available lasers operating in the CW regime are often used
with wavelengths of 1070 and 1943 nm. Polymer materials
are typically used to replace metals in vehicles due to their
lighter weight, improved impact resistance, and lower cost.
For instance, in unmanned aerial vehicles, polyamide 6.6
(PA 6.6) is commonly used as it offers high strength, stiff-
ness, and thermal resistance [11]. The absorption, reflec-
tance, and transmission spectra of natural-colored PA 6.6
are available in the literature between 400 and 2000 nm
[12]. The measurements show that the absorption increases
between 1 and 2 μm while the reflectance decreases. This
should give 2 μm lasers an advantage over 1 μm lasers for
material processing such as cutting, perforating, or drilling.
Our investigation focuses especially on the perforation time
of polymer materials, a polymer process that has received
little coverage in the literature. In the past, perforation of
polymer materials has been reported [4], but only on rein-
forced polymer materials using a multi-kW multimode fiber
laser at a wavelength of 1 μm.
Experimental setup
The experimental setup is depicted in Fig.1 and is inspired
by a similar experiment on polymer material perforation
[4]. The collimated laser radiation from a commercial fiber
laser (IPG Photonics) is launched onto the sample. The
lasers had wavelengths of 1070 and 1943 nm, and were
chosen based on previous experiments found in the litera-
ture on polymer material [4, 13]. Both lasers had a beam
quality M2 < 1.1 and a maximum output power of 290 W
at 1070 nm and 200 W at 1943 nm. The 1070 nm fiber
laser had a collimated beam diameter of 8.6 mm, while
the 1943 nm laser had a collimated beam of 5.8 mm. To
achieve a fair comparison, the 1943 nm laser beam was
shaped using a telescope with two plano-convex lenses to
realize a beam diameter of ~ 8 mm on the sample. Thus,
both laser beams achieved a comparable irradiance up to
~ 0.8 kW/cm2 on the sample, limited by the fiber laser
power available. The irradiance was calculated using the
following formula I = 8P/πD2, where I is the irradiance,
P the power, and D the gaussian beam diameter meas-
ured at 1/e2 of the irradiance. The laser beam diameter
on the sample was measured using a beam profiling cam-
era. Beam profile measurements, using an Ophir Pyrocam
3, were performed for both laser wavelengths up to their
maximum output power. The camera was placed behind a
highly reflective mirror instead of the sample to capture
these measurements. This also allowed us to check that no
beam deformation occurred, which could have theoreti-
cally been the result of thermal blooming [14]. For the per-
foration measurements, a beam dump was placed behind
the sample to block further propagation of the beam once
perforation was achieved. A calibrated photodiode fac-
ing the beam dump provided feedback on the transmit-
ted power and perforation time. The laser was controlled
using a trigger generator while an oscilloscope collected
the data starting from the switch on time of the laser until
perforation was achieved. A camera was included in the
setup to monitor the sample processing safely. The sample
was slightly tilted with respect to the beam propagation
axis in order to prevent a potential reflection propagating
back inside the laser [15]. The setup also included a fume
extractor located above the sample, not shown in Fig.1.
During this experiment, two types of samples were tested:
Fig. 1 Experimental setup for
the investigation of the polymer
perforation time

Journal of Polymer Research (2024) 31:51 Page 3 of 6 51
natural-colored and black-colored PA 6.6 (Tecamid 66).
All samples had the same dimensions: 10 × 10 × 1 cm3.
In order to provide an insightful comparison between
the two laser wavelengths, we conducted perforation tests
at varying fiber laser output powers. This corresponded to
different irradiances on the sample. For each laser power,
10 samples of PA 6.6 were perforated to provide statistics
on the perforation time and thus attain a reliable value. To
quantify the perforation time, we used the following defini-
tion: the perforation time corresponds to the moment when
50% of the power is initially transmitted through the sample.
Results
Figure2 shows the results of the perforation on 10 samples
of PA 6.6 with natural color. All samples were perforated
by the 1943nm fiber laser with an irradiance on sample of
0.8kW/cm2. It is noted that all samples look similar after
exposure to the laser irradiance: a conical hole is observed
with a larger diameter on the front sample side. The poly-
mer material directly exposed to the laser radiation appears
melted and carbonized. A detailed description of the various
damaged areas after perforation can be found in reference
[4]. An increase of the hole size with laser power could be
observed over all tested samples and laser wavelengths.
Figure3 shows some of the experimental results of trans-
mitted power over time for different samples of natural-
colored PA 6.6. The left side (respectively the right side)
shows the measurement performed at a laser wavelength of
1070nm (respectively 1943nm) with an irradiance on the
sample of 0.68kW/cm2 (respectively 0.8kW/cm2). The time
scale begins with the laser switching on. The laser’s acti-
vation time is negligible compared to the perforation time.
Upon irradiating the sample with a 1070nm fiber laser,
some power is immediately transmitted through the sample;
this is expected due to the low absorption of polymer mate-
rial at the chosen wavelength. After ~ 200s, the transmitted
Fig. 2 Natural-colored perfo-
rated samples of PA 6.6
Fig. 3 Transmitted power over time for natural-colored PA 6.6

Journal of Polymer Research (2024) 31:51 51 Page 4 of 6
power increases sharply; this corresponds to a very small
hole made through the sample at the end of the perfora-
tion process. After the material is perforated, the size of the
hole increases until the majority of the power is transmitted.
Once the perforation is achieved and most of the power is
transmitted, we observe some drops in transmission. This
is attributed to material melting and dropping in the laser
beam, which reduces its transmission temporarily. Smoke
was also observed during the process; it traveled vertically
and did not noticeably impede the laser propagation. Addi-
tional information on the process of perforating polymer
materials can be found in references [4] and [16]. When irra-
diating the sample with a 1943nm fiber laser, we observe
that as soon as the laser switches on, no transmitted power is
observed. After approximately 10s, the first perforation of
the sample is observed. The behavior is similar to the irradi-
ance with a 1070nm fiber laser. Comparing the two perfora-
tion measurements, better uniformity of the measurement
curves is found when irradiating with a 1943nm fiber laser.
The same measurements as those shown in Fig.3 were
performed in a second round, this time using black-colored
PA 6.6. The experimental results of transmitted power over
time for different samples are shown in Fig.4 for an irra-
diance of 0.82kW/cm2 on the sample. The measurement
curves follow a similar temporal evolution to the previ-
ous measurements with natural-colored PA 6.6. However,
the perforation time using the 1070nm fiber laser is much
shorter than previously observed. In addition, we note that
the measurement results are more chaotic than the previous
results with the natural-colored PA 6.6. During the laser
irradiance process, darker smoke could be observed traveling
horizontally toward the laser. We believe that this behavior
is the cause of the decrease in transmitted power over time
[10]. This effect has already been observed and reported [4].
This indicates that the fume extractor used in the experimen-
tal setup was too weak to extract the smoke quickly enough.
With the 1070nm fiber laser, ignition of the material could
sometimes be observed at irradiances of 0.82kW/cm2 and
above. This results in a significant reduction in perforation
time as illustrated by the green and yellow curves in Fig.4
on the left side. Ignition of the sample was not observed with
the 1943nm fiber laser.
The measured average perforation times with their respective
standard deviations are shown in Fig.5. It is observed that across
all cases considered, the average perforation time decreases as
the laser irradiance increases. The trend of these measurements
follows an exponential decreasing function. However, it should
be noted that fitting these data did not yield useful physical
values for predicting the perforation time beyond the studied
Fig. 4 Transmitted power over time for black-colored PA 6.6
Fig. 5 Average perforation time and standard deviation versus laser
irradiance on sample

Journal of Polymer Research (2024) 31:51 Page 5 of 6 51
range of irradiances. Regarding the 1070nm wavelength, the
perforation time shows a significant decrease, with a difference
of greater than tenfold between the natural-colored and black-
colored PA 6.6 samples. On the other hand, for the 1943nm
wavelength, the perforation time shows little dependency on the
PA 6.6 color. Furthermore, we observed that within the tested
range of irradiances, the perforation time is shorter using a
1943nm laser source than when using a 1070nm laser source.
Regarding the natural-colored PA 6.6, the standard deviation
of the perforation time demonstrates little variability and there-
fore is not noticeable on the figure. On the other hand, for the
black-colored PA 6.6, the standard deviation is increased. This
is attributed to the horizontal traveling smoke perturbating the
laser propagation. For irradiances greater than 0.8kW/cm2
at a wavelength of 1070nm, we note that the standard devia-
tion increases significantly as a result of the ignition of some
samples. As a result, stable perforation of the material was not
achieved for these irradiances.
Conclusion
We investigated the perforation time of PA 6.6 using fiber lasers
with two different wavelengths: 1070 and 1943nm. The com-
parison was performed at equivalent laser irradiances on polymer
samples. Two different PA 6.6 colors were investigated: natural
and black. We demonstrated that at equivalent beam diameter and
comparable irradiance level, a 1943nm laser source perforates a
sample of PA 6.6 significantly faster than a 1070nm laser source.
The difference in perforation time is found to be more than ten-
fold faster for the natural-colored PA 6.6, while for black-colored
PA 6.6 the difference in perforation time is less pronounced. In
conclusion, when dealing with material processing of PA 6.6, in
particular the perforation of a sample, it is recommended to use
2μm laser sources instead of 1μm laser sources. In the future,
other polymer materials and especially reinforced polymer materi-
als will be studied to investigate wavelength-dependent effects in
interaction morphology and perforation time.
Acknowledgements Funding by the German Federal Ministry of
Defense and the BAAINBw is gratefully acknowledged.
Funding Open Access funding enabled and organized by Projekt
DEAL.
Data availability Data underlying the results presented in this paper are
not publicly available at this time but may be obtained from the authors
upon reasonable request.
Declarations
Conflict interests The authors declare no conflicts of interest.
Open Access This article is licensed under a Creative Commons Attri-
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