Welding

Introduction to Welding
Welding is a Fabrication process.

Joining two or more elements to make a

single part is called as fabrication processes

It essentially involves joining of pieces

either permanently or temporarily.
processes
Mechanical joining by
means of bolts, screws
and rivets
Adhesive bonding by
means of glues
Welding, brazing and
soldering
 
Definition of Welding
 Welding can be defined as a process, of

joining two similar or dissimilar metals

where coalescence (Joint) produced
between two metals with or without use of
filler metal with application of heat or
pressure or combination of both.
According to the composition of the joint
joining process classifed as
Autogeneous
Homogeneous
Heterogeneous
In autogeneous no fller material is added
during joining. Ex. solid state welding,
resistance welding
In homogeneous fller metal is added that
same as the parent metal. Ex.
Arc,Gas,thermit welding
In heterogeneous the fller metal is diferent
from the parent metal. Ex. Soldering and
brazing
Soldering and brazing are not welding
process but they are under the welding family
Types of welding
Welding method are
classifed into two categories
1. Fusion welding or non
pressure welding
2. Non fusion welding or
plastic welding or pressure
welding
Fusion welding
In this process the
material is heated to
molten state and allowed
to solidify or by melting
the parent metal joint is
produced.
Ex. Gas welding, Arc
welding, Thermit welding
Classifcation of fusion
welding
I) GAS WELDING:

 OXY ACETYLENE WELDING

 AIR ACETYLENE WELDING

 OXY HYDROGEN WELDING

II) ARC WELDING:

 CARBON ARC WELDING

 MANUAL METAL ARC WELDING

 TIG (Tungsten Inert Gas Welding) or GTAW

 MIG (Metal Inert Gas Welding) or GMAW

 SUBMERGED ARC WELDING

 PLASMA ARC WELDING

 ELECTRO SLAG WELDING

 FLUX CORED ARC WELDING

 SHIELD METAL ARC WELDING

III) CHEMICAL REACTION WELDING

 THERMIT WELDING
• GAS WELDING
By burning of gas , if the heat is generated
for melting of plates is called as gas
welding
• ARC WELDING
By using electric arc , if the heat is
generated for melting of plates is called as
arc welding
• CHEMICAL WELDING
By use of exothermic chemical reaction , if
the heat is generated for melting of plates is
called as chemical welding
Non fusion welding
In this process the pieces of the
metal to be joined are heated to
plastic state and then forced
together by external pressure or
without melting of parent metal
the joint is produced
Ex. Resistance welding and
Solid state welding
Classifcation of Non-fusion
welding
I) RESISTANCE WELDING:
 SPOT WELDING
 SEAM WELDING
 PROJECTION WELDING
 PERCUSSION WELDING
 BUTT WELDING
II)SOLID STATE WELDING:
 FRICTION WELDING
 FORGE WELDING
 EXPLOSIVE WELDING
 DIFFUSION WELDING
 ULTRASONIC WELDING
 COLD WELDING
RESISTANCE WELDING
 It is technique in which the parts to be
joined are held together under pressure
and heat is produced by passing current
through the contact resistance formed
between the two surfaces.
SOLID STATE WELDING
 The joining takes place at a temperature
below the melting points of the metals
being joined and without use of filler metal.
Advantages of Welding
A good weld is as strong as base metal.
Low manufacturing costs.
Welding equipments are not costlier.
Portable welding equipments are available.
Both similar, dissimilar metals and alloys can be
joined easily.
 It is also useful as a method for repairing broken,
worn or defective metal parts.
Disadvantages of Welding
Welding gives out harmful radiations, fumes and
spatter.

Edge preparation of work pieces is required before

starting the welding process.

Jigs and Fixtures are required to hold and support the

work.
Applications of Welding
 Automobile and Transport industry .

 Material handling equipment.

 Chemical and Petroleum industry.
 Pressure Vessels , water and gas tanks
 Pipelines.
 Rail-Road industry.
 Ship building industry.
 Aircraft industry.
Type of welded joints
The joins are determined by the
position of two pieces to be
joined
I)LAP JOINT
II)BUTT JOINT
III)T-JOINT
IV)CORNER JOINT
V)EDGE JOINT
EDGE PREPARATION
WELDING POSITIONS
Gas welding
Gas welding is a fusion welding
process. It joints the metals
using the heat of combustion of
an oxygen or air and fuel
gas(i.e.acytelene, hydrogen,
propane or butane) mixture.
Thus heat melts and fuses
together the edges of the parts
to be welded with or without
addition of fller metal.
Oxy acetelene welding
Melting the edges or surfaces to be joined by
the gas fame and allowing the molten metal
to fow together, thus forming a continuous
joint upon the cooling.
It suitable for join sheets and plates having
thickness 2 to 50mm.
If the thickness is more than 15mm fller
metal is added to the joint.
The composition of the fller rod is nearly
same as the base metal.
To protect the welded zone from the
atmospheric gases always the fller metal is
coated with fux.
• various gas combinations are used to produce the
hot flame to melt the joint.
• During the welding, heat from the flame is
concentrated on the joint edges until the metal melts
and starts to flow. When the molten metal from both
sides melts it starts to fuse, when the metal cools down
the two parts become Permanently joined
The Oxy-acetylene welding Flame
The oxy-acetylene flame has two distinct zones.
The inner zone (Primary combustion Zone) is the
hottest part of the flame. The welding should be
performed so as the point of the inner zone should be
just above the joint edges.
C2H2 + O2 ͢ 2CO + H2 + heat
Primary Combustion zone
 • outer zone the secondary combustion envelope
performs two functions
• Preheats the joint edges
• Prevents oxidation by using some of the surrounding
oxygen from weld pool for combustion and gives off
carbon dioxide and water vapour

CO + H2 + O2 → CO2 + H2O+heat

Secondary Combustion zone

Types of fames
There are three distinct types of
oxy-acetylene fames, usually
termed:
Neutral
Carburizing (or “excess
acetylene”)
Oxidizing (or “excess oxygen” )
The type of fame produced
depends upon the ratio of oxygen
to acetylene in the gas mixture
Neutral fame
Equal amount of O2 and C2H2 are
mixed and burnt in the tortch
It has two zones: an outer cone is in
light blue inner cone is red.
 inner cone devolope heat and outer
cone protects the molten metal from
the oxidation
It is widely used in steel, cast
iron,aluminium etc.
Casburising fame
It is also called as reducing fame
Excess acetylene is supplied
O2 :C2H2 =0.85:0.95
It s consisting of three zones
I) inner cone
II) intermediate cone of whitish
color
III)outer cone of bluish color
Oxidising fame
Excess oxygen is supplied
 O2 :C2H2 =1.15 to 1.5
It is consisting of two cones 1)the
smaller cone which has purplish tinge
2)the outer cone light blue
Due to excess acetylene the combustion is
slightly increases. Since maximum temp.
is higher than neutral fame
Oxy acetelene welding techniques
I) Forward or leftward welding technique
II) Backward or rightward welding technique
The Oxy-acetylene welding equipment
Components in Oxy-acetylene
welding equipment
Gas cylinders
Pressure regulators
Pressure gauges
Welding torch
Welding tip
Hose and hose ftting
Goggles
Gloves
Air acetylene welding
What ever the total oxygen is
required for combustion of
acetylene is obtained only from
the atmospheric air.
Oxy-hydrogen welding
The burning principle is same as
the oxy-acetylene welding
Oxy-acetylene gas cutting
The oxy acetylene gas cutting outft is similar
to oxy acetylene gas welding except torch tip.
The welding tip is replaced by cutting torch
which delivers the gas mixer for preheating
and oxygen for burning the metal
After free heating oxygen supplied with high
pressure is supplied through the central
opening for cutting the metal
A uniformly wide slot called the kerf, is cut by
jet of oxygen
Torch tips
 ARC WELDING
It is a group of welding processes
where coalescence is produced by
heating with an electric arc, with out
the application of pressure and with or
with out use of filler metals depending
up on base plate thickness.
 What is an Electric
 An electric arc is a discharge
Arc?
of electric current across a
gap in a circuit

To initiate the arc, electrode

is brought into contact with
work and then quickly
separated from it by a short
Electrons
(-)
Electrode (cathode)
Air Molecules Power Source

Power
Source

Work Piece (Anode)

} Ionization Region
(+)

Work piece (anode)

Arc Welding Equipment
The main requirement in an arc-welding set-up is the
source of electric power.
They are essentially of two types.
1. Alternating current (AC) machines
Transformer
Motor or engine driven alternator
2. Direct current (DC) machines
Transformer with DC rectifier
Motor or engine driven generator.
Arc Welding Equipment
The transformer does not have any moving part and as a
result operates with less maintenance cost and also has
higher efficiency.
The power used is also less expensive and practically
there is no noise in operation of the welding transformer.
In AC welding, normally only transformers are used.
In DC arc welding, a rectifier or a generator can be used
to supply the required DC power.
DC Arc welding
Straight polarity
In straight polarity electrode is negative and work piece is
positive, more amount of heat will be generated on the
work piece.
It will be used for welding of high thickness and high
melting point materials.
Depth of penetration is maximum.
Weld deposition rate will be less.
Stability of the arc will be more.
DC Arc welding
Reverse polarity
In this electrode is positive and work piece is
negative.
More amount of heat will be on the electrode
due to this it will be used for low thickness and
low melting point materials.
Weld deposition rate is very high.
Depth of penetration will be less.
Stability of the arc will be more.
AC Welding
Work piece connected to neutral terminal and
electrode connected to phase terminal
The heat generated in this method is equal
amount at the both terminals.
The depth of penetration is obtained some
where in between the DCSP and DCRP
Types of welding machines
The welding machines can also be divided into two types,
based on the characteristics.
 Constant Current welding machines(Droop Characteristics)
 Constant Voltage welding machines (Flat or Straight line
Characteristics)
1. Constant Current type(Droop characteristics)
For a small changing the voltage of the arc the
corresponding change in current in the power source
is very less due to this it will be used in ‘Manual arc
welding technique’.
2. Constant Voltage type(Straight line Characteristics)
In this for a small change in voltage of the arc, there will
be a fluctuation of the current in the power source. Due to
this these welding machines will be used in Automatic
welding technique.
 Arc Welding Layout
A pool of molten metal is formed near electrode
tip, and as electrode is moved along joint,
molten weld pool solidifes.
Equipment used for Arc welding:
AC & DC machines
Two cables for conductors
Electrode holder
Electrode (Non consumable & Consumable)
ARC Welding Current & Voltage:
DC-- 30 to 35 V, and while in AC -- 50/ 55V.
In general arc voltage ranges 15 to 25V --
bare electrode, 20 to 40V -- covered
electrodes.
Current for manual operation -- 30 to 500 A,
Two Basic Types of AW
Non consumable electrodes may be made of
Electrodes
carbon, graphite, tungsten which don't
consume during welding process. The filler
metal required has to be deposited by a
separate filler rod.
Consumable electrodes may be made of
various metals depending upon their purpose &
chemical composition of metals to be welded.
And these are classified in to Bare/Plain
electrodes & Coated electrodes.
Coated electrodes are used for:
1. Coatings give off inert gases such as
carbon dioxide under the arc heat which
shields the molten metal pool & protects
it from atmospheric oxygen, hydrogen,
nitrogen pick up.

2. Elements that are required for

stabilization of arc are also added in this
coatings.
Use of Flux
 A substance that prevents
formation of oxides and other
contaminants in welding.

 Provides protective atmosphere for

welding.

 Stabilizes arc.

 Reduces spattering.
 FLUX SHIELDED METAL ARC
WELDING (SMAW)

(or)

MANUAL METAL ARC WELDING

(MMAW)
Definition of SMAW

 Flux shielded metal arc

welding(SMAW) is a welding process
where coalescence is produced by heating
the w/p with an electric arc set up
between flux coated electrode & w/p.
 Electrode it self melts and supplies the
necessary filler metals.
Principle:
When power supply is ‘ON’ an electric arc
struck between coated electrode & w/p.
Arc melts the electrode end and job.
Material is transferred from electrode to
job in the form of droplets, through arc
and deposited along the joint to be welded.
Flux coating melts, produces a gaseous
shield to prevent formation of metal oxides
of molten weld metal.
Shielded metal arc welding
Procedure:
The w/p is kept on base(backing plate) and
fixed to + ve terminal of power supply,
electrode to - ve terminal of power supply.
To form the arc the flux coated electrode is
brought in to contact with w/p in short
sweeping motion and then it is pulled
away.
This initiates the arc & thus melting of
w/p & electrode takes place and leaves the
droplets into the parent metal cavity(gap).
 As electrode melts, flux covering
disintegrates, giving off vapors that
protects the weld area from atmospheric
gases.

 In addition flux provides molten slag

which cover the filler metal as it travels
from electrode to weld pool.

 Once filler metal is hardened in pool it

must be chipped away to reveal the
Advantages:
It is simplest one of all the available.
Equipment cost is low and portable.
Big range of metals and alloys can be joined.
Disadvantages:
Because of limited length of electrode and brittle flux
coated on it mechanization is difficult.
In welding long joints as one electrode finishes weld
is to be progressed with other electrode, unless
properly cared defects may occur at the place where
welding is to be restarted.
As process uses stick electrode it is slower process
compared to MIG welding.
Applications :
 Mainly used to weld Iron & Steel,
Al, Ni, Copper alloys.
 Finds applications in tanks, boilers
and pressure vessel fabrications, ship
buildings, building and bridge
construction.
SUBMERGED ARC
WELDING
(SAW)
It is an arc welding process wherein coalescence is
produced by heating with an electric arc set up between
continuously feeding bare metal electrode & job.
The end of the electrode and molten pool remains
completely hidden and are invisible being submerged
under a blanket of granular material. (FLUX).
SUBMERGED ARC WELDING (SAW)
Principle:
In this process instead of flux covered electrode, granulated flux &
bare electrode is used.
The flux serves as a shield and protect molten weld pool from
atmospheric Contamination.
 Process:
Here granulated flux is delivered ahead of welding
electrode by means of a welding flux feed tube
(HOPPER).
When trigger is pulled and flux starts depositing on
joint to be welded.
Arc is always generated by
touching the bare electrode under
the cover of flux.
Equipment:
Welding head: It feeds flux & filler metal welding
electrode.
Flux hopper: It stores the flux and controls rate of flux
deposition on welding joint.
Welding power source: AC transformer or DC generator
rated up to 1500 Amps may be used.

Flux: It shields and protects molten weld metal from

atmospheric contamination. It may consists of fluorides of
calcium, oxides of calcium, magnesium, silicon, Al.

Electrodes: Composition of electrode depends on material

being welded. Diameter of electrodes1.6, 2, 2.4, 3.2, 4,
4.8, 6.6 mm.
Advantages:
This Process used to weld thicker sections with
deeper penetrations.
Because of high heat concentration high welding
speeds can be used.
High metal deposition rates can be achieved in a
single pass i.e. upto 20 kg/h can be achieved .
Weld metal deposited possesses uniformity, good
ductility.
No edge preparation is necessary for materials
under 12mm thick.
Able to weld plates of thickness as high as 75mm
in butt joints in single pass.
Disadvantages:
• Since operator cant see welding being carried out he
cant judge accurately the progress of weld.
• Process is limited to welding in flat position and on
metal more than 4.8 mm thick.
• C.I, Aluminum alloys, Mg alloys and Zinc cant be
welded.
Applications:
Fabrication of pipes, pressure vessels, boilers, structural
shapes, cranes, locomotives.
Automotive, aviation, ship building and nuclear power
industry.
For welding metals like MS, medium & high tensile low
alloy steels.
Gas Tungsten Arc Welding
(GTAW)

(or)

Tungsten Inert Gas (TIG)

Welding
 It is an arc welding process wherein coalescence is
produced by heating the job with an electric arc struck
between non consumable tungsten electrode and job.
 When arc is produced in between electrode & w/p, inert
gas from cylinder passes through welding head around the
electrode. This shield gas (argon, helium, nitrogen) is used to
avoid atmospheric gases of molten weld pool.
A filler metal (wire) is used ,and these wires are similar to
metals that are to be welded.
Principle of operation:

Welding current, water, inert gas supply are

turned on, arc is either struck by touching
electrode with a scrap metal tungsten piece or
using high Frequency unit.

The torch is brought nearer to job when

electrode tip reaches with in a distance 2 to 3mm
from job, a spark jumps across air gap between
electrode & gap.
 Air path gets ionized and arc is
established.

 After striking the arc it is allowed to

impinge on job and molten weld pool
is created which joins the 2 surfaces.
EQUIPMENT:
1. Welding torch: Equipped with cooling systems using
air or water.
2. Electrode:
The electrode used in GTAW is made of tungsten or a
tungsten alloy, because tungsten has the highest
melting temperature among pure metals, at 3,422 °C
(6,192 °F).
3. Filler rod is used when welding thicker pieces with
edges prepared. Filler metals up to 4.5mm diameter in
form of straight lengths or coils are available.
4. Power source:
 Current power source 8 to 20 kW. It uses both AC &
DC welding machines with good current control.
5. Inert gases:

Argon is the most commonly used shielding gas.When

used with alternating current, the use of argon results in
high weld quality and good appearance.

Helium, is most often used to increase the weld

penetration in a joint, to increase the welding speed, and to
weld metals with high heat conductivity, such as copper
and aluminum.

Argon helium mixture, Argon oxygen mixture, Argon

hydrogen mixture.
Advantages:
It is very much suitable for high quality welding
of thin materials (as thin as 0.125mm) which
requires good surface finish.
 No flux is used.
 Precise control of welding variables (heat).
Because of clear visibility of arc and job operator
can exercise a better control on welding process.
This method can weld in all positions and
produces smooth & sound welds .
Very good process for joining non ferrous metals
(Al) & Stainless steel and High carbon steel.
Disadvantages:
 Lower deposition rates
 More costly for welding thick sections as inert gas makes
this process more expensive than SMAW.
Since TIG welding requires separate filler rod compared
to MIG it is slower process.
Cost of equipment is high compared to submerged arc
welding.
Applications:
Joining Al, Mg, Titanium alloys , SS, and other refractory
metals.
Welding sheet metals and thinner sections.
Precision welding in atomic energy, air craft, chemical &
instrumental industry.
 Metal Inert Gas Welding
(MIG)

(or)

Gas Metal Arc Welding (GMAW)

(or)
metal active gas (MAG) welding
 Uses a consumable bare metal wire as
electrode and shielding accomplished by
fooding arc with a gas.

Wire is fed continuously and

automatically from a spool through the
welding gun

Shielding gases include inert gases such

as argon and helium for aluminum welding,
and active gases such as CO2 for steel
welding.

Bare electrode wire plus shielding gases

MIG Welding is the process in which coalescence is produced by
heating job with an electric arc struck between a continuous and
consumable wire electrode and w/p. No flux is used but arc and
molten metal are shielded by inert gas (argon, helium, carbon
dioxide).
Principle of operation:
Before igniting the arc, gas & water flow is
checked.
Proper current & wire feed speed is set and
electrical connections are ensured.
Arc is struck when current & shielded gas flow is
switched on & electrode is scratched against the w/p
which is the usual practice for striking the arc.
In this type arc is produced between consumable
metal electrode (wire) & w/p.
Electrode wire is continuously fed from wire reel.
Electrode wire from reel passes through holder and
it is melted by arc & deposited over joint resulting
Equipment:
1.Welding power source:
 Most applications of gas metal arc welding
use a constant voltage power supply.
 Alternating current is rarely used with
MIG; instead, direct current is employed
and the electrode is generally positively
charged.
 Major type of power sources are DC
generator & AC transformer with rectifier.
2. Welding torch/Gun/Nozzle:
It energizes electrode, feeds electrode and shielded
gas.
These may be water or air cooled.
Torches may have straight/bent nozzle fitted at the
end.
For welding complicated shapes & intricate joints
bent shape is used.
KEY PARTS:
Gas nozzle :used to evenly direct the
shielding gas into the welding zone.
Gas hose: gas is supplied to the nozzle through a gas
hose, which is connected to the tanks of shielding gas.
3. Wire feed unit:
It supplies electrode to the work (torch) at a
constant speed/different speeds.
Wire spool is manually operated units mounted
else where to facilitate welding over bigger areas.
A standard spool may carry 1 to 15 kgs of wire.

4. Electrode:
Selection of electrode is based on composition of
metal being welded, joint design.
Advantages:
Because of continuous fed electrode, MIG
is much faster process than TIG/ stick
welding.

It can produce joints with deep penetration.

Thin & thick both metals can be joined.

No flux is used.

 MIG produces smooth, neat, clean welded
surface which no further requires cleaning
operations and thus reduces total welding cost.

 Better arc time because of continuous

wire electrode.

 Higher deposition rates.

 Eliminates problem of slag removal.

 Can be readily automated.

Disadvantages:
Process is more complex as compared to TIG
because number of variables are required to be
controlled effectively to achieve good results.
Equipment is more complex, more costly.
Applications:
For welding carbon, silicon, low alloy steels,
stainless steel, aluminum, magnesium, copper.
For manufacture of refrigerator parts.
In industries like ship building, automobile and
aircraft.
RESISTANCE
WELDING
It is group of welding processes wherein
coalescence is produced by heat obtained
from resistance of work to flow of electric
current in circuit of which work is part and
by application of pressure.
(OR)
RW is a fusion welding process where both
heat & Pressure are applied on joint but no
filler metal/ flux is used . Heat necessary for
melting of joint is obtained by heating effect
of electrical resistance of joint.
Principle:
• In RW a low voltage (4 to 12
volts) & very high current(15,000
A) is passed through joint for a
very short time.

• This high temp heats the joint due

to contact resistance at joint &
melts it.

• Pressure on the joint is

continuously maintained & metal
fuses together under this pressure.
• In this process amount of heat
released is directly proportional to
resistance.
• 2
H = Total heat generated in work, joules(J)
I = Electric current, Amperes (A)
R= Resistance of joint, ohms
t= time for which electric current is passing through
joint.(s)
1.Heat balance:
 Heat H, for electrical resistance welding is generated
by passing a large electrical current through two
pieces of metal that are touching each other.
2.Current, I:
 Temp in RW is regulated by controlling magnitude &
timing of welding current.
3. Time:
During RW cycle 4 different segments / periods of timing are set up
on machine:
Squeezing time: It is the time required for the electrodes to align and
clamp the two workpieces together under them and provide the
necessary electrical currunt.
Weld time: During this period welding current flow to the workpieces
till they are heated to melting temperature.
Hold time: It is the during where the pressure is maintained on the
molten metal without the electric current. During this time, the pieces
are expected to be forge welded.
Off time: In this time the pressure on electrode are taken off so that
plates can be positioned for the next spot.
4.Pressure/ Electrode force:
It is the force applied to w/p by electrodes during
welding cycle.
Electrodes used in RW are those which have high
electrical conductivity & better mechanical
strengths like copper cadmium & copper chromium
electrodes.
Functions performed by Electrodes:
They carry current which passes through &
generates heat at the place where 2 w/p are in
pressed contact.
Depending up on area of electrodes face or tip they
determine current density in weld zone.
Advantages:
Faster rate of production and hence suited for
mass production.
No filler rod is required.
Both similar and dissimilar metals can be joined
and metal plates of different thicknesses.
Lower operator skill level than for arc welding
Good repeatability and reliability
Disadvantages:
Skilled persons are needed for maintenance of
equipment & its controls.
Bigger job thicknesses cant be welded.
High initial equipment cost
Limited to lap joints for most RW processes
Applications:
Joining sheets, tubes.
Making tubes and metal furniture.
Welding air craft and automobile parts.
Fuel tanks of cars, tractors.
Types of Resistance
Welding Processes
Spot Welding
Seam Welding
Projection Welding
Percussion welding
Flash Butt Welding
 SPOT WELDING
Spot welding is a resistance welding process in which over
lapping sheets are joined by fusion at one or more spots by
heat generated by resistance to flow of electric current
through w/p’s that are held together under force by 2
electrodes ,one above & other below the over lapping sheets
as shown in diagram.

Spot weld is done to join 2

sheet metal jobs in lap joint
forming a small nugget at
the inter face of 2 plates.
Procedure: Before spot weld one must see that
Job is clean ,i.e free from grease, dirt, paint,
oxide.
Electrode tip surface is clean, since it has to
conduct current into the work. Very fine amount
emery cloth may be used for routine cleaning.
Water is running through the electrodes in order
to: avoid them from getting over heated.cool the
weld.
Proper welding current has been set on current
selector switch.
Proper time has been set on weld timer.
 ROCKER ARM
• It is namedEQUIPMENT
so because
of rocker arm welding
beam movement of
upper arm.

• These are simplest

stationary spot welding
machines that are made
for use with Foot lever,
Air cylinder, Motor &
cam operation.
Foot operated rocker arm machine consists of
2 simple levers connected by a rod &
compression spring.

Force exerted on foot lever is transmitted

through spring to rocker arm lever and then to
welding electrodes.

Generally Rocker arm machines are low cost,

simple machines for welding light gauge MS
with simple welding cycles.
Stages in making spot weld:
Step 1. Electrodes are brought together against
overlapping w/p’s and Pr is applied so that surfaces
of 2 w/p’s under electrodes come in physical contact.
Step 2. Weld current is switched on for a definite
period of time. As the current passes through one
electrode & w/p to other electrode ,a small area
where the w/p’s are in contact is heated.
Step 3. At this stage welding current is cut off, extra
electrode force is then applied or original force is
prolonged.
Step 4: Electrode pressure is released to remove the
spot weld w/p’s.
Metals that are spot welded:
Ferrous metals: Low carbon steels, Hardenable steels,
High speed steel bits, Stainless steel.
Non ferrous: Al, Al Mg alloys, Al manganese alloys,
Copper, Nickel , Nickel alloys.
Advantages:
• Low cost.
• High speed welding
• Less skilled worker can perform.
• High uniformity of products.
• No edge preparation is needed.
RESISTSANCE SEAM WELDING:
The resulting weld is a series of
overlapping resistance spot welds
made progressively along a joint by
rotating the circular electrodes.
RSEW is a specialized process of spot
welding where cylindrical electrodes
are replaced by disc electrodes.
Principle of operation:
Seam welding is similar to spot welding except that
circular rolling electrodes are used to produce a
continuous air tight seam of overlapping welds.
Overlapping(spot) welds are produced by rotating the
electrodes & a regularly interrupted current.
W/p’s to be seam welded are cleaned, overlapped
suitably and placed btn 2 circular electrodes which
clamp the w/p’s together by electrode by the electrode
force.
Current impulse is applied through rollers to material
in contact with them, heat generated thus makes the
metal plastic & pressure from electrode completes the
weld.
Equipment: This machines are similar in construction to
spot welding machines except that electrodes are
mechanically driven rotating discs.
Metals welded:
Low carbon, high carbon , low alloy steels.
Stainless and many coated steels.
Aluminum, Nickel, Magnesium and its alloys.
Advantages:
Can produce very tight joints.
Single seam or several parallel welds can be
produced.
Applications:
 Gasoline tanks
 Automobile mufflers
 Various other sheet metal containers
Resistance Projection Welding
(RPW)
A resistance welding process in which
coalescence occurs at one or more small
contact points on parts
 Contact points determined by design of parts to
be joined
 May consist of projections, embossments, or
localized intersections of parts
Steps in Projection Welding

(2) when current is applied,

(1) start of operation, contact
weld nuggets similar to spot
between parts is at
welding are formed at the
projections;
projections.
FLASH BUTT WELDING

It is a welding process wherein

coalescence is produced over the entire
area of abutting surfaces, by heat
obtained from resistance to electric
current between two surfaces, & by
application of Pressure after heating is
substantially completed.
Principle of Operation:
Flash butt welds are made on a m/c having stationary and one opposing
movable platen, on which are mounted the flash welding dies / clamps.
These clamps securely hold the w/p's to be welded while simultaneously
serving to conduct welding current through these work pieces.
2. The w/p held in movable platen is brought towards one
gripped in stationary platen until 2 come in contact, and
asa welding current is turned on, flash is established. As
flashing continues the ends of w/p's burn off as they reach
higher and higher temperature until finally they attain
welding temperature.
3.At this stage Pr of moving clamp is quickly and
greatly incresed to forge the parts together & expel
the molten metal and slag out of the joint there by
making a good solid weld.
4. The welding current is cut off and w/p's
are unclamped as the fusion weld cools.
Metals welded by Flash welding:
Low carbon steels.
Medium strength, high strength low alloy steels.
Tool steels.
Stainless steels.
Aluminum alloys
Copper alloys
Magnesium alloys
Molybdenum alloys
Nickel alloys
Titanium alloys
Advantages:
Many dissimilar metals with diff melting temperatures
can be flash welded.
Flash welding offers strength factors up to 100%
No special preparation of weld surface is reqd.
Highly alloyed which cant be joined by other process
can be flash welded.
Process is cheaper i.e cost of current per weld is small.
Faster than many other methods.
Disadvantages:
Process presents a considerable fire hazard, where
operator need to protect from flying particles.
Applications:
It is applied primarily in butt welding of metal sheets,
tubing bars , rods, fittings.
Find its applications in automotive & aircraft products,
house hold appliances.
Used to produce assemblies that otherwise would require
more costly forgings or castings.
Thermit Welding
 It is a group of welding processes wherein
coalescence is produced by heating with super
heated liquid metal from chemical reaction of
thermit mixtures with or with out application
of Pressure.
(or)
Thermit welding is the process of igniting
a mix of high energy materials, (which is also
called thermit), that produce a molten metal
that is poured between the working pieces of
metal to form a welded joint.
Thermit welding: (1) Thermit ignited; (2) crucible
tapped, superheated metal fows into mold; (3) metal
solidifes to produce weld joint.
Principle of operation:
It is based on casting & foundry
practice & consists of providing
by means of chemical reaction, a
volume of molten weld metal is
poured in to joint to be welded
as shown in fig.
The chemical or thermit
reaction takes place between
metal oxide(Iron) & metal
reducing agent (Al, Mg).
Thermit reaction is exothermic one few of them
are:
1)The aluminum reduces the oxide of another
metal, most commonly iron oxide.
Fe2O3 + 2Al → 2Fe + Al2O3 + Heat.
The products are aluminum oxide, free elemental
iron, and a large amount of heat.

2)Other metal oxides can be used, such as

chromium oxide, to generate elementary metal.
3CuO + 2Al → 3Cu + Al2O3 + Heat
Procedure:
It is essentially a casting process where molten metal
obtained by thermit reaction is poured in to refractory
cavity made around the joint.
The 2 pieces that are to be joined are cleaned properly
and edge is prepared.
Then wax is poured in to joint so that a pattern is
formed where weld is to be obtained.
A molding flask is kept around joint & sand is
rammed around wax pattern providing necessary
pouring cup, sprue, rises.
A bottom opening is provided to run off molten wax.
Wax is melted through this opening which is also used
to preheat joint & make it ready for weld.
Thermit mixture which is mixed with fluxes is
filled in laddle through bottom opening and
opening is initially closed.
Igniting mixture normally barium peroxide or
magnesium is placed at top of thermit mixture.
This mix is lighted by means of heated metal
rod where complete reactions take place &
molten metal is poured.
Bottom plug of ladle is opened and metal is
allowed to flow in to prepared mold.
Weld joint is allowed to cool slowly.
Advantages:
Heat necessary for welding is obtained from chemical
reaction & thus no costly power supply is reqd.
Therefore broken parts can be easily welded on site
itself.
Weld surface is often smooth enough that
no fnishing is required.

Disadvantages:
It is applicable only to ferrous metal parts of heavy
sections.(mill housings, heavy rail sections).
Process is uneconomical if used to weld cheap metals
or light parts.
Applications:
Mainly used in repair or assembly of large parts:
For repairing fractured rails.
For welding large fractured crankshafts.
For welding broken frames of machines.
For replacing broken teeth on large gears.
For welding cables for electrical conductors.
For end welding of reinforcing bars to be used
in concrete construction.
Thermite reaction proceeding for a railway welding. Shortly after
this, the liquid iron flows into the mould around the rail gap.
 Radiant Energy Welding Processes:
It focus an energy beam on the work piece.
Heat is generated only when energy beam
strikes the work piece.

 Radiant energy processes are :

1) Electron Beam Welding.
2) Laser Beam Welding.
Electron Beam
Welding
Electron Beam Welding:
It is defined as fusion welding process wherein
joint is produced by heat obtained from
concentrated beam composed primarily of high
velocity electrons.

As a result high velocity electrons strike surfaces

to be joined, their kinetic energy is transferred to
thermal energy there by causing the w/p metal to
melt and fuse.

The welding is often done in conditions of a

vacuum to prevent dispersion of the electron
beam.
Principle of Operation:
As the electrons strike the metal parts/work pieces their
kinetic energy is converted to heat (thermal) energy,
instantly vaporizing the metal under temperatures near
25,000c. Due to this high temperature work piece edges
melts and weld takes place.
Because of electron beam is tightly focused the total
heat input is actually much lower than that of arc
welding.
As a result, the effect of welding on the surrounding
material is minimal, and the heat-affected zone is
small(key hole). Distortion is slight, and the work piece
cools rapidly, and while normally an advantage, this can
lead to cracking in high-carbon steel.
 Welding operations can be carried out in :
Hard Vacuum: When welding is to be carried out
in hard/ high vacuum, both electron beam gun and
w/p are enclosed in the same vacuum chamber.
Partial vacuum: In partial vacuum welding
systems beam gun & w/p are contained in separate
chambers. The gun chamber is pumped to 0.1
micron, but w/p chamber is pumped only to
vacuum of 5 to 100 micron.
Atmospheric welding: W/p is placed out side the
vacuum chamber. Electron beam leaves the high
vacuum environment of gun and passes into
atmosphere through orifice.
 Equipment:
1)Electron Beam Gun:
It consists of Tungsten filament, Cathode
electrode, Anode, Focusing coil.
When Tungsten filament is electrically heated in
vacuum to approximately 2000c it emit electrons.
The electrons emitted from heated filament carry
negative charge, are replaced by Cathode control
electrode and are made to pass through the central
hole of Anode.
Cathode electrode(-) and Anode(+) electrode
concentrate and propel electrons.
 The electron beam is the focused by means of
electro magnetic focusing coil (lens). The focusing
coil spreads the electron beam to user needs.

Thus concentrated electron beam focused on to w/p

in a spot from 0.75 to 3 mm in dia when strikes the
w/p, the K.E of electrons is changed into heat that is
great enough to melt the w/p material.

 The purpose of electron beam gun is to accelerate

& focus the electrons given off by filament in to a
narrow, high velocity beam which can be used for
welding.
2) Vacuum pumping chamber:
It is usually rectangular in shape, has heavy glass
windows to permit viewing of work while welding
is in progress.
 Advantages:
Welds produced are of high quality and are made at high
speeds.
Welded joints surfaces are clean & bright having no oxide,
scale, flux slags and thus needed no cleaning up after weld
is completed.
EBW have a highly desirable depth to width ratio. Much
deeper penetration can be obtained in single pass.
Edge & butt welds can be made in metals as thin as 0.025
mm.
Power input is small compared to power required for other
electrical welding devices.
Process can be used at higher welding speeds typically
between 125 & 200 mm/s.
 Disadvantages:
Initial cost of equipment is high and portable equipments are
rare.
Time is required to create vacuum every time a new job is to
be welded.
Precautions are needed to prevent damage from X rays.
Work size is limited by work chamber dimensions.

Applications:
For welding reactive & refractory metals used in atomic
energy & rocketry fields.(Titanium, Tungsten,
Molybdenum).
For welding Automobile, Air planes , Aerospace equipment
where especially low distortion is required.
Laser Beam
Welding
It is a group of welding processes wherein
coalescence is produced by heat obtained from
application of concentrated coherent light
beam impinging up on surfaces to be joined.
LASER is concentrated beam of coherent
monochromatic radiation.
Laser is a device for concentrating light waves
into narrowly defined highly intense beam that
can impart high energy on small area to
produce fusion for welding purposes.
LASER BEAM WELDING:
Principle and operation:
A man made cylindrical ruby crystal, ruby is
Aluminum oxide with chromium dispersed through it.
Ends of ruby crystal is silvered to form mirrors
internally while one end has a tiny hole in the silver
layer through which laser beam emerges.
Around the outside of crystal place flash tube
containing inert gas xenon. Flash tube is designed for
operation of a rate of thousands of flashes/ second.
Flash tube converts electrical energy in to light energy.
Capacitor bank (storage) stores electrical energy. It is
charged by a high voltage power supply. It energizes
flash tube by an appropriate triggering system.
As ruby crystal is exposed to intense light flashes,
chromium atoms of crystal are excited & pumped to
high energy levels. These chromium atoms immediately
drop to an intermediate energy levels with evolution of
heat & drops back to original state with evolution of
discrete quantity of radiation in red fluorescent of light.
 This red light which is obtained is escaped from small
hole in mirror at end of ruby crystal as laser beam.
This narrow laser beam is focused by an optical
focusing lens to produce small intense spot of laser
(light )on job.
Optical energy as it impacts the w/p is converted in to
heat energy. The temperature generated can be made
sufficient to melt the materials to be welded or cut.
Advantages:
Welds can be made inside transparent glass or plastic
housings.
As no electrodes are used electrode contamination or
high electric currents are eliminated.
It permits welding of small, closely spaced components
with welds as small as few microns in diameter.
Because it is light it is clean no vaporized metal or
electrodes dirty up the delicate assemblies.
Because it is light it can be focused to microscopic
dimensions and directed with great accuracy.
Multi layer materials can be joined with differing
thermal properties.
Disadvantages:
It is slow welding process(25 to 250 mm/min).
Limited to depths of app 1.5mm .
Applications:
Laser is high energy beams of light that can both weld
& cut.
For connecting leads on small electronic components
and in integrated circuitry in electronic industry.
To join hard high melting point metal alloys.
In space & air craft industry for welding light gauge
materials.
LASER can weld wire-to-wire, sheet-to- sheet, wire- to-
wire, tube-to- sheet.
Comparison: LBW vs. EBW
No vacuum chamber required for
LBW
No x‑rays emitted in LBW
Laser beams can be focused and
directed by optical lenses and
mirrors
LBW not capable of the deep welds
and high depth‑to‑width ratios of
EBW
Maximum LBW depth = ~ 19 mm
 WELDING DEFECTS
Improper welding procedures & parameters, base
metal which introduces defects (or )faults in weld
metal & around.(i.e heat effected zone)
Few of welding defects that occur are:
 CRACK
 LAMELLAR TEARING
 DISTORTION
 INCOMPLETE PENETRATION
 IMPROPER FUSION
 POROSITY
1) CRACK:
 It may be appeared on weld surface or under the weld
bead which can be microscopic or macroscopic scale
depending on their size.
 HOT CRACKING: It occurs at high temp and very small
to visible. It can be prevented by preheating base metal.
 COLD CRACKING: It occurs at room temp after weld
is completely cooled.
CAUSES: REMEDIES:
 Rigidity of joint Relieve the stresses of joint
 Poor ductility of base Use proper base metal.
metal.
 Fast arc travel speed Maintain proper arc speeds.
 Electrode with high H2 Use proper electrode.
2) LAMELLAR TEARING:
• Lamellar Tearing is a kind
of Weld-cracking that forms
beneath a weld.
• Generally seen at edge of
heat effected zone which
appears as long&
continuous visual separation
line btn base metal &heat
affected
CAUSES: zone. REMEDIES:
• Result of very severe restraint at joint Reduce tesile stress
• Poor ductility Use proper metal.
• Non-metallic inclusions are present as
very thin platelets, with their principal planes
parallel to the plate surface .
3) DISTORTION:
It is change in shape & diff between positions of 2 plates
before welding & after welding.
Formed mainly bcz of shrinkages that takes place in
weldments.
CAUSES REMEDIES
More no of passes with Use proper dia electrode
small dia electrodes.
Type oj joint Use metal as reqd for joint
(v-type joint needs more metal
than u joint to fill groove).
High residual stresses that Relieve the stresses.
are in plates to be welded.
e

4) INCOMPLETE PENETRATION:
Welding current has the greatest effect on
penetration.
Incomplete penetration is usually caused by the use
of  too low a welding current and can be eliminated
by simply increasing the amperage.
• When the weld bead does
not penetrate the entire
thickness of the base plate.

When two opposing weld

beads do not interpenetrate

When the weld bead does not

penetrate the toe of a fillet weld
but only bridges across it.
4) INCOMPLETE FUSION:

• It will be seen as discontinuity in weld zone.

• Some times molten meatl deposited by electrodes
does not fuse properly with cold base metal & the 2
do not unite properly & completely.
CAUSES:
Improper penetration of joint.
Wrong design of joint.
Incorrect welding technique.
Improper cleaning of w/p.
Low arc current.

REMEDIES:
Use proper joint.
Use correct design.
Choose proper welding tech.
Clean the w/ps.
5) POROSITY:
• Porosity is the gas pores found
in the solidified weld bead.
• It is caused by presence of gases
entrapped during solidification
process.
• Main gases that causes porosity are hydrogen, nitrogen,
oxygen.
CAUSES:
• Improper coating of electrodes.
• Long arcs.
• Faster arc travel speeds.
• If rust or oil, grease is present on surface of job