Welding ppt bmp unit 3

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BASICS OF MANUFACTURING
PROCESS 1

L12
 Welding: Introduction, classification of welding
processes. Gas-welding, types of flames and their
applications.
L13
 Electric -Arc welding and its applications,
Resistance welding and its types
L14
 Soldering and brazing processes and their uses
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 It is process of joining two
similar or dissimilar metals
with the application of heat
and with or without the
application of pressure.
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 Welding is a process of joining two or more
similar or dissimilar metals by melting them
locally at the place of intended joint. Filler
material may be added and a pool of molten
metal is made.
 This pool of metal becomes a strong joint
after solidification. Sometimes help of
pressure along with heating is taken to
produce a weld.
 Flux is added to remove impurities and
protect the weld from oxidation.
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 Pressure welding- resistance
welding
 Non pressure welding- arc
welding, gas welding
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Gas Welding
 1. Oxy-acetylene welding
 2. Air acetylene welding
 Oxy-hydrogen welding
 4. Oxy-fuel welding
Electric Arc Welding
 Metal Arc welding
 Carbon arc welding
 Tungsten inert gas welding
 Metal inert gas welding
 Submerged arc welding
 Plasma arc welding
 Fluxed cored arc welding
 Electro slag welding
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Resistance Welding
 Spot welding
 Seam welding
 Projection welding
 Flash welding
Solid Friction welding
 Ultra sonic welding
 Diffusion welding
 Explosive welding
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Thermo-chemical Welding
 Thermit welding
 Atomic hydrogen welding
Low temperature State Welding
 Cold welding
 welding process
 Soldering
 Brazing
 Bronze Welding
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 Welding Source of heat
 Arc welding electric arc
 Gas welding gas
 Resistance welding electric current
 Laser welding laser
 Friction welding friction
 Thermit welding chemical reaction
( exothermic reaction)
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 In this method, metal pieces to be welded are
heated locally to the melting temperature by
creating an electric arc and then allowed to
solidify to form welded joint. Additional metal
for filling the weld is provided by core wire of
electrode (As in metal arc welding) or by filler
rod (As in case of carbon arc welding).
 For creating an arc low voltage high
amperage AC or DC current is used.
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 Filler material is used to supply extra molten
metal to fill the gap between joints. Filler
material has similar composition and lower
melting point then the base material.
 Flux is some time used to remove the oxides
formed during welding process by combining
with the impurities and forming slag, which
floats on the molten metal. Molten slag
covers the weld and protects it from
oxidation.
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The potential difference should be such that
the heat generated at positive terminal is 2/3
and at negative terminal is 1/3. The
temperature of the arc is 3700oC to 4000oC. In
DC welding two types of polarities are used.
In DC welding two types of polarities are used.
Straight Polarity: welding electrode is kept
negative and work piece is kept positive.
Reverse Polarity: In this work piece is negative
and electrode is positive.
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 Power supply- A.C. OR D.C SUPPLY
 ELECTRODE HOLDER
 ELECTRODE- BARE ELECTRODE AND COATED
ELECTRODE
 PROTECTIVE SHIELD
 GLOVES
 WELDING CLOTHES
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 Various equipment used in Electric arc welding:
Following equipment are needed in Electric arc
welding
 High current Low Voltage AC or DC Source :
 In DC arc welding current is generated by a DC
generator. The generator can be driven by means
of an electric motor of by means of a petrol or
Diesel engine. They can be portable or standing
type. The voltage required is 60-80V for striking
the arc and 15-25volts for maintaining the arc.
 In AC arc welding a step down transformer is
used which transforms AC supply from 440 Volts
AC to 80-100 Volts AC.
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 Apart from transformer following equipment are
also needed( as shown in figure of arc welding
set up)
 Well insulated electrode holder
 Wire cables and cable connectors
 Welding helmet and hand screen or shield
 Safety Goggles
 Weld chipping hammer
 Earthling Clamp
 Hand Gloves
 Apron and Sleeves
 Wire brush, chipping hammer
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 Suitable for variety of application and
positions
 High metal deposition rate
 Less training required for welders and less
supervision needed.
 Equipment are easy to use and are less costly
 Equipment are portable and can be used in
confined places
 Auxiliary gas shield is not required
 Suitable for most commonly used metals and
alloys
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 Incorrect welding may result into low weld
toughness
 Lack of fusion of metal if weld parameters are
incorrect
 Slag is to be removed after every pass in
multipass welding
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In this process heat for melting is supplied
by combustion of a fuel gas with oxygen. The
fuel gas can be acetylene, hydrogen, propane
or butane.
The molten metal from the edges of metal
flows and solidifies together in the weld and a
continuous joint is obtained. A filler metal
may be added when the metal is flowing to
fill the cavity.
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 Gas cylinders- oxygen( black colour) and
acetylene ( red colour)gas cylinders
 Hose pipes
 Pressure regulators
 Welding torch or blow pipe with needles
valves
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 Oxy Acetylene Welding : This is used for
welding almost all metals because it produces
comparatively higher temperatures and also
an inert gas envelope consisting of CO2 and
H2O is formed around the weld, which
prevents liquid metal from oxidation. The
temperatures obtained are of the order of
3200oC -3500oC.
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Pressure Regulators: Oxygen and acetylene
cylinders are fitted with pressure regulators to
reduce pressure of gases as per the requirement.
Blow pipes or Torches: Torch for high pressure and
low pressure system differ in design. The low
pressure torch has an inbuilt ejector which draws
acetylene from the low pressure generator and
mixes with the Oxygen. In high pressure torch
there is only a mixing provision for the two
gases. The torch is fitted with regulating valves
for oxygen and acetylene.
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Other equipment: Other equipment needed for gas
welding are
 Keys for cylinders and valves
 Hoses for Oxygen and Acetylene
 Spanners for connecting hoses
 Safety equipment like goggles, Screens, Lather
hand glows and lather apron
 Chipping hammer
 goggles
 Wire brush, Spark lighter etc.
 Trolley to carry oxygen cylinders
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 Oxidising Flame : Oxidizing flame is obtained when the
quantity of oxygen is more than that required for perfect
combustion. The inner cone is pointed and very short in this
case. Such flame is not required except for welding brass.
Maximum temperature of about 3400oC - 3500oC at the tip
of inner cone is obtained.
Neutral Flame : When quantity of oxygen is so adjusted that
it is just sufficient for complete combustion a neural flame is
obtained. The length of the inner cone becomes more. Most
of the metals are welded using this flame. Maximum
temperature of about 3200oC - 3300oC at the tip of inner
cone is obtained.
Carburising Flame
 When the quantity of oxygen is less than required for
complete combustion we get carburizing flame. This 2800oC
- 3150oC at the tip of inner cone is obtained. type of flame is
used for welding lead.
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 Mainly two types of weld joints are made by
gas welding :-
◦ Butt Welds i.e. welding two pieces of metal
without any overlap.
◦ Fillet Welds i.e. joining two pieces perpendicular
to each other or with an over lap.
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 Resistance welding processes are
pressure welding processes in which
heavy current is passed for short time
through the area of interface of metals to
be joined. The basic governing equation
 H = I 2 R T, H- total heat generated
 These processes differ from other
welding processes in the respect that no
fluxes are used, and filler metal rarely
used.
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 All resistance welding operations are
automatic and, therefore, all process
variables are preset and maintained
constant.
 Heat is generated in localized area which
is enough to heat the metal to sufficient
temperature, so that the parts can be
joined with the application of pressure.
Pressure is applied through the
electrodes.
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The heat generated during resistance welding is
given by following expression:
H = I 2 R T
 Where, H is heat generated
 I is current in amperes
 R is resistance of area being welded
 T is time for the flow of current.
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Spot welding
Seam welding
Butt welding
Projection welding
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 In resistance spot welding, two or
more sheets of metal are held
between electrodes through which
welding current is supplied for a
definite time and also force is exerted
on work pieces
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 In seam welding overlapping sheets
are gripped between two wheels or
roller disc electrodes and current is
passed to obtain either the continuous
seam i.e. overlapping weld nuggets or
intermittent seam i.e. weld nuggets
are equally spaced
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 In this process projections are provided in
one of the work piece at the place of intended
welding. Thus surface of the work pieces
come in contact with each other only at the
tip of these projections. As the current is
switched on the projection are melted and the
work pieces are pressed together to complete
the weld. The melted projection form the spot
welds simultaneously. The electrodes and the
holding fixtures are suitably designed as per
the shape of the weld.
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 Very little skill is required to operate the
resistance welding machine
 Process is suitable for high production rate
 HAZ (Heat affected Zone) is very small.
 No filler metal is required
 Possible to weld two dissimilar metals or
sheets of different thickness
 Semi-automatic equipment are available
 No consumable other than electricity is
required.
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 Soldering is a process in which two or more
metal items are joined together by melting and
flowing a filler metal into the joint. Filler metal
has relatively low melting point. Bond is through
wetting action. Resulting joints are not as strong
as the base metal but they have adequate
strength.
 It is often confused with welding but the
difference between them is, in soldering the work
piece is not melted, they are joined using a filler
metal, but in welding work piece is joined by
melting.
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 This method is used for joining metals
particularly when they are in the form of
sheets or wires, by using another metal or
alloy which has fairly low melting point
compared to the base metal to be joined. The
metal or alloy used for this purpose is known
as solder. There are two types of solders soft
solder and hard solder.
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 It is a process of joining metals with the help
of hard solder. Brass is generally the main
constituent of this solder. Brazing solder is
commonly known as spelter which is an alloy
of copper, zinc and tin. Hard solder provides
much stronger joint as compared to soft
soldering. However in this case the metal
piece to be joined is heated to slightly above
the melting point of the filler metal.
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 Cracks may be of micro or macro size and
may appear in the weld metal or base metal
or base metal and weld metal boundary.
 Different categories of cracks are
longitudinal cracks, transverse cracks or
radiating/star cracks and cracks in the weld
crater.
 Cracks occur when localized stresses exceed
the ultimate tensile strength of material.
These stresses are developed due to
shrinkage during solidification of weld metal.
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 Porosity results when the gases are entrapped in the
solidifying weld metal.
 These gases are generated from the flux or coating
constituents of the electrode or shielding gases used
during welding or from absorbed moisture in the
coating. Rust, dust, oil and grease present on the
surface of work pieces or on electrodes are also
source of gases during welding.
 Porosity may be easily prevented if work pieces are
properly cleaned from rust, dust, oil and grease.
 Futher, porosity can also be controlled if excessively
high welding currents, faster welding speeds and
long arc lengths are avoided flux and coated
electrodes are properly baked.
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 Slag inclusions may be in the form of slag or any other
nonmetallic material entrapped in the weld metal as these
may not able to float on the surface of the solidifying weld
metal.
 During arc welding flux either in the form of granules or
coating after melting, reacts with the molten weld metal
removing oxides and other impurities in the form of slag
and it floats on the surface of weld metal due to its low
density.
 However, if the molten weld metal has high viscosity or
too low temperature or cools rapidly then the slag may not
be released from the weld pool and may cause inclusion.
 Slag inclusion can be prevented if proper groove is
selected, all the slag from the previously deposited bead is
removed, too high or too low welding currents and long
arcs are avoided.
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 Lack of fusion is the failure to fuse together
either the base metal and weld metal or
subsequent beads in multipass welding
because of failure to raise the temperature of
base metal or previously deposited weld layer
to melting point during welding.
 Lack of fusion can be avoided by properly
cleaning of surfaces to be welded, selecting
proper current, proper welding technique and
correct size of electrode.
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 Imperfect shape means the variation from the
desired shape and size of the weld bead.
 During undercutting a notch is formed either on
one side of the weld bead or both sides in which
stresses tend to concentrate and it can result in
the early failure of the joint.
 Main reasons for undercutting are the excessive
welding currents, long arc lengths and fast travel
speeds.
 Underfilling may be due to low currents, fast
travel speeds and small size of electrodes.
Overlap may occur due to low currents, longer
arc lengths and slower welding speeds.
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