Class: Senior Secondary School 2 (SS2 / SSS 2)
Term: 2nd Term
Week: 2
Age: 16 years
Duration: 45 minutes
Subject: Metal Work
Curriculum Theme: Pre-Vocational Studies
Previous Lesson: Arc Welding: Meaning and Basic Types.
Topic: Consumable Electrode Arc Welding
Subject Matter: Meaning of consumable electrode arc welding (arc welding using melting electrode), maintenance of the arc, metal transfer across the arc.

Specific Objectives

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

Cognitive Domain:

Define consumable electrode arc welding.
Explain the principle of metal transfer across the arc.

Affective Domain:

Appreciate the importance of safety in arc welding.
Show interest in learning arc welding techniques.

Psychomotor Domain:

Demonstrate how to strike and maintain an arc.
Practice correct arc length control during welding.

Collaborate with peers during practical demonstrations.
Communicate effectively about welding procedures.

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, Book 2
https://www.twi-global.com/technical-knowledge/job-knowledge/welding-processes/smaw
https://www.hobartwelders.com/education/welding-basics/stick-welding

Instructional Materials

The teacher will teach this lesson with the aid of:

Electrodes
Welding machine
Mild steel work pieces
Welding helmet
Welding gloves
Welding apron

Rationale for the Lesson

This lesson helps pupils understand the fundamental principles of consumable electrode arc welding, a widely used joining process. It enables them to grasp how welding arcs are maintained and how molten metal transfers, which is essential for developing practical welding skills and ensuring strong, reliable welds in various applications.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of different types of metals and simple joining methods.

Lesson Content/Board Summary

Consumable Electrode Arc Welding

Meaning of Consumable Electrode Arc Welding

Consumable electrode arc welding, also known as Shielded Metal Arc Welding (SMAW) or manual metal arc welding (MMAW), is a welding process that uses a consumable electrode coated with flux to join metals. An electric arc is created between the electrode and the workpiece, melting both the electrode and the base metal to form a weld pool. The molten electrode metal then fills the gap, creating a strong joint.

Maintenance of the Arc

Maintaining a stable arc is fundamental for successful arc welding. The arc is formed by striking the electrode against the workpiece and then quickly lifting it to create a small gap. The arc length (distance between the electrode tip and the workpiece) must be kept constant for a steady arc and consistent weld quality.

Key points for arc maintenance:

Striking the Arc: Touch the electrode tip to the workpiece and quickly withdraw it slightly (scratching or tapping) to establish the arc.
Arc Length: Maintain an arc length approximately equal to the diameter of the electrode’s bare wire. Too long an arc causes instability, excessive spatter, and poor penetration; too short an arc can cause the electrode to stick to the workpiece.
Electrode Angle: Hold the electrode at an angle (typically 15-20 degrees from vertical in the direction of travel) to ensure proper penetration and slag removal.
Travel Speed: Move the electrode steadily along the joint at a speed that allows adequate fill and fusion of the base metals.

Metal Transfer Across the Arc

Metal transfer refers to how molten metal from the electrode crosses the arc gap and deposits into the weld pool. The type of transfer depends on factors like current, voltage, electrode type, and the shielding provided by the electrode’s flux coating.

In consumable electrode arc welding, common modes of metal transfer include:

Short Circuit Transfer: This occurs at lower currents and voltages. The molten metal droplet from the electrode touches the weld pool before detaching. It is common with smaller diameter electrodes and allows for welding in all positions.
Globular Transfer: Larger droplets of molten metal detach from the electrode tip and fall into the weld pool, primarily under the influence of gravity. This mode can be less stable and produce more spatter.
Spray Transfer: At higher currents and voltages, molten metal is projected across the arc as a fine spray of tiny droplets. This results in a smooth, stable arc and high deposition rates, typically used for flat and horizontal positions.

The flux coating on the electrode melts to form a protective gas shield around the arc and a slag layer over the molten weld pool, which protects the molten metal from atmospheric contamination and helps shape the weld bead as it solidifies.

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 any methods used to join metal parts permanently.
Pupils’ Activity: Pupils respond by mentioning methods like riveting, soldering, brazing, or welding.
Learning Point: Pupils recall prior knowledge related to joining metals.

Step 2: Explanation of Consumable Electrode Arc Welding

Time: 10 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines consumable electrode arc welding, explaining it as a process using a melting electrode to create a joint, and highlights the role of the electric arc.
Pupils’ Activity: Pupils listen attentively, take notes, and ask questions for clarification.
Learning Point: Pupils understand the meaning of consumable electrode arc welding.

Step 3: Components and Principle of Arc Welding

Time: 5 minutes
Teaching Skill: Illustration/Explanation
Teacher’s Activity: The teacher uses diagrams or actual equipment to show the main components of an arc welding setup and explains the basic principle of arc formation.
Pupils’ Activity: Pupils observe the diagrams/equipment and listen to the explanation.
Learning Point: Pupils identify the main parts of a welding setup and understand how an arc is formed.

Step 4: Demonstrating Arc Striking

Time: 5 minutes
Teaching Skill: Demonstration/Practical
Teacher’s Activity: The teacher demonstrates how to strike an arc on a mild steel workpiece using an electrode, emphasizing safety precautions.
Pupils’ Activity: Pupils observe the teacher’s demonstration carefully.
Learning Point: Pupils learn the correct technique for striking an arc.

Step 5: Demonstrating and Practicing Arc Maintenance

Time: 5 minutes
Teaching Skill: Demonstration/Guided Practice
Teacher’s Activity: The teacher demonstrates how to maintain the correct arc length and electrode angle during welding. The teacher then guides pupils to practice maintaining correct arc length with non-powered equipment or simulation.
Pupils’ Activity: Pupils observe the demonstration and practice maintaining the correct arc length.
Learning Point: Pupils develop the skill of controlling arc length for a stable weld.

Step 6: Explanation of Metal Transfer Across the Arc

Time: 5 minutes
Teaching Skill: Explanation/Description
Teacher’s Activity: The teacher explains the concept of metal transfer across the arc, describing how molten metal from the electrode moves to the weld pool and the role of flux.
Pupils’ Activity: Pupils listen, observe, and ask questions about the different modes of metal transfer.
Learning Point: Pupils understand how molten metal is deposited to form the weld.

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 consumable electrode arc welding?
Explain how to strike an arc.
Why is it important to maintain a consistent arc length during welding?
Briefly describe one mode of metal transfer across the arc.

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 and assigns homework, asking pupils to research common defects caused by improper arc maintenance.
Pupils’ Activity: Pupils listen to the summary and copy the homework assignment.
Learning Point: Pupils consolidate their learning and prepare for further study.

Lesson Keywords

Arc Welding – A welding process that uses an electric arc to melt and join metals.
Consumable Electrode – An electrode that melts and becomes part of the weld metal during the welding process.
Arc Length – The distance between the tip of the electrode and the workpiece during welding, which must be kept constant for a stable arc.
Metal Transfer – The process by which molten metal from the electrode travels across the arc gap to the weld pool.
Flux Coating – The chemical covering on an electrode that provides shielding gas and slag to protect the weld.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide additional resources on different types of electrodes or advanced welding techniques. For pupils who need more support, the teacher can offer one-on-one guidance during practical demonstrations and provide simplified diagrams or step-by-step guides for arc maintenance.

Note for teachers using this lesson plan

Ensure all safety precautions are strictly followed during any practical demonstration involving welding equipment. Emphasize the importance of personal protective equipment (PPE). If actual welding cannot be performed, use visual aids, videos, and simulations to demonstrate the concepts effectively. Encourage pupils to ask questions and engage actively in discussions.