This document discusses various welding and joining processes. It begins by classifying welding into fusion welding, where the metal is melted and solidified, and plastic welding, where the metal is heated to a plastic state. It then describes various gas, arc, resistance, and special welding techniques. Brazing and soldering processes are also covered, where a filler metal is used to join below and above 450°C, respectively. Common defects in welding are also listed.

1. UNIT-III
WELDING
Introduction, classification of welding processes – Gas welding, types of
flames and applications. Electric arc welding, Resistance welding, Soldering
and Brazing processes and their uses.

2. Fusion welding
The metal at the joint is heated to a molten state and then it is
allowed to solidify. E.g. – gas welding , Arc welding, Thermit
welding
The metal at the joint is heated to a plastic state and are pressed
together to make the joint. E.g. – Electric resistance welding,
Forge welding
Plastic welding

4. Types of gas welding
2. Air – Acetylene welding
Air taken from the atmosphere and compressed , mixed the acetylene to
the required proportion. Temperature is lower than oxy-acetylene
welding.
3. Oxy – Hydrogen welding
Oxygen and hydrogen gases are mixed with the required proportion. It
is used for low temperature welding metals like aluminium, lead.
1. Oxy – Acetylene welding
 Hottest region - 3200°C
 Acetylene pressure not more than 1.5atm
 Oxygen pressure – HP -0.1 to 3.5 bar, LP – 0.5
to 3.5bar,Torch pressure upto 0.06bar.
 CaC2+2H2O Ca(OH)2+C2H2+127.3 Kj/mol.
 Metal 2mm to 50mm thick are welded.

5. Gas Welding Equipments
Oxygen- black (125-140kg/cm2)
Acetylene-maroon(16kg/cm2)

6. Flame Characteristics
1. Neutral Flame
 Equal quantity of oxygen and acetylene.
 Inner cone develops heat to melt the metal.
 Outer cone are
2. Carburising Flame  More acetylene than oxygen.
 Sharp Inner cone
 White intermediate cone called feather cone
 Bluish Outer cone

7. Flame Characteristics
3. Oxidising Flame
 More oxygen than acetylene.
 Smaller Inner cone
 Outer cone

8. Gas Welding Technique
1. Leftward or Forward Welding
2. Rightward or Backward Welding

9. Manual Metal Arc Welding

10. Arc Welding Equipment
Heat is developed by an electric arc

11. Filler rod – Gas Welding Equipment
To supply additional metal to make the joint. Metal rod as a parent metal.
D=t/2 + 1
Electrode – Arc Welding Equipment
1. Consumable electrodes
It used to produce arc between work and electrode but also provides
filler material during welding
i. Bare electrode ii.Lightly coated electrode(1-5%) iii. Heavily coated
electrode (1to 3mm & 15-30%)
2. Non- Consumable electrodes
Made of carbon, graphite which do not consume during welding
Arc length remains constant and stable.

12. Specification and choice of Electrodes

13. TUNGSTEN INERT GAS WELDING (TIG)
GAS TUNGSTEN ARC WELDING (GTAW)
Tungsten carbide melting point- 330°c
Less than 6.5mm metal thickness

14. GAS METAL ARC WELDING (GMAW)
MIG – METAL INERT GAS WELDING

15. FLUX CORE
When the flux is required continuously or where large quantity of flux has to be
supplied, on that time the flux is used in the form of wire wound on a rotating drum or
reel called as flux core.
1. Submerged Arc welding (SAW)

16. 2. Electro Slag welding (ESW)
FLUX CORE

17. RESISTANCE WELDING

18. 1.0 SPOT WELDING
0.025mm to 1.25mm thickness metal sheats
RESISTANCE WELDING

19. 2.0 BUTT WELDING
1. Upset butt welding 2. Flash butt welding
RESISTANCE WELDING

20. 3.0 SEAM WELDING
RESISTANCE WELDING

21. 4.0 PERCUSSION WELDING
RESISTANCE WELDING

22. PROJECTION WELDING

23. STUD WELDING

24. SPECIAL WELDING
2. Thermit welding

25. SPECIAL WELDING
3. Electron Beam welding

26. SPECIAL WELDING
Plasma Arc welding (PAW)

27. LASER BEAM WELDING

28. SPECIAL WELDING
4. Friction welding

29. FRICTION STIR WELDING

30. DEFECTS IN WELDING
 In complete fusion
 Cracks
 Porosity
 Under cut
 Over lapping

31. BRAZING
Joining of two metal pieces by using a filler metal and the
liquid temperature is above 450 deg C.
Joining of two metal pieces by using a filler metal and the
liquid temperature is below 430 deg C.
SOLDERING

32. METHODS AND PROCESS CAPABILITES - BRAZING
 Torch brazing
Acetylene, natural gas and butane are combined with air or oxygen.
 Furnace brazing
The heat is supplied by gas or electric heating coils.
 Induction brazing
Heated by placing within the field of high frequency induction coil.
 Dip Brazing
Chemical dip - Filler metal placed in molten bath or flux.
Molten metal bath – The assembled parts are first prefluxed and then
immersed into molten bath.
 Resistance brazing
Rapid heating minimizes oxidation and the heat affected zone is small
 Laser brazing and electron beam brazing
Laser beam and electron beam are used to join the metal.

33. METHODS AND PROCESS CAPABILITES - SOLDERING
 Hard Soldering
The filler metal is silver. Also called as Silver soldering.
 Soft Soldering
Soldering iron is copper rod.
 Dip Soldering
A large amount of solder is melted in a closed tank and parts to
be soldered are cleaned and properly dipped in a flux bath.
 Wave soldering
Parts is not dipped into the solder tank but wave is generated in
the tank.

34. FILLER MATERIALS
FLUX MATERIALS
1. Chlorides 2. Borax and boric acid,
3. Borates, 4. Fluorides.

35. TYPES OF ADHESIVE BONDING