Information abut Welding

1. MANUFACTURING PROCESSES
SUBJECT CODE: BEME301T
3RD SEMESTER
UNIT-3
WELDING
Sandhya M. Umare
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL
ENGINEERING
SVPCET NAGPUR

2. Resistance Welding
PRINCIPLE:
 Resistance welding is a thermo-electric process where heat is generated at the interface of the
parts to be joined by passing an electrical current through them or a precisely controlled time
and under a controlled pressure (also called force)
 In resistance welding the parts to be joined are heated to a plastic state over a limited area by
their resistance to flow of an electric current & mechanical pressure is used to complete the
weld.
 A low voltage & very high current is passed through the joint for a very short time. This high
current(amperage) heats the joint, due to contact resistance at the joint & melts it. The pressure
on the joint is continuously maintained & the metal fuses under pressure. The heat generated
in resistance welding can be expressed as
H = I2 R t ,
Where, H = the total heat generated in the work,J
I = electric current, A
t = time for which the electric current is passing through the joint,s
R = resistance of the electrodes, resistance of the work-piece plates, contact resistance between
the two work-piece plates, contact resistance between the electrode &the work-piece.

3.  The amount of heat released is directly proportional to the resistance.
 Resistance welding is the most commonly used method for joining steel sheets.
 No filler metal is needed. and the heat required for the weld pool is created by means of
resistance to the flow of current by the work- pieces. to be welded, when a high welding
current is directed through the work- pieces. An electro conductive contact surface is created
between the work-pieces by pressing them together.

4.  Water cooled electrodes made of alloyed copper are used in resistance welding. Electrodes
convey a pressing force to the joint and direct the welding current to the joint in the
appropriate manner. After welding, the electrodes rapidly cool down the welded joint.
 Work stages in resistance welding are very fast.
 The surfaces to be welded do not usually need to be cleaned before welding, in addition to
which the weld does not usually require grinding or post heating.
 The resistance welding process can be easily automated.
 Resistance welding is a highly efficient production method that is particularly well-suited for
automated production lines and mass production.
 Resistance welding is also suitable for small batch production, because the method is flexible,
equipment simple and the welding process is easy to control.
 In addition, an important advantage of the method is that it can be used for joining a great
number of metallic materials.
 Resistance welding is also suitable for the welding of the most common metal coated steel
sheets. The maximum thickness of work-pieces that can be welded by means of resistance
welding is approximately 6 mm for uncoated steels and 4 mm for coated steels.
 The major types of resistance welding are given as under: (1) Butt Welding (i) Flash butt
welding (ii) Upset butt welding (2) Spot Welding (3)Seam Welding (4) Projection Welding
(5) Percussion Welding

5. Butt Welding
 Their are two types of butt welding : upset &
flash
 Upset Butt Welding:
 The parts to be welded are clamped edge to
edge in copper jaws of the welding machine &
are brought together in a solid contact so that
their point of contact forms a locality of high
electric resistance, while current flows to heat
the joint.
 At this point pressure applied upsets or forges
the parts together. Upset butt welding is used
principally on non ferrous materials for joining
bars, rods, wires, tubing, formed parts. The
current densities range from 300-800 A/cm2 &
the welding voltage is from 5 to 15 V. The
welding pressure ranges from 17 to55 Mpa.
 Upset Butt Welding Diagram

6. Flash Butt Welding
 In flash butt welding process edges are brought
together in light contact. A high voltage starts a
flashing action between the two surfaces &
continues as the parts advance slowly & forging
temperature is reached.
 The upsetting action forces out the impurities
caused by the flashing. The forced out metal is
called the flash.
 The inner metal is then sound & free of oxides 7
cast metal. Many different materials &
combinations can be flash welded; steels &
ferrous alloys other than cast iron are probably
the most easily welded.
 Those materials that cannot be flash butt welded
are lead, tin, zinc,Antimony, bismuth, & their
alloys. The copper alloys in which these metals
are present in large percentage can not be flash
butt welded. The flash butt welding is
extensively used in in automobile construction –
on the body, axle, wheels, frame & other parts.
The current densities range from 300-800 A/cm2
& the welding voltage is from 5 to 15 V. The
welding pressure ranges from 350 to 1400 Mpa
 Flash Butt Welding

7. Spot welding
 It is employed to join overlapping strips, sheets or plates
at small areas.
 The pieces are assembled & placed between two
electrodes.
 These electrodes must posses high electrical & thermal
conductivity & retain the required strength at high
temperatures. So they are made of pure copper for
limited amount of service, & of alloys of copper &
tungsten , or copper & chromium for continuous
working.
 When the current is turned on, the pieces are heated at
the area of contact to a welding temperature, & with the
aid of mechanical pressure the electrodes are forced
against the metal to be welded.
 The pressure may be developed by foot lever or by air
pressure or by hydraulic cylinders. Practically all
combinations of ductile metals & alloys can be spot
welded.
 The spot welding method is used for fabricating all types
of sheet metal structures where mechanical strength
rather then water or air tightness is required.
Spot Welding Diagram

8. Cont…..
 Before spot welding one must make sure that: (i) The job is clean, i.e., free from grease, dirt,
paint, scale, oxide etc. (ii) Electrode tip surface is clean, since it has to conduct the current into
the work with as little loss as possible. Very fine emery cloth may be used for routine
cleaning. (iii) Water is running through the electrodes in order to (a)Avoid them from getting
overheated and thus damaged, (b)Cool the weld. (iv) Proper welding current has been set on
the current selector switch. (v) Proper time has been set on the weld-timer.
 Spot welding electrodes: Spot welding electrodes are made of materials which have (1) Higher
electrical and thermal resistivities, and(2) Sufficient strength to withstand high pressure at
elevated temperatures. So they are made of pure copper for limited amount of service, & of
alloys of copper & tungsten , or copper & chromium for continuous working.For achieving the
desired current density, It is important to have proper electrode shape for which three main
types of spot welding electrodes are used which are pointed, domed and flat electrodes.
 Applications of Spot Welding: (i) It has applications in automobile and aircraft industries (ii)
The attachment of braces, brackets, pads or clips to formed sheet-metal parts such as cases,
covers or trays is another application of spot welding. (iii) Spot welding of two 12.5 mm thick
steel plates has been done satisfactorily as a replacement for riveting. (iv) Many assemblies of
two or more sheet metal stampings that do not require gas tight or liquid tight joints can be
more economically joined by spot welding than by mechanical methods. (v) Containers and
boxes frequently are spot welded.

9. Seam Welding
 It is a continuous type of spot welding wherein spot
welds overlap each other to the desired extent.
 In this process coalescence at the overlapping surfaces is
produced by the heat obtained from the resistance to the
flow of electric current through the work pieces held
together under pressure by rotating circular electrodes.
 The resulting weld is a series of overlapping resistance-
spots welds made progressively along a joint by rotating
the circular electrodes.
 The seam welding is similar to spot welding, except that
circular rolling electrodes are used to produce a
continuous air-tight seam of overlapping welds.
 Overlapping continuous spot welds seams are produced
by the rotating electrodes and a regularly interrupted
current.
 The material of the rotating circular electrodes is same
as of spot welding electrodes.
 Their diameters may vary from 40 mm. to 350 mm.
 Welding currents range from 2000 to 5000A while the
force applied to the electrodes may be as high as 5 to 6
kN. Welding speeds commonly range from 0.5 m/min to
3.5 m/min.
Seam Welding Diagram
Applications 1. It is used for making
leak proof joints in fuel tanks of
automobiles 2.Except for copper and
high copper alloys, most other metals
can be seam welded. 3.It is also used for
making flange welds for use in water
tight tanks.

10. Projection Welding
 It is modification of spot welding,
 This process is a resistance welding process in
which two or more than two spot welds are made
simultaneously on predetermined locations on the
work-piece portions.
 The current & pressure are localized at weld section
by use of embossed, machined ,or coined
projections on one or both pieces of the work.
 These projections act to localize the heat of the
welding circuit.
 The flattening out of these projections under
pressure results in good welds at all points of
contact. Fig shows the projection welding.
 The pieces to be welded are held in position under
pressure being maintained by electrodes.
 The projected contact spot for welding should be
approximately equal to the weld metal thickness.
 The welding of a nut on the automotive chassis is
an example of projection welding.
Projection Welding Diagram

11. Percussion Welding
 The operation is performed with one part held in a
stationary holder & the other in a clamp mounted
on the slide which is backed up against pressure
from a heavy spring.
 In the welding operation, the movable clamp is
released rapidly carrying the part forward.
 When two plates are about 1.5 mm. apart, sudden
discharge of electrical energy is released, causing
an intense arc between the two surfaces.
 To complete , it takes about 0.1 second. No upset
or flash occurs at the weld.
 This area is limited to small areas of 144 mm2
maximum.
 Percussion welding is a fast method & it can
handle dissimilar metals.
 This is highly suitable for welding small wires to
electrical components.
Percussion welding diagram

12. Thermit Welding
 It is primarily a fusion-welding process in which the weld is affected by
pouring superheated liquid thermal steel around the parts to be welded.
 In the case of thermit pressure welding only the heat of the Thermit reaction is
utilized to bring the surface of metal to be welded in a plastic state and
mechanical pressure is then applied to complete the weld
 The thermit is a mixture of finely divided aluminum & iron oxide,the ratio by
weight being approximately three parts of iron oxide to one part of aluminum.
 The mixture is placed in a refractory lined crucible,& it is ignited with aid of
highly inflammable powder composed of barium peroxide.
 The reaction is non explosive & requires about a minute to go to completion.
 The temperature produced by the thermit reaction is approximately 3,000 0 C
or about twice the temperature of the melting point of steel.
 The mixture burns according to following reaction There are two types of
thermit welding processes: (i) plastic or pressure welding process &(ii) Fusion
or non-pressure welding process

13. Cont….
 Based on the chemical reaction between finely divided aluminum and iron oxide
 Weight is being 3parts of iron oxide to one of Al.
 8Al + 3Fe3 O4 = 3Al2 O4 + 9Fe.
 During reaction oxygen leaves iron oxide and combines with aluminum producing Al. oxides or slag and
superheated thermit steel.
 Temperature - 3000‫ﹾ‬C twice the temperature of melting point of steel
 Working: wax pattern is shaped around the parts to be welded
 Sheet iron box is placed around the wax pattern and space between the pattern and box is filled and
rammed with sand
 Pouring and heating gates and risers are cut and flame is directed into the heating opening.
 The wax pattern melts and drain but the heating continues to raise the temperature of the parts to be
welded
 This preheating is done before the liquid metal pour into the mould in order to prevent chilling of the
steel
 Then the burner or torch is removed and the preheating gate is plug with sand
 Superheated metal produced by the thermit reaction in a crucible is poured into the mould surrounding
the surfaces to be welded. After the welding temperature is reached the mechanical presure is applied to
complete the weldd

14. Diagram of Thermit welding

15. Solid State Welding
 Interatomic bonds may be established by bringing atoms of
two surfaces in close enough proximity to assure
adhesion.
 Relative movement of the surfaces under pressure and
controlled roughness are helpful in breaking through
surface films.
 While theoretically no pressure would be required for
bonding
 Solid state welding includes
 1) Friction 2) explosive 3) Ultrasonic 4) diffusion

16. Friction Welding
 In this process heat for welding
obtained from mechanically induced
sliding motion between rubbing
surfaces of work piece
 One piece is fixed in chuck while other
is rotating
 These parts are brought to rub against
each other under pressure they get
heated due to friction when the desired
forging temperature is attained the
rotation is stopped and the axial
pressure increased to obtain forging
action and joint is obtained
 This process is used for dissimilar
metals such as Al. and titanium,
copper and steel etc
Friction welding diagram

17. Explosive Welding
 Strong metallurgical bonds can be
produces between two metals
 It is carried out by bringing two metal
surfaces with high velocity and high
pressure and with proper orientation,
so that large amount of plastic
interaction takes place between two
surfaces.
 Target plate – W/p held fixed
 Flyer plate – movable
 Least costly method
 Simple in working
 Large surface can be welded
Explosive welding diagram

18. Ultrasonic Welding
 Can join similar or dissimilar metals
 Introduction of high frequency vibration energy (20000
to 60000 htz) into overlapping metals into the area to be
joined
 No flux or filler material is used
 No electrical current passes through the weld
 No heat is applied
 Energy is in the form of mechanical energy
 Sonotrode (welding tool) coupled to the part to be
welded and moves in the longitudinal direction the work
piece remain static.
 The parts to be joined are clamped together between a
welding tip and a supporting member under low static
pressure.
 High frequency vibratory energy is then transmitted into
the weld area for a brief interval.
 This process produces a sound bond without filler
material and arc
 Thickness may vary from 0.38 to 2.5 mm depending on
metal.
Ultrasonic welding diagram

19. Diffusion Welding
 It is a process that does not necessarily
need heat to produce fusion weld
 Rather it needs 2 kind of surfaces that
comes in contact under pressure
 This pressure is applied for a period of
hours
 In this process heating is not required if
the temperature raised the diffusion rate
will be cut sufficiently
 It might take many hours to perform
certain bonding
 This process makes it possible to join
metal to metal , metal to ceramic,
 Temperature approaches approx 900 ‫ﹾ‬C
Diffusion welding diagram

20. Electron Beam Machine (New Methods)
 In EBW process, the heat is generated when the
electron beam impinges on work piece. As the high
velocity electron beam strikes the surfaces to be
welded, their kinetic energy changes to thermal energy
and hence causes the workpiece metal to melt and
fuse. This process employs an electron gun in which
the cathode in form of hot filament of tungsten is the
source of a stream of electrons.
 The electrons emitted from filament by thermionic
emission are accelerated to a high velocity to the
anode because of the large potential difference that
exists between them.
 The potential differences that are used are of the order
of 30 kV to 175 kV. The higher the potential
difference, higher would be the acceleration. The
current levels are low ranging between 50 mA to 1000
mA.
 The electron beam is focused by a magnetic lens
system on the workpieces to be welded. The depth of
penetration of the weld depends on the electron speed
which in turn is dependent upon the accelerating
voltage.
 When the high velocity electron beam strikes the
work-piece all the kinetic energy is converted to heat.
EBM

21. Cont….
 As these electrons penetrate the metal, the material that is directly in the path is melted which
when solidifies form the joint. The penetration of the beam is high.
 The depth to width ratios lies between 10:1 to 30:1 can be easily realized with electron beam
welding. It is also possible to closely control this penetration by controlling the accelerating
voltage, beam current, and beam focus.
 The process can be used at higher welding speeds typically between 125 and 200 mm/sec.
 No filler metal or flux needs to be used in this process.
 It is possible to carry out the electron beam welding in open atmosphere.
 For welding in vacuum, the work-piece is enclosed in a box in which the vacuum is created.
When electron beam moves in the normal atmosphere, the electrons would be impinging with
the gas molecules in the atmosphere and would thus be scattered.
 This scattering increases the spot size of the electron beam and consequently there is lower
penetration.
 As the vacuum increases, the scattering effect of the electron beam decreases and hence,
penetration increases.
 The other advantage of using vacuum is that the weld metal is not contaminated. The EBW
process is mainly used for welding of reactive metals (nuclear reactor components), titanium,
zirconium, stainless steel, etc. for aero-space and automotive industries.

22. Laser Beam Machine (New Methods)
 Laser(light amplification by stimulated emission
of radiation) is a concentrated is a concentrated
beam of coherent beam of monochromatic
radiation.
 Laser welding is performed by focusing coherent
monochromatic light beam emitted by the laser
source onto metal parts which are welded by
surface heating & thermal conduction through the
metal.
 The set up consists of radiation stimulated
emission of radiation.
 The laser beam welding is mainly used for
joining components that need to be joined with
high welding speeds, thin and small weld seams
and low thermal distortion.
 The high welding speeds, an excellent automatic
operation and the possibility to control the
quality online during the process make the laser
welding a common joining method in the modern
industrial production.
LBM

23. Cont…
 The application range covers finest welding of non-porous seams in medical
technology to precision spot welding in electronics or the jewelry industry, to deposit
welding in tool and mold-making and welding complete car bodies in automobile
construction.
 Electrons are atomic particles that exist at specific energy levels. These energy levels
are unique and are different for every atom or molecule.
 Electrons in outer rings are at higher energy levels than those in the inner rings.
 A flash of light can bump electrons to higher energy levels by the injection of energy.
 When an electron drops from an outer ring to an inner ring or level, the excess of
energy is given off as light.
 The wavelength or the color emitted is related to the amount of energy released.
Laser beam welding is a fusion joining process that uses the energy from a laser beam
to melt and subsequently crystallize a metal, resulting in a bond between parts.
 Laser beam welding can be successfully used to join many metals to themselves as
well as to dissimilar metals.
 Main applications are related to welding steels, titanium, and nickel alloys.

24. Brazing
….
Process Capabilities
Brazing
• Joining process in which a filler metal is melted and distributed by
capillary action between faying surfaces of metal parts being joined
• Filler metal Tm greater than 450°C (840°F) but less than Tm of base
metal(s) to be joined
• Dissimilar metals can be assembled with good joint strength
– Typical products: carbide drill bits and carbide inserts on steel
shank
– Intricate lightweight shapes can be joined with little distortion

25. Soldering
Soldering
• Joining process in which a filler metal with Tm less than or equal to 4500C
(8400F) is melted and distributed by capillary action between faying surfaces of
metal parts being joined
• No melting of base metals, but filler metal wets and combines with base metal
to form metallurgical bond
• Used extensively in the electronics industry
• Because solders do not generally have enough strength, they are not used for
load bearing (structural) applications
• Can join various metals and thicknesses
– Cu, Ag, Au are easy to solder
– Al, SS are difficult to solder because of their, strong, thin oxide
film.

26. Advantages of Brazing over welding
Any metals can be joined, including dissimilar metals
• Can be performed quickly and consistently, permitting high
production rates
• Multiple joints can be brazed simultaneously
• In general, less heat and power required than FW
• Problems with HAZ in base metal near joint are reduced
• Joint areas that are inaccessible by many welding processes
can be brazed, since capillary action draws molten filler
metal into joint

27. Welding Defects
Cracking
Prevention:
•Change the weld design to minimize
stresses from shrinkage during cooling
•Change welding process parameters, procedure and
sequences.
•Preheat components being welded
•Avoid rapid cooling of the components after welding

28. Incomplete Fusion or Penetration
Produces poor weld beads due to
insufficient heat input.
Prevention:
•Raise the temperature of the base metal
•Clean the weld area prior to welding
•Adequate shielding gas
•Change the design of joints and type of
electrode
Prof.

29. Porosity
Caused by trapped gases during
solidification of the weld area, chemical
reactions during welding or
contaminations.
Prevention:
•Proper selection of electrodes and
filler material
•Preheating the weld area
•Proper cleaning and preventing
contaminants from entering the weld
zone.

30. Slag Inclusion
Inclusions are compounds such as
oxides, fluxes and electrode coating
materials that are trapped in the
weld zones.
Slag Inclusion
Prevention:
•Clean the weld bead surface before the next layer is
deposited.
•Provide adequate shielding gas
•Change the type of electrode

31. Due to under filling/overfilling and
melting away of base metal.
Prevention:
•Improve welding technique.
•Select proper electrode/filler
material.
Similar to slag inclusion

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