ELECTRICAL WELDING, DIFFERENT TYPES, AC WELDING DC WELDING,

1. Electric Welding

2. What is welding ?
 Welding which is the process of joining two metallic components for the desired
purpose, can be defined as the process of joining two similar or dissimilar metallic
components with the application of heat, with or without the application of
pressure and with or without the use of filler metal.
 Heat may be obtained by chemical reaction, electric arc, electrical resistance,
frictional heat, sound and light energy.
 Two types:
1.Fusion welding: Involves melting of parent metal.
eg:: carbon arc welding and gas welding.
2.Non-fusion welding: It does not involve the melting of parent metal.
eg:: resistance welding.

4. Electrical Welding
 The process of welding together, through the use of the heat that is produced by
an electric current, pieces of metal

5.  ADVANTAGES
1) Higher welding speeds
2) Greater affidavit rates
3) Less post welding cleaning
4) Better weld pool perceivability
5) No stub end misfortunes or squandered worker hours brought on by changing terminals
6) Positional welding offers no issues when contrasted with different procedures.
7) The procedure is effortlessly robotized
8) No fluxes required by and large
9) Ultra low hydrogen process

6. DISADVANTAGES
1) Higher introductory setup cost
2) Higher upkeep costs because of additional electronic parts
3) The setting of plant variables requires a high aptitude level
4) Less productive where high obligation cycle prerequisites are vital
5) Radiation impacts are more extreme

7. Resistance Welding
 Resistance welding is that process in which a sufficient strong electric current is sent through the
two metal pieces in contact to the welded which melts the metals by the resistance they offer to
the flow of the electric current
 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.

8.  The process employs currents of the order of few KA, voltages range from 2 to 12
volts and times vary from few ms to few seconds. Force is normally applied
before, during and after the flow of current to avoid arcing between the
surfaces and to forge the weld metal during post heating.
 For good quality welds these parameters may be properly selected which shall
depend mainly on material of components, their thicknesses, type and size of
electrodes.

9. Advantages
 Heat is localized where required.
 Welding action is rapid.
 No filler material is needed.
 Require comparatively lesser skill.
 IT IS suitable for large quantity production.
 Both similar & dissimilar metals can be welded.
 Difficult shapes& sections can be welded.

10. Spot Welding
 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.

11.  The welding cycle starts with
the upper electrode moving
and contacting the work
pieces resting on lower
electrode which is stationary.
 The work pieces are held
under pressure and only then
heavy current is passed
between the electrodes for
preset time. The area of
metals in contact shall be
rapidly raised to welding
temperature, due to the flow
of current through the
contacting surfaces of work
pieces.

12.  Weld Nugget. In resistance spot welding, "the welding of overlapping pieces of
metal at small points by application of pressure and electric current" creates a
pool of molten metal that quickly cools and solidifies into a round joint known as
a "nugget."
 Most of the industrial metal can be welded by spot welding,
 However, it is applicable only for limited thickness of components. Ease of
mechanism, high speed of operation and dissimilar metal combination welding,
has made is widely applicable and acceptable process.
 It is widely being used in electronic, electrical, aircraft, automobile and home
appliances industries.

13. Seam Welding
 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.
Welding current may be
continuous or in pulses.

14.  In this process metals to be welded is
placed between the two wheels
which apply sufficient mechanical
pressure & also carry sufficient current for
producing continuous welds.
 The mechanical pressure applied is
keptconstant & the current is applied for
a regular interval. As the pressure applied,
the welding current switched on &
simultaneous the overlapping surfaces of
the metal are heat is generated due
to flow of current through the in the
welding.
 The electrodes are made of copper
alloys.

15.  Overlapping of weld nuggets may vary from 10 to 50 %. When it is approaching
around 50 % then it is termed as continuous weld. Overlap welds are used for air or
water tightness.
 It is the method of welding which is completely mechanized and used for making
petrol tanks for automobiles, seam welded tubes, drums and other components of
domestic applications.
 Seam welding is relatively fast method of welding producing quality welds. However,
equipment is costly and maintenance is expensive. Further, the process is limited to
components of thickness less than 3 mm.

16. Projection Welding:
 Projections are little projected raised points
which offer resistance during passage of
current and thus generating heat at those
points.
 These projections collapse under heated
conditions and pressure leading to the
welding of two parts on cooling.
 The operation is performed on a press
welding machine and components are put
between water cooled copper platens
under pressure.

17.  These projections can be generated by press working or machining on one part or by
putting some external member between two parts. Members such as wire, wire ring,
washer or nut can be put between two parts to generate natural projection.
 Insert electrodes are used on copper platen so that with continuous use only insert
electrodes are damaged and copper platen is safe. Relatively cheaper electrode inserts
can be easily replaced whenever these are damaged.

18.  Projection welding may be carried out with one projection or more than one
projections simultaneously.
 No consumables are required in projection welding. It is widely being used for
fastening attachments like brackets and nuts etc to sheet metal which may be
required in electronic, electrical and domestic equipment.

19. Butt Welding
 In this case, the two pieces are brought into
contactend-to-end & the butted ends are
heated by a heavy current through the joints.
As in the other forms of resistance welding,
the weld heat is produced mainly by the
electrical resistance of the joint faces
 In the cases, however, the electrodes are in
the form of clamps which hold the work
pieces & also carry the pressure to the joints.
 This process is useful where parts have to be
joined end-to-end or edge-to-edge

21. Flash Butt Welding
 It is similar to butt welding hut with the
difference that here current is applied when
ends of the two metal pieces are quite close
to each other hut do not touch intimately.
 Hence, an arc or flash is set up between
them which supplies the necessary welding
heat.
 In the process heat is applied before the two
parts are pressed together. The work pieces
to be welded are damped into specially
designed electrodes one of which is fixed
where as the other is movable..
 After the flash has melted their faces, current
is cut off & the movable camp applies the
pressure to form weld.

22. Advantages
 Even rough or irregular ends can be flash-welded. There is no need to lev
them by machining & grinding because all irregularities are burnt away durin
flashing period.
 It is much quicker than butt welding.
 It uses considerably less current than butt welding.
 One of its major advantages is that dissimilar metals with different welding temperatures can be flash-welded
Applications
 This process is useful where parts have to be joined end-to-end or edge- to - edge.
 To assemble rods, bars, tubings, sheets & most ferrous metals.
 In the production of wheel rims for automobiles
 & bicycles.
 For welding tubular such as automobiles break cross - shafts.
 For welding tube coils for refrigeration plants etc.

23. Arc Welding
 Arc welding uses a welding power supply to create an electric
arcbetween an electrode and the base material to melt the metals at
the welding point.
 They can use either direct (DC) or alternating (AC) current, and
consumable or non-consumable electrodes.
 The welding region is sometimes protected by some type of inert gas,
known as a shielding gas, and/or an evaporating filler material.

 The voltages require is about 1oo volts
 The arc voltage varies from 20 to 40 volts & current from. 50 to 1ooo
amperes
 The temperature produces by the arcis about 3500-4000c

24. • The arc is struck between
the electrode and the
metal. It then heats the
metal to a melting point.
The electrode is then
removed, breaking the arc
between the electrode and
the metal. This allows the
molten metal to "freeze" or
solidify.
• The arc is like a flame
of intense heat that is
generated as the
electrical current
passes through a
highly resistant air gap.

25. Carbon Arc Welding
 Carbon arc welding (CAW) is a process which produces coalescence of
metals by heating them with an arc between a non-
consumable carbon (graphite) electrodeand the work-piece.
 The process of carbon arc welding uses low voltage, high amp electricity
to heat the metal once an arc is formed between a carbon electrode
and the piece being welded; if an arc is formed between two carbon
electrodes that technique is known as a twin-carbon arc.
 The technique of single-carbon arc welding uses a direct current power
supply which if required, filler rod may be used in Carbon Arc Welding. End
of the rod is held in the arc zone. The molten rod material is supplied to the
weld pool.
 Shields (neutral gas, flux) may be used for weld pool protection depending
on type of welded metal. is connected using a straight polarity.

26. Electrodes
 Electrodes can be classified into Non-Consumable Electrodes and Consumable
Electrodes.
 The composition of electrode depends up on the metal to be welded. For
example for welding mild steel electrode of similar composition is used so as to get
a homogeneous weld joint.
 The size (diameter) of electrode depends up on the amount of weld metal to be
deposited and the gap between the two plates to be welded.
 Higher currents will be required when bigger diameter electrodes are used.

27. Non-consumable Electrodes
 Non-consumable electrodes are those electrodes, which do not consumed during the
welding process. Separate filler metals are necessary to fill the gap between the joints.
 Non-consumable electrodes are made up of higher melting point materials like carbon
(melting point -6700°F), graphite or pure tungsten(melting point - 6150°F).
 Non-consumable electrodes are used in Carbon Arc Welding and TIG Welding.
 Using Non-consumable electrodes, good control over the process is possible.
 As compared to carbon electrodes, tungsten electrodes are more expensive and alloy
tungsten electrodes are still more costlier.
 Alloying tungsten increases emissivity, resistance to contamination, arc stability and
contamination. Also electrode consumption is less.

28. Consumable Electrodes
 Consumable Electrode possess more thermal efficiency than non-consumable
electrode.
 Are consumed during welding operation. May be made of various metals
depending upon the purpose and chemical composition of the metals to be
welded.
 Bare electrodes are used in coil form with out coating in MIG Welding.
 Metal Arc welding make use of coated electrode.
 Commonly used core wire materials are : mild steel, low alloy steel, nickel steel etc.

29. Consumable Electrodes may be classified into
1. Bare Electrodes : There won’t be any coating of flux in case of bare electrodes. Arc
produced by bare electrode is unstable. Joint produced by bare electrodes are not strong
enough. Also irregular metal transfer and atmospheric contamination takes place. Bare
electrodes are used when strength is not a primary concern.
2. Coated Electrodes : Molten metal is exposed to oxygen and nitrogen in the atmosphere
and so undesirable oxides and other substances decreasing the strength of the weld
formed.
 Coated electrodes (Flux Coated) are used to prevent the formation of oxidizes and helps
to form slag. Due to Flux coating the molten metal is not exposed to oxygen and nitrogen
in the atmosphere resulting in strong bond.
 Coated electrodes produce very good weld appearances and defect free joints.
Commonly used fluxes are asbestos, mica, silica etc.
Coated Electrodes are again classified into
a) Lightly Coated Electrodes : Thin coating of Flux.
b) Medium Coated Electrodes: Medium coating of Flux.
c) Heavily Coated Electrodes : Thick coating of Flux.

30. Advantages of Carbon Arc Welding:
• Low cost of equipment and welding
operation;
• High level of operator skill is not required;
• The process is easily automated;
• Low distortion of work piece.
Disadvantages of Carbon Arc Welding:
• Unstable quality of the weld (porosity);
• Carbon of electrode contaminates weld
material with carbides.
• Welding of Sheet Steel, Copper Alloys, brass
, bronze and aluminum.

31. Shielded Metal Arc Welding (SMAW)
 The shielded or manual metal arc (SMA)
process, is widely used for the fabrication of
pressure vessels, pipe work and pipeline joints,
as well as for the repair and maintenance of
industrial machinery.
 An arc is established between the electrode
and the base metal at the joint line. The arc
melts a portion of the base metal and the
electrode to form a weld pool.
 The molten metal is protected from the
surrounding atmosphere by decomposition
of the electrode coating which forms a
gaseous cloud.
 Flux Shielded Metal Arc Welding is an arc
welding process in which weld is produced
by heating the work-piece with an arc setup
between the flux coated electrode and the
work-piece.

32.  Steel when exposed to air forms
oxides and nitrides. These impurities
weaken the weld. To prevent this
molten metal is shielded by
enveloping it completely with an inert
gas or flux.
 In this method a metal rod is used as
negative electrode and work being
welded as positive.
 Arc melts the electrode and the job.
The flux coating melts, produces a
gaseous shield to prevent the
atmospheric contamination of the
molten weld metal.
 The arc produced between these two
electrodes heats the metal to the
melting temperature (about 2400-
2600° C).
 Both A.C and D.C can be used.

33. Advantages :
 Flux Shielded Metal Arc Welding is
the simplest of all the arc welding
process.
 Equipment is portable.
 Big range of metals and alloys
can be welded.
 Good weld quality can be
obtained.
 Cost is fairly low.
Disadvantages :
 Mechanization is difficult due to
the limited length of electrode.
 Process is slow.
 Metal transfer is not clear.
Applications :
 Used for fabrication work and
maintenance work.
 All commonly employed metals
and alloys can be welded.
 The process finds applications in
a) Ship building
b) Pipes and penstock joining.
c) Building and bridges
construction.
d) Automotive and Aircraft
industry.

34. Metal inert gas arc welding (MIG)
 MIG make use of the high heat produced by the electric arc between the
consumable electrode and material to be welded.
 Gas Metal Arc Welding is a shielded metal arc process.
 The electrode is continuously fed through a gun.
 The current ranges from 100 to 400 A depending upon the diameter of the wire.
 The speed of melting of the wire may be up to 5m/min.
 Usually constant voltage D.C machine is used for MIG Welding.
 Welding Gun is either water cooled or air cooled.
 Welding wire is often bare.
 CO2, argon or argon helium mixtures are often used as shielding gases.
 Shielding is done to prevent contamination of weld.

36. Advantages :
 Does not require much skill.
 Continuous welding at high speeds
can be carried out.
 Deeper penetration is possible.
 Process can be mechanized.
 Thick and thin sections can be
welded easily.
 Large metal deposition rates can be
obtained.
 No flux is used.
 Faster compared to TIG and Metal
Arc Welding.
 Welding Equipment is much
complex.
 Difficult to weld small corners.
 Slightly complex than TIG.
Applications :
 Used for welding of carbon, silicon
and low alloy steels, stainless steels,
aluminum, magnesium, copper,
nickel and their alloys, titanium etc.
 Used for manufacture of refrigerator
parts.
 Used in industries like aircraft,
automobile, pressure vessel and ship
building.

37. Gas-Tungsten-Arc Welding(GTAW) or Tungsten Inert Gas
Welding (TIG) :
Principle
 Gas Tungsten Arc Welding is a shielded metal arc process.
 TIG Make use of the high heat produced by the electric arc between the
non-consumable tungsten electrode and material to be welded.
 Tungsten Electrode is used only to generate an arc.
 Filler metal may be or may not be used.
 Shielding is obtained by an inert gas such as helium or argon or mixture of
two.
 Shielding is done to prevent contamination of weld.
 Usually A.C machine is used for TIG Welding (for nonferrous alloys) except
for ferrous alloys d.c is used.

39. Advantages :
 More different types of metals can be welded such as carbon steel, nickel steel, aluminum,
brass, bronze, titanium.
 Unlike metals can be welded to each other like mild steel, stainless steel, brass to copper.
 Heat affected zone is very low.
 No flux is used.
 Clear visibility of arc.
 Smooth welds can be obtained.
Disadvantages :
 Under similar applications MIG is faster than TIG.
 Tungsten if transferred can contaminate the same.
 Costly.
Applications :
 Welding sheet metals and thinner sections.
 Used in precision welding in atomic energy, aircraft and instrument industries.