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What is WeldingJoin together (metal parts) by heating the surfaces to the
point of melting with a blowpipe, electric arc, or othermeans, and uniting them by pressing, hammering, etc
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WeldingParts are joined together by Fusion. Fusion is
brought about by a combination of heat and
pressure between parts being joined. In normal
welding processes very high temperatures andlittle or no pressure is used.
Welding conditions Smooth joint surfaces that match each other
Surfaces clean and free from oxides, grease and dirt.
Metals to be joined have same microstructure
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The metals should be good quality (no internal
impurities)
Welding Preparation
Before starting a weld, the joint edges should be
carefully prepared. Beveling large edges
Cleaning (Chemical/Mechanical)
Weld Joints
Welding Symboles Welding Techniques
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Weld Joints - Parts of a Weld Joint
Joint root
Groove face, Root face and Root edge
Root opening and Bevel
Bevel angle, Groove angle and Groove radius
Weld Joints - Types of Weld Joint
Butt Joint
Lap Joint
T Joint
Corner joint
Edge Joint
Splice Member
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Joint Root
is that portion of a joint to be welded where the membersare closest to each other
The joint root may be
either a point, line, or
an area
The joint roots are
shown as shaded areas
in (A)-(D) and lines in
(E) (F)
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Groove face, Root face and Root edge
Groove face is thatsurface of a member
included in the
groove
Root face (land) is
that portion of the
groove face within
the joint root
Root edge is a root
face of zero width
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Bevel angle, Groove angle and Groove
Radius
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Welding Joints
Butt Joint
A joint between two
members aligned
approximately in the
same plane
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Lap Joint
A joint between two
overlapping members
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T Joint
A joint between twomembers located
approximately at right
angles to each other
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Corner Joint
A joint between twomembers located at
right angles to each
other
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Edge Joint
A joint between the
edges of two or
more parallel or
nearly parallelmembers
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Splice member
is the work piece that spans the joint in a spliced joint
Single-
spliced
butt joint
Double-spliced
butt joint with
joint filler
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Basic components of awelding symbol
Reference Line (Required element)
ArrowTail
Reference Line must always be horizontal,
Arrow points to the line or lines on drawing
which clearly identify the proposed joint or weld
area.
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Weld Symbol Terminology
ARROW SIDE
OTHER SIDE
Work
Fillet Weld (Arrow Side Only) Fillet Weld (Both sides)
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Welding Techniques
There are many different methods of welding. The difference
between them is outlined by two important features
The way the metal is heated
The way additional filler metal if any is fedinto the weld
Types of Welding
Electric arc welding
Gas Welding
Resistance Welding
Friction Welding
Robotic Welding
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Electric Arc Welding
The heat for fusionis supplied by an electric arc
Arc is formed between electrode and work this melts
and fuses the joint edges
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Manual Metal Arc (MMA)
Most widely used of all
the arc welding processes
Commonly called stick
welding
Applications
repair work, structural steelwork,
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In arc welding an electrode is used to conduct currentthrough a workpiece to fuse two pieces together.,
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The Electrode and
Coating
Coating is a combination of chemicals
Cellulosic electrodescontain
cellulose
Rutile electrodestitanium oxide
(rutile)
Basic electrodescontain calciumcarbonate (limestone) and calcium
fluoride (fluorspar)
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Advantages of Electric arc welding
Dis-advantages
Used with many electrode types & sizes Used in all positions
Used on great variety of materials
Flexibility in operator control makes it the
most versatile of all welding processes
Low cost of equipment
Rod becomes shorter & periodically needs replacing
Slows production rate (% time welder welding)
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MIG is similar to MMA in that heat
for welding is produced by forming
an arc between a metal electrode and
the workpiece.But we use very long
electrode wire rolled on pulley.
Metal Arc Gas Shielded (MAGS)
MIG
ApplicationsWelding Sheets and Heavy plates, production
welding by robots on cars
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MIG is similar to
MMA in that heat for
welding is producedby forming an arc
between a metal
electrode and the
workpiece; theelectrode melts to
form the weld bead.
The main difference
is that the metal electrode is a small diameter wire fed from aspool and a sheilding gas is used. As the wire is continuously
fed, the process is often referred to as semi-automatic welding.
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Advantages
Large gaps filled or bridged easily Welding can be done in all positions
No slag removal required
High welding speeds
High weld quality
Less distortion of work piece
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Equipmnt used in MAGS
Three major elements are :
Welding torch and accessories
Welding control & Wire feed motor
Power Source is Transformer
Shielding Gas
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Welding torch and accessories
The welding torch guides the wire and shielding gas to the
weld zone.
Brings welding power to the wire also
Major components/parts of the torch are the contact tip,
shielding gas nozzle, gas diffuser, and the wire conduit
NOZZLE
CONTACT TIP
GAS DIFFUSER
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Welding control and wire feed motor
Main function is to pull
the wire from the spooland feed it to the arc
Controls wire feed speed
and regulates the starting
and stopping of wire feed
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Sheilding Gas
Purpose of shielding gas is toprotect the weld area from thecontaminants in the atmosphere
Gas can be Inert, Reactive, or
Mixtures of both Argon, Helium, and Carbon
Dioxide are the main three gasesused in MAGS
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Tungsten Arc Gas Shielded (TAGS)
TIGTIG is similar to MMA in that
heat for welding is produced
by forming an arc between a
metal electrode and the
workpiece
ApplicationsUsed in joining magnesium and
Aluminium, stainless steels
for high quality welding
Thin sheet material
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In the TIG process the arc
is formed between a
pointed tungsten
electrode and the work
piece in an inert
atmosphere of argon or
helium. The small intense
arc provided by thepointed electrode is ideal
for high quality and
precision welding.
The electrode is not consumed during welding. When filler metalis required, it must be added separately to the weldpool. There
are two currents one for starting the arc the other switched on
using a trigger or foot pedal, this is a high frequency current
to maintain the arc, this is generated by a separte unit.
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Advantages
Superior quality welding
Can be used in mechanised systems
Used to weld aluminium and stainless
steels
Low distortion
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Equipment used in TAGS
Power source
Electrodes
TIG must be operated with a
constant current power source -
either DC or AC
Electrodes for DC welding are normally pure
tungsten. In AC welding, as the electrode will be
operating at a much higher temperature, It should
be noted that because of the large amount of heatgenerated at the electrode, it is difficult to
maintain a pointed tip and the end of the
electrode assumes a spherical or 'ball' profile.
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Sheilding Gas
Argon
Argon + Hydrogen
Argon/Helium
Helium is generally added to increase heat
input (increase welding speed or weld
penetration). Hydrogen will result in cleaner
looking welds and also increase heat input,however, Hydrogen may promote porosity
or hydrogen cracking.
Shielding gas is selected according to the material being welded.
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Gas Welding (Oxy-acetylene)
Separate cylinders and
a hose pipe from each
cylinder transports the
gases to a torch.
Gas and fuel mix inthe torch
burns @ 3100C.
A number of welding processes use a flameproduced by burning a mixture offuel gasand
oxygen. The gas usually used isAcetylenebut other
gases are also used.
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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
PermanentlyjoinedAdditional Filler
Metalis fed in by
hand into the weld
pool, at regular
intervals where it
becomes molten
and joins with the
parent metal.
Th O t l ldi Fl
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Carburising
This kind of flame
is used for welding
High carbon steel
& cast iron.
Amount of
acetylene gas is
high in carburising.
Neutral
A flame resulting
from the burning ofgases supplied in the
proper proportions
for perfect
combustion as
approximately equal
volumes of acetyleneand oxygen
Oxidising
Widely used for
cutting and notsuitable for welding.
When the amount of
oxygen increases, the
flame shortens but
temperature goes toohigh.
The Oxy-acetylene welding Flame
G d
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Gases usedOxygen extracted from air and compressed into
cylinders at high pressure. Cylinder is black.These
cylinder have no welding joint these are complete tube
like cylinders. Pressure contains 1800 psi
Acetylene (C2H2) is a fuel gas. Cannot be compressed
directly as explodes at high pressures. Cylinder colour
coded maroon. We made these cylinders by welding
three parts. Pressur contains 250 psi
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Gas Pressure Regulators
One gauge indicates the pressure of the cylinder and the
other indicates the pressure in the supply pipe to the torch.
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Welding torch
Oxygen and acetylene are delivered to the torch by separatehoses. Each gas is controlled by a valve on the torch. The
two gases mix in the torch and after they are ignited burn at
the nozzle.
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Flashback Arrestors
These are positioned on both the fuel gas and oxygen
supply between the hose and the regulator. Their purpose
is to prevent the return of a flame through the hose into
the regulator.
BackFire
Back fire is a process in which a
Tiny fire particle goes into the cylinder
Through torch and pipe. As a result
It cause big blast.
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Filler Rods and fluxes
Filler rods are used for welding the parts to eachother. they come in different diameters.
Fluxesprotect the weld pool from contamination by
oxygen and nitrogen, they are normally in paste
form placed on a heated filler rod before weldingbegins.11
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Advantages of gaswelding
The equipment is inexpensive, simple and is easily
portable.
Useful for welding light
metals such as automobilebodies and repair works.
Alarge variety ofmaterial can be welded.
Welds can be producedat reasonable cost.
Disadvantages of gaswelding
Equipment must always behandled carefully as incertain circumstancesacetylene is explosive.
A high temperature flamefrom a hand held torch isdangerous when handledcarelessly.
It causes more distortion. The process is not
satisfactory for heavysections.
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Resistance welding
Resistance welding uses the application of electric
current and mechanical pressure to create a weld
between two pieces of metal. Weld electrodes conduct
the electric current to the two pieces of metal as they are
forged together.The welding cycle must first develop
sufficient heat to raise a small volume of metal to the
molten state. This metal then cools while under pressureuntil it has adequate strength to hold the parts together.
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Spot welding
Seam Welding
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Spot welding
Ideal for joining light sheet metal. Theelectrodes are made from copper.
Pressure is applied to the electrodes and
an electric current is passed through the
circuit. The high resistance between the
joint faces causes rapid heating andfusing of a small globule of metal from
both faces.
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Seam welding
The rollers allow the workpiece to
move through the welder
continously. A stream of electrical
pulses pass through the rollers andwelds the joint
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Resistance Welding Benefits
High speed welding
Easily automated
Suitable for high rate production
Economical
Resistance Welding Limitations
Initial equipment costs
Lower tensile and fatigue strengths
Lap joints add weight and material
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Friction welding is a solidstate joining process thatproduces coalescence bythe heat developed
between two surfaces bymechanically inducedsurface motion.
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Friction welding
One part is held stationary while
the other part is rotated
When the parts are hot enough the
rotation is stopped and the parts
forged together
Workpieces
Non-rotating viseMotor
Chuck
SpindleHydraulic cylinder
Brake
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Advantage of frictionalwelding
Easily joins dissimilarmetals.
Friction welds are higherstrength.
Friction welds often costless.
Friction welds minimizethe Heat Affected Zone.
No need of furnace .
A machine of sufficientpower is needed.
T oo high power needed. Tight concentricity
requirements.
Disadvantages offrictional welding
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Robotic welding
A computer sends instructions in electrical
signals or pulses. An interface converts these
digital pulses into analogue electricity for the
motors. The robot is fitted with sensors whichcan send feedback on the position of the robot.
Robots are driven using actuators which
control the robotic arm from an input signal.They can use hydraulic (large robots),
pneumatic(small actuators with simple
control movements) or electrical principles of
operation.
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Advantages of Robotic welding
Faster production rates
Efficent continous operation
Safe working practice
Reliable and consistent welds
Full automation
Cost effective
ExamplesAutomated welding of motor vehicles
skeletel frames and bodies.
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