2. 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
3. Welding conditions continued….
• 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 Symbols
Weld defects
Welding Techniques
4. 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
5. 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)
6. 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
7. Root opening and Bevel
• Root opening is
the separation
between the
work pieces at
the joint root
• Bevel
(chamfer) is an
angular edge
preparation
13. Edge Joint
A joint between the
edges of two or
more parallel or
nearly parallel
members
14. 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
15. 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.
17. 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
• Resistance Welding
• Friction Welding
• Robotic Welding
18. 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
19. Manual Metal Arc (MMA)
Metal Arc Gas Shielded (MAGS) MIG
Tungsten Arc Gas Shielded (TAGS) TIG
Submerged Arc Welding (SAW)
Types of Electric Arc Welding
20. Manual Metal Arc (MMA)
• Most widely used of all
the arc welding processes
• Commonly called “stick”
welding
Applications
repair work, structural steelwork,
21. Touch electrode against
work withdraw
electrode to establish
arc. Heat of arc melts
base metal, the
electrode’s metal core,
and any metal particles
in electrode’s covering.
Heat also melts,
vaporises, or breaks
down chemically
non-metallic substances in covering for arc shielding.
Mixing of molten base metal and filler metal from
electrode produces coalescence required to effect
joining.
22. Advantages
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 allwelding processes
• Low cost of equipment
• Rod becomes shorter & periodically needs replacing
• Slows production rate (% time welder welding)
23. 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)
24. • Produce gas to shield weld pool from
oxidisising effects of atmosphere
• Fluxing elements help weld pool to form
• Helps slag to form-removes impurities
• Slag slows down cooling preventing
Brittleness
• Can contain alloying elements or additional
filler metal
Function of Electrode Coating
28. DC Generator
An electricity generator is driven by a
motor. The motor can be electric,
petrol or diesel. The generator
provides DC current for the arc
29. Transformer-rectifier
A transformer with an electrical device to
change AC to DC, this is known as a
rectifier. It has the advantage of being able to
supply both DC and AC
30. Basic Transformer-rectifier circuit (AC to DC)
On/Off
switch
Step Down
Transformer
Bridge Rectifier
Smothing
Capacitor
High AC
Voltage
230V
Low AC
Voltage
10-50V
DC
output
+
_
A B C D
33. 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
Applications
Sheet and Heavy plate, production
welding by robots on cars
34. 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.
35. 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
36. Equipmnt used in MAGS
Three major elements are :
Welding torch and accessories
Welding control & Wire feed motor
Power Source
Shielding Gas
37. 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
38. 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
40. 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
41. 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
42. 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.
43. Advantages
• Superior quality welding
• Can be used in mechanised systems
• Used to weld aluminium and stainless
steels
• Free of spatter
• Low distortion
44. 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 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.
45. 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.
46. Submerged Arc Welding (SAW)
Similar to MIG welding, SAW
involves formation of an arc between
a continuously-fed bare wire
electrode and the workpiece
Applications
SAW welding taking place in the flat
position. Ideal for heavy workpieces
Carbon-manganese steels,low alloy
steels and stainless steels
47.
48.
49.
50. The process uses a flux to generate protective gases and
slag, and to add alloying elements to the weld pool. A
shielding gas is not required. Prior to welding, a thin layer
of flux powder is placed on the work piece surface. The arc
moves along the joint line and as it does so, excess flux is
recycled via a hopper. Remaining fused slag layers can be
easily removed after welding. As the arc is completely
covered by the flux layer, heat loss is extremely low. There
is no visible arc light, welding is spatter-free and there is
no need for fume extraction.
Submerged Arc Welding (SAW)
51. Equipmnt used in SAW
SAW is normally operated with a single wire on either AC or
DC current. Common variants are:
• twin wire
• triple wire
• single wire with hot wire addition
• metal powdered flux addition
All contribute to improved productivity through a marked
increase in weld metal deposition rates and/or travel speeds.
Wire
52. Flux
Fluxes used in SAW are granular fusible minerals
The flux is specially formulated to be compatible with a
given electrode wire type so that the combination of flux
and wire yields desired mechanical properties. All fluxes
react with the weld pool to produce the weld metal
chemical composition and mechanical properties
53. 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.
54. 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.
57. The Oxy-acetylene welding Flame
Primary Combustion zone
The oxy-acetylene flame has two distinct zones.
The inner zone (Primary combustion Zone) is the hottest part
of the flame. The welding should be performed so as the point
of the inner zone should be just above the joint edges.
C2H2 + O2 2CO + H2
58. The outer zone the secondary combustion envelope
performs two functions
•Preheats the joint edges
•Prevents oxidation by using some of the surrounding
oxygen from weld pool for combustion and gives off
carbon dioxide and water vapour
Secondary Combustion zone
CO + H2 + O2 CO2 + H2O
59. Equipment used in O-A welding
The oxygen and acetylene hose pipes
Gases used
Gas pressure Regulators
Flashback arrestor
Welding torch/Welding nozzle
Filler rods and fluxes
60. The oxygen and acetylene hose pipes
Reinforced rubber hoses.
Acetylene hose has left hand thread couplings and colour
coded red.
Oxygen hose has right handed thread couplings and colour
coded blue
61. Gases used
Oxygen extracted from air and compressed into
cylinders at high pressure. Cylinder is black. Oil should
never be brought into contact and should not be used on
fittings
Acetylene (C2H2) is a fuel gas. Cannot be compressed
directly as explodes at high pressures. Cylinders are
packed with porous material which is filled with
acetone Acetone absorbs acetylene. Cylinder colour
coded maroon
62. Gas Pressure Regulators
One gauge indicates the pressure of the cylinder and the
other indicates the pressure in the supply pipe to the torch.
63. 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.
Mixer Needle valves
64. 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.
65. Filler Rods and fluxes
Filler rods are used when additional filler metal is
required in the weld area 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
66. 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.
The current density and pressure must be sufficient to
produce a weld nugget, but not so high as to expel molten
metal from the weld zone.
68. 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.
69. 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
70. 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
71. 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
72. 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.
73. 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.
74. Robotic welding Terms
Lead through programming Teaching robot movements
through guiding it manually through a sequence of
operations. These are recorded to memeory
Machine Vision Area of vision robot has, limits which
robot sensors can operate
Working enevelope The area within which a robot can
operate. Where the work is caried out by robotic arm
Yaw left and right movment of robotic arm
Roll rotation of robot about one of its axis
Degrees of freedom These are the number of
independent movements of the arm joints( or actuators)
the robot has.
