Joining (Welding and Brazing) (LiM 2017)

Laser technologies in modern shipbuilding
Nosyrev, Nikolay A.; Steshenkova, Nataliya A.

The level of technological development determines the competitiveness of industrial enterprises and particular in
shipbuilding area. Massive implementation of modern laser techniques is one of the ways to improve quality in
shipbuilding and heavy engineering production. JSC «Shipbuilding and Shiprepair Technology Center» is a leading design
and engineering center in Russian shipbuilding sector and takes an active part in the development and application of
laser technologies for shipbuilding.
The shipbuilding industry requires high-performance production technologies for the heavy gauges. A hybrid laser-arc
welding technology which provides higher productivity, improvement of production effectiveness and reliable quality of
welded joints is the most promising technology for this task.
Results of welding process simulation and experimental researches fulfilled on the preproduction models of
technological complexes developed by JSC SSTC (based on fiber lasers up to 25 kW power) are presented. The welding
technological processes for shipbuilding steels 16-40 mm thickness in different spatial positions were designed (including
approved by qualification agency Russian Maritime Register of Shipping (RMRS)).
The article presents results on researching and development of technology and robotized equipment, based on modular
approach, for laser welding and cladding of maritime machinery items.
Implementation of laser technologies allow to achieve a new level of productivity and manufacturing of structures in
shipbuilding and heavy engineering.

Keywords: hybrid laser-arc welding; laser welding; hull structures, laser cladding, marine engineering


Electromagnetic porosity reduction in laser beam welding of die cast aluminum alloy
Fritzsche, André; Teichmann, Fabian; Pries, Helge; Hilgenberg, Kai; Rethmeier, Michael

Due to the possibility of producing complex geometries with a high dimensional accuracy, aluminum die casting is widely
used for manufacturing of automotive and aircraft components. Although the application of fusion welding processes is
favorable for joining die-cast aluminum parts, the relaxation of dissolved gases remains a major problem until now.
In the present investigation, the advantages of the laser beam welding process (low distortion, high productivity) are
deployed under improved degassing conditions. An oscillating magnetic field is utilized to generate Lorentz forces within
the weld pool. Due to the different electrical conductivities between gases and molten aluminum, the contained gases
are accelerated to the top of the melt.
Depending on the magnetic flux density and the frequency of the magnetic field, a significantly reduction of the porosity
can be detected in partial penetration welding. This method offers great potential for further applications.

Keywords: laser beam welding, die-cast aluminum, electromagnetic weld pool influence


Reduction of the spatter formation due to the use of superposition of two laser intensities
Nagel, Falk; Drechsel, Christine; Bergmann, Jean Pierre

New developments of laser system technology result in an increased power output at better beam quality. However,
available laser power cannot always be transferred to increase the processing speed since imperfections such as the
formation of spatter occurs, especially in the range of 5 m/min to 20 m/min for fiber and disk lasers. The appearance of
spatter is strongly connected to the conditions in and around the capillary.
This paper shows an experimental approach to reduce the spatter formation by using two laser spots. The experimental
trails were executed with austenitic steel (1.4301) sheets using a high power disk laser and a diode laser. The
modification of the resulting intensity reduces the loss of mass. High speed camera footage shows a different behavior
of the weld pool due to the additional laser spot. Moreover, metallurgical cross-sections demonstrate the influence of
the approach on the shape of the melt pool and the resulting weld seam.

Keywords: Spatter formtation; Superposition; Laser intensity; Austenitic tainless steel


Behavior of laser induced keyhole during dissimilar welding of metals
Tomashchuk, Iryna; Mostafa, Massaud; Caudwell, Tobit; Sallamand, Pierre; Duband, Mélanie

Keyhole behavior during laser welding highly influences the final composition and the shape of the weld, which
determine resulting tensile strength. When different materials are welded together, the keyhole formation is likely to be
affected by a mismatch in physical properties. Thus, quantifying and understanding the potential keyhole asymmetry
and/or shift from joint line is important to choose appropriate welding conditions. To this end, novel experiments have
been conducted: keyhole development has been monitored laterally through a quartz window using high
-speed camera.
Two couples of materials were studied: aluminum/magnesium and copper/steel. The first couple that has close
absorption coefficients and fusion temperatures, so the keyhole develops preferentially in magnesium, presumably
because of its lower boiling temperature and latent heat of vaporization. On the other hand, for copper/steel couple, the
keyhole tends to shift from copper to steel, because of strong reflectivity of laser radiation and high thermal conductivity
of copper. This tendency inverts if energy density of copper melting is overpassed: for high laser power keyhole tends to
shift on copper side, because of lower boiling temperature and latent heat of vaporization.

Keywords: laser, keyhole, dissimilar welding


Laser beam welding in mobile vacuum
Reisgen, Uwe; Olschok, Simon; Holtum, Niklas; Jakobs, Stefan

Laser beam welding is firmly established in industrial processing in a variety of forms. Most applications arise in the
welding of thin sheets with sheet thicknesses up to 6 mm as a single process. For larger sheet thicknesses, the laser
beam is used as a part of a hybrid process, e.g. in combination with an arc process. A large variety of materials from
plastics to the typical use with steels to the applications with copper and refractory metals can be processed with the
laser beam. Due to the continuous development of beam sources and optics, a wide range of possible applications
ranging from microsystem technologies to heavy machine construction can be covered. However, in all processes of
laser beam welding of thick plate sheets, deficits in the achievable weld depth and seam quality are found in contrast to
electron beam welding. The new process variants of laser beam welding under low and medium vacuum (LaVa) and the
resulting welding under mobile vacuum (MoVac) were designed and developed as a joining process at the Welding and
Joining Institute ISF, RWTH Aachen University. The LaVa process closes the gap between the two beam welding
processes and opens up new applications for laser beam welding. Especially the laser beam welding under mobile
vacuum allows for the economical joining of thick walled components. The following article gives a short overview over
the development of the LaVa process and its further development, the MoVac process.

Keywords: Laser Beam Welding; Vacuum


Strain behavior during the initiation process of centerline cracks in laser welding of aluminum alloys.
Hagenlocher, Christian; Nolte, Jonas; Weber, Rudolf; Graf, Thomas

Welds in close edge position are affected by high transverse strains. These strains may lead to the formation of hot
cracks. The spatial and temporal behavior of these strains was analyzed during laser welding by means of digital image
correlation. In the experiments, MgSi alloyed aluminum sheets were joined by full penetration welding. Different
welding parameters were investigated. The results show, that the temporal change of the strain (i.e. the strain rate)
predicts the initiation of a centerline crack: A good agreement between the visible beginning of the centerline crack and
the position of the change from negative to positive strain rates was determined.

Keywords: Laser welding; hot crack; digital image correlation; aluminum alloys;


Low electrical resistance of aluminum to copper joints achieved with temporal and spatial laser beam modulation
Jarwitz, Michael; Fetzer, Florian; Weber, Rudolf; Graf, Thomas

Laser welding of pure copper (Cu-OF) to aluminum (Al99.5) in overlap configuration was investigated. It is shown, that
temporal modulation of the laser power reduces the electrical resistance by suppressing inherent instabilities in the
welding process when using copper as the top sheet. The resistance could be reduced by about 12% down to 1.7 μ in
this configuration. Spatial modulation of the laser beam allows to adjust the averaged copper content of the weld seam
when using aluminum as the top sheet by controlling the width and depth of the junction. With this, aluminum to
copper welds with low electrical resistance of 1 μ could be achieved.

Keywords: laser welding; copper; aluminum; dissimilar metals; laser power modulation; spatial beam modulation


Laser deep penetration weld seams with high surface quality
Schultz, Villads; Cho, Won Ik; Woizeschke, Peer; Vollertsen, Frank

In former publications, the authors showed that laser deep penetration welding with transversely beam oscillation and
wire feeding increases the gap bridging ability for butt-joint configurations. Within these experiments the following
phenomena was found. A circular cavity, the so-called buttonhole, was formed directly behind the laser spot at certain
oscillation frequencies. Its diameter corresponds nearly to the melt pool width. The existence of the buttonhole seemed
to correlate with high surface quality of the seam. In this study, welding experiments with 1.5 mm thick aluminum
sheets (EN AW-6082) in butt-joint configuration with filler wire delivery have been carried out. The results show that a
process window with a stable buttonhole exists. It is proven that buttonhole welding allows reliable welding processes
with very smooth almost ripple-free seam surface.

Keywords: laser beam welding; beam oscillation; visible seam quality; aluminium


Detecting and utilizing reflected radiation in laser beam brazing
Mittelstädt, C.; Seefeld, T.; Littau, F

Laser brazing of galvanized steel is a common application in the automotive industry thanks to excellent joint properties
and well-engineered system technology. However, the application utilizes copper base filler material and solid state
lasers for joining at a wavelength of about 1 μm resulting in high losses of reflected radiation. Since there are currently
no thrifty alternatives to either the beam source or the filler material, it is desirable to make use of reflected and
therefore yet unexploited radiation.
The state of the art process configuration for laser brazing features the laser beam impinging almost perpendicular to
the joint and a leading filler wire supply. This contribution addresses an alternative process configuration, at which the
laser beam was leading a steeply inclined filler wire. By this means, reflected radiation could be redirected onto the
substrate to achieve a preheating of the joint. For process monitoring a total of two cameras were used: On the one
hand, laser radiation monitoring (LRM) was achieved using a narrow-band filtered CMOS camera. On the other hand,
high speed camera monitoring (HSM) was used to analyze the braze metal transition and the wetting. By synchronizing
the respective image sequences from LRM and HSM, characteristics of the wetting process like the contour of the braze
metal on the substrate could be transferred from the HSM images to the LRM images by numerical computing. Thereby,
the part of the detected laser radiation that contributes to preheating of the substrate could be allocated and analyzed
in terms of its geometrical shape and relative intensity. Ultimately, by utilizing reflected radiation for preheating a deep
wetting of flange joints could be demonstrated and increased processing speeds could be attained.

Keywords: Joining; System Technology; Process Monitoring


Development of the methods of scandium utilization at the laser welding of aluminum alloys of Al-Cu-Li and Al-Mg-Li systems
Malikov, Alexander Gennadevich

Today, production of aeronautical equipment involves up-to-date high-strength aluminum alloys of reduced density
caused by lithium. Manufacture of wide-body aircrafts includes the technology of riveting of parts which means millions
of rivets. Now, this technology is giving place to welding. Welded joints of aluminum alloys have to meet tough strength
requirements. It is known that scandium used as a dopant increases the strength characteristics when the addition alloy
of aluminum alloys is created. This work deals with the scandium utilization in the laser welding process.
Experimental investigations have been carried out to optimize the laser welding process with the welded joint modified
by scandium. The technique of scandium utilization in the laser welding process has been developed. The effect of
scandium on the micro- and macro-structure, strength characteristics of the welded joints has been studied. It is found
that scandium increases welded joint elasticity for the aluminum alloy of the system Al-Mg-Li (by 20 %), and of the
system Al-Cu-Li (by about two times).

Keywords: laser welding, scandium, microstructure, strength, elasticity;


Mechanical and corrosionproperties of thin Hastelloy C-276 plate by pulsed laser welding with filler wire
Wu, Dongjiang; Ma, Guangyi; Wu, Dongdong; Lei, Mingkai

To meet the special requirements of Hastelloy C-276 welding in extreme environment, tensile tests and electrochemical
corrosion tests of thin Hastelloy C-276 plate by pulsed laser welding with filler wire (LWFW) were carried out. Laser
scanning confocal microscope (LSCM) and Energy Dispersive X-ray Spectrometry analysis (EDS) were carried out to study
the corrosion mechanisms and the corroded surface element distribution features. The results indicated, the tensile
strength of welding joint with a certain positive reinforcement was higher than that of base metal. Also, all tensile tests
were broken at the base metal. In the neutral solution, the corrosion resistance of the weld was greater than that of the
base metal. However, in the weak acidic solution, the corrosion resistance of the weld and base metal were similar. In
both solutions, the intergranular corrosion occurred at the weld, selective corrosion at the base metal, and a Mo-rich
passivation film was grown on the surface of the weaker corroded region.

Keywords: Pulsed laser welding; Filler wire; Hastelloy C-276; Mechanical properties; Electrochemical corrosion properties


Effect of material gauge on laser weld pool mixing between dissimilar steels
Métais, Alexandre; Sallamand, Pierre; Tomashchuk, Iryna; Gaied, Sadok

Welding dissimilar steels offers a great potential to increase safety and/or decrease the weight of cars while at the same
time reducing their cost. Thickness and grades have to be optimized to decrease weight of vehicle, but safety is also
assured by the quality of the joint. Thus, the prediction of the local chemical composition in the weld is essential to
determine the mechanical behavior of the weld.
The goal of the present paper is to present the effect of the thickness ratio on laser weld pool mixing between dissimilar
steels. Numerical results are obtained by a multiphysical model (including heat transfer, turbulent flow and transport of
species) developed within COMSOL Multiphysics finite element software. In order to validate the developed model,
SEM-EDX analyses on experimental cross-sections have been performed to obtain quantitative mapping of elements
distributions in the melted zone. The comparison shows a good agreement between numerical model and experimental

Keywords: Laser welding ; dissimilar materials ; melt pool ; mixing ; different thickness


Evaluation of a laser-hot-wire hybrid process for producing deep Net-Shape welds
Näsström, Jonas; Frostevarg, Jan

Joining thick steel sheets is a challenge for heavy constructions such as vehicle and offshore industries. This is usually
accomplished through time and resource consuming arc welding techniques; producing welds with wide HAZ. Laser
welding is often a valid option, having improved but limited penetration depths and gap bridging capabilities. Here an
alternative laser welding technique is applied, utilizing a laser beam to melt a resistance-heated filler wire, to fill a
narrow gap in multiple passes. To increase availability, the process uses readily available weld laser (defocused) and
welding equipment to heat and deliver heated filler wire. Using macroscopy, SEM and high speed imaging, the presented
process and its individual phenomena has been evaluated; identifying process strengths and limitations. It is shown that
the technique can produce multi-pass welds with a sound, near net-shaped surface. From evaluation, recommendations
are derived to help suppress imperfections such as centre-line cracking.

Keywords: Thick steel; Laser; Welding; Hot wire; High Speed Imaging; Multi-pass


Laser welding of HCT980XD at subzero temperatures to improve Heat Affected Zone material properties
Gerhards, Benjamin; Oliver, Engels;Reisgen, Uwe; Olschok, Simon

The ultrahigh strength dual-phase steel HCT 980 XD is a commonly used material for automotive body parts. The excel-
lent material properties result from a ferritic-bainitic matrix with embedded areas of martensite . When fusion welded ,
however, this brings the disadvantage of softeningin the heat affected zone (HAZ), which leads to crack initiation there
during tensile tests. The state of the art research of laser welding of these steel grades sugges ts that there is no possibil-
ity to cope with the strength and hardness drop in the HAZ. One possibility to improve the material characteristics is to
increase the heat dissipation out of the workpiece . Therefore, a clamping device was designed which completely consists
of copper, to improve heat dissipation. A continuous nitrogen gas flow suppresses condensation of moisture in the air to
prevent the formation of ice because of falling below the dew point. This experimental setup allows to carry out welding
trials at subzero temperatures of down to - 100 °C
Preliminary laser welding experiments conducted at - 90°C showed that it is possible to almost double the strain with an occurring crack in base metal during tensile tests. The cause for this change in material behavior is an alteration of mi-
crostructure in the HAZ, when welding trials which were carried out at room temperature are compared to trials welded
at -90 °C.
As 90°C is not a suitable temperature for industrial applications , further trials were conducted to determine the mini-
mum temperature required to a chieve the improved material behavior.

Keywords: Laser; HCT980XD; subzero temperatures; heat a ffected zone;


Joint tracking in zero gap laser butt welding using vision and spectroscopic sensing
Nilsen, Morgan; Sikström, Fredrik; Christiansson, Anna-Karin; Ancona, Antonio

A critical issue in robotized laser beam welding of zero gap butt joints is to position the laser beam correctly in relation
to the joint. An offset from the joint may cause a detrimental lack of sidewall fusion, a serious defect that is difficult to
detect even when using non-destructive testing. In the case of machined parts, when the joint gap and misalignment are
close to zero, available joint tracking systems will probable fail to detect the joint position. The proposed solution for this
issue is a dual sensing approach using a vision and spectroscopic system. The vision system consists of a camera, LED
illumination and matching optical filters integrated into the laser beam welding tool. Images of the area in front of the
melt pool are obtained and by applying a vision and tracking algorithm the joint position can be tracked. In the
spectroscopic system, a fast and high-resolution spectrometer captures the spectral emissions from the laser induced
plasma via a fiber coupled collimator. The plasma electron temperature is calculated from the spectra acquired by the
spectrometer and is then correlated to variations in the process. Welding experiments, using a 6 kW fiber laser have
been conducted to evaluate the performance of the systems. Promising results are shown by combining the information
from the vision and spectroscopic systems.

Keywords: Joining; Joint tracking; Optical spectroscopy; Vision sensor; Hybrid sensing


Investigation of solidification cracking susceptibility of type 316L stainless steel during laser beam welding using an in-situ observation technique
Bakir, Nasim; Pavlov, Vitaly; Gumenyuk, Andrey; Volvenko, Sergey; Rethmeier, Michael

Laser welding is a widely established manufacturing process in many industry sectors. Solidification cracking as well as
the weldability of materials is still since many years a highly contentious issue, particularly regarding the causes of the
hot crack formation. Many of studies have been conducted to determine the critical conditions of occurrence of the
solidification cracking. In this study a 2D in-situ observation technique in conjunction with laser diodes as the
illuminating source has been employed to measure the arising strain field during the laser beam welding process. For the
first time the employed technique enabled the in-situ measurement of the transient strain field at the surface of the
workpiece directed to the laser beam in the critical range, where the solidification cracking normally occurs. Thus the
critical threshold strain values at high temperatures characterizing transition from crack free to crack concomitant
welding process could be deduced.

Keywords:optical measurment technique ;critical strain;solidification cracking: Laser beam Welding


Modelling of temperature-controlled laser joining of aluminum and galvanized steel
Weller, Daniel; Fetzer, Florian; Weber, Rudolf; Graf, Thomas

Numerical modelling of a temperature-controlled laser joining process of aluminum to galvanized steel is presented.
First, the temporal evolution of the interface temperature is calculated by the use of an integrated virtual proportional-
integral-derivative (PID) controller. The obtained interface temperature is then used to predict the thickness of the
intermetallic layer by solving Fick’s second law assuming one-dimensional diffusion and considering the temperature
dependence of the diffusion coefficient. The results show good agreement with experimentally obtained values of the
thickness of the intermetallic layer.

Keywords: Laser joining; dissimilar materials; temperature control; intermetallic phase; process modelling


Laser beam submerged arc hybrid welding for thick metal sheets
Engels, Oliver; Lohrasbi, Hassan; Olschok, Simon; Reisgen, Uwe; Aueulan, Yingyot; Brezing, Alexander

The Laser beam Submerged Arc Hybrid welding technique (LB-SAW Hybrid) is a suitable welding process for joining thick
metal sheets of up to 50 mm plate thickness in double-sided single pass technique. Especially in pipeline manufacturing,
LB-SAW Hybrid has the potential to replace the currently used time consuming conventional welding processes.
However, despite the LB-SAW Hybrid being under constant research, the behavior of this welding process is still not
completely understood.
This contribution presents the latest welding results which were achieved with the LB-SAW Hybrid technique on metal
sheets with a plate thickness of 40 mm. The influence of the inclination angle of the laser optics and the SAW-torch
regarding the penetration depth as well as the metallurgical composition of the hybrid weld metal are shown. Due to the
hybrid process, it was possible to achieve an increase in the maximum reachable penetration depth of several
millimeters compared to a serial process setup using the same power. Additionally, the intermixing of the alloying
elements in the transition area between SAW- and laser beam-dominated weld seam area are demonstrated in this
contribution. Furthermore, the microstructure of the hybrid weld metal is presented and discussed.

Keywords: Welding ; Hybrid ; Laser beam ; Submarged arc


Welding of high thickness steel plates using a fiber coupled diode laser with 50kW of output power
Engels, Oliver; Weinbach, Matthias; Olschok, Simon; Reisgen, Uwe

Welding in the plate thickness range between 10 mm and 25 mm is increasingly gaining importance in the industry, e.g.
shipbuilding and pipeline production. Modern laser beam welding methods allow for economical joining in this thickness
range. Tolerances regarding the weld preparation, however, are challenging for such a welding process. Variable welding
gaps are unavoidable in this plate thickness range and need to be bridged efficiently and reliably.
Thanks to the perpetual development of the diode laser technology by Laserline, fibre coupled diode laser beam sources
with a continuous wave (cw) output power of 50 kW and above are available today. Diode lasers have the highest wall
plug efficiency of all laser systems reaching more than 50% overall efficiency and have proven themselves even in the
harshest of production environments. In combination with a large spot diameter this allows for the economical joining of
steel plates with a large plate thickness and the typically occurring tolerances.
This paper presents the first welding results obtained with structural steel in the plate thickness range between 20 mm
and 25 mm. Weldings in butt joint and T-joint configuration with sawed zero-gap and different pre-set joint gaps are
shown and discussed. Besides weld seams with a high degree of quality also typical weld defects and other distinctive
features are demonstrated.

Keywords: Diode Laser; high Power; Welding


Adaptive de-noising and smoothing technique for signal in the monitoring of laser welding
D'Angelo, Giuseppe; Pasquettaz, Giorgio; Giunti, Tommaso

Laser weld monitoring is usually based on the feedback from photodiodes able to provide information about radiation
from plume, the reflected laser light and the thermal condition of the melt. By using the optical emissions, it is possible
to evaluate laser process quality, in particular, to find out the relationship between emission characteristics and weld
quality characteristics. The optical signals detected during the laser welding are typically contaminated by different kind
of noises that affect the photo-detector. To avoid this phenomenon, it is necessary to smooth and de-noise the signal for
getting a “clean” signal. One of the most effective methods of dealing with noise contamination is to filter the noise out
of the signal while retaining as much as possible of the region of interest in the frequency spectrum. Advanced filtering
techniques such as discrete wavelet transforms, Wiener filtering have been used to that end. Although these methods
have proven useful, their main drawback is the complexity of devising an automatic and systematic procedure, i.e., a
mother wavelet function must be selected when using discrete wavelet transforms, the filtering function parameters
must be chosen when using the Wiener filter, etc. This work presents an alternative to the digital filtering methods. It is
a non-parametric technique based on principles of multivariate statistics. The original time series is decomposed into a
number of additive time series, each of which can be easily identified as being part of the signal, or as being part of the
random noise. The proposed technique significantly improves components localization. For giving practical applicability
to the proposed method, we compare the methods by analyzing signals detected during the laser welding,
demonstrating the expected advantages.

Keywords: Singular spectrum analysis; transient signal analysis


Spatter occurrence when using laser beam oscillated welding for aluminum
Sommer, Martin; Weberpals, Jan-Philipp; Heider, Andreas; Prokop, Mario

In the past years, laser beam welding has evolved to a cutting-edge technology for high production facilities such as
body-in-white manufacturing. Hereby, laser beam processing is characterized by a slender weld seam geometry and a
comparably low heat input. However, the possible occurrence of spatters leads to quality issues, for instance the
contamination of the part. Furthermore, a weakening of the weld joint induced by mass losses due to spatters can result
in a production breakdown.
Following recent trends of laser beam oscillation techniques, this research has drawn attention to the quantification of
the spatter formation and their trajectories depending on the oscillation pattern when welding thin-sheeted aluminum.
Experiments were performed with a high-power diode laser with beam converter. Multiple oscillation patterns were
realized by using a scanning unit, which allowed beam oscillations longitudinal and perpendicular to the feed direction.
By doing so, the rectilinear welding velocity is superimposed by the oscillation of the laser beam with a significantly
increased beam velocity, which lead to a reduction of the spatter formation in the weld pool. Moreover, the direction of
the occurring spatters is mainly depending on the oscillation pattern. For instance, a more defined release of the
spatters is accomplished by the means of a sinusoidal laser beam oscillation. Finally, the results show a reduction of the
spatter occurrence with the application of a circular laser beam oscillation.

Keywords: laser beam welding; beam oscillation; spatter; aluminum


Influence of oscillation parameter on melt pool geometry and hot cracking susceptibility during laser beam welding of high strength steel
Mann, Vincent; Holzer, Matthias; Hofmann, Konstantin; Korbacher, Andreas; Roth, Stephan; Schmidt, Michael

As the alloying content of high strength steels is increased in comparison to mild steels, the susceptibility for hot
cracking is raised simultaneously due to the larger solidification range of the materials. Besides the alloying composition,
hot cracking is also influenced by thermal strains and the temperature field within the welding process, which can hardly
be manipulated in conventional laser beam welding.
Here laser beam welding with beam oscillation offers new possibilities to influence the temperature field as well as the resulting thermal strains and also the solidification conditions. Thus within this paper the influence of oscillation
parameters on melt pool geometry and hot cracking susceptibility during laser beam welding of high strength steels is
investigated. The experimental results show, that solidification conditions are influenced and hot cracking susceptibility
is decreased by applying a superimposed beam oscillation during the welding process.

Keywords: Marco Processing; Joining; Welding


Three-dimensional X-ray transmission in-situ observation of spatter formation and reduction in laser welding of stainless steel
Kawahito, Yosuka; Nishimoto, Kouji; Kawakami, Hiroshi; Katayama, Seiji

The objective of this research is to reveal effects of angle of incidence or defocusing distance upon spatter formation
and reduction in melt-run welding of a SUS304 stainless steel plate with a 6-kW power laser beam on basis of a high-
speed video camera and a three-dimensional X-ray transmission in-situ observation apparatus. The high-speed video
images at 150 mm/s in welding speed show the convex molten-pool surface behind a keyhole inlet was elongated and
scattered as large spatters over 0.1 mm in size. According to the X-ray images, a melt flew to the elongated part at
approximately 2.3 m/s in velocity, which caused the rapid increase of the spatters in size. A 2-mm inner defocusing
distance or a 20-degrees angle of advance for an incident laser beam decreased number of spatter by half or one third
owing to circulating melt flow behind the keyhole inlet. It was revealed that the large spatter reduction was effective to
deceleration or change in direction of the melt flows behind the keyhole inlet, which led to not only suppressing
formation of the elongated surface but also improving the frequency that the spatters went back to the molten pool.

Keywords: melt flow, keyhole, spatter, angle of incidence, defocusing distance, laser welding ;


Hollow core waveguide for simultaneous laser plastic welding
Catania, Felice; Scaltrito, Luciano; Sirianni, Paolo; Messere, Massimiliano; Cocuzza, Matteo; Marasso, Simone; Perrucci, Francesco; Pirri, Candido Fabrizio; Ferrero, Sergio

Welding of plastics is a very important process in many industrial fields such as electronic packaging, medical
applications, textile joining and automotive. It is often used when finished structure is too large to mold, for cost
effectiveness or when dissimilar materials have to be joined. It is also employed in MEMs and Bio-MEMs applications, for
example for microfluidic devices, where joint areas are very small, and need an amount of precision that other
techniques can’t provide.
This work focuses on description of transparent laser plastic welding technique, comparing simultaneous and quasi-
simultaneous welding, and the development of an experimental setup for an automotive application. There are different
laser welding methods, like simultaneous welding, where all the joining interface is irradiated at the same time and
often includes a hollow guide to direct laser beam, and quasi-simultaneous welding, for example contour welding or
scanning welding, where the laser spot is driven on joining interface via movement of the source or changing the path of
the laser beam. An innovative tool end experimental setup was made to evaluate the simultaneous versus quasi-
simultaneous welding to join polymeric material for an automotive application. A DFSS design of experiment was used. A
LIMO laser bar diode @808nm with a maximum output power of 50 Watts, was coupled to a multi-mode 400 μm glass
core optical fiber (Boscottica) with a numerical aperture of 0.22, by a LIMO Beam Transformation System HOC 150/500
(1401.612). The beam at the output of the fiber was guided through two different optical systems to the welding joint to
test the two methods. A SANYO stepper motor was used for the quasi-simultaneous welding. Different kind of plastic
materials were joined, Hostacom TRC 787N and THERMORUN TT875NE/BE. We performed static pull tests and dynamic
pull test, and found optimum and baseline configuration.

Keywords: laser; joining; transparent laser welding; simultaneous welding;


Hybrid laser-arc welding of steel S700MC butt joints under different sheet thickness
Petronis, Egidijus; Cerwenka, Georg; Emmelmann, Claus

In this paper is discussed Hybrid Laser-Arc Welding (HLAW) of high strength steel S700MC. High strength steel is
commonly used at the heavy industry for the steel frames, beams and sandwich panels welding. Assurance of high
process productivity and repeatability it requires state of the art technologies. This investigation was focused for the
different thickness 6 mm and 8 mm butt joints with 2 mm misalignment. Aim of the paper was to obtain understanding
of non-standard seams weldability, microstructure and mechanical properties behavior based on the continuous wave
fiber laser IPG YLS-30000 and metal active gas (MAG) welding combination. Specimens were produced under various
laser-arc parameters and material setups, e.g. welding speed, laser power, wire feed rate speed, joint preparation.
Evaluation of process involved hardness, tensile strength and macroscopic cross-section analysis. The results will be
reported in this paper.

Keywords: Hybrid Laser-Arc Welding; high strength steel S700MC; fiber laser; mechanical properties; misalignment;


Challenges and solutions for copper Processing with high brightness fiber lasers for e-mobility applications
Grupp, Michael; Reinermann, Nils

Components and materials in the automotive industry are changing with the increasing demand for electric vehicles. The
use of copper in engines and in electric power transmission lines leads to new challenges in processing high reflective
materials in high volume. The lack of absorption of NIR lasers together with other physical properties of Copper and
Copper alloys caused in the past inefficient and instable welding processes. With the availability of high brightness and
high power fiber lasers these issues can be overcome by very high power density. This leads to an immediate melting
and creation of a keyhole which increases the absorption compared to the solid material. With adapted process
technologies such as high dynamic beam deflection the welding process can get stabilized and spatter and blowholes can
be avoided or reduced to a minimum. This paper gives an overview on the process chain of Copper processing from
cutting with high brightness fiber lasers to conditioning of Copper wire with high energy pulsed lasers to a stable and
reliably welding process.

Keywords: Joining; surface treatment; Copper; dynamic beam forming; high brightness lasers;


Influence of dual beam on process stability in laser beam welding of high strength aluminum alloy AA 7075
Holzer, Matthias; Zapf, Katrin; Kronberger, Stefan; Henkelmann, Florian; Mann, Vincent; Hofmann, Konstantin; Roth, Stephan; Schmidt, Michael

Lightweight applications in automotive industries require a steady enhancement due to CO2 emissions and thus light
weigth materials have to be applied. So, weldability of high strength aluminum alloy AA 7075 needs to be improved.
However, due to its alloying elements magnesium, zinc and copper with high solidification interval and low vaporization
temperature, the weldability is limited by hot cracking and keyhole instabilities lead to spatter formation. This paper
shows that by using dual beam in laser beam welding, the keyhole can be laterally enlarged and therefore stabilized.
Moreover, the energy input can be changed in order to decrease temperature gradient during solidification which leads
to a reduction of hot cracking. By applying different beam orientations and distances of dual beam, an improvement of
process stability and enhanced solidification conditions could be reached. Process stability is investigated by
implementing high speed imaging; hot cracking susceptibility is determined by metallographic inspections. In addition,
mechanical characterization shows an increase of weld seam quality and strength.

Keywords: Laser beam welding, dual beam, high strength aluminum, AA 7075, hot cracking


The influence of ambient pressure during laser beam welding of aluminium high pressure die castings on the occurrence of weld bead porosity
Teichmann, Fabian; Müller, Sebastian; Dilger, Klaus

Due to the occurrence of porosity and incomplete fusion, aluminium high pressure die castings are materials that are
known to be difficult to weld. Porosity is mainly caused by hydrogen which is trapped within the weld bead during
solidification as a result of insufficient degassing. This is aggravated by the increase in the solubility of hydrogen in
aluminium by a factor of around 20 when the temperature of aluminium exceeds its melting point. Electron beam
welding (EBW) and friction stir welding (FSW) are two state of the art technologies to minimise these defects. These
methods use high frequency beam deflection to enhance degasification or welding below melting temperature to
prevent the formation of porosity. Alternatively, common laser beam welding can be used as well but it has the
drawback of high sensitivity to casting quality. However, laser welding under low or medium vacuum (VLBW) offers
several well-known advantages, such as the increase of penetration depth or enhanced degasification when welding
ferrous metals. Consequently, the current study focuses on the influence of reduced ambient pressure during laser
beam welding on the occurrence of weld bead porosity when welding these materials. The investigations were carried
out for various high pressure die casting materials from different levels of quality. All results are based on the outcome
of x-ray computed tomography testing. It was shown that the overall weld bead porosity can be reduced and mechanical
strength can be improved when welding under vacuum conditions.

Keywords: laser beam welding; vacuum; aluminium high pressure die casting


Advantages of three-focal fiber technology in laser brazing of galvanized steel
Darvish, Mohammad; Esen, Cemal; Gurevich, Evgeny; Mamerow, Holger; Ostendorf, Andreas

Application of laser as a prominent high quality tool for brazing is growing more and more. Today, this technology
innovates new possibilities of highly precise and fast joining process which was not possible with the traditional
methods. In automotive industry, car bodies are mostly made of galvanized steel. Because of the zinc coating,
conventional laser brazing methods using monofocal beam face joining challenges. Normally, edges of the seam are
neither rectilinear nor well defined. As a result, the seam surface will not be smooth and splashes or pores can be
observed around the joint. A new brazing technology based on three-focal fiber is studied and produced by IPG Laser
GmbH to introduce a practical solution to all so far mentioned problems. The aim of this publication is to prove the
validity and advantages of three-focal fiber technology for brazing of galvanized steel. Optimal process parameters to
approach a very high quality and clean brazing results are defined. Brazed joints are evaluated by microsections and
microscope analysis.

Keywords: Laser joining; fiber laser; optics; zinc; three-focal; galvanized steel


Experimental investigations on laser-based hot-melt bonding and injection molding for laser-structured metal plastic hybrids
Amend, Philipp; Wolf, Michel; Mrotzek, Tino; Laumer, Tobias; Roth, Stephan; Gude, Maik; Schmidt, Michael

The use of thermoplastics in lightweight construction is continuing to grow. This implies the need for suitable joining
techniques to combine thermoplastics with other materials, such as metals, to gain tailored multi-material parts. In this
paper latest results of experimental investigations on laser-based hot-melt bonding and injection molding for laser-
structured metal plastic hybrids are presented. As materials stainless steel and short-fiber reinforced polyamide are
used. The stainless steel surface is structured with a nanosecond pulse laser before joining to improve the mechanical
adhesion between the dissimilar materials. Thereby, different structure depths in the range between 16.6 ± 1.2 μm and
66.5 ± 2.5 μm as well as different hatch distances between 70 and 300 μm are realized. The laser-based joining process is
carried out irradiating the metallic surface multiple times. Positioned below the metal in T-joint configuration, the
thermoplastic melts as a result of heat transfer and acts as hot-melt. Besides, hybrid joints are manufactured using
injection molding. For experiments, the mold temperature as well as the melt temperature are varied.
Regardless of the joining process, the hybrid joints are mechanically characterized by tensile tests. The results demonstrate that for both joining processes strong laser-structured metal plastic hybrids can be realized.

Keywords: Laser-based hot-melt bonding; injection molding; multi-material design; laser structuring


Laser beam welding in vacuum of dissimilar metals for surgical instruments
Otten, Christian; Stefan Jakobs;Klein, Stephan; Markus Schleser

Laser beam welding under vacuum to weld the austenitic stainless steel X20Cr13 to the martensitic stainless steel
X5CrNi18-10 has been investigated. The objective of this study was to determine process parameters to produce a full
penetration joint and to examine weld quality and mechanical properties. It could be demonstrated that a 3 mm depth
joint could be realized with very good mechanical properties and without any imperfections by using only 450 W beam

Keywords: laser beam welding in vacuum; stainless steel; welding of dissimimilar metal


Spiking behaviour and capillary instabilities observed during welding of ice
Berger, Peter W.; Fetzer, Florian; Hu, Haoyue

The spiking phenomenon is well known in partial penetration welding of metals. Depending on the welding parameters,
pore filled spikes can be found in longitudinal sections. Unfortunately, the generation of those spikes cannot be
observed even with X-ray videography due to the highly dynamic behavior and small size of the capillary tip. Transparent
materials such as ice, however, allow direct inspection of the capillary’s dynamic behavior with high local and temporal
resolution. The pores inside of spikes indicate that the spiking process is at least sometimes accompanied by capillary
instabilities. These instabilities can also be visualized during welding of ice. It was found that the frequency of capillary
fluctuations can be much higher than the spiking frequency. Measurements of the capillary depth with inline coherent
imaging confirm this behavior also for the case of welding metals.

Keywords: laser welding; spiking; capillary; high-speed observation; simulation


Perspectives of laser-beam welding of ultra-high steels
Dahmen, Martin; Lindner, Stefan; Petring, Dirk

The increasing demand for sustainable manufacturing in sheet metal processing and vehicle manufacturing led to the
application of new alloys with ultra -high strength and increased ductility. Due to strengths of up to 2 GPa in martensitic
steels or the increase of strength by twinning in high -manganese steels me chanical joining is not possible. Fusion
welding is an option where the limitation of energy input leads to the application of laser beam welding as the joining
technology in this class of materials . Investigations on welding similar and dissimilar joints of martensitic stainless steel
and a stainless high -manganese steel and a variety of different steel grades , respectively, were undertaken.
Contradictory demands on the conduct of the welding process were revealed. Martensitic steels require a heat
treatment whereas the TWI P steels react positively on a mechanical treatment. Especially in dissimilar welds effects of
the gauge length, the strength of the individual partners, and local micros tructure in the weld caused by intermixing
effect determine strength and fracturing of the joints. The contribution gives an overview over the results and shows the
potential for the application of laser beam welding for joining in assembly of structural parts.

Keywords: Joining; laser beam welding; ultra-high strength steels; high-manganese steels; mechanical properties; weld metallurgy


Laser beam welding and straightening of Titanium T-joints for aircraft structures
Alvarez, Pedro; Zubiri, Fidel; Froend, Martin; Fomin, Fedor; Riekehr, Stefan; Kashaev, Nikolai; Bauer, Stefan

This work deals with the development of laser beam welded (LBW) fuselage structures made of Titanium alloys. State of the art disk and fiber lasers have been employed to weld T-joints between Titanium Grade 2 sheets and Ti-6Al-4V Grade 5 stringers. Both skin sheet and stringers had a thickness of 0.8 mm. Optimum LBW parameters and process window have been determined for both laser sources with 400 and 500 microns spot size, respectively. Full penetration welds and minimum underfills (less than 80 μm) have been achieved without the addition of filler metal. Due to the reduced thickness and stiffness of the skin, LBW led to significant distortion in samples with multiple welded stringers. A subsequent laser straightening (LS) process has been applied in order to reverse welding induced distortions. The results show the feasibility of manufacturing these aircraft structures based on T-joints between Titanium alloys. The work is completed with the analysis of ongoing developments to ensure required quality standards in large 3D HLFC structures, including seam tracking and process monitoring.

Keywords: laser beam welding (LBW); laser straightening (LS); titanium alloys; T-joints; aircraft structures