Welding - Joining Processes

ME8351 MANUFACTURING TECHNOLOGY 1
UNIT 2 JOINING PROCESSES
S.BALAMURUGAN
ASSISTANT PROFESSOR
MECHANICAL ENGINEERING
AAA COLLEGE OF ENGINEEERING & TECHNOLOGY

WELDING
• It is the process of joining two or more similar or dissimilar
metals with or without the application of heat, with or without
the application of pressure, with or without the application of
filler materials.
WELDING
FUSION WELDING NON FUSION OR PRESSURE
GAS ARC CHEMICAL HOT COLD
GAS WELDING OXY – ACETYLENE, AIR - ACETYLENE
ARC WELDING TIG, MIG, SUBMERGED ARC, ELECTROSLAG WELDING
CHEMICAL THERMIT WELDING
HOT NON FUSION SOLDERING, BRAZING, RESSITANCE WELDING
COLD NON FUSION CRYOGENIC WELDING, COLD PRESSURE WELDING
ME 8351 MANUFACTURING TECHNOLOGY -1 S.BALAMURUGAN, AP/MECHANICAL, AAACET

CLASSIFICATION BASED ON FILLER MATERIALS
AUTOGENEOUS No filler metal is added to the joint interface
EX – Electric Resistance Welding
HOMOGENEOUS Filler metal is added & it is similar to parent metal
EX – Arc Welding, Electron Beam Welding & Diffusion Welding
HETROGENEOUS Filler metal is added but it is different to parent metal
EX – Brazing & Soldering
WELDING

• FUSION WELDING – the metal at the joint is heated to molten state & it is
allowed to solidify.
• NON FUSION WELDING – the metal parts are heated to a plastic state &
they are pressed together to make joint.
ADVANTAGES
• Permanent Joint - Economical way of join components
• Welded joint can be stronger than the parent material if a filler metal is
used that has strong properties.
LIMITATIONS
• Most operations are performed manually – Skilled labor required
• It does not allow for convenient dis assembly
• Defects are difficult to detect.
WELDING

WELDING EQUIPMENT
• GAS CYLINDERS
• Oxygen Cylinder – Black Colour, 125-140 Bar, 6.23 m3
• Acetylene Cylinder – Maroon Colour, 16 Bar, 7.6 m3
• PRESSURE REGULATORS
• Regulators are used to reduce & control the working pressure of the gases
• Working pressure – Oxygen – 0.7 bar to 2.8 bar
• Working pressure – Acetylene – 0.07 bar to 1.03 bar
• Depending on the thickness of the work pieces to be welded
• PRESSURE GAUGES
Four Pressure Gauges – 2 for Oxygen, 2 for Acetylene
1st pressure gauge – Show cylinder pressure
2nd pressure gauge – show the working pressure of welding
• HOSES
• The regulator of each cylinder is connected to the torch through two long hoses
• Oxygen Cylinder – Black Colour
• Acetylene Cylinder – Red Colour

• CHECK VALVE
• Safety valve attached between
hoses & regulator outlets
• It allow gases to flow in only one
direction to prevent back flow
• GOGGLES
Used to protect eyes from flame heat,
Ultraviolet & Infrared rays
• SPARK LIGHTER
It is an ignitor to start the burning of
Oxy-Acetylene gases
• WELDING GLOVES
Used to protect the hand from injury
caused by heat & Metal Splashes
• WIRE BRUSH
Used to clean the weld joint before &
after welding
WELDING EQUIPMENT

WELDING EQUIPMENT
WELDING TORCH
• Oxygen & Acetylene gases are mixed in the mixing chamber of Torch
• A flame will be produced at the tip of the torch called Nozzle
• Nozzle tip made up of Copper or Copper Alloy
• Based on type of metal & Its thickness, different tips used
• Control valves are used to quantify the oxygen & Acetylene to control
the flame

OXY – ACETYLENE GAS WELDING
C2H2 + O2 2CO + H2 + HEAT
2CO + O2 2CO2 + HEAT
H2 +
𝟏
𝟐
O2 H2O + HEAT
OXYGEN CYLINDER – Black Colour,
125-140 Bar
ACETYLENE CYLINDER – Maroon
Colour, 16 Bar
• Heat required for melting of plate is obtained by burning of oxyacetylene gas
mixture
• Mixing of gases takes place in Torch Body, this mixture possessing high pressure
• This high pressure mixture is passed through the convergent nozzle, the pressure
energy gets converted into the velocity energy.
• The high velocity mixture coming out of the nozzle, is given initiation of burning,
the continuous flame will be produced.
• Flame Temperature - 3200°C
• Rubber hose pipes are used for Acetylene cylinder, Colour, Size & Thread
distinction provided to avoid interchanging of hose pipes

TYPES OF FLAMES
• Neutral Flame
O2
C2H2
= 1, Tmax = 3260°C
N – length of inner core, N = 10 to 15 mm
• Used for joining or cutting all ferrous & Non ferrous
metals.
• Oxidizing Flame
O2
C2H2
= 1.15 to 1.5, Tmax = 3380°C
• Not suitable reactive metals, Al & Mn (Oxidation)
• Used for high melting point metals
• Carburizing Flame
O2
C2H2
= 0.85 to 0.95, Tmax = 3040°C
• Used for high carbon steels
• Not suitable for high melting point metals

TORCH ANGLE
• Angle made by the axis of the torch with axis
of work piece is called Torch Angle.
• With increased torch angle, the exposing area
of flame to weld bead decreases, So flame
density increases.
FACTORS AFFECTING SELECTION OF
TORCH ANGLES
• Thickness of plates to be joined
• Melting Point of plates to be joined
• Thermal Conductivity of plates to be joined
• Place of Welding – At the beginning of
welding, Large torch angles used. At the
end of welding, Small torch angles used.

WELDING TECHNIQUES
FORE HAND or LEFT HAND WELDING
• Focused towards non-welded portion
• Efficient when it is done from right to
left
• Preheating of weld bead will takes
place in this
• The force of flame is pushing back
the molten slag particles into the weld
pool.
• Slag inclusion may present in the
weld bead
BACK HAND or RIGHT HAND WELDING
• Focused towards welded portion
• Efficient when it is done from left to
right
• Post heating of weld bead will takes
place in this
• The force of flame is pushes out the
molten slag particles from the weld
pool, so no slag inclusion in the weld
bead.
• This welding is faster by 20-25%
• Less acetylene needed 15-25%

FILLER RODS
• It supplies the additional molten metal to the weld bead.
• If the thickness of the plate less than 5 mm(Square Joint), No
filler rod used.
• When, thickness greater than 5 mm. U, V & J joints are used.
Additional metal need to be supplied using filler rods.
Filler Rods – Low Carbon Steel, Medium Carbon Steel & Brass
Filler Rod Diameter d =
𝒕
𝟐
+ 𝟏, t – Thickness of the metal
PROPERTIES OF FILLER RODS
• The density of filler rod material must be nearly equal to the
density of parent metal
• Melting point of filler rod must be less than melting point of
parent material
• Viscosity of molten metal of filler rod must be low, then this
will spread over the surface of the weld bead.

FLUX
• Most oxides present on the metal surface – Joints is not cleaned properly
• Oxides formed during welding(Reaction between oxygen & Molten metal)
• This oxides have high melting point than base metal, it will prevent the
proper fusion of base metals
• To dissolve this oxides, some materials added to the welding zone, Called
Flux
• The flux reacts with oxides, form Slag. Slag has low melting point, more fluid
& lighter, will float on the surface of the molten metal.
• This slag will cover the molten metal, preventing the absorption of O2, N2
• The slag is chipped off after the weld metal has cooled & solidified.
• FLUX – Dry powder, Paste, Thick Solution or Coating of Electrode
• For Aluminum alloys – Mixture of alkaline fluorides, chlorides & Bisulphates
• For copper alloys – Mixture of sodium & potassium borates
• Ferrous metals – Mixture of Borax, Sodium carbonate & Potassium
carbonate

OXY – ACETYLENE GAS WELDING
ADVANTAGES
• The equipment is low cost, portable
• It can weld most common materials
• The gas flame temperature is lower & easily controllable
• Sheet metal operations (Automobile & Aircraft industry)
DISADVANTAGES
• Oxygen & Acetylene gases are expensive
• Safety problems involved in their handling & Storing
• Not suitable for thick sections, This flame takes long time to heat up
the metal
OXY – HYDROGEN WELDING
Temperature - 2500 °C, Low melting point materials
Oxygen & Hydrogen in the ratio of 1:2
2H2 + O2 2H2O +Heat

ARC WELDING
• An arc is generated between two conductors of electricity.
• Cathode & Anode, they are touched to establish the flow of current & then
separated by small distance.
• Very high velocity of electrons, the Kinetic energy possessed by electrons is
very high. Upon striking on the surface of anode, this Kinetic energy is
converted into Heat energy
• Temperature 5000 - 6000°C
• Heat required for melting & joining of plates is created by Electrical Arc is
called Arc Welding.
• DIRECT CURRENT STRAIGHT POLARITY (DCSP)
• Work piece – Positive Terminal – Heat generation 67% in W/P
• Electrode – Negative Terminal - Heat generation 33% in Electrode
• High Melting Point materials & High Thickness plates can be joined
• Low heat generation in electrode, deposition rate is low, So Low welding speed.
• DIRECT CURRENT REVERSE POLARITY
• Work piece – Negative Terminal – Heat generation 33% in W/P
• Electrode – Positive Terminal - Heat generation 67% in Electrode
• Low heat generation in work piece, Low melting point materials & Low thickness plates
can be joined
• High melting rate of electrode, Welding speed high.

POWER SOURCES

ARC – WELDING ELECTRODE
NON CONSUMABLE ELECTRODE
• Made up of Carbon, Graphite, Tungsten
• Carbon & Graphite – D.C Welding machine
• Tungsten – D.C as well as A.C welding machine
• Filler material added separately
• Non-consumable, it is stable & easy to maintain
CONSUMABLE ELECTRODE
• During welding, they melt & supply the filler material
BARE ELECTRODE
• Straight Polarity - Used to weld wrought iron & mild steel
• Hand Arc welding – Sticks or Rods
• Automatic Welding – Continuous Wire (Coil)
LIGHTLY COATED ELECTRODE
• Coating weight 1 – 5 % of the electrode weight
• Light coating is used to increase the Arc Stability –
COATED ELECTRODE (1 – 3 mm)
• Coating weight 15 – 30 % of the electrode weight
• Coating is brittle – only Straight stick electrodes
Slag Forming
Ingredients
Asbestos, Mica, Silica
Arc Stabilizing
Ingredients
Potassium Silicate,
Mica, Calcium oxide,
Sodium oxide
Deoxidizing
Ingredients
Cellulose, Calcium
Carbonate, Dolomite,
Starch
Binding material
Sodium Silicate,
Potassium Silicate,
Asbestos

AC WELDING MACHINE
(TRANSFORMER)
DC WELDING MACHINE
(GENERATOR)
• Efficiency more (80 -85%) • Efficiency less (30 -60%)
• Power consumption is less • Power consumption is more
• Cost of equipment is less • Cost of equipment is more
• Any terminal can be connected to work
piece or electrode
• Positive terminal - Work piece
• Negative terminal - Electrode
• Voltage higher, not safe • Voltage is low, safe operation
• Suitable for Ferrous Metals • Suitable for Ferrous & Non-Ferrous
metals
• Maintenance is difficult & Costly • Maintenance is Simple & Cheap
• Preferred for Thicker Sections • Preferred for Thin Sections

MANUAL METAL ARC WELDING
• Shielded Metal Arc Welding or Stick Welding or Manual Metal Arc Welding
• The metals are melted & joined by heating them with an arc between a
consumable coated electrode & the work piece
• The stick electrode – Core metal wire with an outer coating, Flux
• The flux assists in creating & stabilizing the arc & it provides shielding
• Flux removes impurities from molten metal in the form of Slag
• Slag gets deposited over the weld metal, protects from rapid cooling
• Without applying any external pressure, work pieces are joined by electric
arc(5000°C - 6000°C)
• Electrode supplies the filler materials.
• To get better depth of fusion, electrode is kept at 70° inclination to the
vertical, Heat Generated ∝ Current, Arc Gap ∝ Voltage
• Arc Crater – Molten metal is forced out of the pool by the electric arc

GAS TUNGSTEN ARC WELDING - TIG
• The electric arc is produced between a non-consumable electrode & the work piece
• The inert gas from the cylinder is passed through the nozzle of the welding head
around the electrode.
• Inert Gas – Argon, Helium, Nitrogen & CO2
• Electrode - Tungsten – High Melting Point, it will not melted during welding
• TIG Torch – Water cooled
• It holds the electrode tungsten
• It delivers the welding current to the tungsten via welding power cable
• It delivers the shielding gas to the TIG torch nozzle, nozzle directs this gas to
weld pool

ADVANTAGES
• Applicable for wide range of materials – Aluminum, Stainless steel,
Manganese & copper alloys
• No flux required
• Welding speed is high
DISADVANTAGES
• It emits brighter UV rays
• Equipment is costly
• Transfer of molten tungsten from the electrode to the weld
APPLICATIONS
• Thin parts & Sheet metals can be welded easily
• TIG welding is widely used in the automotive industry. TIG strategies are
known to reduce corrosion over time, so car fenders are frequently welded
in this way to avoid rust.
GAS TUNGSTEN ARC WELDING - TIG

GAS METAL ARC WELDING - MIG
• The electric arc is produced between a consumable metal wire electrode & the
work piece
• During welding, the arc & welding zone are surrounded by an Inert Gas – Argon,
Helium & CO2
• Consumable metal wire electrode – Feed Unit - Same chemical composition of
Base metal
• The operator control – Torch Positioning & Speed
• Power Source – D.C Generator or A.C Transformer can be used
• D.C power source preferred, 100A – 400A depends on the diameter of wire
• Welding Head – Air or Water cooled
• Thick plates can be welded
• Materials to be Weld – Carbon steel, Stainless Steel, Aluminum with special feeder

ADVANTAGES
• No flux is required, there is no slag to remove
• High welding speed
• Simple welding process, Training the operator is easy
• Easy automation possible
DISADVANTAGES
• The process is expensive
• More maintenance
• Outdoor welding is not easy due to wind, affect the shielding gas
APPLICATIONS
• Automotive repair
• Used to reinforce the surface of a worn out railroad track
GAS METAL ARC WELDING - MIG

SUBMERGED ARC WELDING
• In this process, joining is produced by heating with an arc between a bare wire
electrode & the work piece
• Flux – To avoid the oxidation reaction, Flux along with coated electrodes, the
oxidation reaction may not be completely removed.
• The complete welding setup is dipped in the flux powder.
• The arc is not visible outside.
• The metal electrode is continuously fed from the reel by moving head
• The flux powder is fed in front of the moving head, supplied from a hopper
• Flux powder – Silica, Metal oxide – Not only protects the weld surface – Act as a
Deoxidizer & Scavenger

ADVANTAGES
• Wire electrodes are inexpensive
• Weld spatters are eliminated
• Nearly, 100% deposition efficiency is achieved
DISADVANTAGES
• It can not be used for works which is inclined or vertical
• Slag has to be removed continuously after it has melted in order to
avoid entrapment between passes.
APPLICATION
• Used in heavy steel plate fabrication work – Structural shapes
• Used in Pressure Vessels, Boilers, Tanks, Nuclear reactors
• Fabrication of Trusses & Beams
SUBMERGED ARC WELDING

PLASMA ARC WELDING
• It is a process where a coalescence is produced by the heat which is
developed from a special setup between a tungsten alloy electrode and the
water cooled nozzle (Non Transferred ARC ) or between a tungsten alloy
electrode and the job (Transferred ARC).
• One gas is used to form the Arc plasma.
• Second gas is used to shield the arc plasma.
Current: 50-350A, Voltage: 27-31V,Plasma Arc Temp - 28000 °C

• The plasma torch contains a tungsten electrode fixed in a nozzle which is
made of copper . The arc is started between the electrode and the tip of
nozzle. Then the arc or flame is transferred to the material to be welded.
• The small opening forces the gas to travel through a constricted opening or
orifice. This concentrates the heat to smaller area. This ability allows welder
to produce a very high quality weld.
• Non transferred arc mode: In Non transferred arc mode the current flow is
from the electrode inside the torch to the nozzle containing the orifice and
back to the power supply. It is used for plasma spraying.(Metal Plating)
• Transferred arc mode: In transferred arc mode the current is transferred
from the tungsten electrode inside the welding torch through the orifice to
the workpiece and back to power supply. It is used in welding metals.
• This process gives higher welds speed ,less distortion, more consistent
welds ,less spatter and more control on the weld area.
PLASMA ARC WELDING

ELECTRO SLAG WELDING
• It is a welding process where coalescence is produced by molten slag which melts
the filler material & the surface of the workpieces to be welded.
• An arc is established between the steel backing plate & the electrode wire only at the
very beginning of operation, The arc heats the flux & melts it to produce the slag
• Sufficient thick layer of molten slag is formed, Arc action stops & then Electric current
passes from the electrode to the workpiece through the conductive slag pool.
• The temperature of molten slag is about 1700 - 1900°C. this heat is used to fuse the
edges of the workpiece & the electrode
• The liquid metal coming from the welding electrode & the heated base metal collects
in a pool under the slag bath & slowly solidifies.
• It is a progressive process of melting & solidification from the bottom upward.

ADVANTAGES
• Extremely high deposition rates
• Steel plates with higher thickness can be welded (up to
450mm)
• Flux consumption is very low
• During the process, as no arc exists, No spattering
occurs
DISADVANTAGES
• It is difficult to close cylindrical welds
• Carried out in vertical uphill position
• Uneconomical for joints below 60 mm
APPLICATION
• Heavy plates, Forgings & Castings can be welded
ELECTRO SLAG WELDING

RESISTANCE WELDING
• In this process, the coalescence is produced by the heat obtained from
resistance of the work to the electric current in a circuit and by the
application of pressure & without the use of a filler metal
• H ∝ I2Rt
• H – Heat Generated in Joules, I – Current in Amperes, R – Resistance in
ohms, t – time for which the current flows, in seconds
• Large electrical current = 3,000 – 1,00,000 Amp.
• Voltage = 1 – 25 Volts
• Low resistance copper Electrode
• High resistance at the joint of metals
• The welding of overlapping pieces of
metal at small points by application of
pressure and electric current" creates
a pool of molten metal that quickly
cools and solidifies into a round joint
known as a "nugget

ADVANTAGES
• Filler rod is not required
• Less skilled workers are required
• Both similar & Dissimilar metals can be welded
• Rate of production is fast
DISADVANTAGES
• Initial cost of equipment is high
• Workpieces of higher thickness cannot be welded
• Special surface preparation required
APPLICATION
• Joining of sheets, bars, rods & tubes
• Welding of Aircraft & automobile parts
RESISTANCE WELDING

RESISTANCE SPOT WELDING
• It is a resistance welding process in which overlapping sheets are joined by local
fusion at one or more spots by the heat generated by resistance to the flow of
electric current through workpieces
• Joining – Up to 3 mm thickness
• Current = 3,000 – 1,00,000 Amp. for few seconds as per the nature of materials &
its thickness
• Temperature = 815 - 930°C, H ∝ I2Rt
ADVANTAGES – Low cost of the machine, Less skilled labor, Edge preparation not
required, Welding speed is high
APPLICATION – Used in Automobile & Aircraft industry

• It is a resistance welding process where coalescence at the surfaces is
produced by the heat obtained by resistance to the flow of electric current
through the work parts held together under the pressure of electrodes.
• It is a series of overlapping resistance spot welds made progressively
along a joint by rotating the circular electrode
RESISTANCE SEAM WELDING
• The workpiece is placed between the
wheels(electrodes) which serve as conductors
for producing continuous welds.
• For increasing the speed of operation, a coolant
is applied to conserve the electrodes & cool the
work piece rapidly
ADVANTAGES
• It can produce gas tight & liquid tight joints
• A single seam weld or several parallel seams
may be produced
DISADVANTAGES
• Performed only a straight or Uniform curved line
• Difficult to weld workpieces with thickness
greater than 3 mm
H ∝ I2Rt

PROJECTION WELDING
• It is a resistance welding process where coalescence is produced by the
heat obtained from resistance to flow of electric current through the
workpiece parts held together under pressure by electrodes.
• The resulting welds are localized at predetermined points by projections
• The flattening out these projections under pressure, results in good welds
at all points of contact.

RESISTANCE BUTT WELDING
UPSET BUTT WELDING
• The two workpieces to be welded
are first brought together under
pressure.
• Current is then applied, heating the
contact area enough to allow the
applied pressure to forge the parts
together.
FLASH BUTT WELDING
• First stage - Flashing action. The
current applied to the workpieces
produces a flashing or arcing across the
interface of the two butting ends of the
material.
• The flashing action increases to the
point of bringing the material to a plastic
state.
• Second stage - the upset or forging
action. The two ends of the workpieces
are then brought together with a very
high force sufficient enough to cause
the material to upset.
H ∝ I2Rt

• It is a resistance welding process where coalescence is produced
simultaneously over the entire area of abutting surfaces by heat obtained
from an arc produced by a rapid discharge of electrical energy.
• Light force or pressure is applied at the ends of two workpieces.
• D.C Voltage is applied, ionizes the air gap between the workpieces &
makes the flow of current. The arc will be generated between the faces of
workpieces.
PERCUSSION WELDING
H ∝ I2Rt

FRICTION WELDING
• In this welding process, the friction is used to generate heat at the interference
surface. This heat is further used to join two work pieces by applying external
pressure at the surface of workpiece.
• Firstly one part of the workpiece is fixed on the chuck which is stationary and the
other part is placed in rotor. Then the rotor is rotated at high speed with the help of an
external power source.
• Now a high pressure is applied on the stationary workpiece which rubs against the
rotating workpiece and generates a high friction . This friction generates heat at the
contact of both the workpieces . It is applied until the plastic forming temperature is
achieved.
• The rotor stops when the pressure is applied increasingly until the whole weld is
formed.

FRICTION WELDING PARAMETERS
• RELATIVE SPEED
• It will decide the maximum interface temperature & the final joint
microstructure
• Low speed – Insufficient heating
• High Speed – Overheated Structures
• FRICTION PRESSURE
• It determines the thermal condition established in weld zone
• The rate at which metal is extruded radially to form an upset
• TIME FOR HEATING
• To ensure that the components surfaces are cleaned by friction & the
weld zone temperature is raised to achieve the required plasticity
• FORGE PRESSURE
• It is selected with respect to hot strength of materials
• Sufficient pressure must be used to heat the weld region & to join the
surfaces

ADVANTAGES
• Produce high quality of welds in a short period of time.
• No filler metal and flux is used in this process.
• It consumes less time than any other process.
• In this process less skill is required to use it.
• Less area is affected by the heat.
DISADVANTAGES
• Preparation of work piece is more critical than making a weld.
• Cost of setup of machine is very high.
• It can only be used for smaller parts of machines , big parts are not
compatible in it.
APPLICATION
• It is used to make tubes and shafts.
• Used in electrical industries for welding copper and aluminum equipment’s.
• It is used to weld Gear levers, drill bits, connecting rod etc.
FRICTION WELDING

FRICTION STIR WELDING(FSW)
• FSW is a solid-state joining process. It works by using a non-consumable tool, which
is rotated and plunged into the interface of two workpieces.
• The tool is then moved through the interface and the frictional heat causes the
material to heat and soften.
• The rotating tool then mechanically mixes the softened material to produce a solid-
state bond.
ADVANTAGES
• Remaining in the solid-state, avoiding many of the defects associated with melting
and solidification during fusion welding, such as pores and solidification cracks.
• The peak temperatures are lower, Producing superior mechanical properties.
• No filler metals, flux or shielding gas are required.
• Fully automated, making the process highly repeatable.

• First both the work plates are clamped together same as in butt joint. These both
plate’s weldable surfaces are in contact with one another.
• Now a rotating tool pin is inserted into work pieces at the interface surfaces until tool
shoulder touched the work piece. This will deform the material plastically due to
heating by friction force.
• This is state of the joining process in which, inter molecular diffusion will deform the
material plastically due to heating by friction force.
• Now the rotating tool is move forward along the joint line. This will form a joint behind
the tool.
• The tool continuously move until the whole weld is form. After the joining process,
tool is separated from the work piece. The hole created by tool pin remains in the
welding plates.
DISADVANTAGES
• It creates a visible hole in welding plates.
• High initial or setup cost.
• It is less flexible compare to arc welding process.
• FSW cannot make filler joints.
APPLICATION
• Aerospace - Fuselage and wing structures
• Automobile - Wheel Rims, Engine chassis cradles
FRICTION STIR WELDING(FSW)

DIFFUSION WELDING
• It is a Solid State Welding process where coalescence of the surface is
produced by the application of pressure at elevated temperatures on
carefully cleaned surfaces, joining by Atomic diffusion.
• It can join Similar or Dissimilar materials.
• The individual peak & Valley in the workpiece are deformed by the
application of increasing pressure.
• In this place, the surface move together under shear, the films are diffused,
metal to metal contact takes place.

EXPLOSIVE WELDING
• Base plate (Backer): This plate remains stationary it provides support and it helps in
reducing or minimizing the damage at the time of detonation.
• Flyer plate (Clad): This plate gets welded on the base plate. It is situated at the
parallel of the base plate or at the angle at which the base plate is inclined.
• Standoff distance: It is very important factor considered for explosive welding. It is the
distance between the flyer plate and the base plate. Generally standoff distance is
taken as double thickness of it.
• Buffer plate: This plate is used to reduce the effect of explosion on upper surface of
flyer plate. This protects the flyer plate from any damage due to explosion.
• Explosives: they are place on the buffer plate or directly on the clad. It produces
explosion for the welding.
APPLICATION - Joining of dissimilar metals can be done for eg – Aluminium to steel, Cu
to stainless steel, Titanium alloys to Cr – Ni steel, Tungsten to Steel, etc.

• The explosive impulse provides high normal pressure & Small sliding pressure between
plates
• At the point of impact, a high instantaneous pressure is generated which is large as
compared to shear strength of the materials.
• This creates the fresh surface free from oxides & Adhere
• Explosives – Tetryl, TNT, RDX,PETN
ADVANTAGES
• This process is very simple; no high skills are required to operate it.
• Extremely large surfaces can be bonded or welded.
• There is no effect on parent properties of the metal after welding, they are unchanged.
• Very small quantity of explosives is used in explosive welding process.
• No part of the work piece gets heated like in other methods of welding.
DISADVANTAGES
• It can weld only ductile metal with high toughness.
• The geometries welded are limited to simple designs– flat, cylindrical, conical.
• Higher safety precautions involved due to explosives used.
• The use of explosives in industrial areas will be restricted by the noise and ground
vibrations caused by the explosion.
EXPLOSIVE WELDING

• The two plastic pieces to be joined is
assembled in the nest (anvil or fixture)
• The horn is made to contact at upper part of the
piece.
• A pressure is applied on the two pieces against
the fixture. The pressure is applied through the
pneumatic or electric driven press.
• Horn is vibrated vertically at very high
frequency (20 kHz to 40 kHz), transmits the
mechanical vibration to the two plastic pieces.
This generates heat energy at contact tip of the
two surfaces and melts them.
• A clamping force is applied on the two pieces
for a predetermined amount of time to fuse
them together to form a strong weld on cooling
and solidification.
• After solidification, the clamping force is
removed and horn retracted. The welded plastic
part is taken out of the fixture as one piece.
ULTRASONIC WELDING
HORN OR SONOTRODE
It vibrates at high frequency
and transmits the mechanical
vibration to the two pieces to
be welded. It also modifies the
amplitude mechanically. It
takes the shape of the part.
The horn is made of titanium
or aluminum.

ULTRASONIC WELDING
ADVANTAGES
• It is fast welding process.
• It can be easily automated.
• It produces clean and precise joint.
• It produces low thermal impact on the materials.
DISADVANTAGES
• It cannot be used to produce large joints (greater than 250 x 300 mm).
• It requires especially designed joints, so it can make tip contact during welding
process.
• High tooling cost for the fixtures.
• Ultrasonic welding process is restricted to the lap joints.
APPLICATION
• Computer and Electrical Industries: Here it is used to join wired connections and to
create connections in small delicate circuits.
• It is used for packaging dangerous materials like explosives, fireworks and
chemical.
• Items such as anesthesia filters, arterial filters, blood filters, dialysis tubes

THERMIT WELDING
• First both the work pieces which are needed to be weld, are cleaned.
• Now a wax pattern is created around the weld cavity.
• A moulding flask is fixed around the joint with the help of mold handle
clamp. This wax pattern is situated at the middle of the flask.
• Now the molding sand rammed around the wax pattern to create mold in
which the molten metal will pour. This mold involves all necessary parts like
runner, riser, pouring basin, gating system, opening for wax pattern etc.
same as involves in casting.
• Now this mold is heated to remove wax pattern. The wax is melted and run
off from the wax pattern outlet prepared at bottom of the sand mold.
• Now the thermite mixture is taken into the refractory crucible. The ignite
powder is placed over the mixture. (1100°C)
• This will start the thermite reaction (2760°C) which liberates a huge amount
of heat. This reaction form molten state of iron which flows from crucible to
sand mould.
• This molten metal fills the weld cavity and fuses the parent metal to make a
permanent joint. This will allow to cool down. After proper cooling, flask is
removed from the joint, machining is done to remove the welding burr or
other extra metal.

ADVANTAGES
• It is simple and easy process.
• Low setup cost.
• Thermite welding can be done at site where casting is impossible.
DISADVANTAGES
• It is used for limited metals like iron and copper.
• It is uneconomical for welding light parts.
APPLICATION
• It is mostly used to weld railroad at the site.
• It is used to joint pipe, thick plate etc. where power supply is not available.
THERMIT WELDING
Thermite Mixture – Aluminum & Iron Oxide
Ignite Powder – Barium Peroxide
8 Al + 3 Fe2O3 4 Al2O3 + 9 Fe +Heat
Molten Iron at Bottom, Aluminum Oxide

ELECTRON BEAM WELDING
• It is a fusion welding process in which
a high velocity electron beam is used
to join two metals together.
• It works on the principle that when a
high velocity beam of electron that has
Kinetic energy strikes the two metal
pieces, the kinetic energy of the
electron transformed into heat.
• The intensity of heat produced is so
much that it melts the two metal pieces
and fuse them together to form a
strong weld.
• The whole process is carried out in
vacuum chamber to prevent it from
contamination.
• Velocity of Electrons 50000 – 200000
km/s

ELECTRON GUN - Used to generate, accelerates and align the electron
beam in a desired direction and spots on the workpiece.
• In self accelerated gun, the acceleration of electron takes by applying
potential difference between cathode and anode.
• Work accelerated gun, the acceleration of the electron takes place by
applying the potential difference between the cathode & workpiece(Anode).
• Cathode (Emitter or Filament): It emits the electron.
Anode: It is a positively charged Electrode and attracts the electron
produced by the cathode.
• For high voltage equipment’s, the potential difference ranges from 70 kV to
150 kV, Small voltage equipment it ranges from 15 – 30 kV.
• Grid Cup: It is used to control the electron beam. It stops the divergence of
electrons produced by the cathode.
• Focusing Unit:
• The magnetic lens focuses the electron beam on the workpiece.
• Deflector coil is used to deflect or guide the beam to the desired
locations. The extent of deflection can be varied by changing the
amount of dc voltage across the deflector plate.

ADVANTAGES
• High welding speed.
• Welding of dissimilar metal can be done.
• High weld quality and precision.
• Materials with high welding temperature can be welded easily.
DISADVANTAGES
• Cost of equipment is very high.
• High skilled operator is required to operate it.
• High vacuum is required.
• High safety measures are need to work with it.
APPLICATION
• It is used in aerospace industries for manufacturing jet components, parts
of structures, transmission parts and sensors.
• It used in electrical and electronical industries to manufactures parts of
copper structures.
• It is used in space industries to build titanium tanks and sensors.

LASER BEAM WELDING
• It is a fusion welding process in which two metal pieces are joined together by
the use of laser.
• The laser beams have enough energy and when it strikes the metal pieces
produces heat that melts the material from the two metal pieces and fills the
cavity. After cooling a strong weld is formed between the two pieces.
• Gas lasers: It uses mixtures of gases as lasing medium to produce laser.
Mixtures of gases such as nitrogen, helium and CO2 are used as lasing
medium.
• Solid-state laser: it uses several solid media such as synthetic ruby crystal
(chromium in aluminum oxide), Neodymium in yttrium aluminum garnet (Nd-
YAG , most commonly used).
• Fiber laser: The lasing medium in this type of laser is optical fiber itself.

• A high voltage power supply is applied on the laser machine. This starts the
flash lamps of the machine and it emits light photons.
• The energy of the light photon is absorbed by the atoms of ruby crystal and
electrons get excited to their higher energy level. When they return back to
their ground state (lower Energy state) they emit a photon of light.
• This light photon again stimulates the excited electrons of the atom and
produces two photons. This process keeps continue and we get a
concentrated laser beam.
• Lens are used to focus the laser to the area where welding is needed.
• As the laser beam strikes the cavity between the two metal pieces to be
joined, it melts the base metal from both the pieces and fuses them together.
ADVANTAGES
• No electrode is required.
• No tool wears because it is a non-contact process.
• The time taken for welding thick section is reduced.
DISADVANTAGES
• Initial cost is high. The welding thickness is limited to 19 mm.
• High maintenance cost.
• Due to rapid rate of cooling, cracks may be produced in some metals.
LASER BEAM WELDING

LIQUID – SOLID STATE BONDING
The joint is made by distributing the molten
filler metal between the closely fitted
surfaces of the parts, without melting the
base metals
BRAZING & SOLDERING
Based on the melting point of filler material
• BRAZING – Above 427°C
• Filler Material (Spelter) – Brass
• Brazing is used to cover a fine gap
between the metal parts to be joined.
• Brazing creates a tight fit between the
metal parts joined.
• SOLDERING – Below 427°C
• Filler Material – 60:40, Tin:Lead Alloy
• When the gap between the metals parts
is not a fine gap, soldering can be used.
• Soldering is a softer metal-joining
process where the metals parts are not
held very tightly.
APPLICATION
• Manufacture of Automobile
radiator
• Plate & Tube Heat Exchanger
• Fans, Joining Wires

STEPS IN BRAZING
• The surfaces to be joined are cleaned(Rinsed & Dried) & fitted closely
together
• A flux is applied to all surfaces where the filler metal is to flow
• Used to prevent oxidation of the base metal & the filler metal
• Borax & Boric Acid
• The joint is heated to Brazing temperature, small amount of filler material is
added to fill the joint,
• Filler metal is preplaced before heating or Applied after reaching the
brazing temp.
• For capillary action to exist, Clearance between the parts being joined
(0.03 to 0.05mm) – Wider clearance leads to reduced strength.
ADVANTAGES
• Corrosion resistance joint obtained
• It preserves metallurgical characteristics of material because low
temperature
DISADVANTAGES
• Joints are not effective at higher temperature
• Need a flux during brazing, & Flux residue must be removed
• Metal to join must very close to ensure capillary action of molten filler metal

• Two parts are joined by the use of a molten filler metal whose melting point is
below the melting point (Solidus) of Base metal (Below 427°C)
• Surface preparation involves cleaning them by chemically & mechanically
• Fitting the surfaces closely to each other
• Covering the clean surface with Flux
• Clearance in joint – 0.05 – 0.20mm
• Flux - Corrosive – Zinc Chloride, Mixture of Zinc Chloride & Aluminum
Chloride – Washed off after Soldering
• Non corrosive type – Rosin, Rosin + Alcohal
ADVANTAGES
• This can be operated at low temperature.
• Base metal does not melt.
• Any metals, non-metals can be joined by this process
DISADVANTAGES
• Strength of joint is less - It is not useful at Long length weldings.
• This is not useful when joint works under high temperature.
STEPS IN SOLDERING

WELD DEFECTS
CRACKS - most unwanted defect of all the other welding defects, At the surface or
inside weld material
Hot Crack – It is more prominent during crystallization of weld joints where the
temperature can rise more than 10,000-degree Celsius.
Cold Crack – This type of crack occurs at the end of the welding process where the
temperature is quite low. Sometimes cold crack is visible several hours after welding
or even after few days.
CAUSES FOR CRACKS
1. Poor ductility of the given base metal.
2. The presence of residual stress can cause a crack on the weld metal.
3. The rigidity of the joint which makes it difficult to expand or contract the metals.
POROSITY
• Porosity in the condition in which the gas or small bubbles gets trapped in the
welded zone.
1. It occurs when the electrode is not coated properly.
2. Using a longer arc may also increase its chances.
3. Increased welding currents. - Rust or oil on the welding surface.

UNDERCUT
• When the base of metal melts away from the weld zone, then a groove is formed
in the shape of a notch, then this type of defect is known as Undercut.
• It reduces the fatigue strength of the joint.
1. If the arc voltage is very high then this defect may occur.
2. If we use the wrong electrode or if the angle of the electrode is wrong, then also
the defect may form.
SPATTER
When some metal drops are expelled from the weld and remain stuck to the
surface.
1. High Welding current can cause this defect.
2. The longer the arc the more chances of getting this defect.
3. Incorrect polarity.
WELD DEFECTS

• Incomplete fusion occurs when the welder does not accurately weld the
material and the metal pre solidifies which leads to a gap which is not filled
with the molten metal.
1. It occurs because of the low heat input.
2. When the weld pool is very large and runs ahead of the arc.
3. Incorrect electrode and torch angle may also lead to incomplete fusion.
Incomplete penetration occur only in the butt welds where the groove of the
metal is not filled completely.
1. Less deposition of the weld metal
2. Use of improper size of the electrode
3. Improper welding technique
WELD DEFECTS

OVERLAP
• When the weld face extends beyond the weld toe, then this defect occurs. In
this condition the weld metal rolls and forms an angle less than 90 degrees.
1. Improper welding technique.
2. By using large electrodes this defect may occur.
3. High welding current
SLAG INCLUSION
• If there is any slag in the weld, then it affects the toughness and metal
weldability of the given material. This decreases the structural performance
of the weld material.
1. If the welding current density is very small, as it does not provide the
required amount of heat for melting the metal surface.
2. If the welding speed is too fast then also slag may occur.
3. If the edge of the weld surface is not cleaned properly then slag may form.
4. Improper welding angle and travel rate of welding rod.
WELD DEFECTS

Welding - Joining Processes

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