The document provides information about arc welding, including: 1) Arc welding is a fusion welding process that uses an electric arc to produce heat and fuse metal pieces. An electric arc is produced between an electrode and base metal when they are separated by 2-4 mm after touching. 2) Both direct current and alternating current can be used for arc welding. Electrodes may be consumable or non-consumable. 3) Key equipment for arc welding includes a welding machine, electrode holders, cables, connectors, and protective gear for the welder.

1. COURSE: MANUFACTURING PROCESSS
CODE: AMEB05
III Semester
Regulation: IARE R18
Institute of Aeronautical Engineering
(Autonomous)
Dundigal, Hyderabad- 500043
G.Praveen Kumar
Assistant Professor
Mechanical Engineering
Prepared by

2. ARC WELDING
The arc welding is a fusion welding process in which the heat required to fuse the
metal is obtained from an electric arc between the base metal and an electrode.
The electric arc is produced when two conductors are touches together and then
separated by a small gap of 2 to 4 mm, such that the current continues to flow,
through the air. The temperature produced by the electric arc is about 4000°C to
6000°C.
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3. ARC WELDING
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A metal electrode is used which supplies the filler metal. The electrode may be flux
coated or bare. In case of bare electrode, extra flux material is supplied. Both direct
current (D.C.) and alternating current (A.C.) are used for arc welding.
The alternating current for arc is obtained from a step down transformer. The
transformer receives current from the main supply at 220 to 440 volts and step down
to required voltage i.e., 80 to 100 volts. The direct current for arc is usually obtained
from a generator driven by either an electric motor, or patrol or diesel engine.
An open circuit voltage (for striking of arc) in case of D.C. welding is 60 to 80 volts
while a closed circuit voltage (for maintaining the arc) is 15 to 25 volts

4. PROCEDURE OF ELECTRIC ARC WELDING
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First of all, metal pieces to be weld are thoroughly cleaned to remove the dust, dirt,
grease, oil, etc. Then the work piece should be firmly held in suitable fixtures. Insert
a suitable electrode in the electrode holder at an angle of 60 to 80° with the work
piece.
Select the proper current and polarity. The spot are marked by the arc at the places
where welding is to be done. The welding is done by making contact of the electrode
with the work and then separating the electrode to a proper distance to produce an
arc.

5. PROCEDURE OF ELECTRIC ARC WELDING
ARC WELDING
When the arc is obtained, intense heat so produced, melts the work below the arc,
and forming a molten metal pool. A small depression is formed in the work and the
molten metal is deposited around the edge of this depression. It is called arc crator.
The slag is brushed off easily after the joint has cooled. After welding is over, the
electrode holder should be taken out quickly to break the arc and the supply of
current is switched off.
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6. ELECTRIC CURRENT FOR WELDING
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Both D.C. (direct current) and A.C. (alternating current) are used to produce an arc in
electric arc welding. Both have their own advantages and applications.
The D.C. welding machine obtains their power from an A.C. motor or diesel/petrol
generator or from a solid state rectifier.
The capacities of D.C. machine are:
Current:
Up to 600 amperes.
Open Circuit Voltage:
50 to 90 volts, (to produce arc).
Closed Circuit Voltage:
18 to 25 volts, (to maintain arc
The A.C. welding machine has a step down transformer which receives current from
main A.C. supply. This transformer step down the voltage from 220 V-440V to normal
open circuit voltage of 80 to 100 volts. The current range available up to 400
amperes in the steps of 50 ampere.
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7. The capacities of A.C. welding machine are:
Current Range:
Up to 400 ampere in steps of 50 ampere.
Input Voltage:
220V- 440V
Actual Required Voltage:
80 – 100 volts. Frequency: 50/60 HZ.
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ELECTRIC CURRENT FOR WELDING
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8. SIGNIFICANCE OF POLARITY
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When D.C. current is used for welding, the following two types of polarity are
available:
(i)Straight or positive polarity.
(ii)Reverse or negative polarity.
When the work is made positive and electrode as negative then polarity is called
straight or positive polarity.
In straight polarity, about 67% of heat is distributed at the work (positive terminal)
and 33% on the electrode (negative terminal). The straight polarity is used where
more heat is required at the work. The ferrous metal such as mild steel, with faster
speed and sound weld, uses this polarity.
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9. SIGNIFICANCE OF POLARITY
On the other hand, when the work is made negative and electrode as positive then
polarity is known as reverse or negative polarity, as shown in Fig. 7.16 (b).
In reverse polarity, about 67% of heat is liberated at the electrode (positive terminal)
and 33% on the work (negative terminal).
The reverse polarity is used where less heat is required at the work as in case of thin
sheet metal weld. The non-ferrous metals such as aluminum, brass, and bronze
nickel are welded with reverse polarity.
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10. Equipments Required for Electric Arc Welding
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The various equipments required for electric arc welding are:
1. Welding Machine:
The welding machine used can be A.C. or D.C. welding machine. The A.C. welding
machine has a step-down transformer to reduce the input voltage of 220- 440V to
80-100V. The D.C. welding machine consists of an A.C. motor-generator set or
diesel/petrol engine-generator set or a transformer-rectifier welding set.
A.C. machine usually works with 50 hertz or 60 hertz power supply. The efficiency of
A.C. welding transformer varies from 80% to 85%. The energy consumed per Kg. of
deposited metal is 3 to 4 kWh for A.C. welding while 6 to 10 kWh for D.C. welding.
A.C. welding machine usually work with low power factor of 0.3 to 0.4, while motor
in D.C. welding has a power factor of 0.6 to 0.7. The following table 7.9 shows the
voltage and current used for welding machine.
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11. 62
Equipments Required for Electric Arc Welding
2. Electrode Holders:
The function of electrode holder is to hold the electrode at desired angle. These are
available in different sizes, according to the ampere rating from 50 to 500 amperes.
3. Cables or Leads:
The function of cables or leads is to carry the current from machine to the work.
These are flexible and made of copper or aluminum. The cables are made of 900 to
2000 very fine wires twisted together so as to provide flexibility and greater
strength.
The wires are insulated by a rubber covering, a reinforced fibre covering and further
with a heavy rubber coating.
4. Cable Connectors and Lugs:
The functions of cable connectors are to make a connection between machine
switches and welding electrode holder. Mechanical type connectors are used; as
they can he assembled and removed very easily. Connectors are designed
according to the current capacity of the cables used.
5. Chipping Hammer:
The function of chipping hammer is to remove the slag after the weld metal has
solidified. It has chisel shape and is pointed at one end.
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12. Equipments Required for Electric Arc Welding
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6. Wire Brush, Power Wire Wheel:
The function of wire brush is to remove the slag particles after chipping by chipping
hammer. Sometimes, if available a power wire wheel is used in place manual wire
brush.
7. Protective Clothing:
The functions of protective clothing's used are to protect the hands and clothes of
the welder from the heat, spark, ultraviolet and infrared rays. Protective clothing
used are leather apron, cap, leather hand gloves, leather sleeves, etc. The high
ankle leather shoes must be wear by the welder.
8. Screen or Face Shield:
The function of screen and face shield is to protect the eyes and face of the welder
from the harmful ultraviolet and infrared radiations produced during welding. The
shielding may be achieved from head helmet or hand helmet
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13. ARC WELDING ELECTRODES
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Arc welding electrodes can be classified into two broad categories:
1.Non-Consumable electrodes.
2.Consumable electrodes.
1.Non-Consumable Electrodes:
These electrodes do not consumed during the welding operation, hence they named,
non-consumable electrodes. They are generally made of carbon, graphite or
tungsten. Carbon electrodes are softer while tungsten and graphite electrodes are
hard and brittle.
Carbon and graphite electrodes can be used only for D.C. welding, while tungston
electrodes can be used for both D.C. and A.C. welding. The filler material is added
separately when these types of electrodes are used. Since, the electrodes do not
consumed, the arc obtained is stable.
2.Consumable Electrodes:
These electrodes get melted during welding operation, and supply the filler material.
They are generally made with similar composition as the metal to be welded.
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14. 14
Arc Welding
Consumable Electrodes
Mild Steel Electrodes Copper Electrodes

15. 15
Arc Welding
Non Consumable Electrodes
Carbon Electrodes Tungsten Electrodes

16. There are a number of advantages to using arc welding compared with many other
formats:
Advantages
Cost – equipment for arc welding is well-priced and affordable, and the process often
requires less equipment in the first place because of the lack of gas
Portability – these materials are very easy to transport
Works on dirty metal
Shielding gas isn’t necessary – processes can be completed during wind or rain, and
spatter isn’t a major concern
Disadvantages
There are a few reasons why some people look to other options beyond arc welding
for certain kinds of projects. These downsides can include:
Lower efficiency – more waste is generally produced during arc welding than many
other types, which can increase project costs in some cases
High skill level – operators of arc welding projects need a high level of skill and
training, and not all professionals have this
Thin materials – it can be tough to use arc welding on certain thin metals
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ARC WELDING PROS AND CONS
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Forge Welding
1. Forge welding (FOW) is a solid-state welding process that joins
two pieces of metal by heating them to a high temperature and
then hammering them together.
2. It may also consist of heating and forcing the metals together
with presses or other means, creating enough pressure to
cause plastic deformation at the weld surfaces.
3. The process is one of the simplest methods of joining metals and
has been used since ancient times.
4. Forge welding is versatile, being able to join a host of similar and
dissimilar metals.
5. With the invention of electrical and gas welding methods during
the industrial revolution, manual forge-welding has been largely
replaced, although automated forge-welding is a common
manufacturing process.

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Forge Welding
Steps in Forge Welding
There are several skills and processes that blacksmiths need to
familiarize themselves with. Aside from the fact that these skills are
essential in many blacksmithing processes, they are also crucial in
minimizing the wastage of resources. Forge welding is undoubtedly
one of these crucial skills and processing.
It only requires excellent eye-hand coordination, as well as speed,
meticulousness and loads of practice. Likewise, it requires you to
understand the welding temperature of the material you are using.
Also, the mode of welding will be dependent on the size and iron
you are trying to create.

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Forge Welding
STEP 1: Prepare the Materials: It is of utmost importance to
note that welding heat varies based on the type of steel being
used. It is best to heat the materials together to about 90% of
their melting temperature. However, what you want to watch for
is a yellow color. Once you get it to that color, you are at the right
temperature; if you keep going after this point, your metal can
turn into a sparkler. This forge welding temperature is when the
carbon in the metal begins to oxidize, which will ruin your metal.
So first bring your steel to good orange heat.
The following are the six steps in Forge Weld:

20. 20
Forge Welding
STEP 2: Fluxing: Then sprinkle with a flux (like a 20 Mule Team
Borax). Forge welding of dirty or contaminated surfaces will yield
poor weld and weak joints. It will also increase the melting
temperature of the metal. Consequently, the forge welding flux
serves as a low-temperature glassy shield that prevents the
oxygen from the steel surface, which causes scales on the
surface. Scales will prevent your metal from welding. It is
advisable to use a flux because you need to have the right
amount of skill and experience or an oxygen-free burner to weld
without scaling your metals.

21. 21
Forge Welding
STEP 3: Heating: After you have fluxed, place the steel back in
the heart of the fire, while avoiding direct air blast as you do not
want to oxidize your metal. You can weld the metals in a
reducing environment. The most common reducing atmosphere
is within the coal forge. Since the environment is short of
oxygen, a layer of iron-oxide is formed on the surface of the
metal. This iron-oxide layer is called wustite. The appropriate
forge welding temperature is dependent on the types of
materials involved in the process. Different materials have their
required temperature, but the presence of impurities can alter
it.

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Forge Welding
STEP 4: Watch Out for Color Change: Allow the steel to get to a
lemon-yellow color (IMPORTANT: do not look into the fire
without using a pair of didymium glasses). It will appear
shimmery and almost slippery. Once the material reaches an
austenitizing temperature, there will be a rapid diffusion of iron
through the metal. The rate of carbon diffusion will increase with
increasing temperature.

23. 23
Forge Welding
STEP 5: Remove Material from Forge: The pieces of steel should
be removed from the heat now as this temperature is just below
the spark causing temperature. Flashes mean that your iron is
contaminated. The forge welding must be done rapidly before
decarburization sets into the process. The fast operation will
consequently prevent the material from becoming slightly too
soft; thus, producing the appropriate amount of hardness.

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Forge Welding
STEP 6: Joining and Hammering: Now, secure your pieces
together with a bit of metal wire until the primary weld forms.
After this step, simply use a power hammer or hydraulic press to
hammer from one end to the other. You have to be careful not to
hit the metal too hard; the hammer blows should be firm and
reliable but not the same force you would use if you were
changing bar shapes. It depends on the thickness of your pieces.
Thicker ones would require more power. Also, you need to be
careful not to miss any spots.

25. 25
Forge Welding

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Applications Forge Welding
The significant applications of weld forging in blacksmithing
include;
1. It is used to create a more substantial metal from smaller
pieces by allowing blacksmiths to join metal and steel.
2. It is particularly useful in the welding process of weapons like
swords.
3. It is crucial in creating architectural structures such as gates
and prison cells.
4. It is useful in the welding barrels of shotguns.
5. Forge welding is usually employed in the production of
various cookware.

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Advantages Forge Welding
The advantages of forge welding include;
1. It is relatively straightforward and less complicated.
2. It can easily be carried out by most blacksmiths because it
doesn’t cost much and requires only small pieces of metal.
3. Forge melting is sufficient to join both dissimilar and similar
metals.
4. The weld joint usually takes most of its properties from the
base material.
5. Forge welding of metals does not require any filler material
to be reliable.

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Disadvantages Forge Welding
The disadvantages of blacksmithing include;
1. It is not useful for mass production of materials.
2. It is preferable for steel and iron.
3. The forge welding process is relatively slow.

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Resistance Welding
The welding process studied so far are fusion-welding processes
where only heat is applied in the joint. In contrast, resistance
welding process is a fusion-welding process where both heat
and pressure applied on the joint but no filler metal or flux is
added.
The heat necessary for the melting of the joint is obtained by the
heating effect of the electrical resistance of the joint and hence,
the name resistance welding.

30. 30
Resistance Welding
Principle
In resistance welding (RW), a low voltage (typically 1 V) and very
high current (typically 15000 A) is passed through the joint for a
very short time (typically 0.25 Sec). This high amperage heats the
joint, due to the contact resistance at the joint and melts it.
The pressure on the joint is continuously maintained and the
metal fuses together under this pressure.
The heat generated in resistance welding can be expressed as:
H = k I² R t

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Resistance Welding
H = k I² R t
Where,
H = the total heat generated in the work, J
I = electric current, A
R = the resistance of the joint, ohms
t = time for which the electric current is passing through the joint, Sec
k = a constant to account for the heat losses from the weld joint.
The resistance of the joint, R, is a complex factor to know because it is
composed of the
a) Resistance of the electrode,
b) Contact resistance between the electrode and the workpiece,
c) Contact resistance between the two workpiece plates, and
d) Resistance of the workpiece plates.

32. 32
Resistance Welding
1. The amount of heat released is directly proportional to the
resistance.
2. It is likely to be released at all of the above-mentioned points, but
the only place where a large amount of heat is to be generated to
have an effective fusion is at the interface between the two
workpiece plates.
3. Therefore, the rest of the component resistances should be made as
small as possible, since the released at those places would not aid in
the welding.
4. Because of the squaring in the equation, the current I needs to be
precisely controlled for any proper joint.

33. 33
Resistance Welding
Schematic of a resistance welding set-up

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Resistance Welding
1. The schematic representation of the resistance welding is shown
and the main requirement of the process is the low voltage and
high current power supply.
2. This is obtained by means of a step down transformer with a
provision to have different tappings on the primary side as
required for different materials.
3. The secondary windings are connected to the electrodes, which
are made of copper to reduce their electrical resistance.
4. The time of the electric supply needs to be closely controlled so
that the heat released is just enough to melt the joint and the
subsequent fusion takes place due to the force on the joint.

35. 35
Resistance Welding
5. The force required can be provided either mechanically,
hydraulically or pneumatically.
6. To precisely control the time, sophisticated electronic timers are
available.
7. The critical variable in a resistance welding process is the contact
resistance between the two workpiece plates and their
resistances themselves.
8. The contact resistance is affected by the surface finish on the
plates, since the rougher surfaces have higher contact resistance.

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Resistance Welding
9. The contact resistance also will be affected by the cleanliness of
the surface.
10. Oxides or other contaminants if present, should be removed
before attempting resistance welding.
11. The lower resistance of the joint requires very high currents to
provide enough heat to melt it.
12. The average resistance may be of the order of 100 micro ohms,
as a result, the current required would be of the order of tens of
thousands of amperes. With a 10 000 A current passing for 0.1
sec, the heat liberated is
H= (10 000)²(0.0001) (0.1) = 1000 J

37. 37
Resistance Welding
13. This is typical for the welding of 1-mm thick sheets.
14. The actual heat required for melting would be the order of 339 J.
15. The rest of the heat is actually utilized in heating the surrounding
areas and lost at other points.
16. The welding force used has the effect of decreasing the contact
resistance and consequently, an increase in the welding current
for the proper fusion.

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Resistance Welding
The Process of Resistance Welding

39. THERMIT WELDING
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40. 40
THERMIT WELDING

41. THERMIT WELDING
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