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11.
Surfacing
and Shape Welding
11. Surfacing and Shape Welding 151
2005
DIN 1910 (“Welding”) clas-
sifies the welding process
according to its applica-
tions: welding of joints
and surfacing. According
to DIN 1910 surfacing is
the coating of a workpiece
by means of welding.
Dependent on the applied
filler material a further
classification may be
made: deposition repair
welding and surfacing for
the production of a composite material with certain functions. Surfacing carried out with wear-
resistant materials in preference to the base metal material is called hardfacing; but when
mainly chemically stable filler materials are
used, the method is called cladding. In the
case of buffering, surfacing layers are pro-
duced which allow the appropriate-to-the-
type-of-duty joining of dissimilar materials
and/or of materials with differing properties,
Figure 11.1.
A buffering, for instance, is an intermediate
layer made from a relatively tough material
between two layers with strongly differing
thermal expansion coefficients.
Figure 11.2 shows different kinds of stresses
which demand the surfacing of components.
Furthermore surfacing may be used for pri-
mary forming as well as for joining by primary
forming.
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base metal/ surfacing metal
similar
for repair welding�
dissimilar
hardfacing (wear protection)
cladding (corrosion prevention)
buffering (production of an appropriate-to-the-type-of-duty joint of dissimilar materials)
�
�
�
Figure 11.1
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Components -Kinds of Stress
� wear caused by very high impact and compressive stress
wear by friction (metal against metal) during high impact and compression stress
strong sanding or grinding wear
very strong wear caused by grinding during low impact stress
cold forming tools
hot forming tools
cavitation
wear parts (plastics industry)
corrosion
temperature stresses
�
�
�
�
�
�
�
�
�
Figure 11.2
11. Surfacing and Shape Welding 152
2005
In case of surfacing - as for all fabrication processes - certain limiting conditions have to be
observed. For example, hard and wear-resistant weld filler metals cannot be drawn into solid
wires. Here, another form has to be selected (filler wire, continuously cast rods, powder).
Process materials, as for example SA welding flux demand a certain welding position which
in terms limits the method of welding.
The coating material must be selected with view to the type of duty and, moreover, must be
compatible with the base metal, Figure 11.3.
For all surfacing tasks a large product line of welding filler metals is available. In depend-
ence on the welding method as well as on the selected materials, filler metals in the form of
wires, filler wires, strips, cored strips, rods or powder are applied, Figure 11.4.
The filler/base metal dilution is rather important, as the desired high-quality properties of the
surfacing layer deteriorate with the increasing degree of dilution.
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Boundary Conditions in Surfacing
component(material)
coating
coatingmaterial(filler)
surfacingmethod
stresscompatibility
manufacturingconditionsavailability
consumable
Figure 11.3
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Materials for Surfacing
wearing protection (armouring)
corrosion prevention
hard facing on
cobalt base
nickel base
iron base
ferritic to martensitic chromium steel alloys
soft martensitic chromium-nickel steel alloys
austenitic-ferritic chromium-nickel steel alloys
austenitic chromium-nickel steel alloys
�
�
�
�
�
�
�
Figure 11.4
11. Surfacing and Shape Welding 153
2005
A weld parameter optimisation has the objective to optimise the degree of dilution in order to
guarantee a sufficient adherence of the layer with the minimum metal dissimilation. A
planimetric determination
of the surfacing and pene-
tration areas will roughly
assess the proportion of
filler to base metal. When
the analysis of base and
filler metal is known, a
more precise calculation is
possible by the determina-
tion of the content of a cer-
tain element in the surfac-
ing layer as well as in the
base metal, Figure 11.5.
Figure 11.6 shows record charts of an electron
beam microprobe analysis for the elements
nickel and chromium. It is evident that - after
passing a narrow transition zone between
base metal and layer — the analysis inside
the layer is quasi constant.
As depicted in Figure 11.7 almost all arc weld-
ing methods are not only suitable for joining
but also for surfacing.
Definition of Dilution
© ISF 2002br-er11-05e.cdr
surface built up by welding FB
penetration area F P
base metal
(X-content - X-content ) [% in weight]
(X-content - X-content ) [% in weight]surfacing layer FM
base metal FM
FP
F + FP B
A = x 100%
A = x 100%
D
D
FM: weld filler metal A : dilutionD
Figure 11.5
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Microprobe Analyses
10
0
20
30
%
Cr
pe
rce
nta
ge
s b
y m
ass
µm0 100 200
distance
300 500
10
%
0
20
30
Ni p
erc
en
tag
es b
y m
ass
µm0 100 200 300 500
distance
Figure 11.6
11. Surfacing and Shape Welding 154
2005
In the case of the strip-electrode submerged-arc surfacing process normally strips
(widths: 20 - 120mm) are used. These strips allow high cladding rates. Solid wire electrodes
as well as flux-cored strip electrodes are used. The flux-cored strip electrodes contain certain
alloying elements. The strip is continuously fed into the process via feed rollers. Current con-
tact is normally carried out
via copper contact jaws
which in some cases are
protected against wear by
hard metal inserts. The
slag-forming flux is sup-
plied onto the workpiece in
front of the strip electrode
by means of a flux support.
The non-molten flux can be
extracted and returned to
the flux circuit.
Should the slag developed
on top of the welding bead
not detach itself, it will
have to be removed me-
chanically in order to avoid
slag inclusions during
overwelding. The arc wan-
ders along the lower edge
of the strip. Thus the strip
is melted consistently, Fig-
ure 11.8.
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inert gas-shielded arc weldingmetal-arc welding submerged arc welding
arc spraying
plasma spraying
electroslag welding
- stick electrode- filler wire
- MIG / MAG- MIG cold wire- filler wire
TIG welding
- TIG cold wire
plasma welding
- plasma powder- plasma hot wire
- wire electrode- strip electrode
arc welding with self-shieldedcored wire electrode
- filler wire
- powder- wire
- wire electrode
Figure 11.7
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flux support
filler metal
slag
surfacing bead
drive rolls + -
flux application
base metal
power source
Figure 11.8
11. Surfacing and Shape Welding 155
2005
Figure 11.9 shows the
cladding of a roll barrel.
The coating is deposited
helically while the work-
piece is rotating. The weld
head is moved axially over
the workpiece.
The macro-section and
possible weld defects of a
strip-electrode submerged-
arc surfacing process are
depicted in Figure 11.10.
Electroslag surfacing us-
ing a strip electrode is
similar to strip-electrode SA
surfacing, Figure 11.11.
The difference is that the
weld filler metal is not
melted in the arc but in liq-
uefied welding flux — the
liquid slag – as a result of
Joule resistance heating.
The slag is held by a slight
inclination of the plate and
the flux mound to prevent it
from running off.
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coarse grain zone lack of fusion mirco slag inclusions sagged weld
crack formationin these areas of
the coarse grain zoneundercutsgusset
base metal
Figure 11.10
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Figure 11.9
11. Surfacing and Shape Welding 156
2005
TIG weld surfacing is a suitable surfacing method for small and complicated contours and/or
low quantities (e.g. repair work) with normally relatively low deposition rates. The process
principle has already been shown when the TIG joint welding process was explained, Figure
11.12. The arc is burning
between a gas-backed non-
consumable tungsten elec-
trode and the workpiece.
The arc melts the base
metal and the wire or rod-
shaped weld filler metal
which is fed either continu-
ously or intermittently. Thus
a fusion welded joint devel-
ops between base metal
and surfacing bead.
In the case of MIG/MAG surfacing proc-
esses the arc burns between a consumable
wire electrode and the workpiece. This
method allows higher deposition rates. Filler
as well as solid wires are used. The wire elec-
trode has a positive, while the workpiece to be
surfaced has a negative polarity, Figure
11.13.
© ISF 2002br-er11-12e.cdr
Process Principle ofTIG Weld Surfacing
rod/ wire-shapedfiller metal
arc
shielding gas nozzle
base metal(+ / ~) surfacing bead
tungsten electrode(- / ~)
Figure 11.12
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molten pool
Figure 11.11
11. Surfacing and Shape Welding 157
2005
A further development of
the TIG welding process is
plasma welding. While the
TIG arc develops freely, the
plasma welding arc is me-
chanically and thermally
constricted by a water-
cooled copper nozzle. Thus
the arc obtains a higher
energy density.
In the case of plasma arc
powder surfacing this
constricting nozzle has a
positive, the tungsten electrode has a negative polarity, Figure 11.14. Through a pilot arc
power supply a non-transferred arc (pilot arc) develops inside the torch. A second, separate
power source feeds the transferred arc between electrode and workpiece. The non-
transferred arc ionises the centrally fed plasma gas (inert gases, as, e.g., Ar or He) thus
causing a plasma jet of high energy to emerge from the nozzle. This plasma jet serves to
produce and to stabilise the arc striking ability of the transferred arc gap. The surfacing filler
metal powder added by a feeding gas flow is melted in the plasma jet. The partly liquefied
weld filler metal meets the
by transferred arc molten
base metal and forms the
surfacing bead. A third gas
flow, the shielding gas, pro-
tects the surfacing bead
and the adjacent high-
temperature zone from the
surrounding influence. The
applied gases are mainly
inert gases, as, for exam-
ple, Ar and He and/or Ar-
/He mixtures.
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workpiece
+-
oscillation
feed direction
shielding gas
arc
surfacing bead
shielding gas nozzle
contact tube
weld filler metal power source
wire feed deviceshielding gas
Figure 11.13
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power sources
HIG
U
workpiece oscillation
surfacing bead
pilot arc
welding arc
filler metal
shielding gas
conveying gas
plasma gas
tungsten electrode
TA
UNTA
Figure 11.14
11. Surfacing and Shape Welding 158
2005
The method is applied for surfacing small and medium-sized parts (car exhaust valves, ex-
truder spirals). Figure 11.15 shows a cross-section of armour plating of a car exhaust valve
seat. The fusion line, i.e.,
the region between surfac-
ing and base metal, is
shown enlarged on the
right side of Figure 11.15
(blow-up). It shows
hardfacing with cobalt
which is high-temperature
and hot gas corrosion
resistant.
In plasma arc hot wire
surfacing the base metal
is melted by an oscillating
plasma torch, Figure 11.16.
The weld filler metal in the form of two parallel wires is added to the base metal quite inde-
pendently. The arc between the tips of the two parallel wires is generated through the appli-
cation of a separate power
source. The plasma arc
with a length of approx. 20
mm is oscillating (oscilla-
tion width between 20 to 50
mm). The two wires are fed
in a V-formation at an an-
gle of approx. 30° and melt
in the high-temperature
region in the trailing zone
of the plasma torch.
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workpiece
wires from spool
plasma powersource
shieldinggas
arc
plasma gas
tungstenelectrode
=
~
surfacingbead
hot wire power source
weld pool
Figure 11.16
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section A
GW
ZW
Figure 11.15
11. Surfacing and Shape Welding 159
2005
For surfacing purposes,
besides the arc-welding
methods, the beam weld-
ing methods laser beam
and electron beam welding
may also be applied. Fig-
ure 11.17 shows the proc-
ess principle of laser sur-
facing. The powder filler
metal is added to the laser
beam via a powder nozzle
and the powder gas flow
is, in addition, constricted
by shielding gas flow.
Friction surfacing is, in principle, similar to friction welding for the production of joints which
due to the different materials are difficult to produce with fusion welding, Figure 11.18.
The filler metal is “advanced” over the workpiece with high pressure and rotation. By the
pressure and the relative movement frictional heat develops and puts the weld filler end into
a pasty condition. The advance motion causes an adherent, “spreaded” layer on the base
metal. This method is not applied frequently and is mainly used for materials which show
strong differences in their melting and oxidation behaviours.
A comparison of the differ-
ent surfacing methods
shows that the application
fields are limited - de-
pendent on the welding
method. A specific
method, for example, is
the low filler/base metal
dilution. These methods
are applied where high-
quality filler metals are
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rotation
bulge
force
surfacing layer
base metal
filler metal
advance
Figure 11.18
Figure 11.17
11. Surfacing and Shape Welding 160
2005
welded. Another criterion for the selection of a surfacing method is the deposition rate. In the
case of cladding large sur-
faces a method with a high
deposition rate is chosen,
this with regard to profit-
ability.
In thermal spraying the
filler metal is melted inside
the torch and then, with a
high kinetic energy, dis-
charged onto the unfused
but preheated workpiece
surface.
There is no fusion of base and filler metal but rather adhesive binding and mechanical inter-
locking of the spray deposit with the base material. These mechanisms are effective only
when the workpiece surface is coarse (pre-treatment by sandblasting) and free of oxides.
The filler and base materials are metallic and non-metallic. Plastics may be sprayed as well.
The utilisation of filler metals in thermal spraying is relatively low.
The most important methods of thermal spraying are: plasma arc spraying, flame spraying
and arc spraying.
In powder flame spraying
an oxyacetylene flame pro-
vides the heating source
where the centrally fed filler
metal is melted, Figure
11.19. The kinetic energy for
the acceleration and atomi-
sation of the filler metal is
produced by compressed
gas (air).
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spraying materialcompressedair
workpiece
flame conefuel gas-oxygenmixture
spray deposit
Figure 11.19
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compressed air
gas mixture
adjustable wirefeed device
spraying wire spray deposit
spraying jet non-bindingsprayed particles(loss in spraying)
fusingwire tip
Figure 11.20
11. Surfacing and Shape Welding 161
2005
In contrast to powder flame
spraying, is for flame
spraying a wire filler metal
fed mechanically into the
centre cone, melted, atom-
ised and accelerated in
direction of the substrate,
Figure 11.20.
In plasma arc spraying an
internal, high-energy arc is
ignited between the tung-
sten cathode and the an-
ode, Figure 11.21. This arc
ionises the plasma gas (argon, 50 - 100 l/min). The plasma emerges from the torch with a
high kinetic and thermal energy and carries the side-fed powder along with it which then
meets the workpiece surface in a semi-fluid state with the necessary kinetic energy. In the
case of shape welding, steel shapes with larger dimensions and higher weights are pro-
duced from molten weld metal only. In comparison to cast parts this method brings about es-
sentially more favourable mechano-technological material properties, especially a better
toughness characteristic. The reason for this lies mainly in the high purity and the homogene-
ity of the steel which is helped by the repeated melting process and the resulting slag reac-
tions. These properties are
also put down to the fa-
vourable fine-grained struc-
ture formation which is
achieved by the repeated
subsequent thermal treat-
ment with the multi-pass
technique. Also in contrast
with the shapes produced
by forging, the workpieces
produced by shape welding
show quality advantages,
Plasma Powder Spraying Unit
© ISF 2002br-er11-21e.cdr
powder injector
jet of particles
copper anode
plasmagas
coolingwater cooling water tungsten cathode arc
anodecarrier
middleframe
gasdistributor
isolationring
backframe
Figure 11.21
Shape Welding - Integration
© ISF 2002br-er11-22e.cdr
shape welding
forming(forging)
joining(welding)
primary forming(casting)
Figure 11.22
11. Surfacing and Shape Welding 162
2005
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Shape Welded Goblet (1936)
Figure 11.23
especially in the isotropy and the regularity of their toughness and strength properties as far
as larger workpiece thicknesses are concerned. In Europe, due to the lack of expensive forg-
ing equipment, very high individual weights
may not be produced as forged parts.
Therefore, shape welding is, for certain appli-
cations, a sensible technological and eco-
nomical alternative to the methods of primary
forming, forming or joining, Figure 11.22.
Figure 11.23 shows an early application which
is related to the field of arts.
The higher tooling costs in forging make the
shape welding method less expensive; this
applies to parts with certain increasing com-
plexity. This comparison is, however, related
to relatively low numbers of pieces, where the
tooling costs per part are accordingly higher,
Figure 11.24.
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sh
afts
boile
r she
ll rings
bra
ces
sp
heri
cal ca
ps
pip
e b
end
s
forged products
shape-weldedproducts
complexity of the parts
€/kg
Figure 11.24
11. Surfacing and Shape Welding 163
2005
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tractionmechanism
joistturntable
phase 1
phase 3
phase 5
phase 2
phase 4
phase 6
phase 7
Figure 11.26
© ISF 2002br-er11-25e.cdr
Shape Welding Procedures
+ several weld heads possible+ no interruption during weld head failure
- core made of foreign material necessary
applications:shafts, large boiler shell rings, flanges
+ free rotationally-symmetrical shapes+ several weld heads possible+ weld head manipulation not necessary+ each head capable to weld a specific layer+ small diameters possible
- component movement must correspond with the contour- number of weld heads limited when smaller diameters are welded
applications:spherical caps, pipe bends, braces
+ transportable unit
- limited welding efficiency
applications:welding-on of connection pieces
Baumkuchenmethode
Töpfermethode
Klammeraffe
Figure 11.25
Figure 11.25 shows the principal procedure for
the production of typical shape-welded parts.
Cylindrical containers are produced with the
“Baumkuchenmethode” method: the filler metal
is welded by submerged-arc with helical mo-
vement in multiple passes into a tube which
has the function of a traction mechanism (for
the most part mechanically removed later).
This brings about the possibility to produce
seamless containers with bottom and flange in
one working cycle.
Elbows are mainly manufactured with the
Töpfer method. On the traction mechanism a
rotationally symmetrical part with a semicircle
cross-section is produced which is later sepa-
rated and welded to an elbow, Figures 11.26
and 11.27. The Klammeraffe method serves
the purpose to weld exter-
nal connection pieces onto
pipes. A portable unit
which is connected with the
pipe welds the connection
pipe in a similar manner to
the Töpfer method.
11. Surfacing and Shape Welding 164
2005
In the case of electron beam surfacing the
filler metal is added to the process in the form
of a film, Figure 11.28.
© ISF 1998
feed direction
metal foil
metal foil feeding
electron beam
surface layer
base material
workpiece
Process PrincipleElectron Beam Surface Welding
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Figure 11.28
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Production of a Pipe Bendby Shape Welding
testing
1. welding of the half-torus2. stress relief annealing3. mechanical treatment4. seperating/ halving5. folding6. welding togehter7. stress relief annealing8. testing
Figure 11.27