Special Issue

Challenges to New Technologies and New Products

Welding With the High Beam Quality Fiber Laser andSuppression of Welding Defects
Using the Beam Mode Control Technology
Tomomichi Yasuoka*, Takashi Kayahara*, Ryosuke Nishii *, Keigo Matsunaga*, Takashi Shigematsu*

The single-mode fiber laser manufactured by Furukawa Electric Co., Ltd. (FEC),
with the small core diameter and the high beam quality, is capable of performing a high aspect ratio processing with little thermal influence, at low power by utilizing a highpower density. Also the multi-mode fiber laser can reach over 10 mm of penetration depth forsteel materials by utilizing its high output power.
However, the commonly used fiber lasers generate many sputters which cause welding defects
and defacements around the processing part. To address these issues, we proceeded with thedevelopment of the beam mode control technology and succeeded in suppressing sputters andin reducing the processing defects.

ABSTRACTINTRODUCTION
1.1. INTRODUCTION
In recent years, the fiber lasers have been receiving a lotof attention, and its replacing of other welding
technologies, so far used, has been studied. This is not
only because, the fiber lasers have a higher beam quality
than the other lasers such as YAG and CO2 which havebeen conventionally used, but also because the fiberlasers have a high reliability as a device also an excellent
energy efficiency and are easy to use.
In this paper, among these lasers, the beam quality of
the fiber laser manufactured by FEC and the basic
processing performances taking advantage of the device
are reported. And, we report the new laser processing
which has opened up the possibility through the progressin the beam mode control technology which is gaining
attention in recent years.

demonstration of the basic processing performance ofthe multi-mode 6kW fiber laser.
2.1 Beam Quality of the Fiber Laser Manufactured
by FECThe external view of the single-mode fiber laser
manufactured by FEC is shown in Figure 1. The inside of
the oscillator is composed of a pumping semiconductor
laser, gain fiber, Fiber Bragg Grating and other parts, andthe oscillated laser light is transmitted to the output end
through the optical fiber. Here, the multi-mode fiber laser,shown in Figure 2, combines multiple single-mode fiber
lasers to oscillate.

THEBEAM
BEAMQUALITYQUALITYANDAND THETHE
2.2. THE
PROCESSINGPERFORMANCEPERFORMANCE OF THE
PROCESSING
THE
FIBER
LASER
MANUFACTUREDBYFEC
FIBER LASER MANUFACTURED
FEC
The fiber lasers have a high beam quality and a very highlight-focusing property, so the weld can penetrates
deeply and in addition the thermal influence can besuppressed during the welding. This chapter starts with
the introduction of the basic optical properties of the fiber
laser manufactured by FEC including a follow-up with the*Advanced Production Technology Development Center,MONOZUKURI Innovation Division

Figure 1 External view of the single-mode fiber laser.

The optical specifications of these fiber lasers areshown in Table 1. Compared with the multi-mode fiberlaser, the single-mode fiber laser has a smaller fiber core
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Welding With the High Beam Quality Fiber Laser and Suppression of Welding Defects Using the Beam Mode Control Technology

diameter. Therefore, the penetration with a very highaspect ratio as shown in Figure 3 is available. When an
optical system having the same magnification is used, thesingle-mode fiber laser has a higher power in a per unit
area than the multi-mode fiber laser. So, regarding thepenetration, as shown in Figure 4, the single-mode laser
with 1 kW processing can obtain the equivalent
penetration depth of that of the multi-mode fiber laser
with 2 kW processing, in a range faster than 20 m/min.
On the other hand, in the low speed range where thedeeper penetration is required, the multi-mode fiber laser
capable of obtaining a high power output is used.
Table 1

Optical specifications of the fiber lasers.
Single-mode
fiber laser

Figure 2 External view of the multi-mode fiber laser.

（a）Multi-mode fiber laser

Wavelength

1070 nm1070 nm1070 nm

Rated output

1500 W

4000 W

6000 W

Fiber core
diameter

14 µm

50 µm

80 µm

Beam quality
M2 (Typical)

1.06

−

−

Beam quality
BPP (Typical)−

2.2 mm mrad

3.0 mm mrad（b）

2.0 mm

1.0 mmFigure 3 Cross-sectional view of the steel processed with 1 kW single-mode fiber laser.
(a) 1 m/min(b) 10 m/min（b）6000
Steel5000

Aluminum alloy

Penetration depth [µm]Penetration depth [µm]（a） 6000

Pure copper

4000
3000
2000
1000
0020406080

Process speed [m/min]

100120

Steel5000

Aluminum alloy
Pure copper

4000
3000
2000
1000
0020406080
Process speed [m/min]

100120Figure 4 Comparison of the penetration depths.
(a) 1 kW single-mode fiber laser(b) 2 kW multi-mode fiber laser

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Welding With the High Beam Quality Fiber Laser and Suppression of Welding Defects Using the Beam Mode Control Technology

2.2 Multi-mode Fiber Laser
Using the multi-mode fiber laser, a bead on a plate test
was performed on steel, aluminum alloy and pure copper.
Figure 5 and Figure 6 show the cross-sectional views on
steel and aluminum alloy. By comparing Figure 3 with
Figure 5, it is found that although the width of bead isincreased, a deep penetration depth is obtained while
maintaining the shape of the high aspect ratio. Also, thepenetration depth on changing the processing speed isshown in Figure 7. Over 10 mm of the penetration depth
can be obtained with stainless steel, steel and aluminum,
in low speed range.
（a）

（a）

（b）

1.5 mm（b）

1.5 mmFigure 6 Cross-sectional view of the aluminum alloy processedwith a 6 kW multi-mode fiber laser.
(a) 1 m/min (b) 10 m/min

14000
Penetration depth [µm]Aluminum alloy

10000

Pure copper

8000
6000
4000
2000
0

1.5 mm

Steel

12000

1.5 mm05101520
Process speed [m/min]

2530

Figure 7 Penetration depth of various materials processed witha 6 kW multi-mode fiber laser.

Figure 5 Cross-sectional view of the steel processed with a 6
kW multi-mode fiber laser.
(a) 1 m/min (b) 10 m/min

BEAM
MODE
CONTROLTECHNOLOGY
3.3.BEAM
MODECONTROLTECHNOLOGYAs described, the fiber lasers can obtain the local and thedeep penetration due to the high beam quality and thehigh power output. Based on this performance, theimprovement in the cycle time during the production andthe processing of materials that are difficult to absorb
laser light have been made possible. On the other hand,during welding using the fiber laser, the scattering of themolten metal, that is the sputtering, occurs a lot. This
sputtering induces various welding defects, decreases inbonding strength and increases with additional
processes. Also, if devices are manufactured by using
these defected materials, it causes a possibility ofdecreasing a process yield rate due to the deterioration of
the device characteristics. In order to achieve a more
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Welding With the High Beam Quality Fiber Laser and Suppression of Welding Defects Using the Beam Mode Control Technology

efficient production process using the fiber lasers, it isnecessary to solve this issue.
Therefore, with the purpose of resolving this issue, thebeam mode control technology has been developed
jointly with FURUKAWA DENSHI CO., LTD. and thesputtering and the welding defects were successfullysuppressed. In this chapter, including the sputtering andthe defect suppression on galvanized steel sheet, copperand aluminum are reported.
3.1 Sputter Suppression in Steel Materials
The galvanized steel sheet is widely used in automobile
bodies and building materials in order to provide antirust
and anticorrosive function. However, when this members
are welded in close contact, a large amount of welding
failures occur due to the zinc vapor generation as shownin Figure 8 (a). This is because the zinc plating on thesurface around the melting part of the steel sheet
evaporates due to the high temperature, and it iseliminated as vapor during welding. Therefore, at present,
the following method is mainly adopted. Gaps about 0.1
to 0.3 mm are formed between the steel sheets, and thezinc vapor generated by the welding is eliminated fromthese gaps. However due to some restrictions in thismethod, such as the choice in the welding shape beinglimited because of the complexity of jigs and thenecessity of eliminating the vapor towards all sides of thewelding point, issues are raised regarding the necessity
to simplify the construction method by introducing thefiber lasers and the inherent fact that there is no degree of
freedom in shape designing.

（a）

（b）

1 mm
Figure 9 Cross-sectional view of the galvanized steel sheet
processed with the beam mode control technology.

3.2

Suppression of the Sputtering and the Welding
Defects in Nonferrous Metals
Copper and aluminum are difficult materials to absorb thelaser light of 1070 nm, and until the fiber laser was developed, the processing with the laser was very hard.
However, recently, these materials are becoming possible
to be processed with the high power density of the fiber
lasers. In recent years the driving of electric automobiles
has been encouraged. Aluminum can contribute to theweight reduction of the automobiles. And, copper is usedin large quantities in electric devices. So the fiber laser
welding process of aluminum and of copper are very
attractive because the production efficiency can beimproved.
On the other hand, when the laser light is applied tocopper for melting, as shown in Figure 10 (a), other than
the sputtering, defects like hollowed holes called blowholes are formed on the surface. Once this defect isformed, when it is used in devices, not only the appearance is damaged but also increase in electrical resistanceand decrease in thermal conductivity are induced, and inworst case the device will not be able to be in functional.
（a）Figure 8 Images of the welding beads on the galvanized steelsheet.
(a) With the conventional single focused spot(b) With the beam mode control technology

By proceeding with the development of the beam modecontrol technology, we succeeded in welding the galvanized steel sheets overlapped without gaps as shown in
Figure 8 (b). In regard to the inside, it can be confirmedthat inside defects are suppressed as shown in Figure 9.

（b）

Figure 10 Images of the beads on the pure copper sheet.
(a) With the conventional single focused spot(b) With the beam mode control technology

By developing the optimum beam mode control technology for the pure copper, we succeeded in the copper
welding without any blow holes as shown in Figure 10 (b).
Applying this technology, 50 copper sheets (8 μm thickness each) were overlapped and welded, the result isshown in Figure 11. In the welding with the normal fiber
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Welding With the High Beam Quality Fiber Laser and Suppression of Welding Defects Using the Beam Mode Control Technology

laser, the copper foils were torn as shown in Figure 11,
while in the welding with the beam mode control technology the copper foils were neatly welded to the insidewithout breaking as shown in Figure 11 (b) (c). Also foraluminum, the suppression in sputtering was confirmed
as shown in Figure 12.

（a）

（a）

（b）

1 mm
Figure 12 Aluminum plates welding.
(a) With the conventional single focused spot(b) With the beam mode control technology（b）

CONCLUSION
4.4. CONCLUSION

1 mm

（c）

This paper reported the basic processing characteristicsof the fiber laser manufactured by FEC, also reported isthe beam mode control technology that can suppress thesputtering and processing defects for various materials.
We believe that by utilizing these technologies we will beable to contribute to the society needs in the coming EV
conversion and in the high efficiency production
technologies. And we would like to propose expanding
these production technologies.
Furthermore, we will proceed further development andwill propose more attractive laser processing solutions.

200 µmFigure 11 Images of the welding beads on copper foils.
(a) With the conventional single focused spot(b) With the beam mode control technology(c) Cross section of (b)Furukawa Electric Review, No. 50 201931