Micro-Joining (Welding and Brazing) (LiM 2017)

Stable conduction and keyhole welding of copper with 275 watt blue laser
Finuf, Mathew; Ream, Stan; Gray, Bill; Pelaprat, Jean Michel; Zediker, Mark; Fritz, Robert

Laser welding of highly reflective materials such as copper has been problematic for infrared lasers due to
the low initial absorption of the material during the welding process. This paper will report on the recent
bead on plate test results with a 275 Watt CW blue laser for welding copper foils up to 500 μm thick at 450
nm where the initial absorption is ~65%. Highly stable conduction mode welding of copper is observed over
a wide processing window using the blue laser source. Stable, low spatter keyhole welding is also observed
with complete penetration of the 500 μm thick copper foil. Both welding regimes exhibit highly stable weld
puddles with minimal porosity and no gaps in the weld bead due to melt ejection. Processing of the parts
can be done at a near orthogonal orientation due to the low reflected energy from the copper surface.

Keywords: Welding; Copper; Blue; Laser


Micro laser joining of capillary tubes for medical applications using filler metal
Adams, T.-E.; Letsch, H.; Mayr, P.

There is a continuously increasing demand for laser beam welding processes in the field of medical devices. Due to
complex component geometry, weld seam contour, the shape of the weld seam and tolerance requirements, the use of
filler metal is unavoidable under certain circumstances. Established autogenous laser beam welding technology may lead
to a significant reduction of wall thickness and is therefore unsuitable for welding complex and thin-walled capillary
tubes with wall thicknesses of less than 200
μm. The present paper introduces a novel technique to address the particular joining geometry of these structures in order
to avoid weld seam irregularities. The process requires bridging the air gap during welding and has been implemented
using an automated wire feed drive, capable of feeding wire diameters between 300 and 600 μm.
Focusing on joining stainless steel capillary tubes (1.4301) with filler metal, metallographic cross sections and tensile
tests were used to evaluate the effect of joining process parameters (e.g. laser spot size, pulse frequency, feeder speed
etc.) on joint properties. Preliminary results were used to establish a process parameter envelope resulting in good and
reproducible joint properties.
Results allow an outlook towards a generalization of the above process parameters, taking into account the special
requirements of joining bent capillary tubes.

Keywords: Micro Processing; Micro-Joining (Welding and Brazing); capillary tubes; medical devices


Control of temperature fields and melt formation in laser transmission welding using adapted laser wavelengths
Schkutow, Andreas; Frick, Thomas

The usage of laser transmission welding of polymers as a joining technique in industrial applications is often limited by
the optical properties of the joining partners and the limited gap-bridging capability. By using alternative laser
wavelengths or multiple beam sources it is possible to adjust the radiation to the properties of the materials and
increase the weld seam quality. Especially for scattering materials, parts without specific laser absorbing additives and in
applications where relatively large gaps occur due to manufacturing tolerances of the parts, adapted wavelengths can
lead to improved results. In this work, the gap bridging during quasi-simultaneous laser transmission welding is
investigated in welding experiments and thermomechanical FE-simulations. Usage of a laser wavelength in the range of
2.0 μm is found to be beneficial in terms of gap-bridging, compared to usually applied diode or solid state lasers emitting
at about 1 μm due to the higher intrinsic absorption in unmodified thermoplastic materials. This leads to increased
temperatures in the transparent joining partner and therefore greater thermal expansion. Furthermore the radiation
shows an increased penetration depth in carbon black filled, laser absorbing materials, also leading to increased thermal
expansion and improved gap bridging. The wavelength of 2.0 μm is also found to improve the strength of weld seams
when turbid materials or materials with scattering additives are used as laser transparent parts, since scattering at small
particles is strongly wavelength dependent, so the longer wavelength features better control of the resulting intensity
distribution in the joining zone.

Keywords: laser transmission welding; adapted wavelength; melt pool geometry; gap bridging;


Welding thin section dissimilar metals with ns pulsed fiber lasers
Gabzdyl, J.; Rosowski, A.

The industrial use of ns lasers for applications such as marking, engraving, cutting and even micro machining is well
known, however, the use of these sources for welding and joining is relatively new. MOPA based ns fiber sources give
unparalleled flexibility offering high peak power pulses with tuneable pulse duration, through to high frequency
modulated quasi-cw modes as well as conventional CW operation.
When compared to CW or QCW sources ns pulsed fiber lasers have low average powers, typically <100W and low pulse energy (1mJ), which currently restricts penetration depths to <1mm. Operating with pulse durations typically in 100-
500ns range, with peak powers of up to 10kW and pulse repetition frequencies of >50kHz these lasers are significantly
differentiated from conventional CW and QCW sources. This ability enables the optimisation of input energy
characteristics for specific joints and is key to their use in joining.
For bonding thin metals, there is a requirement for reliable joining processes that avoid over-penetration, distortion and warping. The challenge is greater for bright metals and for dissimilar metal combinations where fusion welding creates
problem with brittle intermetallics phase formation forming planes of weakness with increased fracture susceptibility.
Using ns lasers for joining is unlike conventional welding in that it does not generate a large melt pool and so formation
of intermetallic phases is restricted. As an example a spot weld in an Al/Cu metal combination can be generated by a
70W ns pulsed laser source using a spiralling beam path, exhibiting a non conventional looking weld joint having good
strength characteristics.
In this presentation a wide range of joint configurations and welding techniques are applied to various materials
combinations including copper to aluminium and stainless steel to aluminium, highlighting the versatility of the ns
pulsed laser source for this application.

Keywords: Micro processing; micro joining; welding; fiber laser; dissimilar materials


Repair of nickel-based superalloys by pulsed Nd:YAG welding with wire feeding
Bielenin, Martin; Bergmann, Jean Pierre

In this paper deposition of IN 625 filler wire on γ’-hardened IN 738 superalloy with pulsed laser beam welding was
investigated. High-speed observation was performed to examine the influence of the spatial and temporal alignment
between the pulsed laser beam and the wire feeder on the material transition from the solid wire onto the substrate.
The deposition process has shown to be extremely sensitive to the wire position and orientation relative to the melt
pool. To obtain stable and repeatable welding conditions influence of the significant parameters, such as the wire feed
rate, the energy input, and the traverse speed should be attentively considered. Significant improvements of the process
stability could be achieved with the adjustment of the wire position in the negative z-direction. The preliminary results
showed the potential of this approach as an alternative automated or partially automated repairing method for worn
turbine components made of nickel-based superalloys.

Keywords: Nickel-Based superalloys; Pulsed laser welding; Pulse shaping, Wire feeding, Inconel 738


Effect of laser assistance in ultrasonic copper wire bonding
Schneider, Friedrich; Long, Yangyang; Ohrdes, Hendrik; Twiefel, Jens; Brökelmann, Michael; Hunstig, Matthias; Venkatesh, Arjun; Hermsdorf, Jörg; Kaierle, Stefan; Overmeyer, Ludger

Due to the required low forces and the necessity of short cycle times in industrial production of electronic
interconnections, the use of the established ultrasonic wire bonding is limited for hard materials such as copper. To
reduce the applied forces and the cycle times, an additional energy source is applied to the process. This is implemented
by integrating a near infrared laser source to the wire bonding setup. The laser radiation is focused on the workpiece
during or immediately before the bonding process for heating the wire. This approach enables locally applied energy to
be increased during the process without affecting surrounding materials. Thick copper wires with 400 μm diameter are
used for bonding to rolled copper plates. For evaluation, the mechanical strengths of the bonds are tested afterwards
and the bonding interface is microscopically examined. To prevent the hazard of oxidation of the bond partners during
the process, the influence of shield gas is considered as well. The results show a direct relation between the applied laser
power and the examined bond strength. This approach opens the opportunity to obtain bonds equivalent in strength to
standard ultrasonic wire bonds but with reduced forces and/or bonding times. Hence the attempt to combine ultrasonic
and laser power shows an advantage over the individual processes in terms of the resulting bond strength and the
handling of the materials and tools.

Keywords: laser heating; hybrid process; electronic interconnection; ultrasonic wire bonding;


Quantification of geometric properties of melting zone in laser-assisted welding
John, Björn; Markert, Daniel; Englisch, Norbert; Grimm, Michael; Ritter, Marc; Hardt, Woldfram; Kowerko, Danny;

By using camera systems suitable for industrial applications in combination with a large number of different
measurement sensors, it is possible to monitor laser welding processes and their results in real-time. However, a low
signal to noise ratio at framerates up to 2,400 fps allows only limited statements about the process behavior; especially
concerning the analysis of new welding parameters and their impact on the melting bath. This article strives towards
research of kinetic and geometric dependencies of the melting zone induced by different laser parameters through
usage of a camera system with a high frame rate (1280×800 by 3,140 fps) in combination with model-driven image and
data processing.

Keywords: laser welding; image processing; regression analysis


Laser joining of textured metal and plastic components
Eckstädt, Johannes; Rauschenberger, Jens

Laser joining of plastic-metal-hybrid-compounds is the subject of a number of research-exploits worldwide. In parallel,
first applications start to emerge, in particular in the automotive sector in the quest of lowering the weight of cars and
trucks. Drive trains, gaskets, car body stiffening elements, and other applications may make use of polymer components
in conjunction with classical metal structures. Evidently, laser joining of polymers to metals presents significantly greater
challenges compared with standard welding processes.
We present recent progress in laser joining processes, including metal texturing, joining the hybrid material, and stress testing. The gamut of metal pre-texturing methods has been extended by a laser process using ultra-short pulses, and
compared to the further optimized incumbent options such as cw laser texturing, ConiPerf, and GripMetal.
Furthermore, the range of load scenarios, the joined samples were tested in was extended to tensile-shear, peel, and tensile load. Weathering tests simulate the environmental influences typical in targeted fields of application. The
polymers used were carbon-fiber or glass-fiber reinforced plastics.
The results show that high breaking tension values, typically higher than the base material strength, may be obtained. However, they also show that texturing and joining methods have to be chosen according to the load pattern, the load
amplitude, and the geometry of the given application. As an outlook, a prototypical application in a real-world
automotive is presented.

Keywords: Laser joining; polymer metal joining; hybrid material; metal surface texturing; ultra-short laser pulses;


Single mode fiber laser micro joining of dissimilar metals: a comparative study
Walter, Dmitrij; Mucha, Patrick; Moldovan, Vasile Raul; Schmieder, Benjamin

In the past few years the need for micro joining of dissimilar metal combinations increased drastically. Especially
consumer electronic products and lithium-ion battery packs are de manding applications in the market environment of
Manz. There are many potential process approaches to overcome the current limitations in terms of connection strength, durability and heat management. Due to this wealth of variants Manz engineers compared two promising strategies capable of thin sheet joining. As initial material combinations 1000 series aluminum and unalloyed copper to low-alloyed steel were welded in an overlap configuration. The process results were qualified by cross-section analysis, penetration
depth consistency and peel off strength. Finally the collected results were compared in respect to process duration,
connected area, peel off strength and commercial aspects.

Keywords: Dissimilar metal; laser welding; Copper; Aluminum; Steel; Micro joining; Single mode fiber lase


Laser welding of copper alloys using a pulsed laser source at green wavelength
Kick, Michael Karl; Ganser, Andreas; Braun, Christian; Dold, Eva-Maria; Tranitz, Hans-Peter; Fuchs, Alexander; Kaiser, Elke; Mueller, Ricus; Zaeh, Michael Friedrich

Welding of copper with solid state lasers is a challenging issue in electronics production. Different requirements have to
be fulfilled with respect to the welding process to meet industrial quality standards. Particular attention is paid to the
formation of spatters, since they can induce a short circuit in circuit boards. Therefore, a stable, spatter-free process
must be provided. Using infrared laser radiation, only a small fraction of the energy is absorbed by the copper material
during the welding process. As a consequence, process instabilities occur. Using green laser radiation is a promising
approach, since the absorptivity of copper materials is significantly higher at green wavelengths. Different studies have
already shown an improvement of the process stability compared to infrared solid state lasers. As frequency doubling is
restricted to low average laser powers, only thin sheets could be welded until now. In this paper, experimental
investigations are presented to identify suitable welding strategies for low spatter welding of copper alloys in lap joint
configuration. A prototype of a pulsed green laser with a pulse power of 4000 W was used to weld 0.8 mm thick pure
copper to 0.8 mm thick sheets of a copper alloy. Different welding strategies, e.g. non-overlapping and overlapping
spots, were considered. A spatter detection was developed to evaluate the process stability during the welding process.
For this purpose, an industrial camera with a high frame rate was mounted to the scanning optics to record the process
through the optical path. The recorded process pictures were evaluated by a machine vision algorithm to count the
spatters for each parameter set and welding strategy. Using a full factorial design of experiments, the influence of the
welding parameters on the spatter formation, the electrical resistance, and the mechanical strength of the weld seam
were analysed.