L a s e r We l d i n g S y s t e m fo r
Va r i o u s 3 - D We l d i n g- Development of Coaxial LaserWelding Head SHUHO TSUBOTA* 1
TAKASHI ISHIDE* 1
MASAO WATANABE* 2
TAKASHI AKABA* 2

Mitsubishi Heavy Industries, Ltd. (MHI) has developed a hybrid welding head that combines arc and laser welding functions, with the aim of applying it to the welding of sophisticated objects of complex shape such as car bodies.
The hybrid welding head eliminates the directivity problem of laser welding by arranging the electrode and laser
beam axes coaxially and reducing the number of controlling axes used for welding. In addition, MHI has extended
the coaxial welding procedure to laser brazing. This paper presents examples of the welding results obtained byusing the newly developed welding head and shows the effects of increasing groove gap tolerance, eliminating thedirectivity of welding, and increasing the penetration depth of brazing filler metal.

In order to solve these problems, a hybrid welding
procedure that combines both arc and laser welding functions has been developed to make laser welding withlarge gap tolerance possible. In order to realize laser
welding processes performed without many welding axes
and directivity, the newly developed welding procedureis characterized by the coaxial arrangement of the laser
beam and filler metal wire. In addition, this coaxial technology has been extended to laser brazing so as to beable to feed brazing filler metal wire coaxially with thelaser beam.
This report introduces the newly developed welding head and highlights its effectiveness with
examples of the results obtained by its practicalimplementation.

1. Introduction
Efforts are actively under way to apply laser welding
to practical use as a welding procedure with high efficiency and low distortion. In particular, notable advances
have been made in YAG laser welding technology for
application mainly in the automobile industry, throughthe easy transmission and stable quality of the laser
beam together with the recent appearance of high power
oscillators (1)-(4) . On the other hand, since the narrow
tolerance for groove gaps in laser welding, the accurate
machining and fitting of a groove, and precise setting of
the welding head on a target object are essential to proper
operation, a greater relaxation of work tolerances is necessary in order for laser welding to be of practical use.

2. Arc-laser hybrid welding
Optical fiber

2.1 Concept of coaxial laser-coaxial hybrid weldinghead
The research and development of hybrid welding systems consisting of both arc and laser welding functions
has been carried forward by many research engineers(5) (6). However, since the arc welding torch is locatedat the side of the laser optical axis in such systems, someaxes are needed to control the arc torch and keep it in agiven direction. This reliable and precise control is necessary to carry out the 3-dimensional welding of assemble
complex components required in the automotive andother industries. Thus, this study has investigated how
to make the arc axis coaxially with the laser axis in order to reduce the number of the axes used. The basic
concept for making the arc and laser coaxial axes isshown in Fig.1
Fig.1.

Reflecting mirror
Collimation lens

Splitting mirrorLens
Arc electrodeLens

Fig. 1 Concept of coaxial arrangement of arc electrodeand laser beam
A laser beam is split into two halves by mirrors. The arc
electrode is located in the space given between the split
half beams, thereby making it possible to realize the coaxial
arrangement of the arc electrode and laser beam.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 2 (Apr. 2005)

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Z (mm)6

Penetration depth (mm)-1210-8Laserbeam
5-4-2
X

42

24 (mm)+253
2
1+4Fig. 2 Beam-focusing state
The figure shows the beam focused close
to the focal point.

Processing table

Dimensions: 400 x 100 x 100 mm
Weight: 5 kg
Rate of Magnification: x 1

400.0

5Output: 2 kW (PW 50 %)Material: SUS 304
Shield gas : Ar

: Spot diameter 0.6 mm: Spot diameter 1.2 mm
0.5
1.0
1.5
2.0
Welding speed (m/min)

2.5

Fig. 3 Effect of focused diameter on depthof penetration
The depth of penetration is increased about 1.3
times by reducing the diameter of the focusedlaser beam from 1.2 mm to 0.6 mm.

Optical fiber

YAG laser oscillator

WireWire-feedingunit

MIGwireOptical fiber

MIG wirefeeding unit
AdjustingscrewBeamfocusingunit

MIG Power unit

LaserController

Arc

Fig. 4 View of MIG-YAG hybrid welding head
External view of a compactly designed welding
head expected to be operated by a robot.

MIG -YAG

DetailedHybrid welding headview of nozzle
Fig. 5 Standard configuration of equipment
General diagram of hybrid welding including auxiliary units.

The laser beam radiated from the optical fiber is splitin half by a splitting mirror and two reflecting mirrors,
after which the split beams are then focused on the target object through focusing lenses. The arc electrode islocated in the space produced between the split laser
beams, thereby realizing the coaxial arrangement of theaxes of the laser beam and arc electrode.
Fig. 2 shows the result analyzed by ray-tracing of
the process in which the split beams are collected together at one place near the focal point. The figure shows
the analysis results obtained when a laser beam radiated from an optical fiber with a core diameter of 0.6
mm is focused in a diameter of 1.2 mm at the position ofjust focus.
In this case, since the laser beam is completely split
at the location 8 mm above the focal point, a space iscreated between the two split-half beams where the electrode can be placed. The focusing properties of the laser
are determined by considering various factors such as
the quality of the beam generated by the laser, dimensions of the head, properties of the target materials(type, thickness, and shape of grooves, etc.), and thearc welding equipment being used in conjunction withthe system.

When considering a joint shape, for instance, a smaller
focused beam diameter is effective for butt joints of a
thick plate, while in fillet welding, a relatively larger
focused beam diameter is better, since a wider bead isrequired instead of deeper penetration, in this case.
Therefore, it is desired to choose the conditions that best
correspond to the target object being welded.
Fig. 3 shows the results of an examination of the effect of a focused diameter on the depth of penetration.
In stainless steel plates welded with an laser output of
2 kW, for example, it can be seen that reducing the focus
diameter from 1.2 mm to 0.6 mm improves penetration
by about 1.3 times.
2.2 Specifications of commercial laser-arc hybrid
welding head
A compact-designed welding head has been developed
based on the prototype unit shown in Fig. 1 as a step incommercializing this equipment.
Fig. 4 shows the appearance and specifications of acompact head, while Fig. 5 shows the standard configuration of the device. Not only is new equipment available
that is provided with all new components, but units arealso available that can be easily combined with an existing laser oscillators and arc welding power units.
Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 2 (Apr. 2005)

2Working procedure

Laser

MIG

MIG-YAG

Welding condition

4 kW300 A/ 24 V

4 kW + 300 A/ 24 V

Section of beadAC 4 CH-T 6 /A 5454 P(Welding speed: 3 m/min)Fig. 6 Comparison of working procedures for lap fillet welding of aluminum alloy
The hybrid welding achieves both the required leg length and depth of penetration, which
are impossible to achieve by laser or MIG welding alone.

A 5083 4 mmt
Weldingcondition

SectionYAG laser:
3 kW
MIG:
80 A/20V
Welding speed:
0.7m/minShield gas:
Ar
Filler wire:
A 5356GrooveA 6061 4 mmt
Gap0 mm

0.5 mm1mm

Material: SUS 304 5 mmt
Wire:TGS 308LK 1.2 mm
Laser output: 3.4 kW
Conditions for MIG: 175 A- 35 V

1.5 mm2 mm

Welding speed: 0.6 m/min
Welding position: Flat
Shield gas: 100%Ar
Preparation of grooves: Shearing

5 mmFig. 8 Example of welding of thick aluminum plate
Example of high-speed one-pass welding of aluminumthick plate (4 mm).

200 mmTransverseshrinkage

Measurement of deformation(mm), (deg)Fig. 7 Enlargement of gap tolerance by hybrid welding
Welding can be performed under constant conditions for groove gaps
between 0 to 2 mm in size.

500 mmLongitudinalwarp

Angulardeformation

108: Transverse shrinkage: Longitudinal warp
: Angular deformation

6420A 6061 (MIG-YAG)

A 6N01 (MIG)

Base metal (Welding procedure)Fig. 9 Comparison of welding distortion
A longitudinal warp in MIG welding can be reduced to 1/9 by hybrid welding.

2.3 Examples of welded results
Fig. 6 shows examples of lap fillet welding joints ofaluminum alloy. It is difficult to ensure a sufficient leg
length in the case of laser welding alone. The bead shape
is apt to become unstable easily and penetration becomes poor within a high-speed zone, in the case of MIG
welding work alone. On the other hand, in hybrid welding, stable beads can be obtained and maintained within
the high-speed zone, while ensuring adequate penetration.
Fig. 7 shows some examples of stainless steel plates
that have been butt-welded with different groove gaps.
In this case, the grooves were prepared by shearing,with gaps of up to a maximum of 2 mm at a pitch of
0.5 mm. The figure shows that the hybrid welding headcan perform welding of a plate with a thickness of 5 mm,

under a constant condition, with gaps of up to a maximum of 2 mm. In other words, welding with a wide gap
tolerance can be performed using the hybrid weldinghead.
Fig. 8 shows examples of the welding results of buttwelded aluminum alloy plates with a thickness of 4 mm
using the hybrid welding head. The figure shows thatthe hybrid welding head can weld plates with a thickness of 4 mm at a high speed of 0.7 m/min. In addition,
the effectiveness of hybrid welding in minimizing deformation is remarkable compared with conventional
MIG welding, as shown in Fig. 99. Another advantage ofthe hybrid welding head is that welding can be done
without the need to depend on the direction of the head,since it is provided with an arc electrode arranged
coaxially with the laser beam.
Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 2 (Apr. 2005)

3As shown in the example of circular welding in Fig
Fig.. 1010,
it is not necessary to adjust the direction of wire feeding, so that the newly developed welding head also
reduces the workload of the operator by eliminating theneed to set precise position settings for welding two- or
three-dimensional objects.

Test conditions
Aluminum alloy (A 5052)
3 k W/125 A
1.0 m/min

3. Laser brazing
3.1 Specifications of commercial laser brazing headAs with the hybrid welding head, MHI has also developed a coaxial laser brazing head capable of feeding
filler metal wire coaxially with a laser beam. This brazing head will be used for laser brazing that is widely
applied to car bodies in automobile production plants in
Europe. This brazing head makes it possible to satisfy auser's need to treat sharp changes in brazing lines, which
are often seen in trunk-lids and other complex compo1 shows the appearance and specifications
nents. Fig. 1
11of the brazing head.
3.2 Example of brazed results
Fig. 12 shows examples of brazing work. The figure shows that the head can stably perform one-stroke
brazing in a plane, as the need for careful setting of
the direction of the head is eliminated by coaxial wire
feeding. In addition, the bead can be formed so thatit corresponds exactly with sudden changes in thebrazing line.

Dimensions: 410 x 120 x 110mm
Weight: 5.2 kg
Rate of magnification: x 1.3

Fig. 10 Example of circular welding
The driving axis of the arc torch is not required even in circular
movement, by using the coaxially arranged arc and laser torches.

Fig. 13 shows a cross section of a flare groove joint.
It is difficult for the filler metal to penetrate into theinterior of the groove when the filler metal wire is
fed from the side of the joint. However,as can be seenin this figure, the filler metal can penetrate sufficiently into the depths of the groove when the hybrid
brazing head is used. From this fact, it is thoughtthat the melting efficiency of the wire is increased
because the wire is preheated by feeding the wire
coaxially with laser beam.

Brazing conditions
Type:

Bead on plate

Material:

Steel plate

Plate thickness:

3.0 mmLaser output:

2.0 kW

Welding speed:

0.8 m/minAppearance of bead

Wire feeding rate: 2.8 m/min
Fig. 12 Example of laser brazing results (1)Coaxial wire feeding can cope with sudden changes in direction, such as in one-stroke
brazing, including shape changes such as right angle inflections and complex forms.

Optical fiber

Wire
Brazing conditions

Nozzle forfeeding wire

Type:

Flare joint

Material:

Zinc coatedsteel plate

Plate thickness:

0.75 mm

Laser output:

3.0 kW

Welding speed:

3.5 m/minWire feeding rate: 7.0 m/min
Fig. 11 View of coaxial laser brazing head
Operability by a robot was improved by arranging
the laser and wire coaxially into a compact unit.

Appearance of bead

Cross section

Fig. 13 Example of laser brazing results (2)Filler metal penetration into a groove is improved by the preheating effect of the laser beam.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 2 (Apr. 2005)

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4. Example of application
One major potential application anticipated of this
newly developed technology is in the welding assemblyof automobile bodies, because of the advantages realized
by the coaxial arrangement of the arc or wire and laser.
Fig. 14 shows some example applications of MIG-YAG
hybrid welding in the assembly of car bodies. The effectiveness of the coaxial wire-feeding method is being
demonstrated through use in various applications.
Fig. 14 Application to assembling car bodies(Concept Car "i" presented by Mitsubishi Motors Corporation)
Example of car bodies assembled by hybrid welding(exhibited at the Motor Shows in Tokyo and Frankfurt in 2003).

5. Conclusion
MHI has developed a hybrid welding head suitablefor welding sophisticated three-dimensional objects suchas car bodies. It has been confirmed that the hybrid welding head, which consists of an arc electrode and a laser
beam arranged coaxially, displays effects that are superior to arc welding, in terms of increased welding speed,
minimal distortion, and greater penetration depth. The
hybrid welding head is also superior to laser welding inensuring the leg length of fillet welding and increasing
the gap tolerance of grooves.
Furthermore, it has been demonstrated that the coaxial arrangement of the arc and laser can reduce thenumber of controlling axes. In addition, it has been shownthat the effect of preheating the wire improves the penetration of brazing filler metal into grooves in laser
brazing and also that the coaxial brazing head makes
brazing without the need to depend on head direction
possible.
This newly developed technology is not just restricted
to being used in combination with YAG laser welding,but can also be also applied in combination with diodelasers or fiber laser welding, which have been the focus
of growing attention in recent years due to their greater
welding power output. MHI not only intends to develop
a line up of welding heads that just conform to immediate user needs, but also to combine this technology withgroove sensing, quality monitoring, and driving systems
to provide these technologies as comprehensively integrated welding systems.

References(1) M. Shirai, Laser Welding on Trough Panel (3 DimensionalBody Part), Proc. of the 55th Laser Material Process Conference (2002), p.1(2) K. Mori et al., Application of Laser Welding for Body inWhite, Proc. of the 55th Laser Material Process Conference(2002), p.7(3) T. Tarui, Trend of Laser Application for Car Body in European Automotive Industry, Proc. of the 61st Laser MaterialProcess Conference (2004), p.152(4) K. Loffler, Laser Applications Golf V : Concept and Implementation in Production, Proc. of European Automotive Laser Application 2004•Cp.181(5) Y. Makino et al., Hybrid Welding Between CO2 Laser Beamand MIG Arc, Proc. of the 53rd Laser Material Process Conference (2001), p.31
(6) N. Tomita et al., Welding of Aluminum Alloy Using LDMIG
Hybrid Welding Robot System, Proc. of the 56th Laser Material Process Conference (2002), p.69

Shuho Tsubota

Takashi Ishide

Masao Watanabe

Takashi Akaba

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 42 No. 2 (Apr. 2005)

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