Class: Senior Secondary School 2 (SS2 / SSS 2)
Term: Second Term
Week: 3
Age: 16 years
Duration: 45 minutes
Subject: Metal Work
Curriculum Theme: Pre-Vocational Studies
Previous Lesson: Consumable Electrode Arc Welding.
Topic: Shielded Metal Arc Welding (SMAW)
Subject Matter: Meaning of SMAW (shielded metal arc welding process), principle of operation, SMAW equipment (DC transformer, electrode holder, flexible cable electrode).

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define Shielded Metal Arc Welding (SMAW).
Explain the principle of operation of SMAW.
Differentiate between AC and DC power sources used in SMAW.

Affective Domain:

Appreciate the importance of safety measures when performing SMAW.
Develop an interest in learning more about welding processes.

Psychomotor Domain:

Identify the major equipment used in SMAW.
Demonstrate how to connect basic SMAW equipment.

Collaborate with peers to identify and handle welding equipment safely.

Reference Materials

The following resources were used in planning this lesson:

Senior Secondary Schools Education Curriculum
State Unified Scheme of Work
Metal Work for Senior Secondary Schools Textbook

Instructional Materials

The teacher will teach this lesson with the aid of:

DC transformer/welding machine
Electrode holder
Welding cables
Electrodes
Welding helmet
Gloves
Welding bench/table

Rationale for the Lesson

This lesson helps pupils understand the fundamental principles and equipment of Shielded Metal Arc Welding (SMAW), a common welding process. This knowledge is important for developing practical skills in metal fabrication and for safety in the workshop.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of metal work tools, different types of metals, and general workshop safety rules.

Lesson Content/Board Summary

Shielded Metal Arc Welding (SMAW)

Meaning of SMAW

Shielded Metal Arc Welding (SMAW), also known as manual metal arc welding (MMAW) or stick welding, is a welding process that uses a consumable electrode coated in flux to lay the weld. An electric arc is formed between the electrode and the base material, melting both and forming a weld pool. The flux coating on the electrode disintegrates, producing shielding gases and slag to protect the weld from atmospheric contamination.

Principle of Operation of SMAW

The principle of SMAW involves striking an electric arc between a flux-coated consumable electrode and the workpiece. The heat generated by the arc melts the tip of the electrode and the surface of the workpiece, creating a molten weld pool. The flux coating on the electrode decomposes due to the heat, producing a gaseous shield that protects the molten metal from oxygen and nitrogen in the atmosphere. The flux also forms a layer of slag over the solidifying weld, which further protects it and helps to shape the weld bead. As the weld cools, the slag is chipped away.

SMAW Equipment

The essential equipment for Shielded Metal Arc Welding includes:

Welding Power Source (Transformer/Rectifier): Supplies the electric current for welding. It can be AC (Alternating Current) or DC (Direct Current).
Electrode Holder: A clamp-like device used to hold the electrode firmly and conduct the welding current to it.
Welding Cables: Insulated copper or aluminum cables that carry the welding current from the power source to the electrode holder and from the workpiece back to the power source (earth clamp).
Earth Clamp (Work Clamp): A device that connects the workpiece to the welding power source to complete the electrical circuit.
Electrodes: Consumable metal rods coated with flux, which melt to form the weld metal and provide shielding.
Personal Protective Equipment (PPE): Includes a welding helmet with a dark lens, leather gloves, protective clothing (e.g., apron), and safety boots to protect the welder from arc rays, heat, sparks, and fumes.

AC and DC Power Sources in Welding

Welding machines provide either Alternating Current (AC) or Direct Current (DC) for welding:

AC Welding Machine: Supplies current that periodically reverses direction. It is generally simpler and less expensive. AC welding is often used for heavy-duty applications and on certain types of electrodes.
DC Welding Machine: Supplies current that flows in one direction only. DC welding provides a smoother arc, better arc control, and is suitable for a wider range of electrodes and materials.
Rectifier: A component within a welding machine that converts AC input power into DC output power. Welding machines that can provide both AC and DC output typically include a rectifier.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher asks pupils if they know what welding is and if they have seen any welding operations before. The teacher then introduces the topic: Shielded Metal Arc Welding (SMAW).
Pupils’ Activity: Pupils respond to the questions and pay attention as the topic is introduced.
Learning Point: Pupils recall prior knowledge and are prepared for the lesson.

Step 2: Meaning of SMAW

Time: 8 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher explains the meaning of Shielded Metal Arc Welding (SMAW) and writes the definition on the board.
Pupils’ Activity: Pupils listen attentively, ask questions for clarity, and copy the definition into their notebooks.
Learning Point: Pupils understand what SMAW is.

Step 3: Principle of Operation of SMAW

Time: 8 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains the principle of how SMAW works, describing the arc formation, melting of electrode and workpiece, and the role of the flux in shielding the weld.
Pupils’ Activity: Pupils listen to the explanation and visualize the process, taking notes as required.
Learning Point: Pupils grasp the fundamental working mechanism of SMAW.

Step 4: SMAW Equipment

Time: 8 minutes
Teaching Skill: Identification/Demonstration
Teacher’s Activity: The teacher displays various SMAW equipment such as the welding machine, electrode holder, welding cables, and electrodes. The teacher names each item and explains its function.
Pupils’ Activity: Pupils observe the equipment, identify them by name, and listen to their functions.
Learning Point: Pupils can identify and state the function of key SMAW equipment.

Step 5: AC and DC Power Sources and Rectifier Function

Time: 6 minutes
Teaching Skill: Explanation/Comparison
Teacher’s Activity: The teacher explains the difference between AC and DC power sources in welding and describes the function of a rectifier in converting AC to DC.
Pupils’ Activity: Pupils listen and understand the characteristics of AC and DC power sources and the role of a rectifier.
Learning Point: Pupils understand the types of electrical power used in SMAW and how they are converted.

Step 6: Practical Demonstration/Connection

Time: 5 minutes
Teaching Skill: Demonstration/Practical Application
Teacher’s Activity: The teacher demonstrates how to safely connect the welding cables to the power source, attach the electrode holder, and connect the earth clamp to a workpiece. The teacher emphasizes safety precautions.
Pupils’ Activity: Pupils observe the teacher’s demonstration and ask questions regarding the connection process and safety.
Learning Point: Pupils learn the correct and safe procedure for connecting SMAW equipment.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

What is Shielded Metal Arc Welding (SMAW)?
Explain the basic principle of operation of SMAW.
Mention three essential pieces of equipment used in SMAW.
How does a rectifier function in a welding machine?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 5 minutes
Teaching Skill: Summarization/Assignment
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterates the importance of safety, and gives homework: “List five safety precautions to observe when performing SMAW.”
Pupils’ Activity: Pupils listen to the summary and copy the homework assignment.
Learning Point: Pupils consolidate their learning and receive further tasks.

Lesson Keywords

SMAW – Shielded Metal Arc Welding, a welding process using a flux-coated electrode.
Electrode – A consumable metal rod coated with flux, used to create the arc and supply filler metal.
Flux – The coating on an electrode that provides shielding gas and slag to protect the weld.
Arc – The electrical discharge between the electrode and the workpiece that generates intense heat.
Rectifier – An electrical device that converts alternating current (AC) to direct current (DC).

Differentiation

For pupils who grasp concepts quickly, the teacher can challenge them to research different types of electrodes and their applications. For those needing more support, the teacher can provide additional visual aids or simplified diagrams of the equipment and process, offering one-on-one guidance during the equipment identification and connection steps.

Note for teachers using this lesson plan

Ensure that all practical demonstrations are conducted with strict adherence to safety protocols. Emphasize the dangers of welding without proper personal protective equipment (PPE). If a functional welding machine is available, ensure it is in good working condition and used under direct supervision. Encourage pupils to ask questions, especially regarding safety and practical application.