Sand Casting, Die Casting and Shell Moulding Methods for SS 3

Class: SS 3
Term: First Term
Week: 2
Age: 16 years
Duration: 45 minutes
Subject: Metal Work
Previous Lesson: Casting, Meaning, Principles and Importance
Topic: Methods of casting:
Subject Matter: I sand casting; Ii die casting; Iii plaster mould cast and shell moulding

Specific Objectives

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

Cognitive Domain

• Define sand casting, die casting, plaster mould casting, and shell moulding.
• Explain the principles behind each casting method.
• State the advantages and disadvantages of each casting method.
• Identify factors influencing the selection of a casting method.
• Compare and contrast the different casting methods.

Affective Domain

• Appreciate the importance of selecting the appropriate casting method for different applications.
• Recognise the skill involved in various casting processes.
• Value the precision and efficiency of modern casting techniques.

Psychomotor Domain

• Identify components used in sand casting, die casting, plaster mould casting, and shell moulding from diagrams or samples.
• Sketch simple diagrams illustrating the setup for each casting method.

Social Domain

• Participate actively in discussions about different casting methods.
• Collaborate with peers in comparing casting techniques.

Reference Materials

The following resources were used in planning this lesson:

• 2025 Revised 9 Years Basic Education Curriculum
• Relevant State Unified Scheme of Work
• Metal Work for Senior Secondary Schools textbook
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Charts showing diagrams of sand casting, die casting, plaster mould casting, and shell moulding setups.
• Samples of products made by different casting methods (if available).
• Video clips demonstrating the casting processes.
• Whiteboard and markers.

Rationale for the Lesson

Understanding various casting methods is fundamental in Metal Work, as it provides students with knowledge of how complex metal parts are formed. This lesson equips students with the ability to identify suitable manufacturing processes, appreciate material properties, and make informed decisions in metal fabrication, preparing them for further studies or vocational pursuits.

Prerequisite/Previous Knowledge

Students should have a basic understanding of metals, their properties, and general metalworking processes.

Lesson Content/Board Summary

Methods of Casting

Sand Casting

Sand casting is a metal casting process that uses sand as the mould material. It is one of the oldest and most versatile casting methods, suitable for a wide range of metals and part sizes.

Process Steps:

1. A pattern (a replica of the desired part) is placed in a sand mould.
2. The sand is compacted around the pattern.
3. The pattern is removed, leaving a cavity in the sand.
4. Molten metal is poured into the cavity.
5. After cooling, the sand mould is broken to retrieve the cast part.

Advantages:

1. Low tooling cost.
2. Can produce very large parts.
3. Suitable for complex shapes.
4. Wide range of metals can be cast.

Disadvantages:

1. Poor surface finish.
2. Low dimensional accuracy.
3. High labour cost for finishing.
4. Mould is destroyed after each use.

Die Casting

Die casting is a metal casting process characterised by forcing molten metal under high pressure into a mould cavity (die). The dies are typically made from hardened tool steel and are reusable.

Types:

1. Hot-chamber die casting: Used for metals with low melting points (e.g., zinc, lead, tin). The melting pot is part of the machine.
2. Cold-chamber die casting: Used for metals with high melting points (e.g., aluminium, magnesium, copper alloys). Molten metal is transferred from a separate furnace.

Advantages:

1. Excellent surface finish.
2. High dimensional accuracy.
3. High production rates.
4. Thin-walled parts can be produced.

Disadvantages:

1. High tooling cost (for dies).
2. Limited to non-ferrous metals (mostly).
3. Not suitable for very large parts.
4. High initial investment.

Plaster Mould Casting

Plaster mould casting is a method similar to sand casting, but it uses plaster of Paris (gypsum) as the mould material. This method is known for producing castings with very fine detail and good surface finish.

Process:

1. A pattern is prepared, often from metal or plastic.
2. A slurry of plaster and water is poured over the pattern.
3. The plaster sets, and the mould is baked to remove moisture.
4. Molten metal (typically non-ferrous, e.g., aluminium, bronze) is poured into the mould.
5. After solidification, the plaster mould is broken away.

Advantages:

1. Excellent surface finish and fine detail.
2. Good dimensional accuracy.
3. Suitable for complex shapes.

Disadvantages:

1. Limited to non-ferrous metals with low melting points.
2. Mould is destroyed after each use.
3. Longer cycle times due to plaster drying.
4. Higher cost than sand casting.

Shell Moulding

Shell moulding is a casting process that uses a resin-bonded sand shell as the mould. It produces castings with better surface finish and dimensional accuracy than traditional sand casting.

Process:

1. A pattern, usually made of metal, is heated.
2. The heated pattern is coated with a mixture of sand and thermosetting resin.
3. The resin cures, forming a thin, hard shell around the pattern.
4. The shell is stripped from the pattern.
5. Two halves of the shell are clamped together to form the mould cavity, and molten metal is poured.

Advantages:

1. Better surface finish than sand casting.
2. Improved dimensional accuracy.
3. Reduced machining allowances.
4. Can be automated for high production.

Disadvantages:

1. Higher pattern cost.
2. Limited part size.
3. Resin fumes can be a health hazard.
4. Mould is destroyed after each use.

Factors for Selecting Casting Methods

The choice of casting method depends on several factors:

1. Material to be cast: Some methods are limited to specific metals (e.g., die casting for non-ferrous).
2. Complexity of part: Intricate designs may require specific moulding techniques.
3. Surface finish required: High-precision parts demand methods like die casting or plaster mould casting.
4. Production volume: High volume justifies the cost of reusable dies (die casting, shell moulding).
5. Cost: Tooling, material, and labour costs vary significantly.
6. Dimensional accuracy: Tight tolerances require more precise casting methods.
7. Part size and weight: Some methods are better suited for large or small parts.

Comparison of Casting Methods

Each casting method offers a unique balance of cost, quality, and production capability:

1. Sand Casting: Most versatile, lowest tooling cost, but poor finish and accuracy. Ideal for large, complex, low-volume parts.
2. Die Casting: Best finish and accuracy, high production rates, but very high tooling cost and limited to non-ferrous metals. Ideal for high-volume, small to medium-sized parts.
3. Plaster Mould Casting: Excellent finish and detail, good accuracy, but limited to non-ferrous, low melting point metals and lower production rates. Ideal for prototypes or artistic castings.
4. Shell Moulding: Better finish and accuracy than sand casting, suitable for medium to high volume, but higher pattern cost than sand casting.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Observation

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Explaining/Questioning

Teacher’s Activity: The teacher greets the students and reviews the previous lesson briefly. The teacher then introduces the topic of “Methods of Casting” by asking students how various metal objects they see daily might have been formed, leading them to the concept of casting.

Pupils’ Activity: Pupils respond to questions and listen attentively to the introduction.

Learning Point: Introduction to casting methods

Step 2: Sand Casting

Time: 8 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains sand casting, its principles, and process steps using diagrams or charts. The teacher highlights its advantages and disadvantages, providing examples of products typically made by sand casting.

Pupils’ Activity: Pupils observe the diagrams, listen to explanations, and ask questions for clarification.

Learning Point: Understanding sand casting

Step 3: Die Casting

Time: 7 minutes

Teaching Skill: Explanation/Illustration

Teacher’s Activity: The teacher explains die casting, differentiating between hot-chamber and cold-chamber methods. The teacher discusses its advantages and disadvantages, emphasising its suitability for high-volume production and precision parts, using relevant examples.

Pupils’ Activity: Pupils listen, take notes, and identify differences between sand and die casting.

Learning Point: Understanding die casting

Step 4: Plaster Mould Casting

Time: 6 minutes

Teaching Skill: Explanation

Teacher’s Activity: The teacher explains plaster mould casting, focusing on the use of plaster of Paris and its benefits for fine detail and surface finish. The teacher also covers its limitations regarding material type and production volume.

Pupils’ Activity: Pupils listen and note the unique characteristics of plaster mould casting.

Learning Point: Understanding plaster mould casting

Step 5: Shell Moulding

Time: 6 minutes

Teaching Skill: Explanation/Comparison

Teacher’s Activity: The teacher explains shell moulding, detailing how a resin-bonded sand shell is formed and its advantages over traditional sand casting in terms of finish and accuracy. The teacher also mentions its disadvantages.

Pupils’ Activity: Pupils listen and compare shell moulding with sand casting.

Learning Point: Understanding shell moulding

Step 6: Factors and Comparison

Time: 5 minutes

Teaching Skill: Discussion/Analysis

Teacher’s Activity: The teacher leads a discussion on the factors that influence the selection of a casting method. The teacher then guides students to compare and contrast the casting methods based on these factors, reinforcing their understanding. The teacher also reminds students about the upcoming workshop visit to see these methods in practice.

Pupils’ Activity: Pupils participate in the discussion, compare the methods, and note the factors for selection.

Learning Point: Factors and comparison of methods

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

1. Define sand casting.
2. State two advantages of die casting.
3. Mention two disadvantages of plaster mould casting.
4. List three factors to consider when selecting a casting method.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Assessment of understanding

Step 8: Note-Taking

Time: 4 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on casting methods into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Recording lesson notes

Step 9: Conclusion

Time: 2 minutes

Teaching Skill: Summarising

Teacher’s Activity: The teacher briefly summarises the key points of the lesson, reiterating the importance of understanding different casting methods in metalwork and encourages students to prepare for the workshop visit.

Pupils’ Activity: Pupils listen and prepare for the next activity or lesson.

Learning Point: Consolidation of casting methods

Continuous Assessment/Further Study

Type: Homework/Further Reading

Instruction: Research and write a short report on the specific types of products commonly manufactured using each of the casting methods discussed in class. Also, prepare a list of questions you would like to ask during the upcoming workshop visit to a metal foundry.

1. Identify five products made by sand casting.
2. Identify five products made by die casting.
3. Identify five products made by plaster mould casting.
4. Identify five products made by shell moulding.
5. List three questions you would ask a foundry worker.

Lesson Keywords

• Sand Casting – A metal casting process using sand as the mould material.
• Die Casting – Forcing molten metal under high pressure into a reusable metal mould (die).
• Plaster Mould Casting – Using plaster of Paris as the mould material for fine detail.
• Shell Moulding – A casting process using a resin-bonded sand shell as the mould.
• Pattern – A replica of the desired part used to create the mould cavity.
• Mould – A hollow form used to shape molten material.

Differentiation

For weaker learners: Provide simplified diagrams and pre-filled comparison tables to help them categorise the information. Focus on identifying key characteristics and one advantage/disadvantage for each method. The teacher can provide a glossary of terms.

For faster learners: Encourage them to research specific applications or industries where each casting method is predominantly used. They can also explore advanced casting methods like investment casting or centrifugal casting.

Suggested Lesson Videos

For visual demonstrations of casting methods, search on YouTube for:

• “Sand Casting Process Explained”
• “How Die Casting Works”
• “Plaster Mold Casting Basics”
• “Shell Molding Process Animation”

Teacher Guide for Using This Lesson Plan

Before the lesson, ensure you have visual aids such as charts, diagrams, or even short video clips demonstrating each casting method. If possible, bring small samples of cast products to show the students. Begin by activating prior knowledge about metal forming. Systematically introduce each casting method, explaining its principles, advantages, and disadvantages. Use clear language and encourage questions. For Step 6, facilitate a comparative discussion, guiding students to identify the factors that dictate the choice of casting method. This is a critical learning point. The workshop visit mentioned in the activities should be planned as a follow-up to this theoretical lesson, providing practical context. During Step 7, ensure questions cover all methods and the comparison aspect. In Step 8, supervise note-taking to ensure accuracy. For weaker learners, provide additional visual support and simplify explanations. Challenge faster learners with questions requiring deeper analysis or research into specific applications. Emphasise safety if discussing the workshop visit.