MANUFACTURING
PROCESSES
JOINING
FUSION-WELDING
PROCESSES
 Introduction
 Oxyfuel Gas welding
 Arc-Welding Processes
:Consumable electrode
 Electrodes
 Arc-Welding Processes
: Non Consumable
Process
 Welding Safety
Introduction
• Definition : Fusion Welding is defined as melting
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together and coalescing materials by means of heat
Energy is supplied by thermal or electrical means
Filler metals : metals added to the weld area during
welding, may or may not be used
Fusion welds made without filler metals are known as
autogenous welds
Oxyfuel Gas Welding
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Welding process that uses fuel gas combined with
oxygen to produce flame
This flame heat melts the metals at the joint
Acetylene fuel is used in gas welding process
Primary combustion process;
C2H2 + O2
2CO + H2 + heat
This reaction dissociates into carbon monoxide and
hydrogen.
Secondary combustion process;
2CO + H2 + 1.5 O2
2CO2 + H2O + heat
Types of flames
• Neutral flame
• Oxidising flame
• Carburising flame
Three basic types of
oxyacetylene flames
used in oxyfuel-gas
welding and cutting
operations:
(a) neutral flame;
(b) oxidizing flame;
(c) carburizing, or
reducing flame. The
gas mixture in (a) is
basically equal
volumes of oxygen and
acetylene.
Filler Metals
• Additional material to weld the weld zone
• Available as rod or wire
• They can be used bare or coated with flux
• The purpose of the flux is to retard the
Pressure-Gas Welding Process
• By heating of the interface.
• After the interface begins to
melt, the torch is withdrawn,
and force is applied to press the
components together
The pressure-gas
welding process.
Oxy-acetylene welding summary
• Relatively cheap
• Well suited to low volume and repair jobs.
• Rarely used on stock thicker than ¼ inch
• Rarely mechanized
• Thus relies on the skill of the welder for quality.
Shielded metal arc welding process
• Consumable electrode coated
with chemicals that provide
flux and shielding
• Sometimes called „stick‟
welding
• The filler metal (here the
consumable electrode) is
usually very close in
composition to the metal being
welded.
• The coating contains
• Cellulose, carbonates, a
silicate binder
• Sometime other metals to
alloy the joint
The shielded metal-arc welding process.
About 50% of all large-scale industrial
welding operations use this process.
The shielded metal-arc welding
process ( also known as stick
welding, because the electrode
is in the shape of a stick).
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Submerged arc welding
Weld arc is shielded by a granular flux ,consisting
of silica, lime, manganese oxide, calcium fluoride
and other compounds.
Flux is fed into the weld zone by gravity flow
through nozzle
Thick layer of flux covers molten metal
Flux acts as a thermal insulator ,promoting deep
penetration of heat
into the work piece
Consumable electrode
is a coil of bare round
wire fed automatically
through a tube
Power is supplied by 2
or 3-phase power lines
The submerged-arc welding process
and equipment. The unfused flux is
recovered and reused .
Gas metal arc welding
• GMAW is a metal inert gas welding (MIG)
• Weld area shielded by an effectively inert atmosphere
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of argon,helium,carbon dioxide & other gas mixtures
Metal can be transferred by 3 methods :
• Spray transfer
• Globular transfer
• Short circuiting
Process capabilities
• GMAV process is suitable
for welding a variety of
ferrous and non-ferrous
metals
The gas metal-arc welding
• Process is versatile ,rapid,
process, formerly known as MIG
(for metal inert gas) welding.
economical, welding
productivity is double that of SMAW
Basic equipment used in gas
metal-arc welding (GMAW)
operations
Flux–cored Arc – Welding
• Flux cored arc welding is similar to a gas metal arc
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welding
Electrode is tubular in shape
and is filled with flux
Cored electrodes produce
more stable arc improve
weld contour and produce
better mechanical properties
Flux is more flexible
than others
The flux-cored arc-welding
process. This operation is similar
to gas metal-arc welding.
Electro gas Welding
• EGW is welding the edges of sections vertically in one
pass with the pieces placed edge to edge
• Weld metal is deposited into weld cavity between the
two pieces to be joined
• Mechanical drives moves shoes upwards
• Single and multiple electrodes are fed through a
conduit and a continuous arc is maintained using fluxcored electrodes at up to 750 A
• Process capabilities :
•Weld thickness ranges
from 12mm to 75mm
•Metals welded are steels,
titanium, aluminum alloys
•Applications are pressure
vessels, thick walled &
large diameter pipes,
storage tanks and ships.
The electrogas welding process
Electroslag Welding:
• Similar to Electro gas welding
• Difference is Arc is started between electrode tip and
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bottom part of the part to be welded
Flux added first and then melted by the heat on the arc
Molten slag reaches the tip
of the electrode and the arc
is extinguished
Heat is then continuously
produced by electrical
resistance of the molten slag
Single or multiple solid as well
as flux-cored electrodes may
be used
Equipment used for electroslag
welding operations.
Arc welding processes
(Non-consumable electrode)
• Typically use a tungsten electrode
• Known as “TIG” (tungsten inert gas) welding
• The electrode is W (tungsten)
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• Tm = 6170°F (3410°C)
• Actually it is slowly consumed
Shielding gases include Ar, He or a mixture
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Used for a wide variety of metals
• can also be used to weld dissimilar metals (but
not very well)
Most commonly used for aluminum and stainless steel
For steel
• Slower and more costly than consumable welding
• Except for thin sections or where very high quality
is needed
Welding Safety
• Some hazards in welding are;
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Surroundings
Personal danger
Noise & shock
Fumes
SOLID-STATE WELDING
PROCESSES
Introduction
Cold welding
Ultrasonic welding
Friction welding
Resistance welding
Explosion welding
Introduction
• Joining without fusion (melting) of the workpiece
• Principle : Two surfaces brought into atomic contact
with sufficient pressure to form bonds and produce a
strong joint
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Cold Welding
Pressure is applied to the
workpieces through dies or rolls
Preferably both work pieces
should be ductile
The work pieces should cleaned
thoroughly
Can not join dissimilar metals
The roll bonding or
cladding process
Ultrasonic Welding
• Surfaces of the two components are subjected to a
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static forces and oscillating shearing force
Produces a strong, solid-state bond
Versatile and reliable for joining metals
Components of an ultrasonic welding machine for lap welds.The lateral vibration
of the tool tip cause plastic deformation and bonding at the interface of the work
piece b)Ultrasonic some welding using a roller c)An ultrasonically welded part
Friction Welding
• Developed in the 1940‟s
• Parts are circular in shape
• Can be used to join a wide variety of materials
• Process can be fully automated
• Can weld solid steel bars up to 250mm in outside
diameter
Sequence of operation in the friction welding process 1)Left-hand
component is rotated at high speed. 2) Right-hand component is brought
into contact under an axial force 3)Axial force is increased;the flash begins
to form 4) Left-hand component stops rotating;weld is completed.The flash
can subsequently be removed by machining or grinding
Shape of friction
zone in friction
welding,as a
function of the
force applied and
the rotational
speed
Inertia Friction Welding
• Modification of Friction Welding
• Energy is supplied by a fly wheel
• The parts are pressed together by a
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normal force
As friction at the interface
increases, the fly wheel slows down
The weld is completed when the
flywheel stops
The principle of the
friction stir welding
process. Aluminum-alloy
plates up to 75mm (3in)
thick have been welded
by this process
Linear Friction Welding
• Parts are joined by a linear reciprocating motion
• Parts do not have to be circular or tubular
• In this application, one part is moved across the face
of the other part using a balanced reciprocating
mechanism
Friction Stir Welding (FSW)
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New Process for welding aerospace metals
Research is being directed towards using this
process for polymers
FSW uses a 3rd nonconsumable tool inserted
between the two bodies to heat the material to be
joined
Resistance Welding
• Developed in the early 1900‟s
• A process in which the heat required for welding is
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produced by means of electrical resistance across the
two components
RW does not requiring the following:
• Consumable electrodes
• Shield gases
• Flux
Resistance Spot Welding
• RSW uses the tips of two opposing solid
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cylindrical electrodes
Pressure is applied to the lap joint until the
current is turned off in order to obtain a strong
weld
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
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
automotive-body assembly
Resistance Seam Welding
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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 gas tight
Seam-Welding
Process in
which rotating
rolls act as
electrode
Overlapping
spots in a seam
weld
(a) (b). (c) (d)
Roll spot
weld
Resistancewelded gasoline
tank
Resistance Projection Welding
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RPW is developed
by introducing
high electrical
resistance at a
joint by
embossing one or
more projections
on the surface to
be welded
Weld nuggets are
similar to spot
welding
a) Resistance projection Welding b)A welded
bracket c) & d) Projection welding of nuts r
threaded hosses and stack
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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
Flash Welding
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Heat is generated from
the arc as the ends as
the two members
contacts
An axial force is
applied at a controlled
rate
Weld is formed in
plastic deformation
(a)Flash-welding process for end-to –end
welding of solid rods or tubular parts (b) &
(c) Typical parts made by flash welding
Stud Welding
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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
The sequence of operation in stud welding,which is used for
welding bars threaded rods and various fasteners onto metal plates
Explosion Welding
• Detonation speeds are usually
low being 2400 – 3600 m/s
• The impact ejects the interface
effectively removing any oxides
or surface impurities.
• The impact mechanically
interlocks the two surfaces
• The explosive may be flexible
plastic sheet
• Pieces of up to 20ft x 7 ft
have been joined
• Very useful in cladding work
• Cladding tantalum (Ta) to ordinary steel
gives the inertness of Ta with the
economy of steel.
• Requires well trained personnel
THE METALLURGY OF
WELDING
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Introduction
Welded joint
Weldability
Testing welding joint
Weld design and process
selection
Introduction
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Strength ,ductility ,toughness of welded joint
Micro structure and grain size depends on the
temperatures
Weld quality depends on geometry,presence of
cracks,residual stresses ,inclusions and oxide films…
Welded Joint
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3-Distinct zones
• Base metal
• Heat – affected zone
• Weld metal
Metallurgy and properties of second and third
zone depend strongly
On metals joined , welding process, filler metals
used & on process variables.
Autogenously is joint produced without the
filler metal
Weld zone is composed of resolidified base
metal
Solidification of Weld metal
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Solidification begins with formation of columnar
grains which is similar to casting
Grains relatively long and form parallel to the heat
flow
Grain structure and size depend on the specific alloy
Weld metal has a cast
structure because it has
cooled slowly, it has grain
structure
Results depends on alloys,
composition and thermal
cycling to which the joint
is subjected.
Pre-heating is important
for metals having high
Characteristics of a typical fusion weld
zone in oxyfuel gas and arc welding.
thermal conductivity
Grain Structure
(a)
(b)
Grain structure in (a) a deep weld (b) a shallow weld. Note that the grains in the
solidified weld metal are perpendicular to the surface of the base metal. In a good
weld, the solidification line at the center in the deep weld shown in (a) has grain
migration, which develops uniform strength in the weld bead.
Weld Beads
(a)
(b)
(a) Weld bead (on a cold-rolled nickel strip) produced by a laser beam. (b)
Microhardness profile across the weld bead. Note the lower hardness of the
weld bead compared to the base metal.
Heat affected Zone
• Heat effected zone is within the metal itself
• Properties depend on
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• Rate of heat input and cooling
• Temperature to which the zone was raised
Original grain size ,Grain orientation , Degree of
prior cold work
The strength and hardness
depend partly on how
original strength and
hardness of the base metal
was developed prior to
the welding
Heat applied during
Intergrannular corrosion of a 310-stainlesssteel welded tube after exposure to a
welding recrystallises
caustic solution. The weld line is at the
elongated grains of
center of the photograph. Scanning
cold worked base metal electron micrographs at 20X.
Weld Quality
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Welding discontinuities can be caused by inadequate
or careless application
The major discontinuities that affect weld quality are
porosity, slag Inclusions, incomplete fusion &
penetration, weld profile, cracks, lamellar tears,
surface damage and residual stresses
Porosity
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Caused by gases released during melting of the
weld area but trapped during solidification,
chemical reactions, Contaminants
They are in form of spheres or elongated pockets
Porosity can be reduced by
•Proper selection of electrodes
•Improved welding techniques
•Proper cleaning and prevention of contaminants
•Reduced welding speeds
Slag Inclusions
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Compounds such as oxides ,fluxes, and electrodecoating materials that are trapped in the weld Zone
Prevention can be done by following practices :
• Cleaning the weld bed surface before the next
layer is deposited
• Providing enough shielding gas
• Redesigning the joint
Incomplete Fusion and Penetration
• Produces lack of weld beads
• Practices for better weld :
• Raising the temperature of the base metal
• Cleaning the weld area, prior to the welding
• Changing the joint design and type of
electrode
• Providing enough shielding gas
Penetration
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Incomplete penetration occurs when the depth of
the welded joint is insufficient
Penetration can be improved by the following
practices :
• Increasing the heat Input
• Reducing the travel speed during the welding
• Changing the joint design
• Ensuring the surfaces to be joined fit properly
Low-quality weld
beads, the result of
incomplete fusion
Weld Profile
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Under filling results when the joint is not filed
with the proper amount of weld metal.
Undercutting results from the melting away of the
base metal and consequent generation of a groove
in the shape of a sharp recess or notch.
Overlap is a surface discontinuity usually caused
by poor welding practice and by the selection of
improper material.
Schematic illustration
of various
discontinuities in
fusion welds.
Cracks
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Cracks occur in various directions and various
locations
Factors causing cracks:
• Temperature gradients that cause thermal
stresses in the weld zone
• Variations in the composition of the weld zone.
• Embrittlement of grain boundaries
• Inability if the weld metal to contract during
cooling
Types of cracks (in
welded joints) caused by
thermal stresses that
develop during
solidification and
contraction of the weld
bead and the
surrounding structure.
(a) Crater cracks (b)
Various types of cracks
in butt and T joints.
• Cracks are classified as Hot or Cold.
• Hot cracks – Occur at elevated temperatures
• Cold cracks – Occur after solidification
• Basic crack prevention measures :
• Change the joint design ,to minimize stresses from
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the shrinkage during cooling
Change the parameters, procedures, the sequence
of welding process
Preheat the components
to be welded
Avoid rapid cooling of
the welded components
Crack in a weld bead, due to the fact
that the two components were not
allowed to contract after the weld was
completed.
Lamellar tears
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Occurred due to the shrinkage of the restrained
components in the structure during cooling.
Can be avoided by providing for shrinkage of the
members & changing the joint design
Surface Damage
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These discontinuities may adversely affect the
properties of welded structure, particularly for
notch sensitive metals.
Residual Stresses
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Because of localized heating & cooling during welding,
expansion and contraction of the weld area Can cause
the following defects:
• Distortion,Warping and buckling of welded parts
• Stress corrosion cracking
• Further distortion if a portion of the welded
structure is subsequently removed
• Reduced fatigue life
Distortion of parts
after welding : (a)
butt joints; (b) fillet
welds. Distortion is
caused by
differential thermal
expansion and
contraction of
different parts of the
welded assembly.
Residual stresses
developed during
welding of a butt
joint.
Stress relieving of weld
• Preheating reduces problems caused by preheating
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the base metal or the parts to be welded
Heating can be done electrically,in furnace,for thin
surfaces radiant lamp or hot air blast
Some other methods of stress relieving : Peening,
hammering or surface rolling
Weldability
• Capacity to be welded into a specific structure that
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has certain properties and characteristics and will
satisfactorily meet service requirements
Thorough knowledge of the phase diagram is essential
Factors such as strength, toughness, ductility, notch
sensitivity, elastic modulus, specific heat, melting
point, thermal expansion, surface tension of the
molten metal, corrosion resistance.
Testing Welded Joints
• Quality of the welding joint is established by welded
joint
• Each technique has capabilities ,limitations and
sensitivity reliability and requirement for special
equipment and operator skill.
Destructive Techniques
Tension Test
• Longitudinal & transverse tension tests are
performed
• Stress strain curves are obtained
Tension-Shear Test
• Specifically prepared to simulate actual welded joints
and procedures.
• Specimen subjected to tension and shear strength of
the weld metal
Bend test
• Determines ductility and strength of welded joints.
• The welded specimen is bend around a fixture
• The specimens are tested in three-point transverse
bending
• These tests help to determine the relative ductility
and strength of the welded joints
Two types of
specimens for
tension-shear testing
of welded joints.
(a) Wrap-around bend test method.
(b) Three-point bending of welded
specimens.
• Other destructive testing
i. Fracture Toughness Test
ii.Corrosion & creep tests
iii.Testing of spot welds
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Tension-Hear
Cross-tension
Twist
(a) Tension-shear test
for spot welds.
Peel
(b) Cross-Tension test. (c) Twist test. d) Peel test
Non-Destructive testing
• Often weld structures need to be tested Non•
Destructively
Non-Destructive testing are :
• Visual
• Radiographic
• Magnetic-particle
• Liquid-penetrant
• Ultrasonic
Weld design & Process Selection
• Considerations:
• Configuration of the components or structure to
be welded, and their thickness and size
• Methods used to manufacture the components
• Service requirements, Type of loading and
stresses generated
• Location, accessibility and ease of welding
• Effects of distortion and discoloration
• Appearance
• Costs
Design guidelines
for welding
General Design
Guidelines
Standard identification
and symbols for welds
Weld Design Selection
Weld
Design
Selection
BRAZING, SOLDERING,
ADHESIVE BONDING AND
MECHANICAL FASTENING PROCESSES
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Introduction
Brazing
Soldering
Adhesive bonding
Mechanical fastening
Joining plastic
Brazing
• Joining process
• A filler metal is placed between two workpieces
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and heated until melted
Two main types of Brazing
• Ordinary
• Braze welding
Use of flux is very important
Filler Metals
• Available in a wide range of
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brazing temperatures
They come in a wide range of
shapes
Choice of the filler metal and its
composition are important
Diffusion of the filler metal in to
the workpeice is an important
consideration
a) Brazing
b) Braze welding operation
Fluxes
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The use of flux in brazing is very important
Generally made of:
• Borax
• Boric acid
• Borates
• Fluorides
• Chlorides
Wetting agents may also be added
Brazing Methods
Torch Brazing
• Performed by heating the joint with a torch
• Depositing the filler metal in the joint
• Suitable part thickness (0.25 – 6.0)mm
• Not a automated process
• More than one torch can be used in this process
Furnace Brazing
• Precleaned & Preloaded with brazing metal
• Heated in a furnace
An example of
furnace
brazing
a)before b)
after
Other Types Of Brazing
• Induction Brazing
• Resistance Brazing
• Dip Brazing
• Infrared Brazing
• Diffusion Brazing
Braze Welding
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Prepared like fusion welding
Filler metal is deposited at the joint with the use
of an oxyacetylene torch
Considerably more filler is used
Temperature is minimal compared to that of
fusion welding; part distortion is minimal
Brazing Process Capabilities
• Dissimilar metals can
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be assembled with
good joint strength
Shear strength of
brazed joints can
reach 800Mpa
Joints commonly used in brazing
Good & poor design
for brazing
Soldering
• The filler metal (solder) melts at relatively low
temperature
• Different types of soldering;
i. Torch
ii. Furnace
iii.Iron
iv.Induction
v. Resistance
vi.Dip
vii.Infrared
viii.Ultrasonic
ix.reflow (paste)
x. Wave
Reflow Soldering
• Solvents present in the paste are evaporated
• The flux in the paste is activated & the fluxing occurs
• The components are carefully preheated
• The solder particles are melted and wet the joint
• The assembly is cooled
Wave Soldering
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Popular approach to attaching circuits to circuit boards
a)Screening or
stenciling paste
onto a printed
circuit board:
1) Stenciling
process 2) a
section of a
typical stencil
pattern b)
wave soldering
process
Types Of Fluxes
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Inorganic acids or salts – clean
the surface rapidly
Noncorrosive resin-based – used
in electrical applications
Soldering is used extensively in
electronics industry
Adhesive Bonding
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Products are joined and assembled by the use of
adhesives
Adhesives properties to be considered
• Strength
• Toughness
• Resistance to various fluids
• Ability to wet the surface to be bonded
Types of adhesives
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Surface must be
clean for joining
parts
Should avoid
joints that might
be subjected to
peeling forces
Design for
adhesive bonding
Process capabilities
Characteristic behavior of (a) brittle (b)
tough adhesive in a peeling test
Adhesive Peeling Test
Design in Adhesive Bonding
Various joint design in adhesive bonding.
(a) single lap (b) double lap (c) scarf (d) strap
Mechanical Fastening
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Threaded Fasters
• Bolts
• Screws
• Nuts
Other Fastening Methods
• Stapling
• Crimping
• Snap-in Fasteners
• Shrink and press fits
Rivets
a) solid b)tubular c) split (bifurcated) d) compression
Joining Plastics
• Heat softens the plastic to a molten state
• Then pressure added & fusion takes place
• External Heat Sources
• Hot air
• Heated tools & dies
• Electrical-Resistance
• Lasers
• Internal Heat Sources
Fig : Design
for riveting (a)Exposed
shank is too long; the result is buckling instead of upsetting
•guidelines
Ultrasonic
welding
(b)Rivets should be placed sufficiently far from edges to avoid stress concentrations (c)Joined sections
• Friction welding
should allow ample clearance for riveting tools (d) section curvature should not interfere with the riveting
process
THE END