This document discusses various welding processes and welded joints. It begins by defining a welded joint as a permanent fusion of two parts together, with or without filler material. It then describes several types of welding processes including fusion welding (brazing, soldering, gas welding, electric arc welding) and pressure welding (friction, forge). The document further discusses specific fusion welding techniques like thermit welding, gas welding and electric arc welding. It also outlines common welded joint designs such as butt, lap, fillet, corner and describes joint preparation and defects that can occur.

1. Gandhinagar Institute of
Technology
Subject :-Machine Designing and industrial drafting
– 130120119126- Pandya Kartik
Topic :- Welding Processes
MECHANICAL
ENGINEERING
4th - B : 3

2. Welding Processes

3. What do you mean by welded
joints??
A welded joint is a permanent joint which is obtained by the
fusion of the edges of the two parts to be joined together, with
or without the application of pressure and a filler material.
Welding is extensively used in fabrication as an alternative
method for casting or forging and as a replacement for bol
ted & riveted joints.
e.g. to reunite metal at a crack, to build up a small part th
at has broken off such
as gear tooth or to repair a worn surface such as a bearin
g
Surface.

4. Types of Welding
Fusion Welding Pressure Welding
Homogeneous Heterogeneous
Brazing SolderingGas Welding
Electroslag
High Energy Beam
Electric Arc
MIG
TIG
Shielded Metal Arc – “Stick”
Friction Welding

5. Classification of welding
processes
•The welding processes may be broadly
classified into the following two groups:
1) Welding processes that use heat alone e.g.
fusion welding.
2)Welding processes that use a combination of heat and
pressure e.g. forge welding.
Fusion welding classification
1. Thermit welding
2. Gas welding
3. Arc welding

6. Fusion welding
• In case of fusion welding the parts to be jointed are held in
position while the molten metal is supplied to the joint.
• The molten metal may come from the parts themselves (i.
e parent metal) or filler metal which normally have the
composition of the parent metal.
• The joint surface become plastic or even molten because
of the heat from the molten filler metal or other source.
•Thus, when the molten metal solidifies or fuses, the joint is
formed.

7. Fusion Welding
BASE METAL
WELD
SOLIDIFIED SLAG
ARC POOL
WELDING ATMOSPHERE
CORE WIRE
ELECTRODE COATING
ARC STREAM
PENETRATION
DEPTH

8. Thermit welding
• In thermit
welding, a mixture of iron oxide and aluminium
called thermit is ignited and the iron oxide is reduced
to molten iron.
• The molten iron is poured into a mould made around th
e joint and fuses with the parts to be welded.
• The thermit
welding is often used in joining iron and steel
parts that are too large to be manufactured in one piece
, such as rails, truck frames, locomotive frames
etc….

9. Gas welding
• A gas welding is made by applying the flame of an oxy-
acetylene or hydrogen gas from a welding torch upon the
surfaces of the prepared joint.
• The intense heat at the white cone of the flame heats up
the local surfaces to fusion point while the operator mani
pulates a welding rod to supply the metal for the weld.
• A flux is being used to remove the slag. Since the heatin
g rate
in gas welding is slow, therefore it can be used on thinner
materials.

10. Electric arc welding
• electric arc welding, the work is prepared in the same mann
er as for gas welding.
In this case the filler metal is supplied by metal welding electro
de.
• The base metal in the path of the arc stream is melted, formi
ng a pool of molten metal, which seems to be forced out of t
he pool by the blast from the arc.
• A small depression is formed in the base metal and the molt
en metal is deposited around the edge of this depression,
which is called the arc crater.
• The slag is brushed off after
the joint has cooled.

11. Arc welding
Electric current flowing through a high resistance air gap ge
nerates an intense arc with temperatures ranging
3,000 to 5,500 centigrade.
Arc welding is the most
common
method used with structural
steel

12. Types of welded Joints
The American Welding Society defines a joint as
“the manner in which materials f it together . there are f ive basic types of weld
joints:
•Butt joint.
•T -joint.
•Lap joint.
•Corner joint.
•Edge joint.
Joint Preparation
Weld joints may be initially prepared in a
number
Of ways.
These include:
•Shearing.,Casting,Forging.
•Machining,Stamping,Filing,Routing.
•Oxyacetylene cutting (thermal cutting process).
•Plasma arc cutting (thermal cutting process).
•Grinding.

13. Joint Design
BUTT JOINT
STRAP JOINT
LAP JOINT
FILLET JOINT
CORNER JOINT

14. Lap Joints
•The lap joint or the fillet joint is obtained by overlapping the
plate and then welding the edges of the plates.
The cross-section of the fillet is approximately triangular. The
fillet joints may be approximately triangular.
The fillet joints may be classified as below.
• 1. Single transverse fillet,
• 2. Double transverse fillet, and
• 3. Parallel fillet joints.

15. Butt Joints
•The butt joint is obtained by placing the plates edge to edge. In butt welds,
the plate edges do not require bevelling if the thickness of plate is less
than 5 mm. On the other hand, if the plate thickness is 5 mm to 12.5 mm,
the edges should be bevelled to V or U-groove on both sides The
buttthe edges should be bevelled to V or U-groove on both sides.
The butt joints may be
• 1. Square butt joint,
• 2. Single V-butt joint
• 3. Single U-butt joint,
• 4. Double V-butt joint, and
• 5. Double U-butt joint

16. Other joints
•The other type of welded joints are corner joint, edge joint and T-joint
The main considerations involved in the selection
of weld type are:
1. The shape of the welded component required,
2. The thickness of the plates to be welded, and
3. The direction of the forces applied.

17. Welding Positions
FLAT
HORIZONTAL
VERTICAL
OVERHEAD
INCREASING DIFFICULTY

18. Weld Defects
 Undercuts/Overlaps
 Grain Growth
◦ A wide T will exist between base metal and HAZ.
Preheating and cooling methods will affect the brittleness
of the metal in this region
 Blowholes
◦ Are cavities caused by gas entrapment during the
solidification of the weld puddle. Prevented by proper weld
technique (even temperature and speed)

19. Weld Defects
 Inclusions
◦ Impurities or foreign substances which are forced into the weld
puddle during the welding process. Has the same effect as a
crack. Prevented by proper technique/cleanliness.
 Segregation
◦ Condition where some regions of the metal are enriched with an
alloy ingredient and others aren’t. Can be prevented by proper
heat treatment and cooling.
 Porosity
◦ The formation of tiny pinholes generated by atmospheric
contamination. Prevented by keeping a protective shield over the
molten weld puddle.

20. Weld Symbols (Butt Joints)
Backing

21. Weld Symbol (Fillet Joints)

22. Weld Symbol (Corner Joints)