The document discusses various joining processes including welding, brazing and soldering. It describes different welding techniques such as gas welding, arc welding and various specialized welding processes. It also discusses resistance welding processes, filler materials, fluxes used and types of adhesive bonding.

1. JOINING PROCESSES
Fusion welding processes – Types of Gas welding – Equipments used –
Flame characteristics – Filler and Flux materials - Arc welding equipments -
Electrodes – Coating and specifications – Principles of Resistance welding –
Spot/butt, seam welding – Percussion welding - Gas metal arc welding –
Flux cored – Submerged arc welding – Electro slag welding – TIG welding
– Principle and application of special welding processes - Plasma arc
welding – Thermit welding – Electron beam welding – Friction welding –
Diffusion welding – Weld defects – Brazing and soldering process –
Methods and process capabilities – Filler materials and fluxes – Types of
Adhesive bonding.

2.  INTRODUCTION:
 The process of joining similar metals by the application
of heat is called ‘Welding’.
 Welding can be obtained with or without application of
pressure and with or without addition filler metal, which
known as ‘ electrode’.
 During welding the edges of these metal pieces are either
melted or brought to the plastic condition.
 A good welded joint is as strong as the parent metal. It is
also used in various industries such as aircraft frame
works, railway wagons, furniture, automobile bodies,
ship building etc


3. Fusion welding
The metal at the joint is heated to a molten state and then it is
allowed to solidify. Pressure is not applied during the welding
process, it is also called as non pressure welding. 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

6. Flame Characteristics
1. Neutral Flame
 Equal quantity of oxygen and acetylene.
 Inner cone develops heat to melt the metal.
 Outer cone are
Used for welding steel, cast iron, copper Al .
2. Carburising Flame  More acetylene than oxygen.
 Sharp Inner cone
 White intermediate cone called feather cone
 Bluish Outer cone
 Used for welding very low carbon steel,
monel metal, alloy steels, non ferrous
materials.

7. Flame Characteristics
3. Oxidising Flame
 More oxygen than acetylene.
 Smaller Inner cone
 Outer cone
 Used for welding brass and bronze.

8.  Gas welding Technique:
 In gas welding, the speed and quality of the welding can
be improved by the proper selection of torch size, filler
material, method of moving the torch along the weld and
the angle at which the torch is held
 Leftward or forward welding:
 This method allows the preheating of the plate
immediately ahead of the molten pool.
 The torch is very slight sideways movement.
 The rod should be moved faster without sideways
movement
 M.S plate up to 5mm thichness and cast iron and non-
ferrous metals

9.  Rightward or backward welding:
 The torch flame moves left to right.
 There is no sideways movement in this welding
 The torch held at an angle between 40 to 50to the plane
of the weld
 Welding rod is at 30 to 40. The welding speed is 20 to
25% higher and the fuel consumption is 15 to 25% lower
than rightward welding
 It provides a better shielding against atmospheric
reaction.
 Advantages:
 Temperature of flame can be easily controlled
 All types of metal can be weld
 The cost of equipment is less

10.  The flame can be used for welding and cutting
 It can be used in the factory of in the field
 Maintenance cost of gas welding equipment is less
 Disadvantages:
 It is not useful joining the thick plate
 It is a slow process
 Strength of weld is not so good as arc welding
 Handling and storing of gas cylinders need more car
 Gas flame takes up a longer time to heat up the metal
than an electric arc.

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

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

13. Specification and choice of Electrodes

14.  Electrode types:
 (i) Consumable electrode and
 (ii) Non-Consumables electrode
 Consumable electrode:
 The Consumable electrode is not only used to produce
arc between work and electrode but also provides filler
material during welding
 These may be made of various metals depending upon
their purpose and the chemical composition of the
metals to be welded.
 1. Bare electrodes 2. Lightly coated electrode
 3. Heavily coated electrode.

15.  Bare electrodes: do not have any coating of flux on their
surface.
 They must be used only straight polarity
 Bare electrode are used, the molten metal reacts with the
atmosphere
 This causes defects in the weld
 Used in the submerged arc welding and inert gas
welding.
 Lightly coated electrodes: have a coating layer of several
tenths of a millimeter and is 1 to 5% of the electrode wt.
 Main purpose of light coating is to increase arc stability.
 It does not prevent oxidation of molten metal.
 The welds due to lack of protection of oxidation reaction
have poor mechanical properties.

16.  Heavily coated electrodes are covered with high quality
covering of 1 to 3mm thick
 This coating composed of ionizing, deoxidizing, gas
generating, slag forming alloying and binding materials.
 The wt of coating is from 15 to 30% of the electrode rod.
 The greatest amount of welding is done.
 Purpose of flux:
 To give stability to the arc
 To produce a gas shield around the arc and the molten
metal. It prevents atmospheric reaction
 To provide the formation of slag so to protect the welding
seam from rapid cooling
 The alloying elements increase the strength of the weld
 Increase deposition efficiency.

17. RESISTANCE WELDING

18. 1.0 SPOT WELDING
0.025mm to 1.25mm thickness metal sheets
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. TUNGSTEN INERT GAS WELDING (TIG)
GAS TUNGSTEN ARC WELDING (GTAW)
Tungsten carbide melting point- 330°c
Less than 6.5mm metal thickness

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

24. 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)

25.  Advantages:
 Very high quality welds are produced
 It is a very fast method
 Deep penetration can be obtained
 Shielding accessory for the eyes is not needed.
 Long joins can be easily welded
 Disadvantages
 It is not suitable for welding works which is inclined and
vertical
 The welding zone is not seen. So it is difficult to guide
the electrode movement.

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

27. SPECIAL WELDING
2. Thermit welding

28.  Welding the parts by using liquid thermit steel around
the portions to be welded.
 Fusion welding process
 Neither arc is produced to heat parts nor flames are
used
 Welding principle is the heat of the thermit reaction
used for welding in plastic state and mechanical
pressure is applied for the joint.
 Thermit is a mixture of al and iron oxide in the ratio 1:3
 This is placed in a furnace and it is ignited.
 Chemical reaction takes place
 Due to this liquid and slag are formed which are used
for welding.

29.  Applications
 Used in steel rolling mills, non ferrous metals, pipes,
cables rails, shafts & automobile parts

30. SPECIAL WELDING
3. Electron Beam welding:

31.  Electron Beam Welding (EBM):
 Beam of electron is used for producing high temp melting the work piece to be welded
 Advantages:
 High quality weld is produced
 Deep welding is possible
 Clean and bright weld can be obtained
 High speed operation can be achieved
 Dimensional accuracy is good
 Energy loss is very less
 Very small part can be welded
 Disadvantages:
 Cost is high
 Skilled persons are required
 It is limited to small size welding
 It is time consuming process
 Applications:
 Used in aircrafts, cams
 Dissimilar metals can be welded
 Refractory and reaching metals can be welded.

32. SPECIAL WELDING
1. Plasma Arc welding (PAW)
a) Transferred type

33. SPECIAL WELDING
4. Friction welding

34. 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

35. 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.

36. 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.

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

38. TYPES OF ADHESIVE BONDING