Class: Senior Secondary School 2 (SS2 / SSS2)
Term: First Term
Week: 2
Age: 16 years
Duration: 45 minutes
Subject: Metal Work
Curriculum Theme: Pre-Vocational Studies
Previous Lesson: Metal Joining Processes and Fasteners.
Topic: Permanent Metal Joining Process (Soldering)
Subject Matter: Meaning of soldering (permanent joining of metals using solder), soft soldering, hard soldering, soldering tools and equipment, soldering operations, flux (cleaning and aiding solder flow).

Specific Objectives

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

Cognitive Domain:

Define soldering as a permanent metal joining process.
Differentiate between soft soldering and hard soldering.
List common tools and equipment used in soldering.
Explain the function of flux in soldering operations.

Affective Domain:

Appreciate the importance of safety precautions during soldering.
Show interest in learning basic soldering techniques.

Psychomotor Domain:

Identify different types of solder wire and flux.
Demonstrate a simple soldering operation under supervision.

Work cooperatively in groups to observe and discuss soldering demonstrations.

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 by A. O. Alabi

Instructional Materials

The teacher will teach this lesson with the aid of:

Soldering iron
Solder wire
Flux
Small metal sheets (e.g., copper, brass) for demonstration
Soldering stand
Safety goggles

Rationale for the Lesson

This lesson helps pupils understand a fundamental method of permanently joining metals, which is a valuable skill in various technical fields and for everyday repairs. It provides practical knowledge essential for vocational development and problem-solving.

Prerequisite/Previous Knowledge

Pupils have basic knowledge of different types of metals and some simple metal fabrication techniques.

Lesson Content/Board Summary

Permanent Metal Joining Process: Soldering

Meaning of Soldering

Soldering is a permanent metal joining process where two or more metal items are joined together by melting and flowing a filler metal (solder) into the joint. The solder has a lower melting point than the base metals being joined, so the base metals do not melt during the process. The solder forms a metallurgical bond between the surfaces.

Types of Soldering

The two main types of soldering are:

Soft Soldering: This process uses solders with melting points below 450°C. It is typically used for electrical connections, plumbing, and joining thin sheets of metal. The joints are not very strong and are not suitable for high-stress applications. Common solders are tin-lead or lead-free alloys.
Hard Soldering (Brazing/Silver Soldering): This process uses solders (filler metals) with melting points above 450°C but below the melting point of the base metals. It creates stronger joints than soft soldering and is used for joining ferrous and non-ferrous metals in applications requiring higher strength and temperature resistance, such as in refrigeration, automotive, and jewelry making.

Soldering Tools and Equipment

The following are common tools and equipment used for soldering:

Soldering Iron/Gun: Provides heat to melt the solder.
Solder Wire: The filler metal (alloy of tin and lead, or lead-free alloys) used to form the joint.
Flux: A chemical agent used to clean the metal surfaces and prevent oxidation during heating.
Soldering Stand: Holds the hot soldering iron safely.
Heat Sink: Used to protect heat-sensitive components from excessive heat.
Wire Brush/Abrasive Paper: For cleaning the surfaces of the metals to be joined.
Safety Goggles: To protect the eyes from splashes and fumes.

Flux and its Function

Flux is a chemical cleaning agent applied to the surfaces of the metals to be joined before soldering. Its main functions are:

To clean the metal surfaces by removing oxides and impurities.
To prevent further oxidation of the metal surfaces during the heating process.
To aid the flow of molten solder into the joint, ensuring good wetting and bonding.

Basic Soldering Operations (Steps)

The general steps for a simple soldering operation include:

Preparation: Clean the surfaces of the metals to be joined thoroughly with abrasive paper or a wire brush.
Apply Flux: Apply a thin layer of appropriate flux to the cleaned surfaces.
Heat the Joint: Heat the joint area with the soldering iron, not the solder directly.
Apply Solder: Touch the solder wire to the heated joint, allowing the molten solder to flow into the joint by capillary action.
Remove Heat and Solder: Once the joint is filled, remove the solder wire first, then the soldering iron.
Cool and Clean: Allow the joint to cool naturally, then clean off any flux residue.

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 introduces the topic by asking pupils if they know how electrical wires are joined or how small metal parts are fixed together. The teacher then relates their answers to the concept of joining metals permanently.
Pupils’ Activity: Pupils respond to the teacher’s questions and share their ideas about joining methods.
Learning Point: Pupils are introduced to the concept of permanent metal joining and its relevance.

Step 2: Meaning of Soldering

Time: 8 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher explains soldering as a permanent method of joining metals using a filler metal called solder, emphasizing that the base metals do not melt. The teacher also explains that solder melts at a lower temperature than the metals being joined.
Pupils’ Activity: Pupils listen attentively, ask questions for clarification, and note down the definition of soldering.
Learning Point: Pupils understand the definition and basic principle of soldering.

Step 3: Types of Soldering

Time: 8 minutes
Teaching Skill: Classification/Explanation
Teacher’s Activity: The teacher explains and differentiates between soft soldering and hard soldering, highlighting the temperature ranges, types of solder used, and typical applications for each.
Pupils’ Activity: Pupils listen and identify the key differences and uses of soft and hard soldering.
Learning Point: Pupils can distinguish between soft and hard soldering.

Step 4: Soldering Tools and Equipment

Time: 7 minutes
Teaching Skill: Identification/Demonstration
Teacher’s Activity: The teacher displays and names the soldering iron, solder wire, flux, and other relevant tools and equipment, explaining their individual uses. The teacher also shows safety goggles and explains their importance.
Pupils’ Activity: Pupils observe the tools, identify them, and ask questions about their functions and safety.
Learning Point: Pupils can identify and state the uses of common soldering tools and equipment.

Step 5: Function of Flux

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains in detail the crucial role of flux in soldering, including cleaning the metal surfaces, preventing oxidation, and aiding solder flow.
Pupils’ Activity: Pupils state the functions of flux and understand its importance in achieving a good solder joint.
Learning Point: Pupils understand why flux is essential in soldering.

Step 6: Soldering Operations

Time: 7 minutes
Teaching Skill: Demonstration
Teacher’s Activity: The teacher demonstrates a simple soldering operation step-by-step using a soldering iron, solder wire, flux, and small metal sheets, emphasizing safety precautions throughout the process.
Pupils’ Activity: Pupils observe the demonstration carefully, noting each step and the safety measures.
Learning Point: Pupils observe the practical steps involved in a soldering operation.

Step 7: Evaluation/Review

Time: 5 minutes
Teaching Skill: Questioning/Assessment
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define soldering.
State two differences between soft soldering and hard soldering.
List three tools used in soldering.
What is the primary function of flux in soldering?

Pupils’ Activity: Pupils answer orally and in writing.
Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher briefly summarizes the key points of the lesson, reiterating the definition of soldering, its types, tools, and the importance of flux and proper operation.
Pupils’ Activity: Pupils listen to the summary and prepare for the next lesson.
Learning Point: The lesson’s main points are reinforced.

Lesson Keywords

Soldering – A permanent process of joining metals using a filler metal (solder) that has a lower melting point than the base metals.
Solder – The filler metal alloy used in soldering, typically tin-lead or lead-free.
Flux – A chemical agent that cleans metal surfaces and prevents oxidation during soldering.
Soft soldering – Soldering done with filler metals melting below 450°C.
Hard soldering – Soldering (brazing) done with filler metals melting above 450°C.

Differentiation

For pupils who grasp concepts quickly, the teacher can challenge them to research different types of solder alloys and their specific applications. For pupils requiring more support, the teacher will provide additional one-on-one guidance during the demonstration and review key concepts using visual aids.

Note for teachers using this lesson plan

Ensure all safety precautions are strictly followed during the demonstration, especially when using the soldering iron. Emphasize the importance of proper ventilation. Encourage pupils to practice simple soldering techniques under close supervision to develop practical skills.