13. Special Processes - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...13....

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


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


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


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


Rotary TransformerResistance Welding

Figure 13.9


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



pressurerollers

pressurerollers

line inductorcoil inductor

br-er13-11e.cdr


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


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


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


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


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

br-er13-17e.cdr


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


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


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


Possible Material Combinationsfor Diffusion Welding


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


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


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


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


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


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


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

13. Special Processes - kau.ac.krmercury.kau.ac.kr/welding/Welding Technology I - Welding...13....

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