Fundamental of Welding Science and Technology

Module-1
Lecture 1: Introduction of Welding

Pankaj Biswas (PhD)

Department of Mechanical Engineering
IIT Guwahati
1
 Contents
 Syllabus of the course
 Definition of welding
 History of welding
 Common welding base material
 General advantage of welding
 General disadvantage of welding
 Welding as compared to casting
 Welding as compared to riveting
 Practical applications of welding

2
 Syllabus of the Course
Week Module name and contents to be covered No. of
lectures
planned
1 Introduction and classification of welding:
i. Introduction ii. Classification of welding processes 2
iii. Type of welding joints iv. Type of edge preparation.

2 Nomenclature and symbol of welding joints:

i. Welding joint design ii. Different types of
nomenclature of welding joints ii. Welding symbols 2-3
3 Power source of welding:
i. Types of power source and their characteristics.
2
4 Physics and principle of arc welding:
i. Welding heat sources ii. Arc initiation iii. Type of arc
iv. Forces affecting the arc and metal transfer v. Arc 3
blow.
3
 Syllabus of the Course cont...
Week Module name and contents to be covered No. of
lectures
planned
5 Different type of welding methods and their details:
i. Oxy fuel gas welding ii. SMAW iii. GTAG 2-3

6 Different type of welding methods their details:

i. GMAG ii. SAW iii. ESW 3

7 Different type of welding methods their details:

i. EGW ii. Resistance spot welding, iii. Friction welding, 3
iv. PAW

8 Welding defects and inspection:

i. Different types of welding defects ii. Destructive & non 2
destructive testing.
4
 Reference/Text Books
 V. M. Radhakrishnan, Welding Technology and Design, New age.
2002.
 J. A. Goldak, Computational Welding Mechanics, Springer 2005.
 O. Grong, Metallurgical Modelling of Welding, 2nd Ed. IOM
publication , 1997.
 L-E Lindgren, Computational Welding Mechanics, Woodhead
Publishing Limited, 2007.
 Dr. O. P. Khanna, Welding Technology, Reprint: 2002.
 A. O. Brien, Welding Handbook: Welding Processes, Part 1, Vol.2,
AWS,2004.
 J. F. Lancaster (Ed), The Physics of welding, Pergamon, 1986.
 R.W. Messler, Principles of Welding, John Wiley and Sons,1999.
5
 Introduction

 Welding: In general, it is a process of joining two material plates

and make an integrated one.

 The large bulk of materials that are welded are metals and their
alloys. The welding is also applied to the joining of other material
such as thermoplastics.
 In welding heat is supplied either by electrical arc or by a gas
torch or by some other means.
 The most essential requirement is Heat but in some processes
Pressure is also employed.

6
 History of Welding
 Middle Ages:
Blacksmiths of the Middle Ages welded various types of iron tools by
hammering. The welding methods remained more or less unchanged
until the dawn of the 19th century.
 Late 19th Century
 Engineers/scientists apply advances of electricity to heat and join
metals (Joule, Le Chatelier, etc.)
 Early 20th Century
 Prior to 1st World War welding was not trusted as a method to
join two metals due to crack issues.
 1930’s & 40’s
 Industrial welding gains acceptance and is used extensively in the war
effort to build tanks, aircraft, ships etc. The use of welding in today’s
technology is extensive. It is a remarkable rise since about 1930. 7
 History of Welding
 19th Century (1800): In this century, major weldings were made.

1830:
Englishman Edmund Davy discovered acetylene in 1836 and
acetylene was soon utilized by the welding industry.

1880:
In 1881, French scientist Auguste De Meritens succeeded in fusing
lead plates by using the heat generated from an arc.

1890:
During the 1890's, one of the most popular welding methods was
invented i.e. carbon arc welding. In this time, thermite welding
was also invented in 1893.
8
 History of Welding (cont.)
 20th Century (1900):
1900:
 Coated metal electrode was first introduced by Strohmenger. A
coating helped the arc to be much more stable.
 A number of other welding processes were developed during this
period i.e. seam welding, spot welding, flash butt welding, and
projection welding.
1919:
 After the end of World War I, the American Welding Society was
established by Comfort Avery Adams. The aim of the society was
the advancement of welding processes.
1920:
 Automatic welding was first introduced which was invented by P. O.
Nobel. In 1920, an early predecessor of GMAW was invented by P.
O. Nobel of General Electric. 9
 History of Welding (cont.)
1930: The New York Navy Yard developed stud welding. Stud
welding was increasingly used for the construction industry and also
for shipbuilding.
1940: The GTAW was another significant milestone in the history
of welding which was developed in Battelle Memorial Institute in
1948.
1960: There were several advancements in the welding industry
during the 1960's. Electroslag welding and Plasma arc welding
were invented during this time.
1990: In 1991, Welding Institute invented FSW. It is a solid state
joining process which utilizes frictional heat of a rotating tool and
stirring effect of the tool probe for solid state joining.
 The use of welding in today’s technology is extensive. This growth
is faster than the general industrial growth. 10
 Common Welding Base Material
 Metals can be classified as:
1. Ferrous
2. Non-ferrous Material
1. Ferrous materials finding day-to-day welding application are:
i) Wrought Iron (Less than 0.035% Carbon)
ii) Cast Iron [Carbon and Silicon % are: 2.3 to 4.5% and 0.5 to 3%
respectively)
iii) Carbon Steel [Low (0.05–0.3%), Medium (0.30–0.59%) and
High (0.6–1.5%)]
iv) Cast Steels [Carbon content between 0.2 to 2.1% by weight,
depending on the grade, also other alloying elements manganese,
chromium, vanadium, and tungsten]
v) Stainless steel [More than 11.5% chromium], etc.
11
 Common Welding Base Material cont..

2. Non-Ferrous materials finding day-to-day welding application

are:
i) Aluminium and its alloys

ii) Copper and its alloys

iii) Magnesium and its alloys

iv) Nickel and its alloys

v) Zinc and its alloys,

12
 General Advantage of Welding
 Advantages:

A good weld is as strong as the base metal.

General welding equipment is not very costly.
Portable welding equipment is also available.
Welding permits considerable freedom in design.
A large number of metals/ alloys both similar and dissimilar can
be joined by welding.
Welding can join workpieces by spots, as continuous pressure
tight seams, end-to-end and in a number of other configurations.
Welding can be mechanized.

13
 General Disadvantage of Welding

 Disadvantages:
 Welding gives out harmful radiations (light), fumes and spatter.
 Welding results in residual stresses and distortion of the workpieces.

 Jigs and fixtures are generally required to hold and position the parts
to be welded.
 A skilled welder is a must to produce a good welding job.

 Welding heat produces metallurgical changes. The structure of the

welded joint is not same as that of the parent metal.
 A welded joint, for many reasons, needs stress-relief heat-treatment.

14
 Welding as compared to casting
 Machine tool beds which were earlier cast are now fabricated
using welding. In many fields welding has replaced casting
processes.

 Some of the reasons for the same as follow:

 Welding is more economical and is a much faster process as

compared to casting.

 Fabricated mild steel structures are lighter as compared to cast ones.

 Fabricated mild steel structures have more tensile strength and

rigidity as compared to cast ones.

 Cost of pattern and storing is eliminated.

15
 Welding as compared to casting cont.

 As compared to casting fewer persons are involved in a welding

fabrication.

 Structural shapes not easily obtainable with casting can be

produced by welding without much difficulty.

 Welding design involves low costs and it is very flexible also.

 Fabrication by welding saves machining cost involved in cast part.

16
 Welding as compared to riveting
 Bridges, ships and boilers which were previously riveted are now
welded.

 Welding is more economical and is a much faster process as

compared to riveting.

 Welded pressure vessels are more pressure tight as compared to

riveted ones.

 Ratio between weight of weld metal and the entire weight of

structure is much lesser than the ratio between the weight of rivets
and entire weight of the structure.

 Cover plates, connecting angles, gusset plates, etc., needed in

riveted construction are not required when welding the structures.
17
 Welding as compared to riveting cont.

 Members of such shape that present difficulty for riveting can

be easily welded.

Welding can be carried out at any point on a structure, but,

riveting always requires enough clearance to be done.

A welded structure possesses a better finish and appearance than

the corresponding riveted structure.

Layout for punching and drilling of holes is not required in

welding.

18
 Welding as compared to riveting cont.

Drilling holes in the plate in order to accommodate rivets, breaks

material continuity and weakens a riveted structure.

Making changes in an already cast or riveted structure is extremely

difficult, if not impossible. On the other hand a welded structure can
be repaired without much difficulty.

Welding can produce a 100% efficient joint which is difficult to

make by riveting.

Riveting high strength steels presents the problems of acquiring high

strength steels rivets.

19
 Practical Applications of Welding
 Welding has been employed in industry as a tool for:
 Regular fabrication of automobile cars, air-crafts, refrigerators,
ships, offshore structure etc.
 Repair and maintenance work, e.g., joining broken parts, rebuilding
worn out components, etc.
 A few important applications of welding are listed below:
i. Aircraft construction :
(a) Welded engine mounts.
(b) Turbine frame for jet engine.
(c) Rocket motor fuel thanks.
(d) Fittings, etc.
ii. Automobile construction :
(a) Arc welded car wheels.
(b) Frame side rails.
(c) Automobile frame, brackets etc.
20
 Practical Applications of Welding (cont.)
iii. Bridges:
(a) Pier construction.
(b) Section lengths etc.
iv. Buildings:
(a) Column base plates.
(b) Trusses.
(c) Erection of structure, etc.

v. Pressure vessels and tanks:

(a) Clad and lined steel plates.
(b) Shell construction.
(c) Joining of nozzles to the shell, etc.

vi. Storage tanks:

(a) Oil, gas and water storage tanks.

vii. Rail road equipment:

(a) Rail
(b) Under frame
(c) Air receiver
(d) Engine etc. 21
 Practical Applications of Welding (cont.)

viii. Piping and pipelines:

(a) Rolled plate pipings.
(b) Open pipe joints.
(c) Oil, gas and gasoline pipe lines, etc.

ix. Ships:
(a) Shell frames.
(b) Deck and bulkhead stiffeners.
(c) Girders to shells etc.

x.Trucks and trailers.

xi. Machines tool frames, cutting tools and dies.

xii. Household and office furniture.

22
 Practical Applications of Welding (cont.)

 In addition, arc welding finds following applications in repair

and maintenance work:

 Repair of broken & damaged components and machinery such as

tools, punches, dies, gears, press and machine tools frames.

 Fabrication of jigs, fixtures, clamps and other work holding

devices.

 Being noiseless as compared to riveting, welding find extensive

use, when making modifications, addition or extension in hospital
buildings.

23
 Next Lecture Outline

• Classification of Welding and Joints

24
Classification of Welding Process

25
 Joining Process
 There are basically two types of joining process:

1. Mechanical Bonding
2. Atomic Bonding

1. Mechanical Bonding classification:

a) Temporary (With Screw Elements)

b) Permanent/ Semi-permanent
i) Rivets
ii) Stitches
iii) Staples
iv) Shrink-fit

2. Atomic Bonding classification: Welding

26
 Classification of Welding
 Welding classification can be done based on the following aspects:

1. Depending upon the source of heat

2. Depending upon the application of pressure
3. Depending upon the different phages of base and filler material
4. Depending upon the composition of the joint
5. Depending upon the position of electrode
6. Depending upon the mechanism

27
 Types of Welding
 Depending upon the source of heat:

(i). Arc welding

(ii). Gas welding

(iii). Resistance welding

(iv) Thermo-chemical welding process

(v) Mechanical energy welding process

(vi) Radiant energy welding process

28
 Types of Welding
 Different welding techniques name (depending on source of heat):
• Projection
(i). Arc welding • Percussion
• Carbon arc (CAW) • Flash Butt
• Metal arc (SMAW) (iv) Thermo-chemical welding
• Tungsten inert gas(TIG/GTAW)
process
• Metal inert gas (MIG/GMAW) • Thermit welding
• Plasma arc (PAW) • Atomic hydrogen welding
• Submerged arc (SAW)
(v) Mechanical energy welding
• Electro-slag (ESW)
• Electro gas(ESW) process
• Friction
(ii). Gas Welding • Ultrasonic
• Oxy-acetylene • Diffusion
• Air-acetylene • Forge
• Oxy-hydrogen • Roll
• Pressure gas • Explosive
(iii). Resistance Welding (vi) Radiant energy welding
• Butt process
• Spot
• Electron-beam (EBW)
• Seam • Laser (LBM)
29
 Next Lecture Outline

• Classification of Welding and Joints

30