Fusion welding involves melting materials together using heat from sources like gas flames or electric arcs. It allows for joining of metal parts. Solid-state welding uses pressure, and sometimes heat, but no melting, to join metals. Welding is used in many industries like manufacturing, construction, and automotive as it allows for joining of metal parts that would otherwise be difficult or impossible to form as a single piece.

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, rock
ets 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
1. Oxy-acetylene
2. Air-acetylene
3. Oxy-hydrogen
(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
(iv). Thermit Welding
(v)Newer Welding
1. Electron-beam
2. Laser

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
– 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