Class: Senior Secondary School 2 (SS2 / SSS2)
Term: Second Term
Week: 6
Age: 16 years
Duration: 45 minutes
Subject: Metal Work
Curriculum Theme: Pre-Vocational Studies
Previous Lesson: Welding Electrodes and Coatings.
Topic: High Quality Weld
Subject Matter: Factors for maintaining high quality weld (correct electrode type, electrode size, current, arc length, travel speed, electrode angle, manipulation of spatter)

Specific Objectives

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

Cognitive Domain:

Define what constitutes a high quality weld.
Identify the key factors that contribute to maintaining a high quality weld.
Explain how each factor influences the final weld quality.

Affective Domain:

Appreciate the importance of precise control over welding parameters for safety and durability.
Develop a keen eye for detail in assessing weld quality.
Show willingness to practice and refine welding techniques to achieve high quality.

Psychomotor Domain:

Select the correct electrode type and size for a given welding task.
Adjust welding machine current and maintain proper arc length.
Demonstrate correct travel speed, electrode angle, and manipulation during welding.

Collaborate with peers in discussing and practicing welding techniques.
Share observations and feedback on weld quality during practical sessions.

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.
https://www.twi-global.com/technical-knowledge/job-knowledge/factors-affecting-weld-quality
https://www.esab.com/gb/en/education/blog/what-makes-a-good-weld.html

Instructional Materials

The teacher will teach this lesson with the aid of:

Welding machine
Various types and sizes of electrodes
Steel samples for practical demonstration
Chipping hammer and wire brush
Safety gear (welding helmet, gloves, apron)

Rationale for the Lesson

This lesson helps pupils understand the critical elements that ensure strong and durable welds in metal fabrication. Learning these factors enables pupils to produce high-quality work, which is essential for structural integrity and safety in various applications.

Prerequisite/Previous Knowledge

Pupils are expected to have basic knowledge of welding safety, different types of welding processes, and the general function of a welding machine.

Lesson Content/Board Summary

High Quality Weld

A high quality weld is a strong, uniform, and defect-free joint that meets the required specifications for strength, appearance, and integrity. It is free from cracks, porosity, undercut, and excessive spatter, ensuring the welded structure performs as intended.

Factors for Maintaining High Quality Weld

To achieve and maintain a high quality weld, several factors must be carefully controlled:

Correct Electrode Type: The electrode type must match the base metal and the desired weld properties. Different electrodes are designed for specific materials (e.g., mild steel, stainless steel) and welding positions, affecting penetration, strength, and finish.
Electrode Size: The diameter of the electrode influences the amount of current that can be used and the depth of penetration. A larger electrode generally requires more current and produces a wider, deeper weld, while a smaller electrode is suitable for thinner materials or intricate work.
Current (Amperage): The welding current determines the heat input into the weld. Too low current results in poor fusion and a weak, narrow bead, while too high current causes excessive penetration, burn-through, and uncontrolled spatter. The correct current ensures proper melting and fusion.
Arc Length: This is the distance between the tip of the electrode and the workpiece. A short arc length (tight arc) produces a concentrated heat, deeper penetration, and a stable arc. A long arc length results in a wider, flatter bead, less penetration, more spatter, and an unstable arc.
Travel Speed: The speed at which the electrode moves along the joint affects the bead shape, penetration, and heat input. Too slow travel speed causes excessive material buildup, overheating, and potential burn-through. Too fast travel speed leads to a narrow, shallow bead with insufficient fusion and undercut.
Electrode Angle: The angle at which the electrode is held relative to the workpiece and the direction of travel influences bead shape, penetration, and slag removal. A slight drag angle (typically 10-15 degrees in the direction of travel) is common for most manual welding, promoting good penetration and bead appearance.
Manipulation of Spatter: Spatter consists of small metal droplets expelled from the arc that adhere to the workpiece or surrounding areas. While some spatter is unavoidable, excessive spatter indicates incorrect parameters (often high current or long arc) and can degrade weld appearance and require significant post-weld cleaning. Proper technique minimizes spatter.

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 greets the pupils and reviews the previous lesson on basic welding safety and equipment. The teacher then asks pupils what they think makes a strong and good-looking weld, linking their responses to the day’s topic: High Quality Weld.
Pupils’ Activity: Pupils respond to questions about the previous lesson and share their initial ideas about weld quality.
Learning Point: Pupils recall prior knowledge and are introduced to the concept of weld quality.

Step 2: Explanation of Electrode Type and Size

Time: 8 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains the importance of selecting the correct electrode type and size for different materials and applications. The teacher shows various electrodes and discusses their uses.
Pupils’ Activity: Pupils observe the different electrodes and ask questions for clarification regarding their types and sizes.
Learning Point: Pupils understand how electrode type and size affect weld characteristics.

Step 3: Explanation of Current and Arc Length

Time: 8 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains how current (amperage) affects heat input and penetration, demonstrating how to adjust it on the welding machine. The teacher also explains the concept of arc length and its impact on weld stability and quality.
Pupils’ Activity: Pupils pay attention to the explanation and observe the current adjustment on the machine. They ask questions about maintaining the correct arc length.
Learning Point: Pupils learn about the roles of current and arc length in achieving a quality weld.

Step 4: Explanation of Travel Speed and Electrode Angle

Time: 8 minutes
Teaching Skill: Explanation/Modeling
Teacher’s Activity: The teacher explains how travel speed and electrode angle influence bead shape, penetration, and slag control. The teacher demonstrates the correct travel speed and angle using a mock setup or a brief practical example.
Pupils’ Activity: Pupils observe the demonstration of travel speed and electrode angle and try to mimic the movements.
Learning Point: Pupils understand the effects of travel speed and electrode angle on weld quality.

Step 5: Explanation of Manipulation and Spatter

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher discusses proper electrode manipulation techniques to achieve desired bead patterns and explains how to minimize spatter through correct parameter settings and technique.
Pupils’ Activity: Pupils listen and take notes on electrode manipulation and spatter control.
Learning Point: Pupils learn about electrode manipulation and strategies to reduce spatter.

Step 6: Teacher Demonstration and Practical Application

Time: 6 minutes
Teaching Skill: Demonstration/Practical Application
Teacher’s Activity: The teacher demonstrates practical welding, consciously applying the discussed factors to produce a high-quality weld on a steel sample. The teacher points out the effects of varying each factor.
Pupils’ Activity: Pupils closely observe the teacher’s demonstration, noting the practical application of each factor discussed.
Learning Point: Pupils see the theoretical concepts applied in a practical welding scenario.

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 a high quality weld?
List four factors that contribute to maintaining a high quality weld.
How does incorrect current setting affect weld quality?
Explain the importance of maintaining a correct arc length during welding.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 3 minutes
Teacher’s Activity: The teacher summarizes the key factors for achieving high quality welds and encourages pupils to practice these techniques. The teacher assigns practical exercises for the next lesson or as homework.
Pupils’ Activity: Pupils listen to the summary and note down any assignments.
Learning Point: Pupils consolidate their learning and are prepared for further practice.

Lesson Keywords

Weld Quality – The degree to which a weld meets specified standards for strength, appearance, and integrity.
Electrode Type – The classification of a welding rod based on its coating and intended use.
Electrode Size – The diameter of the welding rod, which dictates current range and weld bead size.
Arc Length – The distance between the tip of the electrode and the workpiece during welding.
Travel Speed – The rate at which the welding arc moves along the joint.
Spatter – Small molten metal droplets expelled during welding that solidify near the weld bead.

Differentiation

For pupils who grasp concepts quickly, the teacher will challenge them to identify specific defects caused by improper control of each factor. For pupils needing more support, the teacher will provide simplified explanations and more direct, guided practice with individual factors.

Note for teachers using this lesson plan

Ensure all safety precautions are strictly followed during demonstrations and any practical sessions. Emphasize that consistent practice is key to mastering these factors for high-quality welding. Use visual aids like charts showing common weld defects and their causes.