Special Issue

Laser processing for copper

Development of Laser Welding Applications
With Blue-IR Hybrid-Laser
Tomomichi Yasuoka*1, Nobuyasu Matsumoto*1, Masamitsu Kaneko*1,Takashi Shigematsu*2

With the trend of promoting carbon neutrality in the world, the vehicle electrification has begun to progress. When electrified, it is expected that the numberof copper containing components will increase and the number of joining portion will increase.
On the other hand, in copper welding with Infra-Red (hereinafter IR) fiber laser is said to be difficult to achieve a welding quality which has no welding defects, due to frequent occurrences ofspatters and blowholes. We believe that Furukawa Electric’s hybrid laser based on its characteristics could achieve the targeted welding quality without causing any defects during welding,
and we are moving forward in the development of the applications. In this paper, the development results especially on the applications to in-vehicle batteries and motors are reported.

ABSTRACTINTRODUCTION
1.1.INTRODUCTION
Currently, in the world, the efforts to control the greenhouse gas emission are proceeding in order to prevent
global warming. Japan, as is the case, has begun to workon various measures towards the achievement of the carbon neutrality in 2050. Among them, the efficient use ofelectrical energy is thought to play a major role.
Especially, the vehicle electrification is focused on theissue and some manufacturers are even considering touse Electrified Vehicles (xEV) for all models sold at thattime.
When vehicles are electrified, the amount of coppers
used in batteries, motors and other components and theirjoining portions are expected to increase. The joining iscarried out by various methods such as Tungsten Inert
Gas (TIG) welding, ultrasonic welding and laser welding,but in recent years, the laser welding technologies has
been attracting attention from the viewpoint of reduction
in joining time and improvement in the degree of freedomon the joining shape. We have proposed a welding technology using IR fiber lasers. In particular, the IR fiber laser
and the beam mode control technology proposed by
Furukawa Electric have been well received by various
customers due to its impact in the spatter suppression
and the welding defect suppression.
Advanced Optical Process Development Section,
Advanced Laser Development Project Team,
Incubator Department, Research and Development Division*2
Industrial Laser System Department,
FITEL Products Division, Communications Solutions Division*1

On the other hand, copper has a problem that the lightabsorption rate is very low about 5%, because the wavelength of the laser light is longer than that of the IR fiberlaser. Furthermore, when the beam mode control is not
used, with a difficulty in a molten pool control, spattersoccur frequently and under this influence blowholes
occur frequently too, resulting in impossibility to obtain
the required welding quality for the components. To solve
this problem, there is a tendency to increase the absorption rate of the laser light by shortening the wavelength ofthe laser for welding. Visible light lasers such as blue andgreen, which have a higher absorption rate than IR, but
the output of these lasers are still low. In consideration of
the required welding time and the quality for each component, sufficient output is not guaranteed, in the current
situation.
Here, it was considered that these problems could be
solved by using an oscillator combined with a 450 nm
band blue semiconductor laser and an IR fiber laser byutilizing the molten pool control know-how through beammode control developed at Furukawa Electric. Currently,
the above new laser and a new process using it are being
proposed.
In this paper, as typical examples of the application ofthese newly proposed processes, the applications of thelaser welding to batteries and motors, which are major
components for xEV mentioned at the beginning, will bedescribed.

Furukawa Electric Review, No. 52 202129

Development of Laser Welding Applications With Blue-IR Hybrid-Laser

APPLICATIONTHE
HYBRIDLASER
LASER
2.2.APPLICATIONOFOFTHE
HYBRIDTOBATTERYBATTERYCOMPONENTSCOMPONENTSTO
The lithium-ion battery is manufactured through processes such as “coating”, “electrode cutting”, “current collector welding”, “sealing” and “modularization” as shown inFigure 1. Above all, for the lithium-ion battery whose battery capacity is determined by the surface area of thelaminated electrodes in the current collector, a multilayering technology for the current collector is required.
Furthermore, in advancing the multi-layering of the electrode foils, suppressing the copper powder generation
during the joining process is also a technical issue. If
copper powder is generated in the joining process, metal
precipitation is induced in the active material of the battery cells. Then the precipitates break through the separator which is situated to prevent contact between the posi-tive electrode and the negative electrode, resulting in ashort circuit. This can cause the battery overheat, and in
the worst case, leads to an accident such as ignition.
In order to solve these problems, it is necessary todevelop and to apply a laser welding technology that
does not generate the spatter in the current collector
welding process. So, it is expected and bringing attention
on the achievement of a multi-layer electrode foil welding
technology that leads to improvement in the battery performance and its safety. However, when the current collector welding is performed using a general fiber laser, as
described above, because of the low laser light absorption rate in the solid state copper, the molten portion isnot stable due to the rapid local heat input. And the foil inthe surface layer is torn as shown in Figure 2, or the spatter is generated as shown in Figure 3, which both raises
issues.

Places of laser application

Electrode cutting
Cut

Kneading

Coating

Slit, tab, cut

Welding

Slitter and press
processing are required
Reduction of set-upchangeApplicable technology:
Ultra-fast modulation(new technology)

Welding
Welding

Modularization
With bolted connections andother welding, connections are
weak and speed is low
Improve reliability andproductivity
Applicable technology:
Beam mode controlLamination
Current collector
welding

Sealing, sealing plugWith seam welding and pulsed
laser welding, defects aregenerated and speed is low Eliminate welding defects
and improve productivity
Applicable technology:
Beam mode control

Assembly

Ultrasonic joining welds
relatively few layers
Multi-layered structure
Applicable technology:
Blue-IR hybrid laser
Beam mode control

Figure 1 Example of manufacturing process for lithium ion battery.

Spatter

500 µmFigure 2 Surface of current collector welding witha general fiber laser.

Figure 3 Status of processing with a general fiber laser.

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Development of Laser Welding Applications With Blue-IR Hybrid-Laser

BRACE is a Blue-IR hybrid laser using two types oflasers, and makes possible to flexibly control the input
heat distribution by appropriately adjusting the respective
laser conditions. Then the defects shown in Figure 2 canbe prevented by forming a stable molten pool even forprocessed products like a metal foil. With this stable molten pool forming, deep penetration processing can beachieved by suppressing the spatter generation, which isa serious problem in the current collector welding process. Regarding the principle, see the separate paper“Features of Blue-IR Hybrid Laser and Copper ProcessingTechnique” included in this special issue.
Figure 4 shows a welding result, using BRACE, for alaminate consisting of 50 copper foils and a copper plate
simulating a current collector. As can be seen from thesurface and the cross-sectional photographs, it is demonstrated that a high-quality welding is achieved while
ensuring a sufficient welding width and suppressing theoccurrence of welding defects such as spatters and blowholes. Figure 5 shows the welding result of a structure inwhich a copper foil is placed between two copper plates.
As described, welding is possible even for the structure
consisting of copper plates and a copper foil that havedifferent shapes.

500 µm500 µmFigure 4 Current collector welding example 1 with BRACE.

500 µmAPPLICATIONTHE
HYBRIDLASER
LASER
3.3.APPLICATIONOFOFTHE
HYBRIDTOMOTORMOTORJOINING
JOINING POINTS
POINTSTOAs mentioned at the beginning, as the electrification progresses, demands and types of motors will be increasing.
So, it is considered that demands for productivity
improvement will increase also complicated motor
shapes differed from the conventional ones will appear.
Therefore, considering the contribution to these from theviewpoint of the welding, the shortening of the welding
time and the welding corresponding to various joining
shapes are required. The laser welding is available byirradiating the laser light to arbitrary points. In view ofthis, the welding with the shape shown in Figure 6, which
is different from the conventional overlapping shapewelding, can be easily available. Even if the shape of themotor becomes complicated, its welding will be available.
On the other hand, in the conventional fiber laser welding which focuses on a laser beam with a high energy
density at one point, spatters and blowholes occur in thesame manner as the welding process for battery.
Considering that the motor is an electric device, it is easy
to imagine that the spatter occurrence not only causes a
decrease in the strength of the welded portion, but alsoadhere to the inside of the circuit and induces an unintended short circuit which leads to an equipment failure.
Figure 7 shows a condition when hairpin welding is performed with using of BRACE. From this figure, it can beseen that the welding is performed with a considerable
suppressing of the spatter. Currently, the hairpin welding
with BRACE takes more than 0.3 seconds. Considering
the improvement of motor productivity in the future, it isnecessary to shorten this welding time, and for the purpose of reducing the welding time to 0.1 seconds or less,currently the output of oscillators is being increased andthe development of the process technology is proceeding. We believe that we will be able to provide a shortertime and a high-quality welding, in the future.

500 µmFigure 5 Current collector welding example 2 with BRACE.

Figure 6 Free-form welding results using a laser welding.

（a）

（b）

Figure 7 Welding of rectangular wire with BRACE.
(a) State of welding (b) Welded sample

Furukawa Electric Review, No. 52 202131

Development of Laser Welding Applications With Blue-IR Hybrid-Laser

Furthermore, in collaboration with NITTOKU Co., Ltd.,
we are currently developing a welding machine equippedwith a laser and a Galvano Scanner as shown in Figure 8.
The laser can be selected for the IR-multimode lasers, aswell as for the hybrid lasers. We would also like to make itpossible to propose not only as oscillators but also as aprocessing equipment to customers who are considering
the application of the laser welding in motor manufacturing processes.

CONCLUSION
4.4.CONCLUSION
As mentioned in this paper, BRACE is a product thattakes advantages of the knowledge gained in the beammode control technology and the copper welding technology developed by Furukawa Electric, and currently its
adaptation to batteries and motors is being promoted.
Regarding proposals in this field, and in addition to theoscillator and the joining process technology, we areworking with our partner in order to make also possible
proposals for a processing equipment.
In addition, it is also possible to bring in customer’ssamples to our Chiba Works and try them for process
examination using BRACE. Furthermore, in June 2021, aCo-application laboratory was opened at YOKOHAMARESEARCH CENTER in NICHIA CORPORATION, and it ispossible to try it there. (Figure 9)
We will proceed with the development of the welding
technology, aiming to be able to make proposals towards
a society where electrification and even carbon neutrality
can be achieved.

Figure 8 Winding welder equipped with BRACE (prototype).

Figure 9 Co-application laboratory (YOKOHAMA RESEACH
CENTER, NICHIA CORPORATION).

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