1. Introduction to Welding
Dr. H. K. Khaira
Professor in MSME
MANIT, Bhopal

2. Welding
Welding is the process of joining together pieces of metal or metallic parts by bringing them into intimate proximity and heating the place of content to a state of fusion or plasticity

3. Welding
A concentrated heat source melts the material in the weld area; the molten area then solidifies to join the pieces together
Sometimes a filler material is added to the molten pool to strengthen the weld

4. following are the key features of welding:
The welding structures are normally lighter than riveted or bolted structures.
The welding joints provide maximum efficiency, which is not possible in other type of joints.
The addition and alterations can be easily made in the existing structure.
A welded joint has a great strength.
The welding provides very rigid joints.
The process of welding takes less time than other type of joints.

5. largely used in the following fields of engineering:
Manufacturing of machine tools, auto parts, cycle parts, etc.
Fabrication of farm machinery & equipment.
Fabrication of buildings, bridges & ships.
Construction of boilers, furnaces, railways, cars, aeroplanes, rockets and missiles.
Manufacturing of television sets, refrigerators, kitchen cabinets, etc.

6. Types of Welding
Fusion Welding
Pressure Welding

7. Fusion Welding

8. Fusion Welding
It is defined as melting together and joining metals by means of heat.
It uses heat to melt the base metals and may add a filler metal.
The thermal energy required for these operations is usually supplied by chemical or electrical means.
Filler metals may or may not be used.

9. Welding Metallurgy
The base metal(s) and filler metal mix together during melting, forming an alloy when they solidify
The solidification of the metals can be considered as casting a small amount of metal in a metal mold

10. Fusion Welding All fusion welding process have three requirements.
Heat
Shielding
Filler metal
The method used to meet these three requirements is the primary difference between welding processes.

11. Types of Fusion Welding
(i). Arc welding
Carbon arc
Metal arc
Metal inert gas
Tungsten inert gas
Plasma arc
Submerged arc
Electro-slag
(ii). Gas Welding
Oxy-acetylene
Air-acetylene
Oxy-hydrogen
(iv). Thermit Welding
(vi)Newer Welding
Electron-beam
Laser

12. Types of Fusion Welding
(i). Gas Welding (iv). Thermit Welding
1. Oxy-acetylene (v)Newer Welding
2. Air-acetylene 1. Electron-beam
3. Oxy-hydrogen Laser
(ii). Arc welding
1. Carbon arc
2. Metal arc
3. Metal inert gas
4. Tungsten inert gas
5. Plasma arc
6. Submerged arc
7. Electro-slag

13. Pressure Welding
When pressure is used to join two metal parts with or without heat, it is known as pressure welding.

14. Types of Pressure Welding Processes
(i). Resistance Welding
1. Butt
2. Spot
3. Seam
4. Projection
5. Percussion
(ii). Solid State Welding
1. Friction
2. Ultrasonic
3. Diffusion
4. Explosive

15. Factors Affecting Welding
Heat source
Weld Metal Protection
Heat affected zone
Weldability

16. Heat Sources

17. Heat Sources in Welding
1. Combustion of fuel gas
2. Electric arc
3. Electrical resistance
4. Friction
5. Chemical reaction
6. Other sources

18. Power density of heat sources
As the power density of the heat source increases, the heat input to the workpiece that is required for welding decreases.
Power density we get
Deeper weld penetration
Higher welding speeds
Better weld quality
Less damage to the workpiece

19. Variation of heat input to the workpiece with power density of the heat source.

20. Variation of weld strength with unit thickness of workpiece heat input per unit length of weld.
Heat input Weld strength

21. Power density of heat sources
Heat input Weld strength

22. Weld Metal Protection

23. Weld Metal Protection
During fusion welding, the molten metal in the weld “puddle” is susceptible to oxidation
Must protect weld puddle from the atmosphere

24. Weld Metal Protection
Methods
Weld Fluxes
Inert Gases
Vacuum

25. Weld Fluxes 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

26. Inert Gases Argon, helium, nitrogen, and carbon dioxide
form a protective envelope around the weld area
Used in
MIG
TIG
Shielded Metal Arc

27. Vacuum Produce high-quality welds Used in electron beam welding
Nuclear/special metal applications
Zr, Hf, Ti
Reduces impurities by a factor of 20 versus other methods
Expensive and time-consuming

28. Heat affected zone

29. Heat affected zone
The surrounding area of base metal that did not melt, but was heated enough to affect its grain structure is known as heat affected zone

30. Heat affected zone

31. Heat affected zone

32. Heat affected zone

33. Weldability

34. Weldability
Weldability is the ease of a material or a combination of materials to be welded under fabrication conditions into a specific, suitably designed structure, and to perform satisfactorily in the intended service

35. Weldability Metallurgical Capacity Mechanical Soundness Serviceability
Parent metal will join with the weld metal without formation of deleterious constituents or alloys
Mechanical Soundness
Joint will be free from discontinuities, gas porosity, shrinkage, slag, or cracks
Serviceability
Weld is able to perform under varying conditions of service (e.g., extreme temperatures, corrosive environments, fatigue, high pressures, etc.)

36. Summary
Fusion welding melts the material then allows it to solidify and join it together
Solid-state welding uses pressure, and sometimes heat, to allow the metal to bond together without melting
Welding allows the production of parts that would be difficult or impossible to form as one piece