ADVANCE WELDING: Welding Arc and Power Sources Unit 1 Part 1 Notes

Que 1.1. What is welding ? Explain the importance of welding.


A. Welding :

1. The term welding is used to cover a wide range of bonding techniques.

2. It is defined as a localized coalescence of metals, wherein coalescence is

obtained by heating to suitable temperature with or without the

application of pressure and with or without use of filler metal. The filler

metal has a melting point approximately the same as base metal.

3. A good welded joint is as strong as the parent metal. The product is

known as weldment.

B. Importance of Welding :

1. The welding process is readily adaptable to stream line structure and

the welded joints are very tight.

2. Welded joints are strong, especially under static loading. However, they

have poor fatigue resistance due to stress concentration, residual stresses

and various weld defects, such as cracks, incomplete fusion, slag

inclusion. But all these drawbacks can be overcome to a large extent.

3. Now a days many processes of welding have been developed and probably

there is no industry which is not using welding process in the fabrication

of its products in some form or the other.

4. Welding is most rapid and easiest way of fabrication and assembly of

metal parts.

5. Welding is extensively used in the following fields : automobiles industry,

aircraft machine frames, structural work, tanks, machine repair work,

ship building, and refineries, fabrication of metal structures.

Que 1.2. What are the advantages and limitations of welding ?


A. Advantages of Welding :

1. Welding results in a good saving of material and reduced labour content

of production.

2. Low manufacturing costs.

3. It gives the designer great latitude in planning and designing.

4. Welding is also useful as a method for repairing broken or defective

metal parts.

5. Without welding techniques, the light weight methods of fabrication, so

vital to the automotive and aircraft industries, would be unthinkable.

6. Welding joint is as stronger as base metal and its efficiency is upto 100 %.

7. Alteration and amendment is possible in existing structure by welding


B. Limitations of Welding :

1. Special jigs and fixtures are required for welding.

2. Edge preparation is required before welding which is time and labour

consuming process.

3. Skilled person is needed for welding purpose.

4. Ultraviolet rays and infrared rays generated during the welding process

are harmful for operator’s skin as well as for eyes.

5. Welding heat produces metallurgical changes in workpiece.

6. During welding, thermal stresses developed in the workpiece, heat

treatment processes are required to relieve the thermal stresses.

Que 1.3. What are the applications of welding ? Give in detail.


Applications of welding are as follows :

i. Automobile and Transport Industries :

1. Wherein cars, trucks, jeeps and many other transportation machines

and equipments are fabricated.

ii. Building Construction Industries :

1. Welding is greatly used in building industries for joining frames of doors

and windows, reinforcement in concrete works, railings and staircases.

2. When building is a steel frame construction comprising of steel roofing

frames covered with asbestos sheets or galvanized iron sheet, welding

has still greater role to play in joining the structural components for

joining building, frames and trusses.

iii. Railroad Industries :

1. Railroad industries is another important field where welding is involved

in the production of locomotive under frames, bogies, trolleys, railway

bridges, electric frame network, signal, equipment, lighting towers,

platform shades and bodies etc.

iv. Pressure Vessels and Tanks Industries :

1. Pressure vessels and tanks are widely used in various industries for

carrying or storing the fuel and other liquids.

2. These are made by welding together the bent steel plates.

3. Oil, gas and water storage tanks are also steel fabricated.

v. Aircraft Industries :

1. In aircraft industries welding is extensively used for joining the aircraft

components of alloy steel, stainless steel and aluminium alloys.

2. Welding is used for the production of allied equipment that assists aircraft

in operations and maintenance like material handling system, transport

means for men and luggage etc.

vi. Storage Tank Industries :

1. Storage tanks are used to store the large quantity of liquid or gas.

2. They are as large as cannot build in a single unit therefore these are

manufactured in parts for simplicity after that they can build in a single

unit by welding.

vii. Pipeline Industries :

1. The welding process is efficiently used in pipeline industries to provide

the seamless joint of the pipes.

2. Welding of pipe reduces the corrosion of joint as compared to riveting.

3. The welding provides more strength and high reliability to the pipes as

compared to the pipes manufactured by other processes.

viii.Petrochemical Industries :

1. Chemical and petroleum industries make good use of welding for the

fabrication of plant and machinery, stainless steel vessels and storage

tanks besides many other structures.

ix. Earth Moving Equipment Industries :

1. Earth moving equipment manufacturing industries largely depends on

the welding for the fabrication of earth moving machines like bulldozers,

loaders, trenches and drilling ridge for all oil exploration and water

tubewells and other related machines.

x. Material Handling Equipment Industries :

1. In this field welding is used for fabrication of overhead cranes, jib cranes

and tower cranes etc.

Que 1.4. What is the way in which welding processes can be

classified ? Explain.


A. According to Source of Energy Employed for Heating : These

may be divided into two groups as follows :

i. Pressure Welding :

1. In these processes, the parts to be joined are heated to a plastic state and

forced e.g., forge welding, thermit pressure welding etc., to form the


ii. Fusion Welding :

1. In these processes, the material at the joint is heated to the molten state

and allowed to solidify to make the joint, without the application of


2. Some joints may be made without the addition of a filler metal, but in

general, a filler metal must be added to the weld to fill the space between

the parts being welded.

3. The filler metal deposited should be of the same composition as the base

metal. Examples are gas welding, electric arc welding etc.

B. According to the Composition of Filler Metal : These may be divided

into three groups as follows :

i. Autogenous Welding :

1. In these processes, no filler metal is added to the joint interface, for

example, cold and hot pressure welding and electric resistance welding.

ii. Homogeneous Welding :

1. In these processes, filler metal is added and is of the same type as the

parent metal, for example welding of plain low carbon steel with a low

carbon welding rod and welding of 70-30 brass with a 70-30 brass welding

rod etc.

iii. Heterogeneous Welding :

1. In these processes, a filler metal is used but is of a different type from

the parent metal, for example brazing and soldering processes.

Que 1.5. What factors should be considered while selecting a

welding process ?


Factors considered while selecting a welding process are as follows :

1. Type of metal and its metallurgical characteristics, joint location and

welding position, its end use, cost of production, the quantity required,

product size and its location, performance desired, welders skill, training

and experience, joint accessibility, joint design, accuracy of assembly

desired, welding equipment available, work sequence, and installation


2. The process chosen should be suitable in terms of technical

requirements and cost. These two factors may not be compatible with

each other and thus may force a compromise.

3. The welding process and filler metal should be so selected that the weld

deposit is compatible with the base metal and will have mechanical

properties similar to or better than the base metal.

Que 1.6. Describe in detail health and safety measures in welding.


1. Every welder should be aware of health hazards like fires, explosion,

electrocution, burns, welder flush, oxygen depletion, toxic fumes/gases/

particles/vapours, radiation, trips and falls, and take adequate steps and

measures to safeguard themselves against these hazards.

2. Exposure to welding smoke could cause irritation to eyes, chest,

respiratory tract, inflammation of lungs.

3. Gases and particles in welding fume may be toxic or non toxic. While

particles of size greater than 5 μm are filtered by nose, and less than

0.1 m are breathed out, particles between size 0.1 and 5 μm are retained

in lung.

4. Maximum acceptable concentration (MAC) in general is 6 mg/m3.

5. Welding fume extraction equipment helps to reduce concentration.

6. Use material safety data sheets to identify hazardous material used in

welding e.g., use cadmium free silver solders, asbestos free electrodes.

7. Ultraviolet radiation given off by welding reacts with oxygen and nitrogen

in the air to form ozone and nitrogen oxides. Even 0.2 mg/m3 of

concentration is harmful and causes irritation of nose and throat and

serious lung diseases.

8. Electrical hazards also exist in welding even though welding source

operates at low voltage.

9. To keep insulation of electrode holder and cable high, these should be

kept dry and in good condition. Machines should conform to safety


10. All machines with moving part must be guarded for safety of workers.

Keep welding area clean of equipments, cables,, hoses etc. to prevent

trips and falls.

11. Intense light and radiation can damage retina/cornea of eye. Use auto

darkening helmet, welding curtain and sound protection curtain for

safety of welding operators and others.

12. All welding processes require protective measures. Use extraction hood

over the workplace to avoid exposure of fumes and gases to workers.

Use proper ventilation and welding helmet with overpressure.

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