Introduction
This document is a learning guide. It is meant for people who want to learn basic arc welding skills. The guide is divided into two parts, the theoretical and the practical part. The theoretical part elaborates on the required knowledge a person will need to be able to perform the practical part.
This document is divided into eight learning units. These learning units represent the enabling objectives towards performing the required skills.
The theoretical portion will be spread into three sessions of 3 hours, whereas the practical part will be spread into two sessions of three hours.
Same is detailed below:
| Learning Units | Time Allotted | Sessions | Strategy |
| 1, 2 and 3 | 3 Hrs | One | On-line |
| 4, 5 and 6 | 3 Hrs | Two | On-line |
| 7 and 8 | 3 Hrs | Three | On-line |
| Practical Exercises |
| Practical Exercise No. 1 | 3 Hrs | Four | Face to Face |
| Practical Exercise No. 1 | 3 Hrs | Five | Face to Face |
After each learning unit a self test has been designed for you. It is important that you attempt each of them. Countercheck your answer with the key for each learning unit.
To move to the next learning unit, you need to be successful in the previous one. You need to score at least 80% of the total mark which is very easy indeed.
The practical sessions will be conducted under my supervision in a convenient workshop.
Competency Statement
- Perform Basic Arc Welding
Performance
- Deposit Stringer Beads In Flat Position
Conditions
- Using a welding transformer
- Using the rutile type electrode Ø 3.2 mm
- In flat position
- On Mild Steel Plate 6 mm thick
Standard
- Good start and end of weld
- Straightness of weld beads
- Uniform width of welds
- Fine ripples
- Free from external derfects
Pre-requisites
People following this manual shall be in a position to read and understand English. Basic knowledge of using common workshop tools like marking out and measuring tools would be a definite advantage.
The Cognitive and Skills to be Learnt
Cognitive
After following this package you shall be able to
- Identify the features of an AC welding machine
- Explain the working principle of an AC welding transformer
- Identify arc welding accessories
- Identify safety apparels for an arc welding operation
- State the safety precautions related to arc welding and accessories
- Select common tools used in arc welding
- Select current for welding
- Explain the different arc length
- State the variation in welding procedure on welds
- Select electrodes for welding
Skills
After following this package you shall be able to
- Strike and maintain an arc and lay short length beads
- Deposit straight line beads on 6 mm mild steel plate in flat position
Learning Unit One
At the end of this lesson you shall be able to
- Identify the features of an AC welding transformer
- Explain the working principle of an AC transformer
- Explain the care and maintenance of a welding transformer
AC Welding Transformer
This type of welding machine converts AC main supply into AC welding supply. Fig. 1 below illustrates.
AC main supply has high voltage-low current
AC welding supply has high current-low voltage
The welding machine is a step down transformer that reduces the main power supply 220-240 volts to a safe voltage.
Constructional features
It consists of an iron core made up of special alloy. Two coils of wire are wound over he core without any interconnection between them.
One coil is called the primary winding and the second is called the secondary winding. In terms of the number of turns, the primary coil has got more than the secondary side of the transformer.
A current regulator is attached to the secondary output to adjust the current according to various sizes of electrodes.
Two welding cables are attached to the welding outputs terminals. One is for the electrode holder and the other is for the work. The transformer may air-cooled or oil-cooled.
Working Principle
The AC main supply 220-240 Volts is connected to the primary winding which produces the magnetic flux in the core.
The magnetic flux affects the secondary winding and induces high current-low voltage welding supply
Care and Maintenance
- Transformer body must be properly earthen
- Transformer oil to be changed after recommended period
- Do not run machine continuously on its maximum capacity
- Switch off the main supply while cleaning internally and eternally
- Do not change current when welding is going on
Self Test Unit One Marks Scored: /20
Check your understanding by answering the following questions
- AC welding machines are generally …………….. transformers. (2 Marks)
- The unit for measuring current is …………………. (2 Marks)
- The cooling system of a welding transformer may be either:
a) …………………..
b) ………………….. (4 Marks)
- Explain the term step down transformer as far as machines are concerned.
……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… (4 Marks)
- What is the role of the current regulator?
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………. (3 Marks)
- List FIVE precautions regarding AC transformer. (5 marks)
Learning Unit Two
Arc Welding Accessories
At the end of this lesson you shall be able to
- Identify the welding accessories
- Explain the function of each accessory
Arc Welding Accessories
Some very important items which you, as welder are going to use with an arc welding machine, are called welding accessories.
Electrode holder (Fig.1)
The electrode holder is used to hold the electrodes at different angles during welding. The electrode holder is connected to the welding machine by a welding cable.
Earth Clamp (Fig.2)
It is used to connect the earth cable firmly on the job or welding table.
Welding Cables
These are used to carry current from the welding machine to the work and back. The lead from the welding machine to the electrode is called electrode cable. The lead from the work through the earth clamp is called earth cable. The cables are made up of super flexible rubber insulation, having fine copper wires and woolen fabrics reinforcing layers. Welding cables are made of different sizes. (Fig. 4)
Lugs
The cable connection should be made with suitable cable attachments (Fig 5). Loose joints or bad contacts cause overheating of the cables.
Welding Hand Screens and Helmet
These rare used to protect the eyes of the welder and face of a welder from arc radiation and sparks during arc welding.
A hand screen is designed to hold in hand (Fig 6A)
A helmet screen is designed to wear on the bead. (Fig 6B)
Screens are made of non flammable, no-reflective materials with coloured filter glasses fitted with plain glasses on both sides to see the arc and molten pool while welding.
Clear glasses are fitted on each side of the coloured glass to protect it from weld spatters. The helmet screen provides better protection and allows the welder to use his both hands freely.
Coloured filter lens are made in various shades; to suit welding at different current ranges.
Recommendations For Filter Glasses
| Shade No. of Coloured Glass | Range of Welding Current in Amperes |
| 8-9 10-11 12-14 | Up to 100 100 to 300 Above 100 |
Chipping Hammer ( Fig.7)
It is used to remove slag from the weld bead. It is provided with a chisel edge and a point for chipping off slag in any position
Wire Brush (Fig 8)
It is used for cleaning the workpiece prior to welding and general cleaning of welds.
Chipping Goggles (Fig 9)
It is used to protect the eyes while chipping the slag or grinding the job.
Self Test Unit Two Marks Scored: /30
Check your understanding by answering the following questions
1 Welder’s shield is fitted with a clean glass to protect from…………….
2 While performing arc welding, the work must be connected to ………..cable.
3 The material with which the apron is made of is ……………….
4 The electrode holder is connected to the welding source by ……………
5 The output current given by a transformer is …………… (5x2 Marks)
6 Name the welding accessories in Fig 1.
(7 Marks)
7 Identify the protectors used in welding Fig 2
(6 Marks)
8 Match the following
a A A Tongs 1 To remove spatters
B Chipping Hammer 2 To check squareness
C Try square 3 For removing slag
D Hand shield 4 For handling hot jobs
5 To protect face from ultra violet rays
b A Electrode holder 1 It is fitted with lenses and filter glass
B Helmet 2 It is made of copper or copper alloys
C Wire brushes 3 It protects from electric shock
4 Used for cleaning the surface of welded components
5 Protects from arc radiation and sparks
(7 marks)
