Basics of welding explained with welding types and classification

1. Basic of Welding 1
Welding and Related Processes
Session-I
By Rahul S.

2. Basic of Welding 2
Content:
• Introduction
• Weldability
• Types of welding
• Classification of welding processes
• Metallurgy of weld
• Gas welding
– Oxy-Acetylene Welding
• Welding Equipment

3. Basic of Welding 3
Introduction
• Welding is process of joining similar metals by application of
heat
• Fabrication industry depends on the welding
• Deriving new material depends on its weldability

4. Basic of Welding 4
Weldability
• Capacity of being welded having specific properties as weld strength,
proper structure
• Weld quality and the ease it can be done
• Weldabilty depends on
– melting point
– thermal conductivity
– thermal expansion
– surface condition
– change in microstructure
• Metallurgical, chemical, physical and thermal characteristics can be
controlled by,
– proper shielding atmosphere
– proper fluxing material
– proper filler material
– proper welding procedure
– proper heat treatment of the metal before and after deposition

5. Basic of Welding 5
Types of Welding
• Plastic welding
– Pressure welding
– Metal heated upto plastic state and then forced together by external pressure
– e.g. forge welding, resistance welidng.
• Fusion welding
– nonpressure welding
– metal is heated to molten state and the allowed to solidify
– e.g. gas welding, thermit welding.
• Cold-welding
– Without application of heat
– parts are joined by application of pressure, by bonding of inter surface
molecular structure
– used for nonferous materials like aluminium and its alloys.

6. Basic of Welding 6
Classification of welding processes

7. Basic of Welding 7
Metallurgy of weld
• Fusion welding
– Number of runs made to deposite the weld material
– In single run long columnar crystal will meet at the centre.
– In multirun welding second run normalises the first layer, results inthe proper
grain structure.
– In multirun there is possibility of slag and gas inclusions.
• Pressure welding
– Metal is heated to the plastic condition and compressed while hot
– hot working result in some grain refinement
• Heat affected zones

8. Basic of Welding 8
Structural changes in Welding

9. Basic of Welding 9
Gas Welding
• Burning a combustible gas with air or oxygen in a concentrated
flame of high temperature
• Flame is used to heat and melt the parent metal and the filler rod
• Oxy-Acetylene Welding
– Oxygen and Acetylene are used for the producing the flame
– The flame melts the edges or surface to be joined, so molten metal flows
and solidify to produce a joint on cooling
– Used from 2mm to 50mm thickness plates
– For thickness more than 15mm filler rod to be used
– Filler rod material mostly as same as the parent material
– Flux to be used to avoid impurities and the oxidation

10. Basic of Welding 10
Oxy-Acetylene Welding
• Flame temperature of different gases

11. Basic of Welding 11
Oxy-Acetylene Welding
• Neutral Flame
– Oxygen and acetylene are in same proportion
– Sharp brilliant cone of short distance from tip of the torch
– Outer cone faintly luminous and bluish in colour
– First developes heat and secong protect molten metal from oxidation
• Carburising Flame
– Excess of acetylene
– Sharply defined inner cone
– intermediate cone of whitish colour
– Bluish outer cone
– It gives higher carbon content results in hard and brittle weld
• Oxidising Flame
– Excess of oxygen
– Small inner cone which has purplish tinge
– Outer cone or envolope
– Used for welding brass

12. Basic of Welding 12
Gas welding technique

13. Basic of Welding 13
Welding Equipment
• Welding torch
• Welding tip
• Pressure regulator
• Hose and hose
fittings
• Goggles, gloves and
spark-lighter
• Gas cylinder

14. Basic of Welding 14
• Thank you...
– Next session will be on other welding processes as arc welding,
resistance welding, thermit welding etc