Presentation Topic :
Welding
What is Welding
Join together (metal parts) by heating the surfaces to the
point of melting with a blowpipe, electric arc, or other
means, and uniting them by pressing, hammering, etc
Welding
Parts 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 and
little 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
• 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
Weld Joints - Parts of a Weld Joint
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•
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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
• Corner joint
• Lap Joint
• Edge Joint
• T Joint
• Splice Member
Joint Root
is that portion of a joint to be welded where the members
are 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)
Groove face, Root face and Root edge
• Groove face is “ that
surface 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
Root opening and Bevel
• Root opening is
the separation
between the
work pieces at
the joint root
• Bevel
(chamfer) is an
angular edge
preparation
Bevel angle, Groove angle and Groove
Radius
Welding Joints
Butt Joint
A joint between two
members aligned
approximately in the
same plane
Lap Joint
A joint between two
overlapping members
T Joint
A joint between two
members located
approximately at right
angles to each other
Corner Joint
A joint between two
members located at
right angles to each
other
Edge Joint
A joint between the
edges of two or
more parallel or
nearly parallel
members
Splice member
is “ the work piece that spans the joint in a spliced joint
Singlespliced
butt joint
Double-spliced
butt joint with
joint filler
Basic components of a welding symbol
Reference Line (Required element)
Arrow
Tail
Reference Line must always be horizontal,
Arrow points to the line or lines on drawing
which clearly identify the proposed joint or weld
area.
Weld Symbol Terminology
OTHER SIDE
ARROW SIDE
Fillet Weld (Arrow Side Only)
Fillet Weld (Both sides)
Work
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 fed into the weld
Types of Welding
• Electric arc welding
•
• Gas Welding
• Robotic Welding
• Resistance Welding
Friction Welding
Electric Arc Welding
The heat for fusion is supplied by an electric arc
Arc is formed between electrode and work this melts
and fuses the joint edges
Manual Metal Arc (MMA)
• Most widely used of all
the arc welding processes
• Commonly called “stick”
welding
Applications
repair work, structural steelwork,
 In arc welding an electrode is used to conduct current
through a workpiece to fuse two pieces together.,
The Electrode and
Coating
Coating is a combination of chemicals
•
Cellulosic electrodes contain
cellulose
•
Rutile electrodes titanium oxide
(rutile)
•
Basic electrodes contain calcium
carbonate (limestone) and calcium
fluoride (fluorspar)
Advantages of Electric arc welding
• 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
Dis-advantages
• Rod becomes shorter & periodically needs replacing
• Slows production rate (% time welder welding)
Metal Arc Gas Shielded (MAGS)
MIG
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.
Applications
Welding Sheets and Heavy plates, production
welding by robots on cars
MIG is similar to
MMA in that heat for
welding is produced
by forming an arc
between a metal
electrode and the
workpiece; the
electrode melts to
form the weld bead.
The main difference
is that the metal electrode is a small diameter wire fed from a
spool and a sheilding gas is used. As the wire is continuously
fed, the process is often referred to as semi-automatic welding.
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
Equipmnt used in MAGS
Three major elements are :
Welding torch and accessories
Welding control & Wire feed motor
Power Source is Transformer
Shielding Gas
Welding torch and accessories
GAS DIFFUSER
NOZZLE
CONTACT TIP
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•
•
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
Welding control and wire feed motor
 Main
function is to pull
the wire from the spool
and feed it to the arc
 Controls wire feed speed
and regulates the starting
and stopping of wire feed
Sheilding Gas
• Purpose of shielding gas is to
protect the weld area from the
contaminants in the atmosphere
• Gas can be Inert, Reactive, or
Mixtures of both
• Argon, Helium, and Carbon
Dioxide are the main three gases
used in MAGS
Tungsten Arc Gas Shielded (TAGS)
TIG
TIG is similar to MMA in that
heat for welding is produced
by forming an arc between a
metal electrode and the
workpiece
Applications
Used in joining magnesium and
Aluminium, stainless steels
for high quality welding
Thin sheet material
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 the
pointed electrode is ideal
for high quality and
precision welding.
The electrode is not consumed during welding. When filler metal
is 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.
Advantages
• Superior quality welding
• Can be used in mechanised systems
• Used to weld aluminium and stainless
steels
• Low distortion
Equipment used in TAGS
Power source
TIG must be operated with a
constant current power source either DC or AC
Electrodes
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 heat
generated at the electrode, it is difficult to
maintain a pointed tip and the end of the
electrode assumes a spherical or 'ball' profile.
Sheilding Gas
Shielding gas is selected according to the material being welded.
• 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.
Gas Welding (Oxy-acetylene)
A number of welding processes use a flame
produced by burning a mixture of fuel gas and
oxygen. The gas usually used is Acetylene but other
gases are also used.
Separate cylinders and
a hose pipe from each
cylinder transports the
gases to a torch.
Gas and fuel mix in
the torch
burns @ 3100°C.
During the welding heat from the flame is
concentrated on the joint edges until the metal
melts and starts to flow. When the molten metal
from both sides melts it starts to fuse, when the
metal cools down the two parts become
Permanently joined
Additional Filler
Metal is fed in by
hand into the weld
pool, at regular
intervals where it
becomes molten
and joins with the
parent metal.
The Oxy-acetylene welding Flame
Carburising
Neutral
Oxidising
This kind of flame
is used for welding
High carbon steel
& cast iron.
Amount of
acetylene gas is
high in carburising.
A flame resulting
from the burning of
gases supplied in the
proper proportions
for perfect
combustion as
approximately equal
volumes of acetylene
and oxygen
Widely used for
cutting and not
suitable for welding.
When the amount of
oxygen increases, the
flame shortens but
temperature goes too
high.
Gases used
Oxygen 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
Gas Pressure Regulators
One gauge indicates the pressure of the cylinder and the
other indicates the pressure in the supply pipe to the torch.
Welding torch
Oxygen and acetylene are delivered to the torch by separate
hoses. 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.
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.
Back Fire
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.
Filler Rods and fluxes
Filler rods are used for welding the parts to each
other. they come in different diameters.
Fluxes protect the weld pool from contamination by
oxygen and nitrogen, they are normally in paste
form placed on a heated filler rod before welding
begins.11
Advantages of gas
welding
Disadvantages of gas
welding
 The equipment is inexpensi Equipment must always be
ve, simple and is easily
handled carefully as in
certain circumstances
portable.
acetylene is explosive.
 Useful for welding light
metals such as automobile  A high temperature flame
from a hand held torch is
bodies and repair works.
dangerous when handled
 Alarge variety of
carelessly.
material can be welded.
 It causes more distortion.
 Welds can be produced
 The process is not
at reasonable cost.
satisfactory for heavy
sections.
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 pressure
until it has adequate strength to hold the parts together.
• Spot welding
• Seam Welding
Spot welding
Ideal for joining light sheet metal. The
electrodes 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 and
fusing of a small globule of metal from
both faces.
Seam welding
The rollers allow the workpiece to
move through the welder
continously. A stream of electrical
pulses pass through the rollers and
welds the joint
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
 Friction welding is a solid
state joining process that
produces coalescence by
the heat developed
between two surfaces by
mechanically induced
surface motion.
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
Motor
Spindle
Chuck
Brake
Workpieces
Non-rotating vise
Hydraulic cylinder
Advantage of frictional
welding
 Easily joins dissimilar




metals.
Friction welds are higher
strength.
Friction welds often cost
less.
Friction welds minimize
the Heat Affected Zone.
No need of furnace .
Disadvantages of
frictional welding
 A machine of sufficient
power is needed.
 T oo high power needed.
 Tight concentricity
requirements.
Robotic welding
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.
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 which
can send feedback on the position of the robot.
Advantages of Robotic welding
• Faster production rates
• Efficent continous operation
• Safe working practice
• Reliable and consistent welds
• Full automation
• Cost effective
Examples
Automated welding of motor vehicles
skeletel frames and bodies.