Types of Welding

Question 1

Oxyfuel Gas Welding

Answer 1

> Flame and filler rod
Gas is Oxyacetylene

Advantages:
> Easy for welding and cutting
> Convenient for welding thin sheets, pipes and tubes etc.
> Weld in all directions

Disadvantages:
> Cannot be used to weld thick workpieces
> Expensive gas
> Extensive HAZ

Question 2

Shielded Metal Arc Welding

Answer 2

> Consumable electrode with flux covering it
Electric arc formed between electrode and base metal
Flux coating gives layer of slag and shielding gas to protect weld area from atmospheric contamination
Electrode selected by material strength and weld position
Heat source from AC or DC transformer or DC motor

Advantages:
> Portable and inexpensive
> Outdoor and indoor use
> Suitable for most metals
> All positions
> Control of weld penetration
> General welding, repair, constructing and fabrication

Disadvantages:
> Slag contamination
> Frequent stops to change the electrode
> Electrodes require special care/storage

Question 3

Gas Tungsten Arc Welding

Answer 3

> Electrode is non-consumable
Arc length is 1.5 times the diameter of the electrode diameter
Heat from AC or DC transformer
Filler metal used and applied in shielded gas
Inert gas supplied through electrode holder to ceramic arc shielding cone
Inert gas is He, Ar, CO2 mixtures

Advantages:
> All positions
> Highest quality weld
> Best control of heat and penetration
> Less start/stop
> No cleaning/de-slagging
> Filler metal not required
> Can be used with exotic metals, thin metals and non-ferrous castings

Disadvantages:
> Tungsten contamination of weld is possible
> Externally supplied shielding gas is required
> May not be suitable for outdoors
> Equipment set up is more complicated and experienced operators are required

Question 4

Gas Metal Arc Welding

Answer 4

> Consumable electrode
> Externally supplied shielding gas
> Small HAZ, narrow bead width, deep penetration, faster welding speed
> Now used in all industries
> Heat from DC reverse polarity
> Filler metal is continuous and autofed
> Shielding gas is He, Ar, CO2 or combo

Advantages:
> All postions
> No de-slagging necessary
> High disposition rate
> High welding speed
> Excellent weld quality
> No stopping required

Disadvantages:
> Equipment is fairly complex and less portable
> Externally supplied shielding gas
> Equipment subject to breakdown
> Requires skills in automatic controls
> Possibility of excessive fumes and heat

Question 5

Submerged Arc Welding

Answer 5

> Heat from DC straight polarity
Filler metal is continuously fed
Granular flux surrounding arc area
Excess flux is vacuumed up

Advantages:
> No visible welding arc
> Very high deposition rates obtainable
> Not affected by wind and drafts
> Very high quality weld due to flux shielding
> Good penetration obtainable
> Good for welding metals with large thickness

Disadvantages:
> Welding position restricted to flat
> Externally applied flux
> Flux can become contaminated causing weld porosity
> De-slagging is required after each weld pass
> Requires welders skilled in automatic controls

Question 6

Electrode Classification

Answer 6

E = electrode/electric arc
XX = minimum tensile strength in ksi of the deposited weld metal in the as-welded position
Y = weld positions that the electrode can be used in
YZ = type of covering
Z = current characteristics of the electrode