LEARNING EXPERIENCE – I Competence: Set Electrical Welding Plant ready for operation by following proper safety Precautions.

Enabling objectives:

After undergoing the learning experiences in this module you should be able to :

Set up arc welding equipment for different operations.

Select current and voltage rating for a job.

Test the setup

Observe safety precautions.

Learning Activities:

Read information sheet.

Complete assignment given in assignment sheet.

Complete the practice exercises and check answers.

Get the results checked before proceeding to Learning Experience II.

Element: Set up Arc Welding equipment. Information Sheet

In various situations you are required to make different shapes with metal components to serve the

purpose. Therefore you need to learn the technique to join metals.

Metal Joining Methods: There are three basic types of joining methods.

1) Flexible Joint: This is the simplest process

of metal joining in which components can be

joined and dis-assembled as and when

required without any destruction. Example: Bolting

2) Semi-permanent joint: This is the process

of joining in which components can be dis-

assembled when required with minor destruction

of joining component.

Example: Folding, Riveting

3) Permanent Joint: This is the process of

joining in which component cannot be

disassembled without destruction.

Example: Welding, Soldering

In this module our focus is only on Welding.

Welding is a process of joining metal with the

application of heat.

Welding is applicable to joining of same metal

components.

Applications of Welding: You can see

application of welding in various fields like

1) Furniture making

2) Bridge Construction

3) Building construction

4) Doors and window making etc.

We shall discuss the process of manual metal

arc welding. Welding is a process of joining metal with the

application of heat.

Welding is applicable to joining of same metal only.

Electrical Welding is a fusion welding process.

In this process electricity is used to develop heat

of fusion.

Let’s understand term fusion in following steps:

- It is the process of surface heating up to melting point.

- Melted joining boundaries become fluid and mix together.

- Filler rod provides additional material during fusion.

- Homogeneous bond is formed when the metal cools from liquid to solid state.

Lets learn basics of electricity prior to entering into the subject.

Burning gas

Electric Current : Flow of electricity is called as current. Current is measured in “Ampere”. Types of electric current : There are two types of electric current.

1) Alternating Current (AC) : This is the current which changes its direction and amplitude. Example: Electrical supply in our home. 2) Direct Current (DC) : This is the current which flows in one direction.

Example: Car battery Voltage : This is the pressure which causes current to flow. Voltage is measured in ‘Volts’.

Conductor: Substance which allow to electricity to flow through it is known as conductor.

Example : Copper, Iron , Aluminium etc.

Insulator : Substance which do not allow current pass through it is known as insulator.

Example: Wood, Cotton, Rubber etc.

Principle of arc welding When electric current flows through a conductor,

conductor property restricts this flow. The

restriction in flow of electrical energy results in

development of heat. Eg. Water heater used at

our home.

Amount of heat developed depends upon factors

1) Current (I)

2) Resistance of conductor (R)

3) Time of current flow (T)

Mathematical relation is as follows: H = I2 RT

Applications

1) Day to day fabrication work

2) Maintenance & repair work

3) Vessel fabrication

4) Piping work

5) Building & bridge construction etc

Types Various types of arc welding methods have been developed like:

Manual Metal Arc Welding

Carbon arc welding

Atomic hydrogen arc welding

Tungsten inert gas arc welding

Submerged arc welding

Electro-slag arc welding

Plasma arc welding Except manual metal arc welding rest of the methods are beyond the scope of this training.

Advantages

1) This is the simplest of arc welding processes.

2) Equipment are portable and the cost is low.

3) Process has vast application as variety of electrodes are available.

4) A wide range of metal & alloys can be welded by this process

5) Highest weld quality can be achieved in any position.

Limitations

1) Mechanizations is difficult

2) Best suitable for short weld length

3) Process is slow

4) Skill is required to produce quality welding joints.

Welding machine: Welding machine is basically

a rectifier which converts AC mains supply in to

DC supply.

Welding accessories: During operation apart from welding machine you need several small

equipments or components as follows.

1) Electrode Holder: This is device, which

you use to grip an electrode during

welding. Connect electrode holder to the

welding machine through an electric cable.

You have to always ensure that the holder

grip is insulated for safety reasons.

2) Earth clamp: This is a device, which is

used for connecting job or worktable to the

earth cable.

3) Welding cable: You require welding cable

for current flow from welding machine to

electrode welding cables carry heavy

current so you must be careful about

- Proper size of cable

- Tight cable connection

- Good insulation

4) Welding screen: This is a device, which

protects your eyes and face from spark

and radiations. Different shades of colors

are used in welding screen. You have to

select correct shade with respect to

welding current as shown in the table.

Practice 1: Assemble electrical welding machine and accessories and test the setup.

Current and voltage setting: You may have to join different pieces in the real work situation.

Different current or voltage settings are required for the different jobs. To set current adjust knob

provided to the required value. You will learn current requirement in the next element.

Testing of setup:

1. Ensure that you have taken precaution against electrical shock.

2. Switch on the main switch

- You will observe that the main line signal on

machine starts glowing, at the same time

voltmeter also shows the supply voltage.

- You can listen to a humming sound from

machine.

3. Grip electrode in the holder

4. Rub or touch electrode on metal piece

5. If arc generates, it shows that machine is

ready for welding.

Safety Precautions: You must take following precautions while working with electrical welding

equipment.

1) Wear your safety clothing and chipping goggles.

2) Keep other devices ready, like welding screen, holding tools etc.

3) Ensure you are wearing shockproof gloves and shoes.

4) Get main supply connection done through skilled electrician

5) Ensure that electrical joints are proper.

6) Check by yourself that the cable and electrode holder are not damaged.

7) Do not allow unwanted persons in the working area.

8) Check by yourself the operation of main switch, current setting knob and earth clamp.

Common tools: During operation you will also need some other tools for holding, cutting and

marking purpose.

Steel Rule: This is a tool that you can use to

measure length and marking points. It contains

graduations in mm, cm and inch.

Precautions:

1. Save edges and corners from wear & tear.

2. Do not use in place of screw driver.

Try square: This is a tool used to check rightness

(90° angle) of the edges. Set base along one of

the edge and check gap along other edge

opposite to light source. If you cannot see light,

means edges are at right angles.

Precautions: Do not use as hammer or

screwdriver.

Center Punch: This is a tool used for marking

points on the sheets. Centre punch is used for

marking centers for radius and marking points on

a job.

Scriber : This tool consists of sharp points as

shown in figure. Scriber is used to mark lines on a

job by scratching.

Precautions:

1. Do not use as center punch.

2. Save points from damages.

Compass : This tool consists of two pivoted legs

with sharp points. Compass is used to mark

circles and arcs. To mark arc or circle place one

of the leg on center point marked with center

punch. Set other leg so that point-to-point

distance is equal to the radius of the curve with

steel rule. Hold grip handle and rotate about the

center.

Hammer: This is a commonly used tool. Hammer

is used to blow impact. Different types of

hammers are available according to purpose of

use.

Chisel: This is tool used for cutting metal pieces

and removing welds.

Tong: This a tool used to hold hot pieces.

Hacksaw: This a tool used to cut metal along

straight line. It consists of frame and blade. Blade

can be replaced whenever required. In case of

hacksaw blade, tension is very important,

improper tension causes damage to the blade. To

check tension tap blade with finger, ringing sound

indicates proper tension.

File: This is a tool used for finishing and removing

burrs. Files are available in different shapes and

roughness. Bastard file, rough files and fine files

are used for heavy, medium and fine cuts

respectively.

Chipping hammer: This is the tool, which helps

you to remove slag from the weld.

Wire brush: This is a device, which you need for

cleaning of job before welding operation.

Self Test Answer the following. Q1. What is the source of heat of fusion in

electrical welding?

Q5. Write two limitations of electrical welding.

Q2. What is the unit of current?

Q6. What is the purpose of electrode holder?

Q3. Write two applications of electrical welding.

Q7. List two safety precautions.

Q4. Write two advantages of electrical welding.

Q8. What is the function of chipping hammer?

Write True (T) or False (F):

1) AC current flows only in one direction.

2) Ampere is the unit of voltage.

3) Insulator does not allow current to flow through it.

4) Welding machine converts AC current to DC current.

5) Chipping hammer is used to remove weld.

Solution to Self test

A1. Electricity is the source of heat of fusion in

electrical welding. A5. The two limitations are

1) Mechanizations is difficult.

2) Best suitable for short weld length.

A2. The Unit of current of current is Ampere. A6. This is device, which you use to grip an

electrode during welding.

A3. The two applications are 1) Furniture making 2) Bridge Construction.

A7. Two safety precautions are as follows

1) Wear safety clothing and chipping goggles.

2) Ensure you are wearing shockproof gloves and

shoes.

A4. The two advantages are

1) This is the simplest of arc welding

processes.

2) Equipment is portable and the cost is low.

A8. This is the tool, which helps you to remove

slag from the weld.

True and False: 1) False

2) False

3) True

4) True

5) True

LEARNING EXPERIENCE – II

Competence : Fabricate articles using electrical welding techniques.

Enabling objectives :

After undergoing learning experiences you should be able to :

Perform pre-welding operations.

Select equipment and accessories

Select appropriate voltage and current setting for a job.

Fabricate articles using arc-welding equipment.

Perform post weld operations.

Learning Activities :

Read information sheet.

Complete assignment given in assignment sheet.

Complete the practice exercises and check answers.

Get the results checked before completion of the module.

Element: Fabricate different articles using Electrical welding equipment

Information sheet In the last element you learnt about the setup and general information. To use electrical welding

machine to fabricate an article you should know :

- How welding takes place.

- What is the procedure?

- How to select correct electrode.

- How to prepare an edge.

- What are the common defects?

As you already know in the arc welding heat

of fusion is produce by electrical energy.

When you perform arc welding you will have to make arrangements as shown in the figure

First you have to generate the arc by bringing

electrode near the job. When there is small air

gap between electrode and the job, arc is

generated. The arc causes heating of job

boundaries to molten state at the same time

melt the electrode. When this molten filler

material deposits on job it causes a

homogenous bond.

How to produce an arc:

Before starting welding operation you should

Clean the work piece mechanically or

chemically to remove rust, oil and grease etc.

This ensures proper bonding of metal during

welding.

Set the work piece on worktable in flat position. Wear your safety clothes and devices.

Check machine for proper connections and damaged cables Select suitable welding electrode as per the table and fix to the electrode holder.

Switch on the welding machine

Set current and voltage ratio.

Strike an arc. You can strike arc in two ways:

By Scratch:

Keep welding screen in front of your eyes.

Bring electrode near the job, so that electrode

is at an angle of 750-800 with the job surface

and tip is about 2-3 cm above the surface.

Twist your wrist quickly. While doing so,

electrode scratches the job. This action

generates an arc.

You should see this arc through the welding

screen and maintain a gap equal to the dia of

rod.

By tap: - Touch electrode to the job.

- Lift the electrode slowly; this action will

generate an arc.

- Maintain the arc.

- If electrode sticks to the job you should

remove it quickly from the job to prevent

overheating just twist you wrist to

withdraw it.

How to produce a welding bead:

- Generate arc.

- Maintain electrode angle 900 with

surface and 700 with line of weld.

- Move electrode vertically down

smoothly so that arc is maintained.

- Withdraw electrode quickly at the end

of welding.

To perform correct welding selection of correct electrode is essential, so lets learn about the

electrodes.

While performing arc welding you need an electrode. It basically serves two purposes.

1) It completes welding circuit.

2) It provides additional material during fusion.

An electrode is made of metallic wire of standard dia and length. This wire is coated with a

material known as flux but sometimes not.

Various types of electrodes are available in the market, therefore electrodes are classified in

different categories.

Classification is based upon 1) Method of coating

2) Coating factor

3) Type of flux coating

4) Core wire material

Coating factor: This is the ratio of coating dia to the core wire dia.

Coating dia Coating factor = --------------------------- Core wire dia

1) If ratio is 1.25 to 1.3 electrode is light

coated.

2) If ratio is 1.4 to 1.5 electrodes is

medium coated.

3) If ratio is 1.6 to 2.2 electrodes is heavy

coated.

Function of flux: During welding flux performs following functions

1) It stabilizes the arc.

2) It protects molten metal from oxidation.

It compensates loss of elements burnt.

Types of flux

1) Cellulose Flux: This flux contains cellulose. These types of flux give deep penetration

and form very less slag during welding.

2) Rutile flux : This flux contains silicate and some part of cellulose. These fluxes are

used for wider gap filling.

3) Iron oxide flux: This flux contains iron oxide and silicates.

4) Basic flux : This flux contains fluoride and calcium carbonate. Basic flux form

large pool of molten metal and slag.

Codification of Arc Welding Electrodes

Necessity of coding: As you know various types of electrodes are available for different purposes.

It is necessary for you to identify suitable electrode for your purpose. You can chose appropriate

electrode only if you can understand special number i. e. code of an electrode.

Electrode coding mainly consists of:

1) Prefix E to indicate coated electrode for manual metal arc welding.

2) Type of flux

A – Acid, B – Basic ,C – Cellulose, R – Rutile , S – Others

3) Mechanical properties: These are the

properties of weld in terms of strength. Refer

table, You can find that code no 4 corresponds

to Ultimate tensile strength in the limit of 410-

510 N/mm2 while Min yield strength to 330

N/mm2

4) Welding position: Refer corresponding

table code 2 indicates that welding rod is

unsuitable for vertical position otherwise can be

used for all other welding positions.

5) Welding voltage : Refer the table , code 3

indicates that 70 volts Ac is necessary to use

this electrode.

Thus a code ER 4211 represents Manual metal arc electrode covered with rutile coating, having ultimate 410-510 N/m2, yield strength

330 N/mm2 elongation 22%, can be used for all welding position, voltage required 50V.

Arc Length: When you produce an arc, the distance between electrode and the job is called as arc

Code Ultimate Yield Tensile Strength Strength (min) N/mm2 N/mm2 4 410-510 330 5 510-610 360

Code Welding position 1 All 2 All except vertical 3 Flat butt, flat fillet 4 Flat butt, flat fillet 5 Vertical down 6 Any other

Code Polarity in Open circuit DC welding Voltage in AC Welding 0 - Ve - 1 +Ve/-V e 50 2 -Ve 50 3 +Ve 50 4 +Ve/-Ve 70 5 -Ve 70 6 +Ve 70 7 +Ve/-Ve 90 8 -Ve 90

length

Short Arc: If you maintain distance between

electrode and job less than the dia of electrode,

the arc produced is short arc.

Characteristics 1) You can hear popping sound.

2) You can observe rapid filler rod

consumption

3) You can observe convex weld bead

formation.

4) You can observe more fusion and

penetration.

5) You can see less spatters

You can see irregular ripples

Long Arc: If you maintain the distance between

electrode and job more than the dia of filler rod

while welding, the arc produced is long arc.

Characteristics 1) You can hear humming sound

2) You can observe un-stability of arc

3) You can see more spatters

4) You can observe poor fusion &

penetration

5) You can see wide and coarse ripple.

Normal Arc: If you maintain the gap between

job and electrode equal to the dia of electrode,

the arc produced is normal arc.

Characteristics

1) You hear cracking sound

2) You can see less spatters

3) You can observe correct fusion &

penetration

4) You can see proper shaped weld bead.

Welding Joints & Positions

Type of welding joint refers to the shape formed

by placement of joining edges. There are 5

basic types of joints.

1) Butt joint

2) Corner joint

3) Edge joint

4) Lap joint

5) Tee joint

Flat Position: In this position nozzle points

towards the ground. Nozzle is moved in any

direction.

Horizontal Position: In this position nozzle

points towards vertical plane opposite to your

body but moves only left to right or right to left.

Vertical Position: In this position nozzle points

towards vertical plane opposite to your body but

moves only up and down.

Overhead Position: In this position nozzle

points towards the plane above your head.

Nozzle can be moved in any direction.

Types of weld

Weld type refers to the ways of depositing metal on joining pieces. There are 4 basic types of welds

as follows

Bead weld: This type of weld is formed

when one or more weave beads are

deposited on unbroken surface. The

purpose of this weld is to obtain desired

property or dimension.

Application: This type of weld is used for

strengthening the metal sheet, repair of worn

out shafts etc.

Butt weld: Butt weld is formed when the metal to be deposited penetrates the cavity formed by

pieces to be joined which are in same plane.

Application: This type of weld is used to join pieces, which are in same plane e.g. Pipe joints.

Fillet weld: Fillet weld is formed when metal is deposited at the line of interface for joining

Application: This weld is used for joining pieces, which are not in the same place.

Butt weld: Butt weld is formed when the metal

to be deposited penetrates the cavity form by

pieces to be joined which are in same plane.

Application: This type of weld is used to join

pieces, which are in same plane e.g. Pipe

joints.

Fillet weld: Fillet weld is formed when metal is

deposited at the line of interface for joining.

Application: This weld is used for joining

pieces, which are not in the same place.

Other terms related to weld

Leg Length: The distance between points

where two ends of weld deposit touches the

plate being joined on either side of a tee joint

and point of joint.

Reinforcement : Excess metal deposited over

the surface of parent metal.

Root: The distance between parts to be

joined. This distance is filled by weldment.

Root face: Face below the chamfered

surface.

Root run: The first run of weld deposited over

the joint.

Sealing run: Small weld deposited at one side

for sealing purpose.

Common welding defects

Undercut: Groove formed in the parent metal.

Cause Remedy

Current too high Adjust

Welding speed fast Adjust

Faulty electrode

manipulation

Correct

Wrong electrode angle Correct

Overheating of job Correct arc length

.

Overlap : Molten metal flows over parent

metal.

Cause Remedy

Low current Adjust

Slow welding speed Adjust

Long arc Adjust

Large dia electrode Use correct dia

Porosity : Holes or lack of material in weld.

Cause:

1.Presence of contamination like moisture.

2. Fast cooling of weld metal

3. Improper cleaning of edges.

Remedy: 1. Remove oil , grease , and moisture during

pre welding operations.

2. Use good quality of flux.

3. Avoid long arc.

Spatter : Small droplet deposition around

welding line.

Cause Remedy

High welding current Adjust

Long arc Correct

Poor electrode quality Replace

Melting of edges: Parent metal melts at

edges.

Cause Remedy

Oversize electrode. Replace

High welding current Adjust

Wrong electrode

manipulation

Correct

Crack: Hairline separation of metal in the

weldment.

Cause Remedy

Fast cooling Correct

Pre-stressed metal Relieve stresses

More passes run Reduces passes run

Incomplete penetration: Failure of molten

metal to reach up to root.

Cause Remedy

Lesser bevel angle Correct

Low current Adjust

Large dia electrode Replace

Slag Inclusion: Entrapped foreign material.

Cause Remedy

Incorrect edge

preparation

Correct

Wrong electrode Replace

High current Adjust

Long arc Adjust

Assignment I

Join given pieces using square butt joint in flat position.

You are provided with:

1. Safety devices.

2. Electrical welding equipment

3. Welding accessories.

4. Piece of M S plate. Procedure:

1) Clean surfaces and prepare square

edges.

2) Take safety precautions.

3) Set pieces as butt joint with root gap

1.5 mm.

3. Tack weld on both ends as well as

center with 3.15 mm electrode and

130 Amp.

4. Deposit one side single run with

3.15 mm welding rod and 110 Amp.

Maintain electrode 90o with surface

and 80o with line of weld.

5. Move electrode forward steadily.

6. Remove slag from weld and inspect.

Material Name:

Size Scale

Instructor’s Signature:

Assignment 2

Join given pieces using fillet and lap joint. You are provided with:

1. Safety devices. 2. Electrical welding equipment 3. Welding accessories. 4. Pieces of MS plate.

Procedure:

1. Take safety precautions. 2. Clean surfaces and square the edges. 3. Set the pieces in the form of lap joint as

shown. 4. Set job in flat position and tack the pieces

at the ends and center.

5. Deposit root run with 3.15 mm electrode and 130 Amp current..

6. Maintain electrode angle 45o with surfaces and 80o with line of weld.

7. Remove slag and clean.. 8. Deposit covering run with weaving

motion, with 4 mm electrode and 170 Amp current.

9. Prevent edges from melting.

10. Remove slag, clean and inspect for

defects.

Material Name

Size Scale

Instructor’s Signature

Assignment 3

Join given pieces using fillet weld and corner joint in flat position You are provided with:

1. Safety devices. 2. Electrical welding equipment 3. Welding accessories. 4. Pieces of MS plate.

Procedure: 1. Clean edges and surfaces. 2. Take safety precautions. 3. Set joining pieces at right angle for

corner joint using fixture. 4. Select welding rod 3.15 mm dia and

set current 130 Amp. 5. Tack weld at both the ends. 6. Clean tack weld and check for

alignment.

7. Keep tacked pieces in flat position.

8. Set current 125 Amp and deposit root run to obtain complete penetration.

9. Remove slag and inspect for defects. 10. Select 4 mm electrode and set current

to 170 Amp. Deposit intermediate run with slight weaving.

11. Remove slag and inspect for defects 12. Deposit final run using weaving motion. 13. Clean welded joint and inspect for

defects. Starting Date : Finishing Date:

Instructor’s Observations:

Material Name:

Size

Scale

Instructor’s Signature:

Assignment 4

Join given pieces using tee fillet joint You are provided with:

1. Safety devices. 2. Electrical welding equipment 3. Welding accessories. 4. Pieces of MS plate.

Procedure: 1. Take safety precautions.

2. Clean surfaces and square the edges.

3. Set pieces in inverted tee (⊥) shape set

right angle with square and hold pieces

with the help support.

4. Tack welds the pieces at ends and

center.

5. Set tee in flat position.

6. Deposit root run with 3.15 mm

electrode and 130 Amp current.

7. Ensure electrode angle 45o with

surfaces and 80o with line of weld.

8. Remove slag and clean.

9. Deposit covering run with 4 mm

electrode and 170 Amp current.

10. Remove slag, clean and inspect for

defects.

Material Name:

Size

Scale Instructor’s Signature: