13.
Special Processes
13. Special Processes 183
2005
Apart from the welding processes explained earlier there is also a multitude of special weld-
ing processes. One of them is stud welding. Figure 13.1 depicts different stud shapes. De-
pending on the application, the studs are equipped with either internal or external screw
threads; also studs with pointed tips or with corrugated shanks are used.
In arc stud welding, a dis-
tinction is basically made
between three process
variations. Figure 13.2.
depicts the three variations
– the differences lie in the
kind of arc ignition and in
the cycle of motions during
the welding process.
The switching arrange-
ment of an arc stud weld-
ing unit is shown in Fig-
ure 13.3. Besides a power
source which produces
high currents for a short-
time, a control as well as a
lifting device are necessary.
Figure 13.1
rammed flange
br-er13-01e.cdr
Figure 13.2
drawn-arcstud welding
capacitor-discharge studwelding withtip ignition
drawn-arc studwelding withferrule ignition
ceramic ferrulecold-upsettip ignition
ignitionring
br-er13-02e.cdr
13. Special Processes 184
2005
In drawn-arc stud welding the stud is first mounted onto the plate, Figure 13.4. The arc is
ignited by lifting the stud and melts the entire stud diameter in a short time. When stud and
base plate are fused, the stud is dipped into the molten weld pool while the ceramic ferrule is
forming the weld. After the solidification of the liquid weld pool the ceramic ferrule is knocked
off.
Figure 13.5 illustrates tip
ignition stud welding.
The tip melts away imme-
diately after touching the
plate and allows the arc to
be ignited. The lifting of the
stud is dispensed with.
When the stud base is mol-
ten, the stud is positioned
onto the partly molten
workpiece.
Studs with diameters of up
to 22 mm can be used.
Welding currents of more
than 1000 A are necessary.
The arc stud welding proc-
ess allows to join different
materials, see Figure 13.6.
Problematic are the differ-
ent melting points and the
heat dissipation of the indi-
vidual materials. Aluminium
studs, for example, may
not be welded onto steel.
Figure 13.3
A
V
liftingdevice
stud holdingdevice
stud
ceramicferrule
workpiece
welding timeadjustment
control device
power source
br-er13-03e.cdr
Figure 13.4
stu
d m
ove
me
nt
cu
rren
t
start lifting dipping end
L
L
(L + P)>projection
P
0 1 2 3 4
time
time
PP
L
br-er13-04e.cdr
13. Special Processes 185
2005
The relatively high welding currents in the arc
stud welding process cause the somewhat
troublesome side-effects of the arc blow. Fig-
ure 13.7 depicts different arrangements of cur-
rent contact points and cable runs and illus-
trates the developing arc deflection (B,C,E). A,
D and F show possible countermeasures.
In high-frequency welding of pipes the en-
ergy input into the workpiece may be carried
out via sliding contacts, as shown in Fig-
ure 13.8, or via rollers, as shown in Fig-
ure 13.9. Only the high-frequency technique
allows a safe current transfer in spite of the
scale or oxide layers. Through the skin effect
the current flows only conditionally at the sur-
face. Therefore no thorough fusion of thick-
wall pipes may be achieved.
Figure 13.6
unalloyed sructuralsteel S235J0 and/orcomparable steels
otherunalloyed
steels
stainlesssteels acc.
DIN EN 17440
heat resistingsteels acc.SEW 470
aluminium andaluminium
alloys
unalloyed structural steel S235J0,S355J0 and/or comparable steels
(acc. DIN EN 10 025)
other unalloyed steels
stainless steelsacc. DIN EN 17440
heat resisting steelsacc. SEW 470
aluminium andaluminium alloys
explanation of the weldability classification numbers:
1 = well suitable (transmission of energy)2 = suitable (transmission of energy possible with restriction)
3 =
0 = not possible
suitable only up to a point (not for transmission of energy
1 2 3 2 0
2 2 3 2 0
3 3 1 3 0
2 2 2 2 0
0 0 0 0 2
base meatl
stud material
br-er13-06e.cdr
Figure 13.5
a b
c d© ISF 2002br-er13-05e.cdr
Phases of Capacitor-DischargeStud Welding With Tip Ignition
13. Special Processes 186
2005
Only welding of small wall
thicknesses is profitable –
as the weld speed must be
greatly reduced with in-
creasing wall thicknesses,
Figure 13.10.
Figure 13.8
moving directionof the pipe
pressurerollers
sliding contacts(fixed)
interstagetransformer
HF-valvegenerator
∼
© ISF 2002br-er13-08e.cdr
High-Frequency Weldingof Pipes
Figure 13.7
A B
C Dbr-er13-07e.cdr
~
rotary transformer
Isolation
copper electrode wheel(water-cooled)
slot pipe
pressure rollers
counterpressure rollers
© ISF 2002br-er13-09e.cdr
Rotary TransformerResistance Welding
Figure 13.9
13. Special Processes 187
2005
In induction welding – a process which is
used frequently nowadays – the energy input
is received contactless, Figure 13.11. Varying
magnetic fields produce eddy currents inside
the workpiece, which again cause resistance
heating in the slotted tube. A distinction is
made between coil inductors (left) and line
inductors (right).
Also in case of induction welding flows the
current flows only close to the surface areas
of the pipe. Only the current part which
reaches the joining zone and causes to fill the
gap may be utilised. Figure 13.12 illustrates
two current paths. On the left side: the useful
current path, on the right side: the useless
current path which does not contribute to the
fusion of the edges.
Figure 13.13 shows the
effective depth during the
inductive heating for differ-
ent materials, in depend-
ence on the frequency. As
soon as the Curie tempera-
ture point is reached, the
effective depth for ferritic
steels increases.
Figure 13.10
weld
ing s
pee
d
wall thickness
0
20
40
80
0 2 4 6 8 10 12 16mm
m/min
1
2
3
4 56
1:2:3:4:5:6:
36 kA;57 kA;75 kA;
125 kA;150 kA;200 kA;
100 kVA;200 kVA;300 kVA;500 kVA;
1200 kVA;1850 kVA;
60 Hz60 Hz60 Hz60 Hz
120 Hz120 Hz
© ISF 2002Br-er13-10e.cdr
Welding Speeds inHF-Resistance Welding
Figure 13.11
moving directionof the pipe
moving directionof the pipe
pressurerollers
pressurerollers
line inductorcoil inductor
br-er13-11e.cdr
13. Special Processes 188
2005
The application of the in-
duction welding method
allows high welding speeds
of more than 100m/min,
Figure 13.14.
Figure 13.13
0,04
0,02
0,060,080,10
0,2
0,4
0,60,81,0
2
4
68
10mm20
1 4 10 100 200 kHz 1000frequency f
effe
ctive
dep
th δ
3
1
2
45
6
7
1
23456
7
steel (ferriticsteel (austenitic)brassaluminium copperbrasscopperaluminiumsteel (ferritic)
800°C20....1400°C800°C600°C850°C20°C20°C20°C20°C
© ISF 2002br-er13-13e.cdr
Standard Values of the EffectiveDepths During Inductive Heating
Figure 13.14
we
ld s
pee
d
wall thickness
0
20
40
80
0 2 4 6 8 10 12 16 mm
m/min
60
100
120
160
14 20
0 50 100 200mm
100
%
0
pipe diameter
corr
ective
facto
r
high frequency200 - 450 kW
600 kW
200 kW
300 kW
450 kW
60 kW 100 kW 150 kW
© ISF 2002br-er13-14e.cdr
Welding Speeds in Induction Welding
Figure 13.12
l
b b
d
s
δ2
δ1
δ1
width of the heating inductorwall thickness of the pipecurrent penetration depthon pipe backside
bsδ1
δ2
d
current penetration depthat the strip edgesoutside diameter of the pipedistance inductor- welding pointl
br-er13-12e.cdr
13. Special Processes 189
2005
Aluminothermic fusion
welding or cast welding is
mainly used for joining
railway tracks on site. A
crucible is filled with a mix-
ture consisting of alumin-
ium powder and iron ox-
ide. An exothermal reac-
tion is initiated by an igniter
– the aluminium oxidises
and the iron oxide is re-
duced to iron, Fig-
ure 13.15. The molten iron
flows into a ceramic mould
which matches the contour of the track. After the melt has cooled, the mould is knocked off.
Figure 13.16 shows the process assembly.
Explosion welding or ex-
plosion cladding is fre-
quently used for joining
dissimilar materials, as,
for example, unalloyed
steel/alloyed steel, cop-
per/aluminium or
steel/aluminium. The mate-
rials which are to be joined
are pressed together by a
shock wave. Wavy transi-
tions develop in the joining
area, Figures 13.17 and
13.18.
Figure 13.16
weld cross-section
slag mould
workpiece
mould
riser
blow-holeorifice
riser
runnergate
workpiece
cast-aroundbulge
thermit slag
thermit steel
channel betweenriser and runnergate
runner gate
blow-holeorifice
iron or sand plug
foundry sand
thermit crucible
slag mould
riser
thermit bulge
thickness of thecast b
riser
workpiece
runner gate
preheating
air
gas fuel
A
B
b
bc
cut A-B
br-er13-16e.cdr
Figure 13.15
3FeO + 2Al Al O + 3Fe - 783 kJ2 3
Fe O + 2Al Al O + 2Fe - 758 kJ2 3 2 3
3Fe O + 8Al 4Al O + 9Fe - 3012 kJ3 4 2 3
br-er13-15e.cdr
13. Special Processes 190
2005
The determined cladding
speed must be strictly
adhered to during the
welding process. If the
welding speed is too low,
lack of fusion is the result.
If the welding speed is
exceeded, the develop-
ment of the waves in the
joining zone is erratic.
Figure 13.19 shows the
critical cladding speeds
for different material com-
binations.
Figure 13.20 shows a diagrammatic representation of a diffusion welding unit. Diffusion
welding, like ultrasonic welding, is welding in the solid state. The surfaces which are to be
joined are cleaned, polished and then joined in a vacuum with pressure and temperature.
After a certain time (minutes, right up to several days) joining is achieved by diffusion proc-
esses.
The advantage of this costly welding method lies in the possibility of joining dissimilar materi-
als without taking the risk
of structural transformation
due to the heat input. Fig-
ure 13.21 shows several
possible material combina-
tions. The joining of two
extremely different materi-
als, as, e.g. austenite and a
zirconium alloy, may be
obtained by several inter-
mediate layers.
Figure 13.18
Br-er13-18e.cdr
Figure 13.17
a) b)
Amboßanvil
explosive charge explosive chargebuffer buffer
flyer plate flyer plate
parent plate parent plate
igniter
anvil
igniter
d
vd
A
A'
KvK
B
B'
vP
tvF β
vd
AA'
KvK
B
B'
vP
t
v Fα β
K vK
B
B'
vP
v F
β
αβ90 - + /2
α /290 -
K v = vK D
B
B'
vPvF
β
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13. Special Processes 191
2005
Figure 13.22 shows the structure of a joint
where nickel, copper and vanadium had been
used as intermediate layers. As the diffusion
of the individual components takes place only
in the region close to the surface, very thin
layers may be realised.
Figure 13.19
materialsflyer plate/parent plate
critical speed [m s ]-1
vk1 vk2 vk3
aluminium/aluminium
copper/copper
steel/steel
copper/aluminium
aluminium/steel
cooper/steel
aluminium/zinc
copper/zinc
600
1200
2100
1000
1200
1400
500
800 1400
1000
2400
1600
1400
2700
1600
1000
3300
3000
>4000
>3600
>3900
© ISF 2002br-er13-19e.cdr
Critical Cladding Speedsin Explosive Cladding
Figure 13.20
HF-generator
working pressure1,33 mPa
workpieces
loading device
recorderp,T = f(t)
hydraulic aggregate unit
pumpingstation
measuring amplifier
P
© ISF 2002br-er13-20e.cdr
Schematic Representationof a Diffusion Welding Unit
Figure 13.21
niobium
zirconium
tungsten
molybdenum
titanium
nickel
copper
aluminium
stainless steel
tool steel
structural steel
cast iron
ca
st ir
on
str
uctu
ral ste
el
too
l ste
el
sta
inle
ss s
tee
l
alu
min
ium
co
pp
er
nic
kel
tita
niu
m
mo
lyb
den
um
tun
gste
n
zir
con
ium
nio
biu
m
tan
talu
m
tantalum
material
very good weld quality
good weld quality
bad weld quality
not tested/results not reported
© ISF 2002br-er13-21e.cdr
Possible Material Combinationsfor Diffusion Welding
13. Special Processes 192
2005
In cold pressure welding -
in contrast to diffusion weld-
ing - a deformation is pro-
duced by the high contact
pressure in the bonding
plane, Figure 13.23. The
joint surfaces are moved
very close towards each
other, i.e., to the atomic
distance. Through transpo-
sition processes as well as
through adhesion forces
can joining of similar and
dissimilar materials be real-
ised.
Ultrasonic welding is used as a microwelding method. The process principle is shown in
Figure 13.24. The surface layers of overlap arranged plates are destroyed by applying me-
chanical vibrator energy. At this instance are joining surfaces deformed by very short local-
ised warming up and point-interspersed connected. The joining members are welded under
pressure, where one part small amplitudes (up to 50 µm) relative to the other is moved with
with ultrasonic frequency.
As far as metals are con-
cerned, the vibratory vector
is in the joining zone, in
contrast to ultrasonic weld-
ing of plastics. The ultra-
sonics which have been
produced by a magne-
tostrictive transducer and
transmitted by a sonotrode
lie in the frequency range
of 20 up to 60 Hz.
Figure 13.23
dies
guideand buffer
specimen A
specimen B
d2
d1
br-er13-23e.cdr
Figure 13.22
X10CrNiTi18 9 Ni Cu V Zr2Sn
br-er13-22e.cdr
13. Special Processes 193
2005
Figure 13.25 shows possible material combinations for ultrasonic welding.
Further microwelding proc-
esses are methods which
are also called heated ele-
ment welding methods, as,
for example, nailhead
bonding and wedge bond-
ing. These methods are
applied in the electronics
industry for joining very fine
wires, as, for example, gold
wires from microchips with
aluminium strip conductors.
In wedge bonding a wire
is positioned onto the contact point via a feeding nozzle. The welding wedge is lowered and
the wire is welded with the aluminium thin foil,
Figure 13.26. The wire is cut with a cutting
tool.
In nailhead bonding, the wire which emerges
from the feeding nozzle may have diameters
from 12 to 100 µm. By a reducing hydrogen
flame its end is molten to a globule, Fig-
ure 13.27. The nozzle then presses this glob-
ule onto the part aimed at and shapes it into a
nail head.
Figure 13.28 depicts this type of weld.
A further method related to welding is solder-
ing. The process principle of soldering is
briefly explained in Figure 13.29.
Figure 13.25
copper, Cu-Zn-alloy
beryllium+alloy
germanium
gold
ironmagnesium+alloy
molybdenum+alloy
nickel+alloy
palladium+alloy
platin+alloy
siliconsilver+alloy
tantalium+alloy
tintitanium+alloy
tungsten+alloy
zirconium+alloy
aluminium+alloy
copper, C
u-Z
n-a
lloy
bery
lliu
m+
allo
y
germ
aniu
m
gold
iron
magnesiu
m+
allo
y
moly
bden
um
+allo
y
nic
kel+
allo
y
palla
diu
m+
allo
y
pla
tin+
allo
y
sili
con
silv
er+
allo
y
tanta
lium
+allo
y
tin
tita
niu
m+
allo
y
tungste
n+
allo
y
zirconiu
m+
allo
y
alu
min
ium
+allo
y
© ISF 2002br-er13-25e.cdr
Possible Material Combinations for Ultrasonic Welding
Figure 13.24
HF-generator
process observationoptics
sonotrode
pressure force
workpiece
anvil
ultrasonic vibrator
sonotrode tip
br-er13-24e.cdr
13. Special Processes 194
2005
Figure 13.28
br-er13-28e.cdr
Figure 13.27
heated wedge
(tungsten-carbide)
wedge bonding Al-strip conductor nailhead
gold wire5-50 mm
H -flame2
br-er13-27e.cdr
Figure 13.26
heated wedge
(tungsten-carbide)
wedge bonding Al-strip conductor cutting toolgold wire
5-50 mµ
br-er13-26e.cdr
13. Special Processes 195
2005
The individual soldering methods are classified into different mechanisms depending on the
type of heating, Figure 13.30. There are two basic distinctions: soft soldering (melting tem-
perature of the solder is approx. up to 450°C) and brazing (melting temperature of the braz-
ing solder is approx. up to 1100°C. For high-temperature soldering solders with high melt-
ing points (melting temperature is approx. up to 1200°C) are used. This process is frequently
subject to automation.
Figure 13.29
© ISF 2002br-er13-29e.cdr
Soldering - Definitionand Process Principle
In soldering, atomar forces of attraction are effective.
Similar and dissimilar metals are joined by addition of
a solder with a low melting point. In the boundary area
transposition processes occur between solder and
base metal. This is called a “two-dimensional”diffusion.
In the subsequent diffusion glowing phase
(high-temperature soldering) the solder may be
completely absorbed by the base metal.
A distinction is made between soft soldering (melting
temperature of the solder is below 450°C) and brazing
(melting temperature of the solder is 450°C up to 1100°C)
as well as high-temperature soldering (melting
temperature of the solder is up to 1200°C). Heating of
the component for melting the solder may be effected in
various ways.
Figure 13.30
© ISF 2002br-er13-30e.cdr
Classification of Soldering Methods
classification accordingto the type of heating:
- flame brazing
- iron soldering
- block brazing
- furnace soldering
- salt bath brazing
- dip soldering
- wave soldering
- resistance soldering
- induction brazing