Micro-Joining (Welding and Brazing) (LiM 2019)

500-Watt Fiber Coupled Blue Laser System Welding Results
Mark S. Zediker, Jean Phillipe Feve, Matthew Silva Sa, Jean Michel Pelaprat, Mathew Finuf, Robert Fritz

This paper will present the welding results from a 500-Watt fiber coupled blue laser system. The system is based on
200-Watt blue laser modules that are coupled to a 400-μm optical fiber. The optical fiber is terminated with QBH
connectors which allows the easy adaption to most welding heads. The test results with this laser using a 2:1 welding
head (215-μm spot) showed a substantial improvement in welding speed or penetration over previous results obtained
with a prototype free-space coupled system. The prototype free-space system was tested at a 20-degree angle of
incidence and the motion system was a FANUC 6-axis robot. The speed improvements for this system are attributed to
three factors: 1) the improved beam uniformity, 2) the ability to process at normal incidence, and 3) the use of a
precision 3-axis gantry system. A summary of the improved welding results will be presented.

Keywords: Welding; Copper; Blue; Laser


Hybrid joints of polymer and thin metal parts fabricated by laser technology: performance under realistic conditions
E. Rodríguez-Vidal, Carmen Sanz, R. Bayón

Direct thermal joining of polymeric and metallic materials is currently arising as an alternative technology for the
generation of hybrid joints. The focus of this study is on developing hybrid joints of polymethyl methacrylate PMMA and
thin AISI430 parts by laser technology and the analysis of their performance under operating conditions required by
home appliance applications. Mechanical resistance, mechanical stability at thermal shocks, salt spray tests and
aesthetic requirements have been addressed. Firstly, the thin metal part was locally structured by pulsed laser radiation
producing micro-patterns to improve the adhesion of the PMMA part. Secondly, the polymer-metal interface was
irradiated by a Continuous Wave fiber laser by transmission method to achieve the joint between both materials. The
assessment of mechanical stability at 400 thermal cycles up to a peak temperature of 85⁰C is a real challenge
considering the remarkable differences in terms of thermal properties of both materials.

Keywords: polymer-metal hybrid joints; laser joining; laser surface modification


Laser overlap joining from copper to aluminum and analysis of failure zone
Karthik Mathivanan, Peter Plapper

Joining of copper and aluminum sheets are very crucial for battery application. When joining from copper sheet, keyhole
mode of welding is essential to overcome the reflectivity and melting threshold of copper. However, in dissimilar
material interaction the resulting intermetallic (IMC) phases are brittle, which result in reduced performance.
This paper analyses the joint with laser beam irradiated from the copper side (Cu on top). The idea is to distribute the
intermetallic compounds inside the joint to obtain a ductile behavior. The zones of failure and the distribution of the
intermetallic phase is studied. The microstructural analysis of the fusion zone and mechanical strength of the joint are

Keywords: Battery application; Aluminium-copper joints; Laser welding;failure analysis; Intermetallic compounds.


Laser welded titanium cubesats
Sheila Medeiros de Carvalho, Rafael Humberto Mota de Siqueira, Milton Sergio Fernandes de Lima

Cubesats are a type of nanosatellites with wide use in applications such as earth observation, deep space missions and
the military. This work intends to present the fabrication and characterization of a 1U titanium-made cubesat frame. The
cubesat was built from laser weld two Ti6Al4V plates to four cp-Ti tubes. The microstructure of the plate-to-tube weld is
characterized by martensitic titanium in the fusion zone and to a partially reverted β-phase in the plate heat-affected
zone. The hardness of the fusion zone attained 300 HV and is intermediary between both base materials. The yield
strength of the plate-to-tube component was 220±10 MPa, which is much higher than the maximum hydrostatic
pressure during the launching by a VBS30 vehicle. As a conclusion, the cubesat frame could be considered for more
specific mission-targeted tests.

Keywords: laser beam welding; cubesat; titanium alloys


Residual stresses and crack formation in laser welding of amorphous polymers
Andreas Schkutow, Thomas Frick, Samir Lamrini, Karsten Scholle, Peter Fuhrberg

Residual stresses in welded parts can limit the mechanical performance and reliability of the components. In polymers,
especially in amorphous thermoplastics, tensile residual stresses in the presence of certain media can lead to
environmental stress cracking, which can result in catastrophic failure of the connection. In this work the mechanisms of
stress generation in welding of plastics is compared to metallic materials and methods for evaluating residual stresses
are discussed in terms of suitability to polymer materials. The application of solvents in liquid and vapor phase is shown
to be a useful tool for intentionally inducing stress cracking in laser-welded parts to evaluate and compare residual stress
levels and orientations in the weld zones. Appropriate process parameters are examined for reducing welding stresses.

Keywords: laser transmission welding; polymers; residual stresses; environmental stress cracking;


Laser microwelding and sealing of thin, polymeric lab-on-chips
Ares-Blanco Félix, Otero-Ramudo Nerea, Romero-Romero Pablo, Guadaño Gonzalo, Hein Marko, Gründig Bernd

Transmission laser welding is proposed as an alternative to adhesive bonding for joining thin foils in polymer Lab-on-a-
Chip manufacturing. A 532 nm wavelength continuous wave laser was used, together with an acousto-optic modulator
and a galvanometer scan head to modulate and deliver the laser beam to the workpiece. A wide range of parameters
was tested to study the influence of the laser modulation (frequency, duty cycle), scan speed and laser power up to 5W
on the resulting welding tracks. Under 200 μm thick polycarbonate films were welded with a modulated laser.
Continuous, homogeneous welding tracks under 100 μm width were achieved, completing sealing paths for complex
microfluidics in seconds. These results prove that laser welding is a high productivity solution for the current problem of
joining polymeric films with micrometric accuracy, not possible with nowadays alternatives based on adhesive bonding.

Keywords: Lab on a chip; Laser welding; microwelding; laser sealing; polymer welding; microfluidic


Towards industrial usage of ultrashort pulse welding
Felix Zimmermann, Sebasitian Hecker, Michael Jenne, Daniel Flamm, Myriam Kaiser, Jonas Kleiner, Marcel Schäfer

Laser welding of transparent materials using ultrashort laser pulses is attracting attention for an increasing number of
applications in the field of medical industry, consumer electronics, microelectronics and others. Nonlinear absorption
and heat accumulation at high repetition rates allow for local melting the weld partners at the interface. After cooling, a
permanent joint with high stability up to the bulk material remains. However, due to basic material properties the
(crack-free) weld seam dimension is limited and so the welding performance, e.g. the focus tolerance or gap size that
can be bridged requiring high surface quality. In contrast, advanced process strategies such as wobble welding or
temporal modulation of pulse energy enable improved welding performance providing tools for tailoring the induced
material modification as it will be shown by in situ microscopy. Moreover, these techniques may also serve for in-line
control of the welding process and to optimize applications such as material functionalization or high-speed cutting.

Keywords: Micro Processing; Micro Welding; Processing of Transparent Materials


A Novel Approach for Welding Metallic Foils Using Pulsed Laser Radiation in the Field of Battery Production
Hoda Mohseni, Maximillian Schmoeller, Michael F. Zaeh

In the production of battery cells for electromobility, many cell internal and external joining operations are required.
These connections must have both high mechanical strength and excellent electrical properties. In particular, the cell-
internal contacting poses a great challenge, as multi-layered stacks of highly conductive metallic foils have to be joined
while the bonding areas are in immediate proximity to temperature-sensitive materials. Conventionally, these bonds are
produced by ultrasonic welding due to the reduced occurrence of intermetallic phases and the low heat generation. This
process is limited in terms of the strength and thickness of the welds. Within this work, experiments were conducted on
contacting metallic foils by pulsed laser beam welding. The aim was to join stacks of 15 oxygen-free copper foils with a
layer thickness of 15 μm at a high weld seam quality and with good process stability. Suitable parameters for welding
with temporally power modulated pulses (spike pulses) were determined. The results were compared to continuously
welded (cw) samples. In comparison, pulsed welding showed a great potential for producing high quality welds over the
entire thickness of the foil stack and was characterized by low susceptibility to mechanical weld defects.

Keywords: Li-ion Battery, Metallic Foils, Welding, Pulsed-Laser Welding


Laser micro welding – a flexible and automatable joining technology for the challenge of electromobility
A. Haeusler, S. Hollatz, K. Brenzel, J. Helm, A. Olowinsky, A. Gillner

In our everyday life, electrified objects such as mobile phones, bicycles and automobiles are indispensable. The constant
trend towards the electrification of everyday objects reveals a variety of possible designs of single battery cells or
battery cells connected to a module, which have to be produced automatically in large quantities depending on the
Laser micro welding offers decisive advantages compared to conventional joining methods such as ultrasonic or
resistance welding. In addition to a high degree of automation, a laser-based joining process is contactless, highly
flexible and requires no additional materials which increase the transition resistance. The key technology here are highly
brilliant fiber laser sources which, due to their good focusability and the resulting small spot sizes, can provide high
intensities with a simultaneously low total energy input. The presented work contains the results of the contacting of
different types of battery cells by laser beam micro welding.

Keywords: Laser Micro Welding; Copper; Battery Cells