ppt

1. CHAPTER 4
joining and assembling process
 joining processes fall into three major categories:
 Welding
 Adhesive bonding
 Mechanical fastening
Welding: is the process of joining similar or dissimilar
materials by the application of heat and/or pressure.
 Generally welding processes can be classified into three
basic categories:
 Fusion welding
 Solid-state welding
 Brazing and soldering

2. Advantages
 Cost effectiveness
 Strong and tight joining
 Simplicity of welded structure design
 Welding process can be mechanised and automated
Applications
 Replaced riveting in many applications including:- steel
structures, boilers, tanks, and motor car chassis.
disadvantages
 Internal stresses,
 Distortions and changes of structures in the weld region
 Harmful effects: light, ultra violate radiation, fumes, high
temperature
 Permanent joint.

3. Classification of welding processes:
(I). Electrical energy
welding(fusion)
1. Consumable electrode
 Gas Metal Arc Welding
 Shield Metal arc welding
 Submerged Arc Welding
 Flux cored arc welding
2.No consumable electrode
 Gas Tungsten Arc Welding
 Atomic hydrogen welding
 Plasma Arc Welding
3.Radiant Energy Welding
Processes
 Electron-beam welding
 Laser-beam welding
(II)Solid State Welding(no filler
& no melting
Friction
Ultrasonic
Diffusion
Resistance Welding
• Spot
• Seam
• Projection

4. (iii). Chemical energy Welding
 Oxy-fuel gas welding
iv. Brazing and Soldering
(v) .Related Process
 Oxy-acetylene cutting
 Arc cutting
 Hard facing

5. 1) Oxy-fuel gas welding
 Uses a fuel gas combined with oxygen to produce a flame.
 This flame is the source of heat that is used to melt the
materials at the joint.
 The most common gas welding processes uses acetylene, is
known as oxy-acetylene gas welding (OAW).

6.  oxygen and acetylene cylinders have different so hoses
cannot be connected to the wrong cylinders.
Acetylene hoses are red
in color with left hand
thread.
Oxygen hoses are green
in color and have right
hand thread.

7. Type of flames on OAW
 Neutral flame: Acetylene and oxygen mix at the ratio of
1:1.
 Oxidizing flame: A flame with excess oxygen is known as
oxidising flame
 Reducing flame: If oxygen is insufficient for full
combustion, the flame is known as a reducing or carburising
flame

8. Types of flames

9. 2) ARC WELDING PROCESSES
Use an electric arc as a heat source to melt metal.
The arc is struck between an electrode and the work piece to be
joined. The electrode can consist of consumable wire or rod, or may
be a non-consumable tungsten electrode.
Most of these processes use some shielding gas while others employ
coatings or fluxes to prevent the weld pool from the surrounding
atmosphere.

10. The various arc welding processes are:
 Shielded Metal-Arc Welding (SMAW)
 Gas Metal Arc Welding (GMAW)
 Gas Tungsten Arc Welding (GTAW)
 Flux Cored Arc Welding (FCAW)
 Submerged Arc Welding (SAW)

11. A) Shielded Metal-Arc Welding (SMAW)
 A consumable electrode – a filler metal rod coated with
chemicals for flux and shielding (230-460mm long and
2.5-9.4mm in Diameter.
 Heat for welding generated by electric arc established
between flux-covered consumable metal rod (electrode)
and work.
 Flux creates a gas shield and the metal slag prevents
oxidation of the underlying metal.

12. SMAW

13. SMAW Equipment Set Up

14. B) Gas Tungsten Arc Welding (GTAW or TIG)
Non-consumable tungsten electrode is used with an
envelope of inert shielding gas around it.
The shielding gas protects the tungsten electrode and the
molten metal weld pool from the atmospheric
contamination.
TIG (tungsten inert gas)

15. The filler metal is supplied from a filler wire.
The shielding gases generally used are argon, helium or their
mixtures.
In this process the arc is formed between a pointed tungsten
electrode and the work piece in an inert atmosphere of argon
or helium.
The filler metals are similar to the metals to be welded, and
flux is not used.
The electrode material may be tungsten, or tungsten alloy.

17. Inert gases
The following inert gases are generally used in TIG welding:
1. Argon
2. Helium
3. Argon-helium mixtures
4. Argon-hydrogen mixtures

18. C) Gas Metal ARC Welding (GMAW)
A bare wire electrode is used and a shielding gas is fed
around the arc and weld pool.
This gas prevents contamination of the electrode and weld
pool by air.
The weld area is shielded by an external source such as
argon, helium, carbon dioxide, or various other gas
mixtures.

20. Gas Metal Arc Welding (GMAW) including MIG and MAG
(i.e Metal Inert Gas and Metal Active Gas MAG welding)
 (MIG)-Argon or helium gas is used for shielding .
This process is generally used for non-ferrous metals.
 MAG (metal-active gas) welding - Carbon dioxide (usually
mixed with argon) is used for shielding.

21. D) FLUX CORED ARC WELDING
 FCAW is a commonly used high deposition rate welding
process that adds the benefits of flux to the welding
simplicity of MIG welding.
 FCAW uses the same types of wire feeders and power
sources as the GMAW process.
 However, the FCAW process uses a tubular electrode with
its core (inner) containing the deoxidizers and
(protectant)slag (inner) containing the deoxidizers, and
(protectant) slag and vapor forming ingredients.

23. E) Submerged Arc Welding(SAW)
This process uses a bare wire electrode and a flux added
separately as granules consisting of lime, silica, manganese
oxide, calcium fluoride, and other elements or powder over
the arc and weld pool.
The arc is formed between a continuously-fed wire electrode
and the Work piece, and the weld is formed by the arc
melting the work piece and the wire.

25. Characteristics of submerged-arc welding
 The flux is fed into the weld zone from a hopper by
gravity through a nozzle:
The functions of the flux:
 Prevents spatter and sparks;
 Suppresses the intense ultraviolet radiation and fumes
characteristics of the SMAW.
 It acts as a thermal insulator by promoting deep
penetration of heat into the work piece.
 The unused flux can be recovered, treated and reused.

26. Electron-Beam Welding (EBW)
 The heat used for welding the two materials is generated
by
 high velocity narrow-beam (concentrated) electrons is
fired through the work, this transfers kinetic energy to the
particles of metal causing them to heat up and melt to
form a weld.
 EBW process requires special equipment to focus the
beam on the work piece, typically in a vacuum.
 The higher the vacuum, the more the beam penetrates, and
the greater the depth-to-width ratio can be achieved.

28. Laser Beam Welding (LBW)
 LBW utilizes a high-power laser beam as the source of
heat, to produce a fusion weld.
 Because the beam can be focused on to a very small area, it
has high energy density and deep-penetrating capability

29.  Brazing is a metal-joining process.
 Brazing is when a filler metal or alloy is heated to its
melting temperature above 450 °C.
 It is then distributed in liquid form between two or more
close-fitting parts by capillary action.
 The filler metal is then brought slightly above its melting
temperature.
 It then interacts with a thin layer of the base metal (known
as wetting) and is then cooled quickly.
 This forms a sealed joint.
 Brazed joints are generally stronger than the individual
filler metals that have been used to make them.
Brazing

30. Soldering
 Soldering is a process in which two or more metals are
joined together by melting and flowing a filler metal into the
joint, the filler metal having a relatively low melting point.
Soft soldering is characterized by the melting point of the
filler metal, which is below 400 °C.
 The filler metal used in the process is called solder.
 Soldering is distinguished from brazing as the filler metal
used has a lower melting point.
 Soldering is normally done by melting the solder with a
soldering iron and applying it to the two metals that are
going to be joined together.