Full penetration hybrid laser arc welding of up to 28 mm thick S355 plates using electromagnetic weld pool support [original]

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Beam Technologies and Laser Application IOP Publishing
IOP Conf. Series: Journal of Physics: Conf. Series 1109 (2018) 012015 doi :10.1088/1742-6596/1109/1/012015

Full penetration h ybrid laser arc wel ding of up to 28 mm
thick S355 plates usi ng electroma gnetic weld pool support
Ömer Üstündag 1* , V jacesl av Avilov, And rey Gume nyuk 1,2 , Michael Reth meier 1,2,3

1 Fraunhofer I nstitute for Production Sy stem s and Desig n T echnolog y , G ermany
2 Federal I nstitute for Mat erials Res earch and T esting, G ermany
3 Institute of Machine T ools and Facto ry Manag ement, T echnische Un iversität Ber lin,
Germ any

* Correspond ing author e- mail: oem er.uestuendag @ipk.fraunho fer.de
Abstract . The laser h y brid welding process off ers many adv antages regarding deep penetration,
increased w elding velocity a nd w ith t he help o f t he supp lied filler w ire an improved br idgeabilit y
to gap and mis alig nment toler ances. High p o wer laser s ystems with a po wer o f ap prox. 30 kW
are already available on the market. Neverthele ss, multi -layer technolog y with an arc pr ocess is
still u sed for welding of plates from a thicknes s fro m 20 mm. A p otential cause is the p rocess
instability with i ncreasin g las er power. It is inevitable that gravity drop -out due to the high
hydrostatic pressure at in creasing wall thic kness especially at welding in flat position and w ith a
low welding speed. The surface tension decreases with increasing root width resulting from low
welding velocities. T o prevent such inad missible defects of the sea m a use of w eld po ol support
is required. Usual w eld p ool su ppo rt sy stems such as ce ramic or pow der supports require a
mechanical d etachment which is ti me-consumin g. T he el ectromagnetic weld pool sup port
system described in this work sho ws an a lternative weld po ol support which w orks co ntactless.
It is b ased o n generating Lore ntz forces in the weld pool due to oscillating m ag netic field and
induced ed dy current s. T his innovative technology offers si ngle pass w elds up to 28 mm in flat
position a nd reduced welding velocity w ith a laser po wer of just 19 kW. It also leads to improved
mechanical-tec hnological prop erties of the seams b ecause o f the slo w co o ling rate. With usage
of an electromagnetic weld pool support the lim ita tion of th e hybrid laser arc w elding process in
the thick sheet metal will be extend.

1. Introduction
The hybrid laser arc weldin g pr ocess i s a coupling of laser beam welding and arc welding pr oces s in a
comm on interact ion zone and was developed in the 19 70s [1] . The aim of this cou pling is to exploi t the
synergy effec ts of both we lding processes and overcom e probl ems that often occ ur i n pure laser beam
welding or arc welding. The hig h powe r density of t he laser beam cre ates a na rrow key hole, which
enables a deep penetration ef fect at hig h welding speeds and low distortion of t he weld ed metal. T he
additional m aterial, which is fed to t he process in the form of m olten filler wire enables a bet ter
bridgeability against gap and other manufactu ring tolerances [2] . Furtherm ore, the m echanical -

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Beam Technologies and Laser Application IOP Publishing
IOP Conf. Series: Journal of Physics: Conf. Series 1109 (2018) 012015 doi :10.1088/1742-6596/1109/1/012015

technologic al properties of the weld ed sam ples can be positively influenced by using of an aim ed filler
m etal and the additiona l energy of the arc in g eneral, which reduces the cooling rate.
For deep penetration welds , an arc lead ing orientation of the process, a short d istance between the
wire tip and the laser beam and a small torch angle are prefer red. Moreover, the f ocal position of the
laser be am should be below to the top surface [3-4]. Fig ure 1 shows s chem e of hybrid laser arc w eld ing
process with the principal factors, which have an i nfluence on t he penetra tion effect, where a i s t he
distance be tween the exten ded wi re tip and the la ser be am, β is the torch angle rela ting to the laser beam
and z f is the focal position of the la ser beam .

Figure 1. Sch eme of hy brid laser arc w elding
High power laser sy stems with a pow er of app rox. 30 k W are already available on the m arket due to
latest developm ents i n laser technology . The hy brid laser arc w elding pro cess is us ed for i ndustria l
applications suc h as in the marine i ndust ry. The Ger m an shipyard Meyer Werft and the Fincantieri
shipyard in I taly have succe ssfully introduc ed t his technolog y [5]. The hybrid lase r arc we lding pr ocess
is used for single- pass welds up to m ax. 20 mm . Material thicknesses beyond t his, can be welded with
the hybrid laser arc weldin g proce ss in multi-layer te chnology . Plates with a thickness up t o 28 mm
could be welded in two lay ers, and 32 m m t hick plates in three to five layers, successfu lly [6].
Alternatively , the root face of thick materials is weld ed by hybrid laser arc welding process. In the
following process the g roov e is filled by an arc welding process such as subm erged ar c welding [7] or
GMA w elding process [ 8]. In m ost instances, m ulti-lay er t echnolog y with an arc process is still used for
welding of pla tes from a thick ness more than 20 mm .
A potential cause of the restricting factors for hybrid laser arc welding of materials with a t hick ness
greater than 20 mm i s the increasing process instabilit y with the growing laser po wer . Another proc ess
limitation is that t he p rocess ca n be realiz ed only at a sufficiently hig h weldi ng speed i n particular in flat
position. The m ain reason f or choosing a hig h welding speed when welding thick m aterials in flat
position is the action of t he grav itational fo rce lead ing to sag ging of the molten m etal. G ravity drop -out
results when the hydrostatic pressur e excee ds t he sur face t ension. T he hy drostati c pressure is dependent
on the material thicknes s and grows by increasing thickness . The surface tension decreases with
increasing w idth of the roo t side, whi ch occurs at slow welding v elocitie s. This explains why the s table
welding proces s is possib le only for higher weld ing speeds.
Th ick m aterials can be weld ed at lower welding speeds i n horizontal position (2G) or with wel d pool
support system s. Conventional weld pool supports such as cerami c backing, powdered metal or anti-
slag gas ar e used [9-10]. Ceramic baking and powdered metal as weld pool support require a mechanica l
detachm ent and rework of the root pa rt, which i s tim e -consum ing.

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Beam Technologies and Laser Application IOP Publishing
IOP Conf. Series: Journal of Physics: Conf. Series 1109 (2018) 012015 doi :10.1088/1742-6596/1109/1/012015

An alternative solution consists i n using oscillating electrom agnetic fields to pre vent sagging and
grav ity drop - out. I t is based on generating Loren tz for ces in the weld pool. An oscillati ng magnetic field
B per pendicul ar to the welding direction is produ ced by an AC mag net and generates eddy currents in
the m aterial. The electric current dens ity j is parallel to the welding direction. The resulting Lorentz F L
force is d irected upwards and counterac ting the hydrostatic pressure. A schematic drawing of t he
electrom agnetic weld poo l suppor t is shown in F igure 2.

Figure 2. Sch eme of elect rom agnetic weld pool support syst em
This technology was demonstrated for laser beam weldi ng of al um inum alloys [11], austenitic [12]
and ferrom agnetic steels [1 3] and for hy brid laser a rc w elding o f ferrom ag netic s teels [14] su ccessfully .
For app lication of elect romag netic we ld p ool support at hy brid las er arc w elding, it will b e necessary to
ensure, that the skin layer depth δ must be smaller than the materi al thickness [14]. The skin depth is
primarily dependent on t he oscillating frequency of the magnetic field and increas es at decreasing
frequency. This i s espec ially important for p reventing the el ectric a rc on the t op si de of the w eld s ample
to be influenced by osci llating mag netic field.
2. Experimen tal Setup
All welding exper iments were executed in flat (1G) position using a 20 - kW -Yb fibre l aser YLR- 20000
with a wav e l ength of 1064 nm and a beam parameter product of 11.2 mm x mrad. T he f ocal length of
the optics was 350 mm . An optical fibre of 200 µm was used for transm ission of the laser beam . The
focus diam eter wa s 0.56 m m . The welding m achine Qineo Pulse 600A functioned as arc we lding power
source. Fo r the exp erim ents the w elding m achine was opera ted in pulse m ode w ith a pulse freque ncy of
180 Hz. All hybrid laser arc welds were execu ted with an arc leading or ientat ion and a t orch angle of
25° relating to the l aser beam . T he distance between the wire tip extension and the impact of t he laser
beam on th e work piece w as 4 mm . A negative focus po sition of the laser beam rela tive to t he wo rkpiece
surface of - 8 mm to - 13 mm . The welding speed was 0.5 m min -1 to 1 m m in -1 .
During experiments the laser head and GMA W t orch was mounted on t he robot arm . T he AC magnet
was in a fixed po sition 2 m m under the workpi ece. T he robot arm and th e m agnet hav e not been moved,
in orde r to ensure that the weld seam was centr ed between the magnet poles. T he welding motion was
realized throug h the m ovem ent of the workpiece by a turn -table. Figure 3 shows the experimental set -
up of full pe netrated hybr id laser arc we lds with el ectrom agnetic weld po ol.
The gap betwee n the two mag net poles was 25 m m , see f igure 3 (bo ttom right). A distance of 2 mm
between t he surface of t he magnet and th e wo rk piece has b een selec ted. The m agnet w as o perated wi th
a oscillating frequency of 1.1 kHz to 1.2 kH z and in a power range of 1.6 kW to 2.6 kW dependent on
the materia l thickness and increasing hy drostatic pressure.

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Beam Technologies and Laser Application IOP Publishing
IOP Conf. Series: Journal of Physics: Conf. Series 1109 (2018) 012015 doi :10.1088/1742-6596/1109/1/012015

Figure 3. Expe rimenta l Set- up of hybrid laser- arc welds with electrom agnetic weld pool support (left),
enlarged v iew (top rig ht) and ov erview of us ed electro m agnet
For t his study , materials of st eel grad e S355 J2 w ith a plate t hick ne ss of 20 mm, 25 mm and 28 mm
were used. The parts with a thickness of 25 mm were assembled i nto a butt joint configuration with a
square groov e. A Y - j oint prepa ration was provided f or 20 mm (root face of 14 mm ) and 28 mm (root
face of 23 mm) . All weld sam ples have been previously milled on the welded side. For the filler wire,
different wires o f types G3 Ni1 ( solid wire) according to EN I SO 14341 and a flu x-cored wire T 69 6
Mn2NiCrMo M M 1 H5 ( Megafil 742M) according to EN ISO 18276 with a diam eter of 1.2 mm were
chosen. T he shielding gas was a mixt ure of argon with 18 % CO 2 with a fl ow rate of 20 l min -1 . The
chemical composition o f the used m aterial and f iller w ires are show n in table 1 .

Table 1. Chem ical com position o f base m aterial and filler w ires , shown in wt%

Material/E lement

S355J2

0.08

1.3

0.29

0.019

0.004

0.08

bal.

Megafil 742 M

0.05

1.6

0.4

0.015

0.5

2.2

0.5

0.003

0.12

bal.

G3Ni1

0.08

1.4

0.612

0.004

0.014

0.73

0.08

bal.

3. Results
Plates with a thick ness of 20 m m, 25 mm and 28 mm could be welded in a single- pass without sag ging
and grav ity drop- out. With an A C p ower of 1.6 kW a t an AC frequency o f 1.2 k Hz, an ideal
compensation of the hydrostatic pressur e with a nearly flat root surface could be reached for full
penetration w elds 20 mm thick structural stee l S355J2. A ccording to EN I SO 12932, which defines th e
quality levels for im perfect ions for hybrid laser arc weld ing of steels, the welde d 20 mm thick plates
can be classified i n the hig hest evaluation group B. The figure 4 shows the comparison for sing le - pass
welded 20 mm thick sa m ples w ith and witho ut electrom agnetic weld pool support system. The laser
power wa s 12.2 kW, an arc power o f 11.2 kW and a welding v elocity of 0.5 m m in -1 hav e been selected.
The root excess weld m etal is approx. 0.3 m m and the width of the root is 5 mm . The groov e i s f illed
completely . A laser profi le scan of the root part is also shown in figure 5 for a qualitative evaluation
over the en tire seam length. I t is ev ident tha t the root i s steady over the entir e seam length. The lim its of
root ex cess weld m etal fo r different ev aluation groups according to EN I SO 12932 are a lso m arked. The
root reinforc em ent can be affecte d by chang es of the AC m agnet power, see [14 ].

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Beam Technologies and Laser Application IOP Publishing
IOP Conf. Series: Journal of Physics: Conf. Series 1109 (2018) 012015 doi :10.1088/1742-6596/1109/1/012015

Figure 4. Cro ss section of 20 mm si ngle - pass welded sam ple; (left) r eference a nd (rig ht) with
electrom agnetic weld poo l suppor t

Figure 5. Ev aluation of ideally com pensated hybr id laser a rc welded 20 m m thick plate with a laser
profile scanne r (top), weld root with m axi mum acceptable root exces s weld m etal acco rding to EN
ISO 12932 (bo ttom)
The possibil ity of reduced welding velocity allows an i ncrease of weldabl e material thickness with a
laser beam power of 20 kW. Single- pass hybrid laser arc welding of 25 mm thick square groove butt
joints could be realized withou t sa gg ing and accor ding t o t he r oot quality requirements of the valid
standard at a welding velocity of 0. 9 m m in -1 with a laser power of 19 kW and a wire feeding rate of
12 m min -1 . A focal position of - 5 mm was se lected. T he magnet was operated at a frequency of 1.2 kH z
and an AC power of 1.9 kW. T he root is compensa ted ideally, see figure 6. Due to the higher welding
velocity comparing to hybr id laser arc welded 20 mm thick plates, the r oot width decreas es to 4.3 mm .
The root exces s weld m etal is 0.7 m m .
A reduction of the we lding speed and a joint preparation allow s a single -pass weld thicker plates up
to 28 mm . A Y - joi nt prepar ation with a root face o f 23 mm was selected. The requ ired lase r power was
19 kW at a welding speed of 0.5 m min -1 . The wire feed ing rate was 12 m min -1 . An AC power of 2.6 kW
was necessary to prevent gravity drop - out at an oscillating frequency of 1.16 kHz . Figure 7 shows a
cross section of a single-pass welded 28 mm t hick steel plate. It is recognisable, that the r oot is ideally
compensated and nearly flat and the groove i s filled co m plet ely. The root w idth is 4.2 mm .

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Beam Technologies and Laser Application IOP Publishing
IOP Conf. Series: Journal of Physics: Conf. Series 1109 (2018) 012015 doi :10.1088/1742-6596/1109/1/012015

Figure 7. Single- pass hybr id laser arc weld ed 28 mm thick structur al steel S355 J2 with
electrom agnetic weld poo l suppor t
The welding param eters for ideal com pensated si ngle-pass welds w ith hy brid laser arc we lding are
summ arized in table 2.

Table 2. We lding param eters for s ingle-pass welds o f thick m aterials w ith differen t thicknesses

t
in mm

Joint
preparation

Root face
in mm

P l
in kW

v w
in m m in -1

v wire
in m m in -1

f AC
in kHz

P AC
in kW

12.2

0.5

1.2

1.6

I-butt

0.9

1.2

1.9

0.5

1.16

2.6

4. Summary
I n su mm ary, single-pass hybrid laser arc welds of 20 mm, 25 mm and 28 mm thick pl ates of structura l
steel S355J2 could be welded without gravity drop - out successful. T he reduc tion of the welding speed
allows an increase of weldable materia l t hick ness with a laser beam power of 20 k W. All welds can be
classified in the highest evaluation group B accord ing to EN ISO 12932. The electrom agnetic weld pool
support system , des cribed in this study, m akes the reduction o f welding speed pos sible with out
imperfectio ns such as inadm issible root excess weld metal. By use of t his system at hybrid laser beam
welding process the potential f ield of application of this technology for real industrial im plementation
can dram atically incre ase and becom e a suitable alter native to conventiona l proc esses, which are still

Figure 6. Ov erview of a single- pass hybrid laser arc welded 25 mm t hick square groov e butt joint
plate ; cro ss section (right)

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IOP Conf. Series: Journal of Physics: Conf. Series 1109 (2018) 012015 doi :10.1088/1742-6596/1109/1/012015

used for m ulti- layer weldin g of thick plates. For practical u se, the AC m ag net m ust be m oved under the
workpiece w ith the sam e v elocity of we ld head.
The reduction o f the welding speed is also fav orable for the cooling tim e and m echanical-
technologic al proper ties of welded structures. Al l weld s were also c rack and po re -free.

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