1. Principles: WELDING PROCESS: Fusion welding Base metal is melted
Filler metal may be added
Heat is supplied by various means
Oxyacetylene gas
Electric Arc
Plasma Arc
Laser

2. Produce high-quality welds Used in electron beam welding
WELDING PROCESS: Fusion welding
Weld Metal Protection
During fusion welding, the molten metal in the weld “puddle” is susceptible to oxidation
Must protect weld puddle (arc pool) from the atmosphere
Methods
Weld Fluxes
Inert Gases
Vacuum
Typical fluxes
SiO2, TiO2, FeO, MgO, Al2O3
Produces a gaseous shield to prevent contamination
Act as scavengers to reduce oxides
Add alloying elements to the weld
Influence shape of weld bead during solidification
Vacuum
Produce high-quality welds
Used in electron beam welding
Nuclear/special metal applications
Zr, Hf, Ti
Expensive and time-consuming
Inert Gasses
Argon, helium, nitrogen, and carbon dioxide
Form a protective envelope around the weld area
Used in
MIG
TIG
Shield Metal Arc

3. Gas Welding (OFW) WELDING PROCESS: fusion welding
Uses the heat of combustion of an oxygen /air and fuel gas (i.e. acetylene, hydrogen propane or butane) mixture is usually referred as ‘gas welding’.
Fuel gas generally employed is acetylene because oxy-acetylene flame is the most versatile and hottest
Other gases such as Hydrogen, Propane, Butane, Natural gas etc.

4. Oxy-Acetylene Welding (OAW)
WELDING PROCESS: fusion welding
Oxy-Acetylene Welding (OAW)
FUEL: Acetylene (C2H2)
COMBUSTION reactions take place in two stages:
1st stage: in a small white cone (3100 C)
2nd stage: in outer bluish flame ( C)
1st stage: C2H2 + O2  2CO + H kJ/kmol
2nd stage: 4CO + 2H2 + 3O2  4CO2 + 2H2 O + 812kJ/kmol

5. Oxy-Acetylene Welding (OAW)
WELDING PROCESS: fusion welding
Oxy-Acetylene Welding (OAW)
FLAMES:
Neutral Equal acetylene & oxygen (1:1) (low carbon steel, mild steels).
Oxidizing Excess oxygen (1.5:1) (Brasses, Bronzes, copper)
Reducing or Carburizing Excess acetylene (0.9:1) (Alloy steels and aluminium alloys)
Carburising
Neutral
Oxidising

6. Oxy-Acetylene Welding (OAW)
WELDING PROCESS: fusion welding
Oxy-Acetylene Welding (OAW)
Equipments:
Cylinders
Acetylene: Cannot be compressed directly as explodes at high pressures. Cylinders are packed with porous material which is filled with acetone. Cylinder colour coded maroon
Oxygen: 13.8 – 18.2 Mpa, Cylinder is black.

7. Oxy-Acetylene Welding (OAW)
WELDING PROCESS: fusion welding
Oxy-Acetylene Welding (OAW)
Equipments:
Hose Pipes
Reinforced rubber hoses.
Acetylene hose has left hand thread couplings and colour coded red.
Oxygen hose has right handed thread couplings and colour coded blue

8. Oxy-Acetylene Welding (OAW)
WELDING PROCESS: fusion welding
Oxy-Acetylene Welding (OAW)
Equipments:
Welding Torch: Oxygen and acetylene are delivered to the torch by separate hoses. Each gas is controlled by a valve on the torch. The two gases mix in the torch and after they are ignited burn at the nozzle.

9. Oxy-Acetylene Welding (OAW)
WELDING PROCESS: fusion welding
Oxy-Acetylene Welding (OAW)
Techniques:
Tip is so positioned that white cone is at a distance of 1.5 to 3 mm from plate
Fore hand welding
- Torch moves in the direction of tip
- Tends to preheat the metal
Back hand welding
- Torch moves backwards
- Outer flame towards already welded joint
Welding Rod is held at a distance of 10mm from flame and 1.5 – 3 mm from the weld metal pool

10. Metal Inert Gas (MIG) / Gas Metal ARC Welding (GMAW)
WELDING PROCESS: fusion welding
Metal Inert Gas (MIG) / Gas Metal ARC Welding (GMAW)
Uses a consumable electrode (filler wire made of the base metal)
Inert gas is
typically Argon

11. Tungsten Inert Gas (TIG) / Gas Tungusten Arc Welding (GTAW)
WELDING PROCESS: fusion welding
Tungsten Inert Gas (TIG) / Gas Tungusten Arc Welding (GTAW)
Electrode acts as a cathode
Non-consumable Electrode
Filler metal can be added to the weld pool

12. Submerged Arc Welding (SAW)
WELDING PROCESS: fusion welding
Submerged Arc Welding (SAW)
Arc forms between a continuously-fed bare wire electrode and the work-piece under blanket of granular flux
Takes place in the flat position
Ideal for heavy work-pieces
Applications
SAW welding is usually for Carbon-manganese steels, low alloy steels and stainless steels, bronze, nickel and other non-ferrous materials

13. Submerged Arc Welding (SAW)
WELDING PROCESS: fusion welding
Submerged Arc Welding (SAW)

14. Submerged Arc Welding (SAW)
WELDING PROCESS: fusion welding
Submerged Arc Welding (SAW)
EQUIPMENTS:
WIRE:
SAW is normally operated with a single wire on either AC or DC supply.
FLUX:
It is granular fusible minerals supplied by means of flux feed tube
Specially formulated to be compatible with a given electrode wire type
React with the weld pool to produce slag which covers the weld metal
Unused flux is recycled via a hopper.

15. Submerged Arc Welding (SAW)
WELDING PROCESS: fusion welding
Submerged Arc Welding (SAW)
POINTS to REMEMBER:
Flux to generate protective gases and slag
Shielding gas is not required
Slag layers can be easily removed after welding
As the arc is completely covered by the flux layer, heat loss
is extremely low and no visible arc light and no spatter
Not possible to carry to any position other than down-hand
position
High welding speed (5m/min), and metal deposition rate
(20kg/hr)can be obtained
Able to weld plate of thickness 1mm – 75mm