Cutting and CFRP-Processing (LiM 2017)

Swift and accurate - investigation of remote laser cutting for open cell foams
Baumann, Robert; Herwig, Patrick; Wetzig, Andreas; Beyer, Eckhard

It is well known that the global climate change is the largest challenge for the society of the 21th century. For managing
the resulting consequences, innovative materials become more and more important for energy efficient applications.
Open cell metal foam contributes promising solutions to the light weight design, battery applications and renewable
energy harvesting. Still, challenges are present concerning the cutting into a defined shape. The remote laser cutting
offers a solution for decreasing the production costs as well as the needed component accuracy. Our investigations
consider that this technique has a high potential concerning cutting speed, which was increased more than 500%
compared to state of the art laser separation. Next to that, the contour accuracy was improved as well, resulting in
tolerances with less than 60 μm. This paper offers insight into the viability of remote laser cutting in overcoming the
challenges dealing with mechanical milling or grinding. Investigating the process concerning thermal stress input as well
as particle attachments will be the next steps in the future.

Keywords: cutting; laser; accuracy; metal foam; Inconel;


Determination of the flow speed of the evaporated material generated during laser processing of CFRP with a cw-laser by means of high-speed imaging
Freitag, Christian; Faas, Sebastian; Boley, Steffen; Berger, Peter; Weber, Rudolf; Graf, Thomas

During laser processing of carbon fiber reinforced plastics (CFRP) the material is mostly removed as vapor. Several
components of the vapor like Bisphenol A or CO are potentially hazardous. To avoid health hazards, a reliable suction is
necessary and therefore the flow speeds of the evaporated material have to be known. We observed the hot plume of
evaporated material during a laser drilling process of CFRP with a continuous-wave laser beam using a high-speed
imaging system. Within the flow of evaporated material the formation of compression shocks was observed.
Compression shocks indicate flow speeds well above the local speed of sound. By measuring the distance between the
first compression shock and the sample surface we calculated the flow speed of the evaporated material. For the applied
process parameters flow speeds of up to 3300 m/s were determined. High-speed imaging also enabled the investigation
of the temporal evolution of the flow speed during the laser drilling process. While the flow speed varies only slightly
during the drilling process, a significant decrease of the flow speed was observed at the moment of breakthrough.

Keywords: Macro Processing; Fundamentals and Process Simulation; CFRP; Plume; Flow Speed


Dynamic beam shaping for thick sheet metal cutting
Goppold, Cindy; Pinder, Thomas; Herwig, Patrick

From industrial view, nothing has a higher priority than a reliable and sustainable machine. This applies not only for
specialized tasks rather for a spectrum of applications. Thin sheet cutting is well controlled but limitations of the cutting
mechanism are challenging in case of thick metal plates above 6 mm. The solution approach of Fraunhofer IWS pursues
dynamic beam shaping (DBS), which is influencing energy distribution and thus essential heat conduction for the laser
cutting process. As a consequence, DBS provides the possibility to improve the performance for laser fusion cutting of
thick metal plates. The authors will give an insight into changed mechanism during laser fusion cutting process due to
DBS and explain how that enables an all-in-one cutting machine of industrial demands.

Keywords: dynamic beam shaping; distribution; laser fusion cutting; oscillation; thick metal


CFRP bonding pre-treatment with laser radiation of 3 µm wavelength: influence of different treatment parameters
Blass, David; Nyga, Sebastian; Katzy, Veronika; Jungbluth, Bernd; Hoffmann, Hans-Dieter; Dilger, Klaus

Due to the mold-based production of composite parts, the surfaces are contaminated with mold-release agent residues.
Those contaminations hinder the adhesion of the surface and therefore prevent the structural adhesive bonding of the
untreated parts. To achieve and guarantee a durable bond, a surface pre-treatment prior to the bonding process is
inevitable. Laser radiation is promising, but unfortunately common laser sources have a high risk to cause material
damage. The bad absorption (IR-laser) or the high amount of thermal interaction (CO2-laser) hinder the establishment of
this treatment method in industrial applications. To solve this problem laser radiation of 3 μm wavelength (which has a
high absorption inside the resin and less thermal interaction) was generated by frequency conversion of an industrial IR
laser and applied to the composite. The results show a good and sensitive treatment of the surface, resulting in high
bonding strengths.

Keywords: Surface treatment; ablation, composite frequency conversionyour


Laser cutting of pure lithium metal anodes
Jansen, Tobias; Blass, David; Kreling, Stefan; Dilger, Klaus

Aiming at a high performance lithium-ion battery, all process steps and materials have to be improved. Lithium metal is
the most promising material for future anodes since their high theoretical capacity of 3860 mAh/g and their low density
of 0.534g/cm3. Apart from the current low cycle stability, challenges lay in the separation and the handling of lithium.
Due to its toughness and adhesive properties, lithium metal anodes can not be separated by conventional processes
(e.g. punching) within a high volume production. The most promising way to produce anodes with high-quality cutting
edges in high numbers is laser cutting. The presented experiments show that in certain atmospheric conditions high-
quality cutting edges can be produced with a pulsed fiber laser.

Keywords: Cutting; lithium; battery systems; electromobility


A comparison of IR- and UV-laser pretreatment to increase the bonding strength of adhesively joined Aluminum/CFRP components
Meinhard, Dieter; Reitz, Valentina; Ruck, Simon; Knoblauch, Volker; Riegel, Harald

For this study two commercial, thermoset CFRP laminates (called A and B) were pre-treated using IR- and UV-laser
prior to adhesive bonding. The achieved surface conditions were characterized by optical methods and correlated with
mechanical properties of adhesively bonded hybrid Al/CFRP single-lap joints. Two opposing effects could be detected on
both CFRP laminates after IR-laser pre-treatment: strength increasing surface activation and reducing weakening of the
fiber-matrix interface in near surface areas. By application of UV-radiation it was possible to activate the surface
damage-free for A whereas B exhibited thermal induced damaging of the fiber-matrix adhesion comparable to IR laser
treatment. Furthermore, it was shown that surface activation by laser pre-treatment strongly depends on the used CFRP
laminate. IR- and UV-laser pre-treatment of A leads to a significant increase of shear strength, whereas for B even a
slight reduction was observed compared to chemical cleaning with acetone which was the reference process.

Keywords: carbon fibers; adhesion; surface treatments; hybrid;


High-power laser surface processing for fast, reliable repair preparation of CFRP
Dittmar, Hagen; Bluemel, Sven; Jaeschke, Peter; Suttmann, Oliver; Overmeyer, Ludger

As various industries, especially aviation and automotive, are applying an increasing amount of parts fabricated from
carbon fibre reinforced plastics (CFRP), proper maintenance and repair procedures are gaining importance, too.
The laser is a potential tool to assist the CFRP repair process by scarfing the damage zone during the repair preparation phase. This study presents a high-power (1.5 kW) nanosecond pulsed laser for this task. Its performance is evaluated in terms of processing time, bulk material removal rate and formation of a heat affected zone. The results of the evaluation show that these lasers pose a serious challenge to conventional tools, especially in combination with additional supportive techniques for process automation.

Keywords: laser scarfing; CFRP; repair preparation; automation


Distance controlled laser ablation of CFRP
Boley, Steffen; Holder, Daniel; Buser, Matthias; Onuseit, Volkher; Graf, Thomas; Schönleber, Martin

Precise ablation of CFRP (carbon fiber reinforced plastic) is difficult due to the highly different thermo optical properties of fibers and plastics in combination with possible inhomogeneous parts of the material. This leads to deviations in terms of surface roughness and actual removed depth during processing. In particular, for repairing expensive parts , precise layer ablation and a certain roughness are the key points to achieve a high strength of the repaired parts. In this approach, optical coherence tomography was combined with a galvanometer scanner. With this setup, the local depth during ablation can be measured with a spatial resolution of 5 μm and temporal resolution of 14 μs. This allows to remove material until the target depth is reached. The ablation track of the next pass is calculated by the previously measured data. As input data for the target ablation geometry, a grey-scaled bitmap picture can be used to produce any kind of 3D surface structure. The experimental validation of this setup was done with a ns laser with an average power of 20 W and a wavelength o f 1047 nm. Each processing pass has an ablation depth of approxi matel y 10 25 μm. There by a defined ablation layer by layer of CFRP part is possible. To reach the target depth of one layer, multiple passes are necessary. The ablation stops a teach area when the target depth has reached. The areas are calculated by slicing the measured surface into constant depth segments. The beam passes only the segments that needs to be removed. On the final processed area , the depth deviation was reduced to 20 μm and the roughness was reduced to below 10 μm independently from the total depth.

Keywords: Micro Processing, System Technology and Process Control, CFRP, controlled ablation ;


Pulsed laser cutting of granite
Riveiro, Antonio; Mejías, Ana; Soto, Ramón; Quintero, Félix; del Val, Jesús; Boutinguiza, Mohamed; Lusquiños, Fernando; Pardo, Juan; Pou, Juan

Natural stones, in particular granites, are excellent materials for construction, engineering or monumental applications.
These materials are able to withstand adverse weather conditions, which ensures a long and durable usage; but also,
their aesthetic appeal is greatly appreciated. Despite, they are widely used, these materials are difficult to machine by
conventional methods. High level of noise and large amount of powder are produced during their cutting. In this work,
CO2 laser cutting of 10 mm thick granite slabs is presented. Influence of the processing parameters on quality
characteristics, during pulsed laser cutting, is studied. Costs associated to the process were calculated, and the main
factors affecting on them identified. Results from the cutting experiments show that it is possible to obtain sound cuts,
free of fractures in this kind of materials at an affordable cost.

Keywords: laser cutting; granite; pulsed mode; quality


Quantitative identification of laser cutting quality relying on visual information
Pacher, Matteo; Monguzzi, Lorenzo; Bortolotti, Lorenzo; Sbetti, Maurizio; Previtali, Barbara

In the industrial practice of the laser cutting, the cut quality is defined in a qualitative manner by skilled technicians.
Specific features lying on the cut edges in fact compose the overall quality, i.e. inclination of striations, presence of burr
and different process zones along the edge. These attributes are evaluated by experts which at the end assess the cut
quality on the base of their personal judgment. On the other hand, measurements of roughness and burr height in
accordance to standards or internal procedures are also carried out. However, measuring is time consuming and more
important is not always in agreement with the qualitative evaluation given by skilled technicians. In this scenario, the
paper presents a method relying on visual information able to measure quantitatively a new class of quality attributes,
which opportunely combined provide an index of performance consistent to the qualitative one based on experience.
In this study, images of the cut edge of 5mm thick stainless steel AISI 304 cut with nitrogen as assisting gas are analyzed.
The image analysis algorithm utilizes both standard gradient techniques, wavelets decomposition and analyses in the
frequency domain for measuring periodic and not periodic quantities. Burr profile is isolated, the typical process zones
are successfully identified and striation’s angle is computed for each zone. The gray analysis method combining multiple
outputs from the image analysis algorithm is applied in order to compute the overall quality. The weights are set to
express correctly the judgement of technicians. The method proved reliable, relatively fast and promising for further
extension to different thicknesses and materials.

Keywords: laser cutting; quality inspection; gray analysis; image analysis


Process emissions during laser processing of CFRP: measurement of hazardous substances and recommendation of protective measures
Walter, Juergen; Hustedt, Michael; Bluemel, Sven; Jaeschke, Peter; Kaierle, Stefan

Regarding resource-efficient lightweight structures, carbon fiber reinforced plastics (CFRP) have a high usage potential
due to their outstanding mechanical properties, especially their high specific strength parallel to the carbon fibers.
Adequate processing methods are required to enable high-quality mass production of CFRP parts e.g. in the automotive
industry. So far, mechanical methods associated with notable tool wear are used in most applications. Laser technology
used for CFRP processing may provide diverse advantageous features such as contact-free processing without any tool
wear, high contour accuracy and reproducibility, and high flexibility concerning workpiece design. In a particular funding
line, the German Federal Ministry of Education and Research (BMBF) supports several cooperative research projects,
dealing with the development of processes for innovative lightweight structures, using CFRP materials amongst others.
If specific laser processing strategies are used for CFRP materials, high quality results can be achieved. However, CFRP laser processing as a thermal method always produces organic particulate and gaseous process emissions. The substances released into the air at the workplace are connected with the risk of adverse health effects for the
employees, and the potentially hazardous compounds in the exhaust air, removed from the processing cabin, may be
harmful for the environment. With respect to the risk assessment, measurements have been performed in the course of
the BMBF-funded projects dealing with CFRP laser processing, yielding emission rates and workplace concentrations
which have been related to the respective limit values (emission limit values for the exhaust air and occupational
exposure limits for the workplace). The results are used to develop recommendations for adequate measures to protect
the employees as well as to handle the process emissions in terms of filtering for environmental protection.

Keywords: carbon fiber reinforced plastics; laser processing; process emissions; occupational safety; environmental protection