This document provides information about welding as part of an online coaching session for GATE-2020 Mechanical Engineering. It defines welding as a process that joins materials by heating them to suitable temperatures with or without pressure. Welding is used to make permanent joints in applications like automobile bodies, aircraft frames, and shipbuilding. The document discusses different types of welding like plastic welding, fusion welding, arc welding, gas welding, resistance welding, thermit welding, solid state welding, and newer processes like electron-beam and laser welding. It provides details on processes like shielded metal arc welding, gas metal arc welding, gas tungsten arc welding, plasma arc welding, and friction welding. It also covers topics like welding positions, joints

1. Online GATE-2020 Coaching
Mechanical Engineering
Manufacturing/Production Technology
Session-8
Welding
20/06/2020
Dr. D V N J Jagannadha Rao
Associate Professor
Gayatri Vidya Parishad College of Engineering
(Autonomous)
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2. WELDING
– Welding is a materials joining process which produces coalescence
of materials by heating them to suitable temperatures with or
without the application of pressure or by the application of pressure
alone, and with or without the use of filler material.
– Welding is used for making permanent joints.
– It is used in the manufacture of automobile bodies, aircraft frames,
railway wagons, machine frames, structural works, tanks, furniture,
boilers, general repair work and ship building.
– Welding is a materials joining process which produces coalescence
of materials by heating them to suitable temperatures with or
without the application of pressure or by the application of pressure
alone, and with or without the use of filler material.
– Welding is used for making permanent joints.
– It is used in the manufacture of automobile bodies, aircraft frames,
railway wagons, machine frames, structural works, tanks, furniture,
boilers, general repair work and ship building.

3. Types of welding positions

4. Types of welded joints

5. TYPES
• Plastic Welding or Pressure Welding
• The piece of metal to be joined are heated
• to a plastic state and forced together by external
• pressure
(Ex) Forge welding
• Fusion Welding or Non-Pressure Welding
• The material at the joint is heated to a molten state and
allowed to solidify
(Ex) Gas welding, Arc welding
• Plastic Welding or Pressure Welding
• The piece of metal to be joined are heated
• to a plastic state and forced together by external
• pressure
(Ex) Forge welding
• Fusion Welding or Non-Pressure Welding
• The material at the joint is heated to a molten state and
allowed to solidify
(Ex) Gas welding, Arc welding

6. Classification of welding processes:
(i). Arc welding
• Metal arc
• Metal inert gas
• Tungsten inert gas
• Plasma arc
• Submerged arc
• Electro-slag
(ii). Gas Welding
• Oxy-acetylene
(iii). Resistance Welding
• Spot
• Seam
• Projection
• Flash
(iv)Thermit Welding
(v)Solid State Welding
Friction
Ultrasonic
Explosive
(vi)Newer Welding
Electron-beam
Laser
(vii)Related Process
Oxy-acetylene cutting
Arc cutting
Brazing
Soldering
(i). Arc welding
• Metal arc
• Metal inert gas
• Tungsten inert gas
• Plasma arc
• Submerged arc
• Electro-slag
(ii). Gas Welding
• Oxy-acetylene
(iii). Resistance Welding
• Spot
• Seam
• Projection
• Flash
(iv)Thermit Welding
(v)Solid State Welding
Friction
Ultrasonic
Explosive
(vi)Newer Welding
Electron-beam
Laser
(vii)Related Process
Oxy-acetylene cutting
Arc cutting
Brazing
Soldering

7. Arc welding
• Equipments:
• A welding generator (D.C.) or Transformer (A.C.)
• Two cables- one for work and one for electrode
• Electrode holder
• Electrode
• Protective shield
• Gloves
• Wire brush
• Chipping hammer
• Goggles
• Equipments:
• A welding generator (D.C.) or Transformer (A.C.)
• Two cables- one for work and one for electrode
• Electrode holder
• Electrode
• Protective shield
• Gloves
• Wire brush
• Chipping hammer
• Goggles

8. Power Source in Arc
Welding
• Direct current (DC) vs. Alternating current (AC)
– AC machines less expensive to purchase and operate, but
generally restricted to ferrous metals
– DC equipment can be used on all metals and is generally
noted for better arc control
• Direct current (DC) vs. Alternating current (AC)
– AC machines less expensive to purchase and operate, but
generally restricted to ferrous metals
– DC equipment can be used on all metals and is generally
noted for better arc control

9. Comparison of A.C. and D.C. arc welding
Alternating Current (from Transformer)
More efficiency
Power consumption less
Cost of equipment is less
Higher voltage – hence not safe
Not suitable for welding non ferrous metals
Not preferred for welding thin sections
Any terminal can be connected to the work or electrode
Alternating Current (from Transformer)
More efficiency
Power consumption less
Cost of equipment is less
Higher voltage – hence not safe
Not suitable for welding non ferrous metals
Not preferred for welding thin sections
Any terminal can be connected to the work or electrode

10. Direct Current (from Generator)
Less efficiency
Power consumption more
Cost of equipment is more
Low voltage – safer operation
suitable for both ferrous non ferrous metals
preferred for welding thin sections
Positive terminal connected to the work
Negative terminal connected to the electrode
Direct Current (from Generator)
Less efficiency
Power consumption more
Cost of equipment is more
Low voltage – safer operation
suitable for both ferrous non ferrous metals
preferred for welding thin sections
Positive terminal connected to the work
Negative terminal connected to the electrode

11. SMAW - DC Polarity
Straight Polarity Reverse Polarity
(–) (+)
(–)
Deeper weld penetration
(+)
Shallow penetration
(thin metal)
AC - Gives pulsing arc
- used for welding thick sections
Electric arc welding --Polarity
(+)
(–)
Deeper weld penetration
(+)
Shallow penetration
(thin metal)
AC - Gives pulsing arc
- used for welding thick sections

12. Arc Welding Equipment

13. Arc and Power Source Characteristics
in Arc Welding
Arc Characteristics
Power Source Characteristics

16. Types of electrodes
1. Consumable electrodes
❑ consumed during welding process
❑ added to weld joint as filler metal
❑ in the form of rods or spools of wire
2. Non-consumable electrodes
❑ not consumed during welding process but does get gradually
eroded
❑ filler metal must be added separately if it is added
1. Consumable electrodes
❑ consumed during welding process
❑ added to weld joint as filler metal
❑ in the form of rods or spools of wire
2. Non-consumable electrodes
❑ not consumed during welding process but does get gradually
eroded
❑ filler metal must be added separately if it is added

17. Arc welding (AW): Arc shielding
1. At high temperatures in AW, metals are chemically reactive
to oxygen, nitrogen, and hydrogen in air
❑ Mechanical properties of joint can be degraded by these
reactions
❑ Arc must be shielded from surrounding air in AW
processes to prevent reaction
2. Arc shielding is accomplished by
❑ Shielding gases, e.g., argon, helium, CO2
❑ Flux
1. At high temperatures in AW, metals are chemically reactive
to oxygen, nitrogen, and hydrogen in air
❑ Mechanical properties of joint can be degraded by these
reactions
❑ Arc must be shielded from surrounding air in AW
processes to prevent reaction
2. Arc shielding is accomplished by
❑ Shielding gases, e.g., argon, helium, CO2
❑ Flux

18. Consumable Electrode AW Processes
❑ Shielded Metal Arc Welding (or Stick Welding)
❑ Gas Metal Arc Welding (or Metal Inert Gas
Welding)
❑ Flux-Cored Arc Welding
❑ Electro-gas Welding
❑ Submerged Arc Welding
❑ Shielded Metal Arc Welding (or Stick Welding)
❑ Gas Metal Arc Welding (or Metal Inert Gas
Welding)
❑ Flux-Cored Arc Welding
❑ Electro-gas Welding
❑ Submerged Arc Welding

19. ❑ Uses a consumable electrode consisting of a filler metal rod and coating
around rod.
❑ Coating composed of chemicals that provide flux and shielding.
AW: Consumable: Shielded Metal Arc
Welding (SMAW)

20. Functions of electrode coatings
• Electrodes are coated with flux covering. The flux coating can
be cellulose or rutile
• Flux reacts with impurities in the metal, forms slag on top of
the weld bead, protects weld from atmospheric contamination
and prevent heat losses from the weld pool.
• Flux generates voluminous amounts of inert gases like carbon-
di-oxide and protect the weld pool from atmospheric
contamination.
• Alloying elements can be introduced into the weld metal
through flux covering
• Electrodes are coated with flux covering. The flux coating can
be cellulose or rutile
• Flux reacts with impurities in the metal, forms slag on top of
the weld bead, protects weld from atmospheric contamination
and prevent heat losses from the weld pool.
• Flux generates voluminous amounts of inert gases like carbon-
di-oxide and protect the weld pool from atmospheric
contamination.
• Alloying elements can be introduced into the weld metal
through flux covering

21. SMAW Applications
❑ Used
for
steels, stainless steels, cast irons, and
certain
and its alloys, copper
nonferrous alloys.
❑ Not used or rarely used
aluminum alloys, and titanium.
❑ Can be used in windy weather.
❑ Can be used on dirty metals (i.e. painted or rusted surfaces).
❑ Good for repair work.
❑ Makes thick welds.
nonferrous alloys.
❑ Not used or rarely used
aluminum alloys, and titanium.
❑ Can be used in windy weather.
❑ Can be used on dirty metals (i.e. painted or rusted surfaces).
❑ Good for repair work.
❑ Makes thick welds.

22. AW: Consumable: Gas Metal Arc Welding
(GMAW) or Metal Inert Gas (MIG) Welding
Uses a consumable bare metal wire as electrode with shielding by
flooding arc with a gas
1. Wire is fed continuously and automatically from a spool
through the welding gun.
2. Shielding gases include argon and helium for aluminum
welding, and CO2 for steel welding.
3. Bare electrode wire (no flux) plus shielding gases eliminate
slag on weld bead. No need for manual grinding and cleaning
of slag
Uses a consumable bare metal wire as electrode with shielding by
flooding arc with a gas
1. Wire is fed continuously and automatically from a spool
through the welding gun.
2. Shielding gases include argon and helium for aluminum
welding, and CO2 for steel welding.
3. Bare electrode wire (no flux) plus shielding gases eliminate
slag on weld bead. No need for manual grinding and cleaning
of slag

23. GMAW-setup

24. Advantages of GMAW over
SMAW
• Continuous welding because of
continuouswire electrode. Sticks must be periodically
changed in SMAW .
• Higher deposition rates.
• Eliminates problem of slag removal.
• Can be readily automated.
• Has better control to make cleaner and narrower
welds than SMAW.
• Continuous welding because of
continuouswire electrode. Sticks must be periodically
changed in SMAW .
• Higher deposition rates.
• Eliminates problem of slag removal.
• Can be readily automated.
• Has better control to make cleaner and narrower
welds than SMAW.

25. GMAW
Applications
• Used to weld ferrous and various non-ferrous and metals.
• Good for fabrications such as frames and farm equipment.
• Can weld thicker metal.
• Metal must be clean to start weld.
• Used to weld ferrous and various non-ferrous and metals.
• Good for fabrications such as frames and farm equipment.
• Can weld thicker metal.
• Metal must be clean to start weld.

26. Non-consumable Electrode Processes
❑ Gas Tungsten Arc Welding
❑ Plasma Arc Welding
❑ Carbon Arc Welding
❑ Stud Welding
❑ Gas Tungsten Arc Welding
❑ Plasma Arc Welding
❑ Carbon Arc Welding
❑ Stud Welding

27. AW: non-consumable electrode processes: Gas
Tungsten Arc Welding (GTAW) or Tungsten Inert
Gas (TIG) Welding
Uses a non-consumable tungsten electrode and an inert gas for arc
shielding
• Melting point of tungsten = 3410°C (6170°F).
• Used with or without a filler metal. When filler metal used, it is
added to weld pool from separate rod or wire.
• Applications: aluminum and stainless steel mostly.
Uses a non-consumable tungsten electrode and an inert gas for arc
shielding
• Melting point of tungsten = 3410°C (6170°F).
• Used with or without a filler metal. When filler metal used, it is
added to weld pool from separate rod or wire.
• Applications: aluminum and stainless steel mostly.

28. GTAW

29. Advantages and Disadvantages of GTAW
Advantages:
1. High quality welds for suitable applications
- Welds are cleaner and narrower than MIG
2. No spatter because no filler metal through arc
3. Little or no post-weld cleaning because no flux
Disadvantages:
1. More difficult to use than MIG welding
2. More costly than MIG welding
Advantages:
1. High quality welds for suitable applications
- Welds are cleaner and narrower than MIG
2. No spatter because no filler metal through arc
3. Little or no post-weld cleaning because no flux
Disadvantages:
1. More difficult to use than MIG welding
2. More costly than MIG welding

30. Applications of GTAW
1. Used to weld ferrous and various non-ferrous and metals.
2. Can weld various dissimilar metals together.
3. Good for fabrications such as aircraft or race car frames.
4. Used for welding thinner metal parts (not as thick as MIG).
5. Metal must be very clean to start weld.
1. Used to weld ferrous and various non-ferrous and metals.
2. Can weld various dissimilar metals together.
3. Good for fabrications such as aircraft or race car frames.
4. Used for welding thinner metal parts (not as thick as MIG).
5. Metal must be very clean to start weld.

31. Plasma Arc
Welding

32. Advantages and Disadvantages of PAW
Advantages:
• Good arc stability and excellent weld quality
• Better penetration control than other AW
processes
• High travel speeds
•Can be used to weld almost any metals
Disadvantages:
• High equipment cost
• Larger torch size than other AW processes
– Tends to restrict access in some joints
Advantages:
• Good arc stability and excellent weld quality
• Better penetration control than other AW
processes
• High travel speeds
•Can be used to weld almost any metals
Disadvantages:
• High equipment cost
• Larger torch size than other AW processes
– Tends to restrict access in some joints

33. Arc welding
Advantages
– Most efficient way to join
metals
– Lowest-cost joining
method
– Affords lighter weight
through better utilization
of materials
– Joins all commercial
metals
– Provides design flexibility
Limitations
• Manually applied, therefore
high labor cost.
• Need high energy causing
danger
• Not convenient for
disassembly.
• Defects are hard to detect at
joints.
Advantages
– Most efficient way to join
metals
– Lowest-cost joining
method
– Affords lighter weight
through better utilization
of materials
– Joins all commercial
metals
– Provides design flexibility
Limitations
• Manually applied, therefore
high labor cost.
• Need high energy causing
danger
• Not convenient for
disassembly.
• Defects are hard to detect at
joints.

34. Heat input in welding

37. Friction Welding (FRW)
• In FRW coalescence is achieved by frictional heat combined
with pressure
• When properly carried out, no melting
occurs at faying surfaces
• No filler metal, flux, or shielding gases normally used
• Process yields a narrow HAZ
• Can be used to join dissimilar metals
• Widely used commercial process, amenable to automation and
mass production
• In FRW coalescence is achieved by frictional heat combined
with pressure
• When properly carried out, no melting
occurs at faying surfaces
• No filler metal, flux, or shielding gases normally used
• Process yields a narrow HAZ
• Can be used to join dissimilar metals
• Widely used commercial process, amenable to automation and
mass production

38. • (1) Rotating part, no contact; (2) parts brought into contact to
generate friction heat; (3) rotation stopped and axial pressure
applied; and (4) weld created
Friction
Welding

39. Applications and Limitations of Friction Welding
Applications:
• Shafts and tubular parts
• Industries: automotive, aircraft, farm equipment,
petroleum and natural gas
Limitations:
• At least one of the parts must be rotational
• Flash must usually be removed (extra operation)
• Upsetting reduces the part lengths (which must be taken into
consideration in product design)
Applications:
• Shafts and tubular parts
• Industries: automotive, aircraft, farm equipment,
petroleum and natural gas
Limitations:
• At least one of the parts must be rotational
• Flash must usually be removed (extra operation)
• Upsetting reduces the part lengths (which must be taken into
consideration in product design)

40. Resistance Welding (RW)
These are a group of fusion welding processes that use a
combination of heat and pressure to accomplish coalescence
• Heat generated by electrical resistance to
current flow at junction to be welded
• Principal RW process is resistance spot welding (RSW)
These are a group of fusion welding processes that use a
combination of heat and pressure to accomplish coalescence
• Heat generated by electrical resistance to
current flow at junction to be welded
• Principal RW process is resistance spot welding (RSW)

41. Resistance Spot Welding

42. Components in Resistance Spot Welding
• Parts to be welded (usually sheet metal)
• Two opposing electrodes
• Means of applying pressure to squeeze parts between
electrodes
• Power supply from which a controlled current can be applied
for a specified time duration
• Parts to be welded (usually sheet metal)
• Two opposing electrodes
• Means of applying pressure to squeeze parts between
electrodes
• Power supply from which a controlled current can be applied
for a specified time duration

43. Resistance Spot Welding (RSW)
In resistance welding process the fusion of faying surfaces of
a lap joint is achieved at one location by opposing electrodes
through passage of huge current for a short period of time
• Used to join sheet metal parts
• Widely used in mass production of automobiles,
metal furniture, appliances, and other sheet metal products
– Typical car body has ~ 10,000 spot welds
In resistance welding process the fusion of faying surfaces of
a lap joint is achieved at one location by opposing electrodes
through passage of huge current for a short period of time
• Used to join sheet metal parts
• Widely used in mass production of automobiles,
metal furniture, appliances, and other sheet metal products
– Typical car body has ~ 10,000 spot welds

44. Spot Welding Cycle

45. Advantages and Drawbacks of Resistance Welding
Advantages:
• No filler metal required
• High production rates are possible
• Lends itself to mechanization and automation
• Lower operator skill level than for arc welding
•Good repeatability and reliability
Disadvantages:
• High initial equipment cost
• Limited to lap joints for most RW processes
Advantages:
• No filler metal required
• High production rates are possible
• Lends itself to mechanization and automation
• Lower operator skill level than for arc welding
•Good repeatability and reliability
Disadvantages:
• High initial equipment cost
• Limited to lap joints for most RW processes

46. Resistance Seam Welding

47. Resistance Projection Welding
(RPW)
In a resistance welding process coalescence occurs at one or
more small contact points on the parts
• Contact points determined by design of parts to be joined
• May consist of projections, embossments, or localized
intersections of parts
In a resistance welding process coalescence occurs at one or
more small contact points on the parts
• Contact points determined by design of parts to be joined
• May consist of projections, embossments, or localized
intersections of parts

48. (1) Start of operation, contact between parts is at projections;
(2)when current is applied, weld nuggets similar to spot welding
are formed at the projections
Resistance Projection Welding
RAVI
VISHWAKARMA

49. Other Resistance Projection Welding Operations
• (a) Welding of fastener on sheet metal
• (b) cross-wire welding

50. Heat input in resistance welding

53. THANKS
53