Macro Processing: Joining (Welding, Brazing) (LiM 2015)

Flow and bead formation characteristics in high power laser welding at different welding positions
Suck-Joo Na, Sang-Woo Han, Sohail Muhammad, Linjie Zhang, Andrey Gumenyuk, Michael Rethmeier, Miikka Karhu, Veli Kujanpaa

The numerical simulations of high power laser keyhole welding at different welding positions are performed by using Volume-Of-Fluid (VOF) method. The main material is SS400. The multi-physics phenomenon is considered using several models, such as the heat flux of Gaussian heat source, the recoil pressure with Clausisus-Clapeyron equation, the Marangoni flow considering temperature gradient, the buoyancy force with Boussinesq approximation, the additional shear stress and heat source due to metallic vapor ejected through keyhole entrance, the bubble formation assumed as adiabatic bubble, and the multiple-reflection by solving proper discriminant, are used. To analyze the fluid flow pattern, the concept of streamline formed by reconstructing the value of the velocity vector is applied. Partial and full penetration cases at different welding positions are considered. The welding position seems to have only a minor influence on bead formation characteristics in both cases. This is probably due to the fact that th e recoil pressure has a major influence when compared to other driving forces. The flow characteristics and fluid velocity in weld pool are analyzed to compare the gravity direction effect at different welding positions. It is observed that the clockwise flow pattern is mainly formed by the recoil pressure on the keyhole surface in the case of partial penetration. The laser energy can't maintain the whole weld pool when the weld pool size becomes too large. And then the solidification starts from the middle part of weld pool and a necked weld pool shape is formed. In the full penetration welding, the weld pool flow patterns are affected by the leakage of laser power through the full penetration keyhole and also by surface tension. Furthermore, the numerical simulation of full penetration welding with AISI316L is also performed to analyze the effect of material properties. The weld bead shapes obtained by simulations were compared with the corresponding experimental results to confirm the validity of the process models adopted and the CFD simulation tool.

Keywords: Macro Processing (Joining, Welding); High power laser keyhole welding; Numerical simulation; Different welding position;
Flow pattern; Weld pool


Energy-Efficient Industrial Production with High-Power Disk- and Direct Diode-Lasers
Matthias Koitzsch, Volker Rominger

This paper presents and discusses two main aspects of energy-efficient production using laser technology: First, the laser
as a tool and the evolution of important laser characteristics; second, potential improvements in design and novel
approaches in production due to the use of lasers are discussed.

Keywords: Energy efficiency; wall plug efficiency; high power disk lasers; high power direct diode lasers


Yb:fiber laser joining of Ti-6Al-4V and AA6013 dissimilar metals
Aline Capella Oliveira, Rudimar Riva, Natalia Maria Antonangelo Athanazio

Titanium and aluminum alloys have been considered to applications in structural components of aircrafts. A common
phenomenon in Al/Ti joints is the presence of brittle intermetallic compound (IMC) in the junction interface region. Laser
beam joining of dissimilar metals can generate acceptable limits of IMC in this region. In the present work, Ti-6Al-4V and
AA6013 sheets (1.0 mm and 1.6 mm thick, respectively) were joined by an Yb:fiber laser. Butt joints were conducted by
varying the relative positioning of laser beam toward Al alloy, from 0 (interface joint) up to 0.5 mm. The welding speed
and the laser average power were fixed , 3.0 m/min and 1000 W, respectively. Metallographic analyses were performed
on the joint cross-section by optical microscopy. The positioning of laser beam has a pronounced influence on the
quality of the joints. Between 0.2 and 0.4 mm, the Ti alloy was not melted, promoting a joint with no severe defects. On
other hand, when the laser beam was positioned near of the interface area, a melted region containing a mixture of
titanium and aluminum was formed with the presence of some defects. EDS line scanning in the junction interface
showed a decreasing of IMC layer in the joints without melted titanium alloy, i.e., with laser beam positioned toward Al
alloy between 0.2 and 0.4 mm. The thickness of interfacial IMC layer was about 15-30 times lower than the interfacial
IMC layer for the melted Ti alloy condition, reaching the mean value of 15 μm.

Keywords: joining; dissimilar metals; Yb:fiber laser


Influence of different zinc coatings on laser brazing of aluminum to steel
Tim Radel, Marius Gatzen, Peer Woizeschke, Claus Thomy

Joining of aluminum to steel is a common challenge in light-weight structures. In case the steel is zinc-coated, aluminum
can be joined to steel using laser processes without the use of flux. However, this is not yet fully understood.
In this paper, the influence of type and thickness of the zinc coating on the wetting behavior of molten aluminum on steel sheets was investigated in bead-on-plate laser brazing. Two hot-dip and two electro galvanized zinc coatings with thicknesses between 6 μm and 10.5 μm were analyzed. Appropriate wetting was observed for all four coatings in the
experiments. The results show that the solidification time, the spreading time and the final wetting length decrease with
increasing coating thickness. Aluminum seams on hot-dip galvanized steel sheets appear smoother than seams on electro
galvanized steel sheets.

Keywords: dissimilar materials, zinc coating, laser brazing


Laser Beam Welding of press hardened ultra-high strength 22MnB5 steel
Benjamin Gerhards, Uwe Reisgen, Simon Olschok, Oliver Engels

Lightweight design is the most challenging topic for OEMs worldwide of this and the following decades. Thus ultra -high
strength steels like the press hardenable 22MnB5 Boron steel gain further importance as construction materials.
Through the press hardening process where the parts are heated up to 900 °C and then quenched in a die, the 22MnB5 steel gains a fully martensitic structure with an ultimate strength of 1500 MPa. To prevent scaling, the steel sheets are usually protected by an aluminum-silicon layer which remains on the parts after the press hardening process. As good as the press hardened 22MnB5 steel is as construction material, there are some issues when it comes to joining. Each heat input into the material harms the costly adjusted material properties. Thus, each welding process reduces the strength in the heat affected zone considerably. Furthermore, each fusion welding process brings the aluminum -silicon
layer into the weld pool.
The effect is a primary problem of laser beam welding. Due to the high welding speed and the missing filler material there
is only little weld pool movement. Especially in the case of welding overlap joints this leads to precipitation of aluminum
at the fusion line, causing a strong metallurgical notch.
This means there are two weaknesses of laser welded 22MnB5 seams: the heat affected zone where the strength is re-duced and the precipitation of aluminum at the fusion line. The latter usually bears the failure during lap shear tests.
Removing the aluminum-silicon layer can shift the crack from the fusion line to the heat affected zone.

Keywords: Laser; 22MnB5; sheet metal; uhss


3D-capable Coaxial Laser Brazing Head
Markus Kogel-Hollacher, Alexander Gatej, David Blázquez-Sánchez, Andreas Bobrowski, Andreas Niete, Nicholas Blundell, Kevin Withers

Laser processing heads for brazing applications still operate with lateral wire feed suffering from two major disadvantages: the reorientation and the low joint strength. The head’s reorientation becomes very complex if small radii are to be processed. Moreover, the joint strength is limited due to shadowing effects of the laser beam by the filler wire. Thus, the preheating of the wire and the base material are inhomogeneous and lead to a reduced wetting ability and thus to reduced strength of the joint. In order to overcome these limitations, the optical system design, which is developed for diode and solid-state laser applications, enables the generation of a donut shaped laser intensity distribution with a concentric and obscuration-free wire feed. Thus, it provides a full-3D-processing capability without lateral interference contours. Despite of the current design still operating with an external seam tracking system, the optical design is already prepared for an internal, coaxial tracking. Despite of the design aiming on the brazing industry, applications in the area of aluminum welding or cladding are also conceivable and currently under investigation. Particularly cladding is of great interest,
since the 3D-capability is of major value.

Keywords: laser brazing, cladding, coaxial wire support, 3D-capability


Robust false friend detection via thermographic imaging
Karin Heller, Steffen Kessler, Friedhelm Dorsch, Peter Berger, Thomas Graf

During the laser deep penetration welding process several weld faults may occur in the solidified material and exert influence on the thermal state. The online detection of an insufficient bonding during overlap welding (commonly referred to as “false friend”) is a specific challenge, because the welding result at the upper and lower seam seems to be satisfactory, but there is no fusion between the two parts.

The experimental sensor setup provides a coaxial thermographic image of the process, which allows conclusions about changes inside the material, if they disturb the surface temperature sufficiently enough. This is the case, when a false friend prevents the heat flow to the lower part of the workpiece and a defined attribute of the thermal image is changed.

To obtain a better scientific understanding of the experimental thermographic results, the behavior of the thermal attribute is fundamentally analyzed within the scope of a simple laser welding model for which the temperature field can be computed analytically. To this case the model of Rosenthal, 1946 (reprocessed by Rykalin, 1957 and Carslaw and Jaeger, 1986) with a moving point source on the surface is adapted to a plate with finite thickness. The thermal information flow from the inside to the top surface is influenced by the processing parameters, laser power and feed rate, by the plate thickness and the material properties. The characteristics in the bulk of the material affects the top surface temperature. This becomes visible in the thermal image. Where and how this influence is detectable is investigated by taking the reflections on the bottom side of the workpiece into account.

A robust detection of a loss of fusion during an overlap welding is predicted by the analytical approach and validated by experiments.

Keywords: Welding; Process Monitoring; Thermal Imaging; Analytical Welding Models


Correlation of keyhole dynamics and pore formation
Joerg Volpp, Frank Vollertsen

Imperfections like pores occurring due to high process dynamics during laser deep penetration welding reduce the weld
quality and the strength of welded joints. It is assumed that keyhole instabilities are responsible for the high process
dynamics. In order to better understand the correlation between pore formation and keyhole dynamics an analytical
process model has been developed describing keyhole radius fluctuations in different depths depending on the process
parameters. Modelled radius oscillation frequencies have been compared to experimentally measured process emissions.
Frequency spectrums of acoustic process emission observations show similar tendencies of keyhole dynamics compared
to the calculations. For pore detection x-ray photography has been used while pore percentage and pore number in the
weld seams have been evaluated. The pore formation in the solidified weld seam is compared to the observed dynamic
characteristics during the process. Higher keyhole frequencies tend to correlate with increased pore numbers at reduced
pore sizes.

Keywords: Laser deep penetration welding; Keyhole dynamics; Acoustic process emission, Pore formation


Properties of steel-aluminum joints generated by combining continuous and pulsed laser radiation
Sascha Frank

The combination of a continuous and a pulsed laser beam in a common process zone makes it possible to join aluminum
and galvanized steel. This method does not require the use of chemical fluxes. It can be applied to different joint
geometries such as double-flanged joints and lap joints. The basic microstructure of these joints is discussed using
metallographic cross-sections. The properties of the intermetallic iron-aluminum compounds are examined in greater
detail using methods such as energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM).
The results from these measurements indicate that the use of wire material alloys containing silicon leads to the
formation of ternary phases. The joints exhibit a high strength in mechanical tests even when cyclic loads are applied.

Keywords: Laser joining; welding; brazing; hybrid; galvanized steel; aluminium; zinc; mixed-metal joints


Laser-GMA-Hybrid Welding of high strength multi-material joints
Felix Möller, Helge Kügler, Sven-F. Goecke, Frank Vollertsen

A particular challenge for welding 22MnB5 and DP800 are the coatings of each steel sheet. As a prevention of oxidation during press-hardening 22MnB5 sheets are protected with an aluminum silicon coating. The dual phase steel DP800 is zinc coated in many cases. In this described case the steel sheets are hot-dip galvanized. The evaporation temperature of zinc is below the melting temperature of steel. For that reason a zinc degassing gap between the sheets is necessary for welding in overlap configuration. At BIAS a laser-GMA-hybrid welding process was established for welding 22MnB5 to DP800. With this process combination weld seams reach a strength exceeding the strength of the heat affected DP800. Tensile tests prove yield strength of 800 N/mm² with failure location in the heat affected zone of DP800. The laser beam was oscillated 0.7 mm transverse to the feed direction with a frequency of 200 Hz. A feed rate of 3 m/min was realized. The laser beam was able to vaporize zinc 5 mm ahead of the GMA -process which was carried out with a wire feed rate of 14 m/min. For this hybrid welding process a 1 mm thick G3Si1 wire was used. Occurrence of pores and spatters could be avoided by a gap of 0.4 mm between overlapping sheets. The aluminum silicon coating of 22MnB5 accumulates at the seam tip.

Keywords: Macro Processing; Welding; Laser; GMA; Hybrid; DP800; 22MnB5


Laser welding inspection on aeronautic material with non-contact real-time optical beam deflection sensor
João Marcos Salvi Sakamoto, Renan Borges Marques, Rudimar Riva, Cláudio Kitano, Gefeson Mendes Pacheco

In this work we show the application of an optical beam deflection sensor for detection of airborne thermal and acoustic
waves generated by laser welding of aeronautical aluminum (AA 6013), and the sensor's potential for process inspection
and control. The principle of working of the sensor is based in the measurement of the refractive index variation (of the
surrounding medium) induced by temperature or pressure variation. The laser welding conditions generates the index
variation which, in turn, deflects the optical beam, modulating the optical intensity. Therefore, the sensor is able to
perform non-contact, non-destructive and surface roughness independent measurements.

Keywords: optical beam deflection; real-time; mirage effect; photothermal deflection; non-contact inspection.


Three-dimensional, multi-factor monitoring and control of laser keyhole welding by inline coherent imaging
Christopher M. Galbraith, Paul J. L. Webster, Cole Van Vlack, Daniel R. Buckley, James M. Fraser

Direct measurements of keyhole geometry such as those provided by inline coherent imaging (ICI) are expanding options for process monitoring for industrial laser keyhole welding. ICI has been used to demonstrate real-time closed loop weld depth control. However, practical processing conditions demand a more robust registration of tool-path to workpiece than the position of the process optics alone can provide. Combining ICI with a beam directing system at the camera port of a commercial, fixed-optic laser head, we gain the ability to dynamically steer the ICI beam across the sample surface at millisecond timescales. Here we show how this 3D capability can be used to implement multiple process monitoring and control threads quasi-simultaneously. By sampling data from multiple points in and around the phase change region, we are able to implement autofocus and continuously correct motion error and distortion in the measured keyhole depth. In addition, transverse  measurement sweeps of the leading region in common joint configurations enable seam-tracking for closed-loop correction of imperfect part geometry. We present results demonstrating seam-tracking and autofocus update rates on the order of kHz while simultaneously providing weld monitoring for quality control. The combined realization of these capabilities makes ICI a more robust and versatile weld process control and quality control solution.


3D weld seam characterization based on optical coherence tomography for laser-based thermal joining of thermoplastics to metals
Philippe Ackermann, Guilherme Mallmann, Robert Schmitt, Jean Pierre Bergmann, Klaus Schricker, Martin Stambke

Laser-based thermal joining of metals to plastics shows a great potential for functional constructions especially in terms
of light weight design. Thereby, the process strategy and time-temperature regime affects the resulting joint zone;
hence process monitoring is a central issue. State of the art monitoring and quality assurance systems for this
technology are limited as no direct information about the joining zone itself is given. Within this paper, a new method
for the quality assurance in metal-plastic hybrids is presented using optical coherence tomography (OCT). This approach
enables the measurement of the joint geometry as well as bubbles, imperfections and the wetted bonding area.

Keywords: optical coherence tomography, metal-plastic joining, laser-based thermal joining, process monitoring and control


Influence of a second heat source on the distortion behaviour during laser beam welding
Falk Nagel, Jean Pierre Bergmann

Due to its several advantages like low heat input, high flexibility and welding speed, laser welding is an established process within numerous industrial fields such as automotive but also food and pharmacy industry. A restricting phenomenon during laser welding of thin sheets is distortion, which can result in a change of the gap width between the welded parts and hence, highly affect the process performance itself and lead to reduced joint and component quality. The distortion is caused by thermally induced strains and the shrinkage in the weld, respectively. By applying a second heat source positioned in a defined distance behind the main heat source, the shrinkage can be counteracted, hence optimizing the welding process. For this investigation, austenitic stainless steel 1.4301 sheets were welded with a CO2 laser, and as a second heat source a diode laser was employed. Several parameters such as travel speed, power and position of the second heat source were varied to evaluate their effect on the process and the joint properties. The influence of the second heat source on the welding process and the welding result is described. The application of a second heat source allows lower demands on the dimension accuracy and clamping devices in order to realize good
welding results.

laser welding, autenitic stainless steel, distorion, CO2 laser, diode laser


Controlled metal transfer from wire by a laser-induced boiling front
Alexander Kaplan, Mohammad Javad Torkamany, F. Malek Ghaini, Mikko Vänskka, Antti Salminen, Karl Fahlström, Joakim Hedegård

The addition of wire is an option during laser welding, laser cladding or laser additive manufacturing. By high speed
imaging of leading wire addition during fibre laser keyhole welding it was observed that for the 40 experiments under
consideration the wire tip always established a concave boiling front. The front appears similar to a keyhole front and is
sort of a continuation of the keyhole, owing to the leading wire employment. For most of the parameters the melt is
transferred downwards from the wire tip into the melt pool surrounding the keyhole front. In other words, hardly any
uncontrolled spatter to the sides was observed. A trailing wire would normally tend to a completely different behaviour.
Typical as well as limiting phenomena of the wire melt transfer mechanism are presented and discussed. Controlled
vertical melt transfer of the wire through the ablation pressure from a laser-induced boiling front, either in contact with
the workpiece surface or positioned higher above, can be a desirable mechanism of metal deposition for the different
techniques, namely welding, surface treatment or LAM. By suitable choice of the laser power density above the boiling
threshold, the here observed mechanism can be applied in a controllable manner. An interesting technique option is
lateral beam oscillation for example by a galvanometer optics which shears off the melt in a manner similar to remote
fusion cutting. The process limits become different to the static technique. The wire melt transfer technique has the
potential to be developed further towards a highly controllable remote drop transfer, e.g. in terms of direction.

Keywords: wire addition; melt transfer; laser-induced boiling front; keyhole welding; LAM


Capillary geometries during welding of metals observed with X-ray technique and calculated using a ray-tracing tool and a finite volume program treating heat diffusion and fluid flow
Peter Wolfgang Berger, Andreas Heider, Meiko Boley

To understand and to predict the seam properties in deep-penetration laser welding, it is important to know the shape of the capillary. High-speed X-ray videography is an adequate technique to observe the average shape and the temporal development of the capillary. Other observation methods use transparent materials in front of the workpiece or instead of the metallic workpiece. Capillary features, which are observed by X-ray technique and which are typical for different materials, will be compared. The investigated materials have in common, that the lower part of the capillary often shows a different behavior compared to the upper part. For example the lower part shows more fluctuations can be more inclined or more often exhabits bulging on the rear side. To understand the observed phenomena better, calculations can be performed. The calculations presented here use a model which combines a ray-tracing module with a finite volume program treating heat conduction and fluid flow. In this model the surface of the capillary is defined by a large number of triangles which are rearranged after each time step in order to fulfill mass, momentum, and energy balance. The structure of this surface is perfectly suited for fast ray tracing. With this model some interesting features of the capillary shape and of the temporal behavior observed during the experiments could be described although momentum transfer within the vapour was not included in the model.

Keywords: laser welding, capillary geometry, modeling, simulation, X-ray technique


Influence of residual stresses induced by forming on the hot cracking sensitivity of laser welding processes of AlMgSi aluminum alloy
Peter Stritt, Christian Hagenlocher, Rudolf Weber, Thomas Graf

In industrial production forming processes are often followed by joining processes such as laser welding. In
most cases forming processes like deep drawing create residual stresses in the work piece. The influence of
those residual stresses on laser welding processes in terms of hot crack formation and the resultant weld
quality are major outcomes of the presented paper.
Cups of 6080 aluminum alloy were produced by deep drawing and the resultant residual stresses were
determined by experiment and simulation. Knowing the local stresses, welding experiments were performed
on the formed part and compared with welding experiments on flat aluminum sheets, which were stress
free before welding.
Several known publications related the hot cracking sensitivity to the local stresses during the dendritic
solidification of the melt. The experiments showed that the addition of residual bending stresses caused by
forming increased the hot cracking sensitivity. This can be derived from analysis of high-speed images during
the welding process and the metallographic analysis of the weld seam after the welding process. Finally
these results were evaluated in the context of existing theories on hot crack formation.

Keywords: Laser welding; aluminum; hot crack; residual stress; forming


Fundamental analyses of hot cracks in remote laser welded aluminium fillet welds
Hans Langrieger, Frank Krafft, Martin Mensinger, Florian Oefele

Remote laser welding is a highly efficient technology for the automotive body in white series production. However, the
application of remote laser welding to high strength aluminium alloys is restricted due to hot cracking. Recent research
activities mainly focus on centerline hot cracks in welds in close-edge position. Crack-free welds can be created within an
edge distance of smaller than 2 mm. In this study remote laser welded fillet joints of high strength EN AW-6082 T6 alloy
were analyzed experimentally concerning their hot cracking behavior. This type of joint design can avoid centerline
cracks. Yet, cracks in transverse direction on a microscopic scale were found along the weld seam by x-ray radiography.
Scanning electron microscope images confirmed that the cracks formed in semi-solid-state. In order to investigate the
influence of welding parameters on the formation of transverse hot cracks a full factorial study regarding the welding
speed, the laser power, the sheet thickness, the protrusion of the lower sheet and the beam position was conducted. In
this study the welding speed and laser power were found to have a major effect on hot crack formation. Additionally
high-speed imaging was used to observe the exact moment and the location of hot crack formation. It can be seen that
transverse hot cracks arise not at the end of the weld pool but beside the weld pool between the weld centerline and
the seam edge. As the solidification behavior during the welding process is a key factor in hot crack formation the
influence of melt pool geometry on hot crack formation was investigated by high-speed imaging. Based on these results
a beam oscillation method was developed to control the melt pool morphology leading to reduced hot cracks in fillet

Keywords: remote laser welding; fillet welds; transverse hot cracks; high strength aluminium


Analysing Hot Crack Formation in Laser Welding of Tempered Steel
Marcel Schaefer, Nicolai Speker, Rudolf Weber, Thomas Graf, Thomas Harrer

Tempered steel is used in many automotive and aviation parts due to its beneficial material properties such as the
combination of high tensile and fatigue strength. Therefore, steel grades like e.g. 42CrMoS4 are used for steering
knuckles, axles, connecting rods, drive shafts, pinions, gearwheels, pistons and other highly stressed components (Key to
Steel, 2007). Laser welding such parts has the advantage of high welding speed, low heat input, low distortion and high
weld seam quality (Huegel and Graf, 2014).
However, seam defects may occur which reduce weld seam strength. In that respect, hot cracks are severe weld defects
which are not tolerated, according to ISO 13919-1. In general hot crack formation depends on three factors affecting
each other (Cross, 2005): energy deposition into the part (heat input; welding parameters), part design (geometry;
restraining conditions) and material properties (solidification temperature range).
To separate the influence of the above-mentioned factors welding experiments were conducted with varying parameters including beam focusing, beam quality and laser power for partial or full penetration depth. Examining the
welding process was done by means of 2D x-ray inspection and longitudinal respective transversal cross sections.
In this paper the analysis of continuous crack formation within laser welds in tempered steel will be presented. Additionally, possibilities to reduce and even avoid such severe seam defects will be discussed. Moreover, a new approach of explanation for the formation mechanism of transverse hot cracks will be presented.

Keywords: Tempered steel; laser welding; hot cracks; 2D x-ray inspection; transverse cracks; 42CrMoS4


Online crack detection during laser welding using passive thermography
Daniel Weller, Peter Stritt, Florian Fetzer, Rudolf Weber, Thomas Graf, Cyrille Bezençon, Jörg Simon, Corrado Bassi

The non-destructive testing of laser welds within the process chain of industrial production is of prime importance for
the quality assurance. In this paper passive thermography was used to detect centerline cracks. These hot cracks are
likely to occur when welding car body sheets in an overlap configuration close to the edge. Welding at this position leads
to a strong heat accumulation. This results in a non-symmetric temperature field causing a heat flow from the edge into
the body across the weld seam. If the weld seam is split due to a centerline crack this heat flow is significantly disturbed.
It was found that this characteristic change of the heat flow is clearly measurable and can be utilized to detect hot
cracking during welding using an infrared camera.

Keywords: Laser Welding, 6000 Series Aluminum, Hot Cracking, Thermography, Process Monitoring


Influence of filler wire and focus diameter on crack formation in laser beam welding of high strength aluminum alloys
Matthias Holzer, Fabian Hoppe, Vincent Mann, Konstantin Hofmann, Florian Hugger, Stephan Roth, Michael Schmidt

Light weight components for automotive industry become more important with increasing demand for electronic driven
vehicles. Up to now, high strength aluminum alloys have a wide use in aeros pace sector. To establish these alloys also in
automotive sector, the development of improved welding techniques are required. However, due to its alloying
elements magnesium, zinc, silicon and copper which increase solidification interval, the weldability of high strength
aluminum alloys of 5xxx, 6xxx and 7xxx series is limited by hot crack formation. Hence, metallurgical as well as systemic
approaches are needed to enable weldability of these alloys. The present paper discusses the influence of different filler
wire materials and spot diameters on hot cracking. Therefore a disc laser is used to weld aluminum alloys without and
with filler wire. Mechanical and metallographic analysis display quality of welds. In particular, tensile tests,
microhardness measurements and cross sections are shown in order to compare welds of 5xxx, 6xxx and 7xxx. It results
that a small focus diameter of 340 μm by trend reduce hot crack formation for AA 6082-T6 and AA 7075-T6 due to low
heat input. Moreover, the use of filler material decreases also hot cracking, while AlSi5 can be identified to have highest
influence with respect to avoid hot crack formation for the hardenable alloys.

Keywords: Joining, laser beam welding, high strength aluminum alloys, hot crack formation


Fundamental Research of 100 kW Fiber Laser Welding Technology
Seiji Katayama, Masami Mizutani, Yousuke Kawahito, Shingo Ito, Daichi Sumimori

Recently 100 kW fiber laser is commercially available, and so the development of welding technology with 100 kW fiber
laser is mostly expected for the utilization of a high power laser. First a focusing optic, a welding nozzle and a power met er
were designed and manufactured for such a high power laser, and laser welding was performed under various conditions.
The penetrations of laser weld beads were investigated and welding phenomena were observed. Consequently deeply
penetrated laser weld beads of more than 40 mm in depth could be produced at 100 kW and 2 m/min, and a sound full -
penetration weld bead could be made in a stainless steel plate of 70 mm in thickness with two passes from both surface
sides. Moreover, it was confirmed that laser weld beads of about 100 mm to 125 mm in depth were formed under the
welding conditions of the high laser power of 50 to 70 kW, the low speed of 0.3 m/min and the low vacuum of 1 kPa.

Keywords: Fiber laser, laser welding, 100 kW laser power, laser welding in vacuum, penetration depth, porosity


Influence of Ambient Pressure on Spatter Formation during Laser Welding of Copper
Andreas Heider, Thomas Engelhardt, Rudolf Weber, Thomas Graf

Due to its high electrical and thermal conductivity, copper has a wide range of applications. Many of those require an efficient and reliable welding process most preferably using a remote laser technique. However, the low absorptivity of copper at the wavelength of 1 μm together with its high heat conductivity makes remote laser welding of copper a challenging task. Welding speeds below 10 m/min are required to obtain penetration depths of several millimeters in copper when using laser sources with average powers below about 8 kW. Such welds suffer from numerous defects such as melt ejections and pores. As these weld defects degrade both, the mechanical and electrical properties of the weld seam, it is important to reduce or even avoid such weld defects especially for industrial applications. For the present paper the influence of the ambient pressure on defect formation was investigated. High-speed X-ray imaging of the welding process was used to analyze keyhole stability. It was seen that spatter formation was strongly reduced for reduced ambient pressure. Simultaneously, the penetration depth was decreased of up to 40% using identical laser parameters. It was seen that changing the ambient pressure directly correlates with a change of both, the shape and the stability of the keyhole.

Keywords: Welding Copper; Laser welding; X-ray; Reduced pressure; Vacuum; Process stabilization; Spatters; Pores; Ejections.


Laser Beam Welding in Vacuum – Overview of Thick-Plate Steel Application and Beyond
Uwe Reisgen, Simon Olschok, Stefan Jakobs, Christoph Turner

Laser Beam Welding (LBW) and Electron Beam Welding (EBW) are both processes that are well established in industry.
EBW has its main application fields in thick-plate joining as well as in manufacturing automotive drive train components
in small indexing vacuum machines. LBW is widely used in thin-plate welding (6 mm and below) as a stand-alone process
or as part of hybrid processes with arc welding variants. Despite the continuous development of laser beam sources
regarding output power and beam quality, the LBW process remains behind the EBW process in terms of achievable
weld-in depths and inner weld seam quality. The process variant of LBW in low to medium vacuum (LaVa) as
investigated and developed by the Welding and Joining Institute (ISF) closes the gap between the two beam-welding
processes and opens up new application fields for the Laser. This includes the joining of thick-walled structures beyond
the possibilities of the common LBW process as well as the energy and quality optimized joining with small weld-in
depths. The following paper will give a brief overview of the LaVa process, the results achieved on unalloyed steel and a
comparison with EBW. Additionally, a brief glimpse of what is possible with LaVa beyond unalloyed steel is given.

Keywords: Laser Beam Welding, Thick-Plate, Vacuum


Multispot laser welding to improve process stability
Klaus Schütt Hansen, Flemming O. Olsen, Morten Kristiansen, Ole Madsen

Two studies about laser welding applying multiple spots in the process zone are presented. The first study aims to investigate how to control the dimensions of a weld pool by applying multiple spots on a row perpendicular to the welding direction. Examinations were performed as bead on plate experiments. The methods ability to increase bridging and sensitivity to alignment tolerances were tested in a butt joint configuration with up to four parts in a single pass. The results showed that both the width and the depth could be controlled independently. The ability to bridge a gap was increased, and tolerances against alignment errors were good. The second study was from a real production in which failures in form of impurities leads to blow outs, and failure in the final product. A study of the ability to perform inline repair welding with multiple spots was performed on specimens where an exaggerated blow out was caused by zinc powder. Results showed large improvements. Porosities were present after the welding which is concluded to originate from the heavy turbulence during the blow out. Spot patterns were produced by splitting the beam from a single mode fiber laser into several spots with diffractive optics.

Keywords: Beamshaping; laser welding; weld geometry; inline repair welding; laser spot pattern; blow out;


Online Detection of Pore Formation during Laser Deep-Penetration Welding
Meiko Boley, Rudolf Weber, Thomas Graf

Pore formation during laser welding still presents a serious problem. Today, inspection of the weld quality is performed
after the welding process. The detection of pores requires non-destructive methods such as computer tomography and
ultrasonic testing [1] or destructive methods such as cross-section analysis. The non-destructive methods require
expensive equipment and trained staff to perform and analyze the inspection, whereas destructive testing of ten is not an
option when welding only few parts.
In this contribution, a novel online method to detect pore formation is presented. Laser deep penetration welding was
observed coaxially using the In-Process Depth Meter (IDM) of Precitec. The IDM is an optical coherence tomography
system, which is capable of measuring optical path lengths. The IDM was operated in the IFSW-X-ray system which allows
simultaneous time-resolved determination of the depth and shape of the keyhole. It was seen, that in many processes the
keyhole is instable. The strong fluctuations in depth and shape often result in the formation of pores [2]. It will be shown,
that the keyhole changes its shape in a very specific manner before, while and after a pore is generated. By comparing t he
X-ray videos and the simultaneously recorded depth data, a signature was found in the measured depth signal, which
indicates the generation of a pore.

X-ray; depth measurement; OCT; IDM


Influence of laser power modulation on the time-resolved temperature distribution in the weld pool during laser welding of copper to aluminum
Michael Jarwitz, Florian Fetzer, Peter Stritt, Rudolf Weber, Thomas Graf

Temperatures were measured with high temporal resolution of 0.1 ms at two positions on the weld pool surface simultaneously at distances of 1 mm and 2 mm behind the keyhole during disk laser welding of Cu-OF to Al99.5 in overlap configuration. The cw welding process shows inherent instabilities resulting in large periodic oscillations of the temperature signals at a rather broad frequency bandwidth between 15 Hz to 30 Hz. These instabilities can be suppressed when laser power modulation is applied at modulation frequencies between 100 Hz and 300 Hz. Thus, the welding process is dominated by the laser power modulation. This leads to a significantly reduced temperature fluctuation range (up to 70%) in this frequency range and the temperature signals as well as the temperature gradient
oscillate mainly with the respective frequency of the laser power modulation. The influence of the laser power modulation is reduced at higher modulation frequencies and the characteristic instabilities of the cw welding pr ocess appear again but are still superimposed by the laser power modulation.

Keywords: laser welding, copper, aluminum, temperature measurement, dissimilar materials, laser power modulation


Simulation of Laser Welding of Dissimilar Metals
Rodrigo Gómez Vázquez, Andreas Otto, Gerhard Liedl, Robert Feichtenschlager

Welding of dissimilar metals in general is a complicated task that involves many difficulties. Currently one of the most
challenging problems is the formation of inter-metallic phases in the joining interface. In this paper we introduce a
simulation model aimed to support the study of laser dissimilar welding by providing useful information on the process
characteristics (e.g thermal distribution, species mixing) including inter-metallics formation. The introduced model is
based on our existing multi-physical solver for simulation of laser processes within OpenFOAM's environment. The
simulation capabilities were extended with new physics for the study of dissimilar welding processes. Multi-species
diffusion and a simplified growth model for the intermetallic layer were included. Implemented diffusion includes
temperature dependency and allows simultaneous mixing of different species. The formation of inter-metallic phases is
calculated by a species reaction model coupled with both species and energy transport models. The thickness of the
inter-metallic layer predicted by the simulations is finally compared with experimental data for aluminum and steel.

Keywords: multi-physical simulation; laser welding; dissimilar materials; inter-metallic phases.


Laser Power Modulation to Minimize the Electrical Resistance of Auminum-Copper Welds
Florian Fetzer, Michael Jarwitz, Rudolf Weber, Thomas Graf

Power modulated overlap-welding of Cu-OF to Al99.5 was investigated with the aim of minimizing the welds electrical
resistance. In-situ X-ray videography was used to measure the intrusion depth of copper into the aluminum sheet with
acquisition rates of up to 5 kHz. Temperatures in the weld pool were measured synchronously and a concurrence of
both signals is found. It is shown that laser power modulation at frequencies from 100 Hz to 400 Hz can increase the
process stability, whereas its influence on the electrical resistance of the joints is negligible. Beside, an influence of the
top material on this resistance was found and we claim the aluminum-top configuration to be superior.

Keywords: Laser welding, diagnostics, dissimilar metals, electrical resistivity ;


Influence of filler wires on weld seam properties of laser beam welded dissimilar copper connections
Vincent Mann, Matthias Holzer, Fabian Gärtner, Florian Hugger, Stephan Roth, Michael Schmidt

Due to its high thermal conductivity and corrosion resistance, copper and its alloys are often used for components of
heat exchangers and pipe applications. These material properties results in a need of high energy densities for fusion
welding which are provided by laser beam welding, for example. Here the small focal diameters lead to high energy
densities and high thermal gradients. This offers the chance for a locally limited heat input and high welding velocities.
However, a disadvantage of laser beam welding is the low gap bridging capability due to the small focal diameters.
A solution for this problem which is already applied for laser beam welding of aluminum and stainless steels is the use of filler wire. Thus this paper investigates the influence of copper filler wires on resulting weld seam properties of laser beam welded dissimilar copper alloy connections. At first the influence of welding velocities on weld seam properties for
different gap sizes is investigated. Moreover the effect of different diameters of filler wires on weld seam geometries is
determined. Here the resulting weld seam properties as geometrical shape and surface structure of the weld seams are
analyzed. Besides this the mechanical and electrical properties of the welded connections are determined by means of
tensile tests and four-point resistance measurements. According to the obtained results, the use of pure copper filler
wire avoids seam and root collapse of the welded joints, decreases the electrical resistance of the welded components
and improves the tensile strength and strain of the welded connections.

Keywords: Macro Processing; Joining; Welding


Comparison of Mechanical and Microstructural Characteristics in Maraging 300 Steel Welded by three different processes: LASER, PLASMA and TIG.
Antonio Jorge Abdalla, Milton Sérgio Fernandes Lima, Leonardo Fanton, Cecília Vieira Gomes, Sandro Lombardo, Deivid Ferreira Silva, Paulo Roberto Sakai

The maraging steel are considered ultra high strength due to its yield strength greater than 1400
MPa and are part of a set of advanced materials of interest for technological development, mainly for
aeronautics and aerospace industry. For this purpose should submit good toughness, fatigue
resistance and acceptable weldability. These steels are used in the aerospace industry as high-
strength fasteners, engine casings and missiles, landing gear structures, among others.
There are few studies of the process of laser welding of this material, making it important to study the feasibility of welding these steels. A comparison between the traditional welding processes (TIG-
Tungsten Inert Gas and PAW-Weldding Plasma Arc) and the laser welding process (LBW - Laser Beam
Welding) was performed.
To evaluate the mechanical properties were used tensile and hardness tests by microindentation,
showing that the maraging steel can be welded with little loss in mechanical properties, with
advantages for the laser welding process.
Microstructural characterization was performed by optic and scanning electron microscopy, showing
that the fused and heat affected area in the process LBW is about 10 times lower than that affected
by TIG and PAW process.


Keyhole shape and element loss in laser beam welding of brass alloys
Florian Hugger, Vincent Mann, Matthias Holzer, Stephan Roth, Michael Schmidt

Deep penetration laser beam welding is characterized by a keyhole where evaporation of the material takes place.
Welding alloys with a significant difference of evaporation temperature of base material and alloying elements leads to
disproportionately high evaporation of the volatile element. This leads to elongation of the keyhole and loss of the
volatile element in the weld.
In this paper full penetration welds of brass alloys of 10%, 20% and 37% zinc by mass are carried out using a solid state
laser. The welding process is detected by high-speed imaging by which vapor capillary elongation as well as capillary
shape is observed for different parameters. Furthermore alloy composition is analyzed and element loss depending
upon alloy composition and feed rate is detected by EDX measurement.

Keywords: Laser beam welding, copper alloys, evaporaton


Experimental Studies of Fiber Laser Welding of a Range of Dissimilar Material Combinations
Mohammed Naeem

The capacity to produce a product utilizing various diverse metals and alloys greatly increases flexibility in design and
production. Various properties such as corrosion, wear and heat of the product can be optimized, and cost saving in
production are often gained. Joining of dissimilar material combinations, however, presents challenges owing to the big
differences in physical, mechanical and electrical properties which are present and this can lead to premature failure of
the welded joint due to the formation of intermetallic brittle phases.
In principle, a laser can weld any material, which can be joined by conventional processes. In the welding of dissimilar metals, good solid solubility is essential for sound weld properties. A sound weld between dissimilar materials is one that
is as strong as the weaker of the two metals being joined, i.e., having sufficient mechanical properties i.e. tensile
strength and ductility so that the joint will not fail in the weld.
At Prima Power Laserdyne detailed experimental studies have been carried to weld a range of different material combinations used in aerospace, electronics and medical industries with continuous wave ( CW) and Quasi Continuous
Wave (QCW) fiber lasers. Investigations including metallurgical and mechanical examinations were carried out by means
of varying laser and processing parameters, such as laser power i.e. continuous wave or pulsed, power density, we lding
speed, etc.

Keywords: Fiber lasers; dissimilar material welding; aluminium alloys;, pure copper; pure nickel; titanium alloy; nickel alloy; stainless
steel and low carbon steel