13. Special Processes

13.
Special Processes
13. Special Processes
183
Apart from the welding processes explained earlier there is also a multitude of special welding processes. One of them is stud welding. Figure 13.1 depicts different stud shapes. Depending 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 distinction is basically made
between
three
variations.
process
Figure 13.2.
depicts the three variations
– the differences lie in the
kind of arc ignition and in
the cycle of motions during
rammed flange
the welding process.
br-er13-01e.cdr
The switching arrangement of an arc stud weldFigure 13.1
ing unit is shown in Figure 13.3. Besides a power
drawn-arc
stud welding
capacitordischarge stud
welding with
tip ignition
drawn-arc stud
welding with
ferrule ignition
source
which
produces
high currents for a shorttime, a control as well as a
lifting device are necessary.
ceramic ferrule
cold-upset
tip ignition
ignition
ring
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Figure 13.2
2005
13. Special Processes
184
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.
lifting
device
The tip melts away imme-
control device
diately after touching the
plate and allows the arc to
stud holding
device
welding time
adjustment
be ignited. The lifting of the
stud
stud is dispensed with.
When the stud base is molpower source
ten, the stud is positioned
onto
the
partly
ceramic
ferrule
V
workpiece
A
molten
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workpiece.
Studs with diameters of up
Figure 13.3
to 22 mm can be used.
Welding currents of more
start
3
lifting
L
dipping
> (L + P)
4
L
projection
P
2
L
end
current
materials, see Figure 13.6.
Problematic are the differ-
1
time
P
ess allows to join different
0
P
The arc stud welding proc-
stud movement
than 1000 A are necessary.
ent melting points and the
heat dissipation of the individual materials. Aluminium
time
br-er13-04e.cdr
studs, for example, may
not be welded onto steel.
Figure 13.4
2005
13. Special Processes
185
The relatively high welding currents in the arc
stud welding process cause the somewhat
troublesome side-effects of the arc blow. Figure 13.7 depicts different arrangements of current contact points and cable runs and illustrates the developing arc deflection (B,C,E). A,
D and F show possible countermeasures.
a
b
c
d
In high-frequency welding of pipes the energy input into the workpiece may be carried
out via sliding contacts, as shown in Figure 13.8, or via rollers, as shown in Figure 13.9. Only the high-frequency technique
allows a safe current transfer in spite of the
scale or oxide layers. Through the skin effect
br-er13-05e.cdr
© ISF 2002
Phases of Capacitor-Discharge
Stud Welding With Tip Ignition
the current flows only conditionally at the surface. Therefore no thorough fusion of thickFigure 13.5
wall pipes may be achieved.
unalloyed sructural
steel S235J0 and/or
comparable steels
other
unalloyed
steels
stainless
steels acc.
DIN EN 17440
heat resisting
steels acc.
SEW 470
aluminium and
aluminium
alloys
unalloyed structural steel S235J0,
S355J0 and/or comparable steels
(acc. DIN EN 10 025)
1
2
3
2
0
other unalloyed steels
2
2
3
2
0
stainless steels
acc. DIN EN 17440
3
3
1
3
0
heat resisting steels
acc. SEW 470
2
2
2
2
0
aluminium and
aluminium alloys
0
0
0
0
2
stud material
base meatl
explanation of the weldability classification numbers:
1 = well suitable (transmission of energy)
2 = suitable (transmission of energy possible
with restriction)
3 = suitable only up to a point
(not for transmission of energy
0 = not possible
br-er13-06e.cdr
Figure 13.6
2005
13. Special Processes
186
Only welding of small wall
thicknesses is profitable –
as the weld speed must be
greatly reduced with in-
A
creasing wall thicknesses,
B
Figure 13.10.
C
D
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Figure 13.7
rotary transformer
moving direction
of the pipe
~
pressure
rollers
Isolation
copper electrode wheel
(water-cooled)
sliding contacts
(fixed)
slot pipe
∼
interstage
transformer
pressure rollers
HF-valve
generator
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counterpressure rollers
© ISF 2002
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Rotary Transformer
Resistance Welding
High-Frequency Welding
of Pipes
Figure 13.8
© ISF 2002
Figure 13.9
2005
13. Special Processes
187
In induction welding – a process which is
80
4
5
used frequently nowadays – the energy input
6
is received contactless, Figure 13.11. Varying
3
m/min
magnetic fields produce eddy currents inside
welding speed
2
the workpiece, which again cause resistance
heating in the slotted tube. A distinction is
40
made between coil inductors (left) and line
1
inductors (right).
20
Also in case of induction welding flows the
0
0
2
4
6
8
10
wall thickness
12
mm
16
current flows only close to the surface areas
of the pipe. Only the current part which
1: 36 kA; 100 kVA;
60 Hz
2: 57 kA; 200 kVA;
60 Hz
3: 75 kA; 300 kVA;
60 Hz
4: 125 kA; 500 kVA;
60 Hz
5: 150 kA; 1200 kVA; 120 Hz
6: 200 kA; 1850 kVA; 120 Hz
reaches the joining zone and causes to fill the
gap may be utilised. Figure 13.12 illustrates
Br-er13-10e.cdr
© ISF 2002
Welding Speeds in
HF-Resistance Welding
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
Figure 13.10
Figure 13.13
fusion of the edges.
shows
the
moving direction
of the pipe
effective depth during the
moving direction
of the pipe
inductive heating for different materials, in dependence on the frequency. As
pressure
rollers
soon as the Curie tempera-
pressure
rollers
ture point is reached, the
effective depth for ferritic
coil inductor
steels increases.
line inductor
br-er13-11e.cdr
Figure 13.11
2005
13. Special Processes
188
The application of the induction
l
δ2
welding
method
of more than 100m/min,
b
b
allows high welding speeds
δ1
Figure 13.14.
δ1
s
d
δ2
b width of the heating inductor
s wall thickness of the pipe
δ1 current penetration depth
on pipe backside
d
l
current penetration depth
at the strip edges
outside diameter of the pipe
distance inductor- welding point
br-er13-12e.cdr
Figure 13.12
160
100
corrective factor
effective depth δ
20
mm
10
8
6
4
1
m/min
2
3
2
1,0
0,8
0,6
0,4
4
5
120
%
0
6
0
7
50 100 mm 200
pipe diameter
100
high frequency
200 - 450 kW
0,2
weld speed
0,10
0,08
0,06
0,04
0,02
1
4
1
2
3
4
5
6
br-er13-13e.cdr
7
10
frequency f
steel (ferritic
steel (austenitic)
brass
aluminium
copper
brass
copper
aluminium
steel (ferritic)
100
200
kHz 1000
800°C
20....1400°C
800°C
600°C
850°C
20°C
20°C
20°C
20°C
80
60
600 kW
40
450 kW
300 kW
20
200 kW
60 kW 100 kW 150 kW
0
0
© ISF 2002
2
4
8
10 12 14
wall thickness
br-er13-14e.cdr
Standard Values of the Effective
Depths During Inductive Heating
Figure 13.13
6
16
mm 20
© ISF 2002
Welding Speeds in
Induction Welding
Figure 13.14
2005
13. Special Processes
189
Aluminothermic
fusion
welding or cast welding is
mainly used for joining
3FeO
+ 2Al
Al2O3 + 3Fe - 783 kJ
railway tracks on site. A
crucible is filled with a mix-
Fe2O3
+ 2Al
ture consisting of alumin-
Al2O3 + 2Fe - 758 kJ
ium powder and iron ox-
3Fe3O4 + 8Al
ide. An exothermal reac-
4Al2O3 + 9Fe - 3012 kJ
tion is initiated by an igniter
– the aluminium oxidises
br-er13-15e.cdr
and the iron oxide is reduced
to
iron,
Fig-
ure 13.15. The molten iron
Figure 13.15
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 explosion
cladding
is
fre-
quently used for joining
mould
runner gate
riser
slag mould
preheating
gas fuel
workpiece
air
riser
c
b
dissimilar materials, as,
for
example,
steel/alloyed
cut A-B
unalloyed
steel,
cop-
thermit steel
steel/aluminium. The materials which are to be joined
are pressed together by a
A
riser
thermit bulge
weld cross-section
b
or
blow-hole
orifice
thermit slag
thermit crucible
slag mould
per/aluminium
workpiece
thickness of the
cast b
channel between
riser and runner
gate
runner gate
blow-hole
orifice
iron or sand plug
B
foundry sand
riser
runner
gate
workpiece
cast-around
bulge
br-er13-16e.cdr
shock wave. Wavy transitions develop in the joining
area,
Figures 13.17
and
Figure 13.16
13.18.
2005
13. Special Processes
190
The determined cladding
adhered
to
during
a)
explosive charge
buffer
flyer plate
igniter
the
parent plate
anvil
vd
t
welding speed is too low,
vd
vP B
α
A'
A
vF
K
If the welding speed is
A'
β
B'
K
vK
t
β B vP
B'
vF
A
vK
B
90 - β + α /2
exceeded, the develop-
v
ment of the waves in the
joining zone is erratic.
explosive charge
buffer
flyer plate
igniter
parent plate
anvil
Amboß
welding process. If the
lack of fusion is the result.
b)
d
speed must be strictly
F
vP
β
K
vK
vF
90 - α /2
B'
K
β
vK = vD
B
vP
B'
br-er13-17e.cdr
Figure 13.19 shows the
critical cladding speeds
for different material com-
Figure 13.17
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 processes.
The advantage of this costly welding method lies in the possibility of joining dissimilar materials without taking the risk
of structural transformation
due to the heat input. Figure 13.21 shows several
possible material combinations. The joining of two
extremely different materials, as, e.g. austenite and a
zirconium alloy, may be
obtained by several interBr-er13-18e.cdr
mediate layers.
Figure 13.18
2005
13. Special Processes
191
measuring amplifier
-1
critical speed [m s ]
materials
flyer plate/
parent plate
working pressure
1,33 mPa
vk1
vk2
vk3
600
1000
>4000
copper/
copper
1200
1600
>3600
steel/
steel
2100
2700
>3900
copper/
aluminium
1000
1400
aluminium/
steel
1200
1600
cooper/
steel
1400
2400
aluminium/
zinc
500
1000
3000
copper/
zinc
800
1400
3300
hydraulic
aggregate unit
P
aluminium/
aluminium
workpieces
HFgenerator
pumping
station
recorder
p,T = f(t)
br-er13-19e.cdr
loading device
© ISF 2002
br-er13-20e.cdr
Schematic Representation
of a Diffusion Welding Unit
Critical Cladding Speeds
in Explosive Cladding
tantalum
niobium
zirconium
Figure 13.22 shows the structure of a joint
tungsten
molybdenum
titanium
nickel
copper
aluminium
stainless steel
tool steel
Figure 13.20
structural steel
cast iron
Figure 13.19
material
© ISF 2002
tantalum
where nickel, copper and vanadium had been
used as intermediate layers. As the diffusion
of the individual components takes place only
niobium
zirconium
in the region close to the surface, very thin
tungsten
molybdenum
layers may be realised.
titanium
nickel
copper
aluminium
stainless steel
tool steel
very good weld quality
structural steel
cast iron
good weld quality
bad weld quality
not tested/
results not reported
br-er13-21e.cdr
© ISF 2002
Possible Material Combinations
for Diffusion Welding
Figure 13.21
2005
13. Special Processes
192
In cold pressure welding in contrast to diffusion welding - a deformation is produced by the high contact
pressure in the bonding
X10CrNiTi18 9
Ni
Cu
V
Zr2Sn
plane, Figure 13.23. The
joint surfaces are moved
very close towards each
other, i.e., to the atomic
distance. Through transpobr-er13-22e.cdr
sition processes as well as
through
adhesion
forces
can joining of similar and
Figure 13.22
dissimilar materials be realised.
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 mechanical vibrator energy. At this instance are joining surfaces deformed by very short localised 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.
dies
d1
As far as metals are concerned, the vibratory vector
is in the joining zone, in
specimen A
contrast to ultrasonic weld-
guide
and buffer
ing of plastics. The ultra-
specimen B
d2
sonics which have been
produced
by
a
magne-
tostrictive transducer and
br-er13-23e.cdr
transmitted by a sonotrode
lie in the frequency range
of 20 up to 60 Hz.
Figure 13.23
2005
13. Special Processes
193
Figure 13.25 shows possible material combinations for ultrasonic welding.
Further microwelding processes are methods which
HFgenerator
are also called heated ele-
process observation
optics
ment welding methods, as,
pressure force
for
sonotrode
example,
nailhead
bonding and wedge bond-
sonotrode tip
ing. These methods are
workpiece
applied in the electronics
anvil
industry for joining very fine
ultrasonic vibrator
wires, as, for example, gold
br-er13-24e.cdr
wires from microchips with
aluminium strip conductors.
Figure 13.24
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
aluminium+alloy
beryllium+alloy
copper, Cu-Zn-alloy
germanium
gold
iron
magnesium+alloy
molybdenum+alloy
nickel+alloy
palladium+alloy
platin+alloy
silicon
silver+alloy
tantalium+alloy
tin
titanium+alloy
tungsten+alloy
zirconium+alloy
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, Figure 13.27. The nozzle then presses this globule onto the part aimed at and shapes it into a
nail head.
Figure 13.28 depicts this type of weld.
aluminium+alloy
beryllium+alloy
copper, Cu-Zn-alloy
germanium
gold
iron
magnesium+alloy
molybdenum+alloy
nickel+alloy
palladium+alloy
platin+alloy
silicon
silver+alloy
tantalium+alloy
tin
titanium+alloy
tungsten+alloy
zirconium+alloy
A further method related to welding is soldering. The process principle of soldering is
briefly explained in Figure 13.29.
br-er13-25e.cdr
© ISF 2002
Possible Material Combinations
for Ultrasonic Welding
Figure 13.25
2005
13. Special Processes
194
heated wedge
(tungsten-carbide)
5-50 µm
gold wire
wedge bonding
Al-strip conductor
cutting tool
br-er13-26e.cdr
Figure 13.26
heated wedge
(tungsten-carbide)
H2-flame
5-50 mm
gold wire
wedge bonding
Al-strip conductor
nailhead
br-er13-27e.cdr
Figure 13.27
br-er13-28e.cdr
Figure 13.28
2005
13. Special Processes
195
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 temperature of the solder is approx. up to 450°C) and brazing (melting temperature of the brazing solder is approx. up to 1100°C. For high-temperature soldering solders with high melting points (melting temperature is approx. up to 1200°C) are used. This process is frequently
subject to automation.
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
classification according
to the type of heating:
transposition processes occur between solder and
base metal. This is called a “two-dimensional”diffusion.
In the subsequent diffusion glowing phase
- flame brazing
(high-temperature soldering) the solder may be
- iron soldering
completely absorbed by the base metal.
- block brazing
A distinction is made between soft soldering (melting
- furnace soldering
temperature of the solder is below 450°C) and brazing
- salt bath brazing
(melting temperature of the solder is 450°C up to 1100°C)
as well as high-temperature soldering (melting
- dip soldering
temperature of the solder is up to 1200°C). Heating of
- wave soldering
the component for melting the solder may be effected in
- resistance soldering
various ways.
- induction brazing
br-er13-29e.cdr
© ISF 2002
br-er13-30e.cdr
Classification of
Soldering Methods
Soldering - Definition
and Process Principle
Figure 13.29
© ISF 2002
Figure 13.30
2005