By: Mr. Sunil Kumar Ojha
Mechanical Engineering Department
JRE Group of Institutions Greater Noida
Joining elements together, which shapes a final
product. Assembly process can be made by
human workers (uneducated but skilled) or by
specialized machines and robots.
Example: Cars, computers, engines, cellophane
Aspect of manufacturing:
1.Impossible to manufacture as a single product
e.g chairs, computer, etc.
2.More economical to manufacture as individual components, which
are then assembled
3.For maintenance or replacement purposes
e.g. car accessories and engines.
4.Different materials due to different properties requirement
e.g. cooking pots and pans.
5.Ease and less costly of transportation
2. Soldering and Brazing
3. Mechanical Fastening
4. Adhesive Bonding
But our presentation will focus on welding
◦ Screwed fasteners, rivets,
Brazing and Soldering
◦ Base metal does not fuse.
◦ Molten filler drawn into close-fit joints by capillary
action (surface tension forces).
◦ Brazing filler melts >450 C, solder <450 C
Introduction to welding
A joint produced by heat or pressure or both
So there is continuity of material.
Filler (if used) has a melting temperature
close to the base material
Introduction to welding
welding is the process of joining in which heat is use
d to join similar or dis-similar metals with or without t
he application of pressure and filler metal.
◦ Welding is a materials joining process which produces
coalescence of materials by heating them to suitable
temperatures with or without the application of pressure
or by the application of pressure alone, and with or
without the use of filler material.
◦ Welding is used for making permanent joints.
◦ It is used in the manufacture of automobile bodies, aircraft
frames, railway wagons, machine frames, structural works,
tanks, furniture, boilers, general repair work and ship
Buildings and bridges structures;
Automotive, ship and aircraft constructions;
Tanks and vessels;
Strong and tight joining;
Simplicity of welded structures design;
Welding processes may be mechanized and
Internal stresses, distortions and changes of micro-
structure in the weld region;
Harmful effects: light, ultra violate radiation, fumes,
Solid phase welding
◦ Carried out below the melting point without filler
◦ Pressure often used
◦ Union is often by plastic flow
Fusion welding or Liquid Phase Welding
◦ Welding in the liquid state with no pressure
◦ Union is by molten metal bridging
Introduction to welding
1) OXYFUEL-GAS WELDING (OFW)
- OFW uses a fuel gas combined with oxygen to produce flame
- Function of the flame - act as a source of the heat to melt the
metals at the joint.
- Common gas welding process uses acetylene (oxyacetylene gas
welding - OAW).
-Application: structural sheet metal fabrication, automotive bodies,
and various repair work.
- OAW process utilizes the heat generated by the
combustion of acetylene gas (C2H2)in a mixture
- These primary combustion process, occurs in the inner
core of the flame, involves the reaction of:
C2H2+ O---->2CO + H2+ Heat (1/3 total heat generated in
- The secondary combustion process involves further burning
of hydrogen and carbon monoxide:
2CO + H2+1.5O2------>2CO2+ H2O + Heat (2/3 of the total
a. General view of oxy torch
b. Cross-section of a torch
used in oxyacetylene
welding. The acetelyne
valve is opened first; the
gas is lit with spark
lighter or a pilot light;
then the oxygen valve is
opened and the flame
c. Basic equipment used in
oxyfuel-gas welding. All
acetylene fittings are left
handed while oxygen are
right handed. Oxygen
regulators are usually
painted green, acetelyne
1. Neutral - ratio 1:1 , no excess oxygen
2. Oxidizing - greater oxygen supply (excess oxygen),
harmful for steel due to oxidizes. Only suit for nonferrous
metal like copper & copper based alloys.
3. Carburizing - insuffientof oxygen (excess acetytelene),
low temperature, thus suitfor applications requiring low heat
like brazing, soldering, flame hardening.
1. To supply additional metal to the weld zone during
2. Filler rods or wire and may be coated by flux
3. The purpose of flux is to retard oxidation of the welded
Fusion Welding Process
2) PRESSURE GAS WELDING
- Involved with two components starts by heating the
- Once when the interface begins to melt, the torch is
- A force is applied to press both components together and
maintain until the interface solidifies.
- The joined end with the occurrence of a flash.
3) ARC-WELDING PROCESSES
- In arc welding, the heat is obtained from electrical energy – by
using AC or a DC power supply.
- The process involved can be either consumable or non-
- An arc is produced between the tip of electrode and the work
piece which need to be welded.
- The arc produces temperatures approximately 30,00 degrees
◦ Most efficient way to join
◦ Lowest-cost joining
◦ Affords lighter weight
through better utilization
◦ Joins all commercial
◦ Provides design flexibility
Manually applied, therefore
high labor cost.
Need high energy causing
Not convenient for
Defects are hard to detect
a.) NON CONSUMABLE ELECTRODE
- The electrode is a tungsten electrode type.
- Need externally supplied shielding gas because of the
high temperature involved in order to prevent oxidation of
the weld zone.
- DC is used and the polarity is important.
- For straight polarity which is also known as direct-current
electrode negative (DCEN); the workpiece is positve (anode) ,
while the electrode is negative (cathode).
- It will produce welds that are narrow and deep.
- For reverse polarity which is also known as direct-current
electrode positive (DECP); the workpiece is negative and
- In this process, weld penetration is less, and the weld zone is
shallower and wider.
i) GAS TUNGSTEN-WELDING (GTAW)
- Also known as TIG welding
- Suitable for thin metals.
- This process is expensive because of the cost of inert gas
- Provides welds with very high quality and surface finish
- Filler metal is supplied from a filler wire
- The shielding gas is usually argon or helium
- This filler metals are similar to the metal that need to be
welded, and flux is not used.
- In this operation, tungsten electrode is not consumed,
therefore a constant and stable arc gap is maintained at a
constant current level.
- Power supply either 200A DC or 500A AC; depending on
the metals to be welded.
- Generally, AC is suitable for aluminum and magnesium.
- Thorium or zirconium may be used in the tungsten
electrodes to improve the electron emission characteristics.
- Contamination of the tungsten electrode by molten metal
ca cause discontinuities in the weld.
- Therefore, contact between the electrode with the molten
metal pool should be avoided.
Non Consumable Electrode
ii) PLASMA-ARC WELDING (PAW)
- In this welding operation, a concentrated plasma arc is
produced and directed towards the weld area.
- The arc is stable and the temperature can reaches up to
33,000 degrees celsius.
- PAW has less thermal distortion, and higher energy
concentration – permitting deeper and narrower welds.
- Plasma: it is an ionized hot gas composed of nearly equal
number of electrons and ions.
- This plasma initiated between the tungsten electrode and
the small orifice by a low current pilot arc.
- Operating current: usually below 100A.
- Filler metal is fed into the arc during welding process.
- There are two methods of plasma-arc welding:
a) Transferred-arc method
- Work piece being welded is part of the electrical
circuit. The arc transfers from the electrode to
the work piece.
b) Nontransferred method
- The arc occurs between the electrode and the
nozzle. The heat is carried to the workpiece by
the plasma gas.
- Welding speeds from 120 to 1000 mm/min.
- Can be welded with part thickness less than 6mm.
i) SHIELDING METAL-ARC WELDING
- Old method , simplest, held manually.
- Most of all industries and maintenance welding currently
performed with this process.
- The electric arc is generated by touching the tip of a
coated electrode against the workpiece.
- Need to have a sufficient distance and movement to
maintain the arc.
- The heat generated, melts a portion of the electrode tip, its
coating, and the base metal in the intermediate arc area.
- The molten metal consists of a mixture of the base metal
(work piece), the electrode metal, and substance from the
coating on the electrode; thus this mixture forms the weld
when it solidifies.
- The electrode coating deoxidizes the weld area and
provides a shielding gas to protect it from oxygen in the
- The equipment consists of a power supply, cables and
- Power supply: can be either DCor AC, ranges between 50 to
- For sheet metal welding, DC is preferred because of the
steady arc produces.
ii) SUBMERGED-ARC WELDING (SAW)
- The weld arc is shielded by a granular flux consisting of lime,
silica, manganese oxide,calcium flouride.
- The flux is fed into the weld zone from a hopper by gravity
flow through a nozzle.
- The thick layer of flux completely cover s the molten metal
and it prevents from spatterand sparks.
- The flux also acts as a thermal insulator by promoting deep
penetration of heat into theworkpiece.
- The consumable electrode is a coil of bare round wire 1.5 to
10 mm in diameter; andfed automatically through a tube
which is called welding gun.
- Electric current: range between 300 to 2000 A.
- Power supply: single or three phase power point; rating up to
- Due to flux is a gravity fed type; therefore this welding
process is limited largely towelds into flat or horizontal
- Circular weld can be made on pipes or cylinders ²provided
that they are rotated during welding process.
-Suitable for carbon and alloy steel and stainless steel sheet
- Welding speeds: as high as 5 m/min.
iii) GAS METAL-ARC WELDING
- Also known as metal inert-gas (MIG).
- The weld area is shielded by an effectively inert atmosphere
of argon, helium, carbondioxide, or other various gas
- The temperatures generated are relatively low.
- Suitable only for thin sheets which is less than 6mm.
-The consumable bare wire is fed automatically through a
nozzle into the weld arccontrolled by wire-feed drive motor.
-There are 3 types of GMAW process:
a) SPRAY TRANSFER
- Small size of molten metal droplets from the electrode are
transferred to the weld area at a rate of several hundred
droplets per second.
- The transfer is spatter free and very stable.
- Using high DC current and voltages with large diameter
- The electrodes are used with argon or an argon rich gas
mixture act as a shielding gas.
Types of Gas-Metal Arc Process
b) GLOBULAR TRANSFER
- Utilizes with carbon-dioxide-rich gases, and globules are
propelled by the forces of the electric-arc transfer of a metal,
resulting in considerable spatter.
- High welding current are used - greater weld penetration
and higher welding speed
c) SHORT CIRCUITING
- The metal is transferred in individual droplets, as the
electrode tip touches the molten weldmetal and short circuits.
- Low currents and voltages are utilized.
- Electrodes are made from small-diameter wire.
- Power required: § 2 kW.
Types of Gas-Metal Arc Process
iv) ELECTRON BEAM WELDING
- Can be welded almost any metal; butt or lap welded and the
thicknesses up to 150mm.
- The thickness of the workpiececan range from foil to plate.
- Generally, there is no involvement of shielding gas, flux, or
- Distortion and shrinkage in the weld area is minimal.
- Heat is generated by high velocity narrow-beam electrons.
- Capacity of electron guns range up to 100 kW.
- The kinetic energy of the electrons is converted into heat
as they strike the workpiece.
- Required special equipment to focus the beam on
the workpiece, typically in vacuum.
- The higher the vacuum, the more the beam penetrates, and
the greater is the depth-to width ratio, range between 10 and
- Sizes of the welds are much smaller compared to
- Parameters can be controlled accurately at welding speeds
as high as 12 m/min; thiscan be done by using automation
and servo motor.
v) LASER-BEAM WELDING
- Utilizes a high power laser beam as the source of heat.
- The beam can focused onto a very small area, and due to
this it has high energy density and deep penetrating
- This process is suitable for welding deep and narrow joints
with depth-to-width ratios ranging from 4 to 10.
- The laser beam may be pulsed for a application such as the
spot welding of thinmaterials with power level up to 100 kW.
- Minimum shrinkage and distortion, good strength and
generally are ductile and free ofporosity.
- Can be automated to be used on a variety of materials with
thicknesses up to 25mm.
- Typical metals and alloys welded: aluminum, titanium,
ferrous metals, copper.
- Welding speeds: range from 2.5 m/min to as high as 80
m/min for thin metals.
Advantages of LBW over EBW:
Laser beams can be shaped, manipulated, and focused
optically by using fiber optics, therefore the process can be
automated easily.The beams do not generate x-rays.
The quality of the weld is better than in EBW with less
tendency for incomplete fusion, spatter, porosity, and less
Example of laser Welding: laser welding of razor blades
Pressure is applied to
the workpieces through
dies or rolls
Preferably both work
pieces should be ductile
The work pieces should
Can not join dissimilar
Fig: The roll bonding or cladding process
Surfaces of the two
subjected to a static
forces and oscillating
Produces a strong,
Versatile and reliable
for joining metals
Fig: a) Components of an ultrasonic welding machine
for lap welds.The lateral vibration of the tool tip c
ause plastic deformation and bonding at the inte
rface of the work piece b)Ultrasonic some weldi
ng using a roller c)An ultrasonically welded part
Developed in the 1940’s
Parts are circular in shape
Can be used to join a wide variety of materials
Fig: Sequence of operation in the friction welding process 1)Left-hand component is rotated at high speed. 2) Ri
ght-hand component is brought into contact under an axial force 3)Axial force is increased;the flash begins to for
m 4) Left-hand component stops rotating;weld is completed.The flash can subsequently be removed by machini
ng or grinding
Process can be fully automated
Can weld solid steel bars up to 250mm in outside diameter
Fig:Shape of friction zone in friction welding,as a function of the force applied and the rotational speed
Developed in the early 1900’s
A process in which the heat required for welding
is produced by means of electrical resistance
across the two components
RW does not requiring the following:
◦ Consumable electrodes
◦ Shield gases
RSW uses the tips of two opposing solid cylindrical electrodes
Pressure is applied to the lap joint until the current is turned
off in order to obtain a strong weld
Fig: (a) Sequence in the resistance spot welding
Surfaces should be clean
Accurate control of and timing of electric current and of
pressure are essential in resistance welding
Fig: b)Cross-section of a spot
weld,showing the weld
nugget and the indentation
of the electrode on the
sheet surfaces.This is one
of the most commonly
used process in sheet-
metal fabrication and in
RSEM is modification of spot welding wherein the electrodes are
replaced by rotating wheels or rollers
The electrically conducting rollers produce a spot weld
RSEM can produce a continuous seam & joint that is liquid and
Fig : (a) Seam-Welding Process in which rotating rolls act as electrode (b)
Overlapping spots in a seam weld. (c) Roll spot weld (d) Resistance-welded gasoline
RPW is developed
resistance at a
embossing one or
on the surface to
Weld nuggets are
similar to spot
Fig: a) Resistance projection Welding b)A welded bracket c) &
d) Projection welding of nuts r threaded hosses and stack
The electrodes exert pressure to
compress the projections
Nuts and bolts can be welded to sheet
and plate by this process
Metal baskets, oven grills, and shopping
carts can be made by RPW
Heat is generated from the arc as the ends as the two
An axial force is applied at a controlled rate
Weld is formed in plastic deformation
Fig : (a)Flash-welding process for end-to –end welding of solid rods or tubular parts
(b) & (c) Typical parts made by flash welding (d)Design Guidelines for flash welding
Small part or a threaded rod or hanger serves as a electrode
Also called as Stud arc welding
Prevent oxidation to concentrate the heat generation
Portable stud-welding is also available
Fig:The sequence of operation in stud welding,which is used for welding bars threaded rods
and various fasteners onto metal plates
Percussion welding (PEW) is a type of resistance welding that blends
dissimilar metals together. Percussion welding creates a high
temperature arc that is formed from a short quick electrical discharge.
Immediately following the electrical discharge, pressure is applied which
forges the materials together. This type of joining brings the materials
together in a percussive manner.
Percussion welding is similar to flash welding and upset welding but is
generally considered to be more complex. It is considered to be more
complex because it uses an electric discharge at the joint, followed by
pressure being applied to join the materials together. Percussion
welding is used to join dissimilar metals together, or used when flash is
not required at the joint. This type of welding is limited to the materials
having the same cross sectional areas and geometries. Percussion
welding is used on materials that have small cross sectional areas.
Advantages of using percussion welding types include a shallow heat
affected zone, and the time cycle involved is very short. Typical times
can be found to be less than 16 milliseconds.
- Welding process in
which components to be joined are heated to hot working tempe
rature range and then forged together by hammering or similar
- Historic significance in development of manufacturing
- Process dates from about 1000 B.C., When blacksmiths
learned to weld two pieces of metal
- Of minor commercial importance today except for its
Roll Welding (ROW)
- SSW process in which pressure sufficient to cause coalescence
is applied by means of rolls, either with or without external heat
- Variation of either forge welding or cold welding, depending o
n whether heating of work parts is done prior to process
- If no external heat, called cold roll welding
- If heat is supplied, hot roll welding
Roll Welding Application
- Cladding stainless steel to mild or low alloy steel for
-Bimetallic strips for measuring temperature
- “Sandwich" coins for U.S mint
Diffusion Welding (DFW)
- SSW process uses heat and pressure, usually in a controlled
atmosphere, with sufficient time for diffusion and coalescence
- Plastic deformation at surfaces is minimal
- Primary coalescence mechanism is solid state diffusion
- Limitation: time required for diffusion can range from seconds t
- Joining of high-strength and refractory metals in
aerospace and nuclear industries
- Can be used to join either similar and dissimilar metals
-For joining dissimilar metals, a filler layer of different me
tal is often sandwiched between base metals to
Explosion Welding (EXW)
- SSW process in which rapid coalescence of two metallic
surfaces is caused by the energy of a detonated explosive
-No filler metal used
-No external heat applied
- No diffusion occurs -time is too short
-Bonding is metallurgical, combined with mechanical
interlocking that results from a rippled or
wavy interface between the metals
-Commonly used to bond two dissimilar metals, in particular to
clad one metal on top of abase metal over large areas
Friction Welding (FRW)
- SSW process in which coalescence is achieved by frictional he
at combined with pressure
- When properly carried out, no melting occurs at faying su
- No filler metal, flux, or shielding gases normally used
- Process yields a narrow HAZ
- Can be used to join dissimilar metals
- Widely used commercial process, amenable to automation a
nd mass production
Application and Limitation of FRW
- Shafts and tubular parts
- Industries: automotive, aircraft, farm equipment, pet
roleum and natural gas
- At least one of the parts must be rotational
- Flash must usually be removed
Upsetting reduces the part lengths (which must be taken int
o consideration in product design)
- Capacity of a metal or combination of metals to be
welded into a suitably designed structure, and for the resulting
weld joint(s) to possess the required metallurgical properties to
perform satisfactorily in intended service
Good weldability characterized by:
Ease with which welding process is accomplished
Absence of weld defects
Acceptable strength, ductility, and toughness in
◦ Parent metal will join with the weld metal without
formation of deleterious constituents or alloys
◦ Joint will be free from discontinuities, gas
porosity, shrinkage, slag, or cracks
◦ Weld is able to perform under varying conditions
or service (e.g., extreme temperatures, corrosive
environments, fatigue, high pressures, etc.)
Figure Characteristics of a
typical fusion weld zone in
oxyfuel gas and arc welding
Soldering is a process of joining two metals
by using another low temperature metal alloy
( Below 427 degree centigrade) .
The surface to be joined are cleaned are cleaned and a
re placed on each other. A flux is employed to prevent
oxidation. Zinc chloride is commonly used for this pur
pose. The soldering iron is heated either electrically or
by some external heat . Then the hot end is dipped int
o the flux and solder is pressed against the surface to
be joined. A joint is formed by melting the solder.
The joining of two metal pieces by means of heat and a
special filler (Spelter) having a melting point above 427
degree Centigrade but lower than the melting point of the
parts to be joined. In brazing the ends of parent metal
are not melted but an alloy, having low melting point is
used. Temperature is raised to the fusion point of this
alloy which when melted runs between the edges due to
capillary action and produces thinning effect resulting in
brazed joint. Through brazing dissimilar materials can be
easily joined. The filler rod is used for joining are of
Bronze material ( 60-40% brass main constituent with
suitable amount of deoxidizer like silicon and tin etc
Application: joining of tubes, radiators, pipes and pipes fitting tool tips electrical items
Advantages: useful for joining of dissimilar material, thin sections easily joined, good
surface finish obtained, High production, Less skill, less cost.
Disadvantage: low strength, not applicable for hardened steel and aluminum alloys.
Inclusion: Entrapment of Slag, Scale, dirt, rust in weld zone etc
Cracks: Discontinuity of weld Metal
Distortion: Change in the indented shape and size of component or
structure due to uneven contraction (shrinkage).
Poor Penetration: failure of weld molten metal to reach the bottom of joint.
Porosity: presence of small pores, voids, gases in the weld metal.
Spatter: Deposition of electrode metal particle adjutant to base metal
Undercut: Groove formed in the parent metal at the toe of a weld pass.
Overlapping: molten metal flows over the surface of the base metal.
Inadequate Fusion: sometime the deposited weld metal by
electrode does not fuse fully with the base metal due to presence of oxides, dirt,
slag or other foreign material.
1. Low Penetration
4. Poor Fusion
5. Blow Holes (Porosity)
7. Scattering of weld
1.Incorrect current, fast speed of
2. selection of wrong electrode, metal
contain too much carbon
3. dirty base metal, higher sulfur
content, improper removal of slag
4. wrong current setting, wrong
clearance between work piece and
electrode, fast speed of welding.
5. Wrong arc length, impurities in in
base metal, old electrode.
6. uneven heating, overheating, thin
cross-section of metals
7. high current, long arc, faulty