Selecting and justifying materials, components and processes

Introduction: Choosing the Right "Stuff"

Welcome! In Design and Technology, one of the most important jobs a designer has is picking the right materials, components, and processes. Think about it: you wouldn't make a frying pan out of chocolate or a rain jacket out of tissue paper! Choosing the wrong material means the product won't work, might be too expensive, or could even be dangerous. In this chapter, we will learn how to select the best options and, more importantly, how to justify (give good reasons for) those choices.

1. Performance Characteristics: How Materials Behave

When selecting a material, you first need to look at its properties. Designers look for specific "performance characteristics" to make sure the material can handle the job.

Physical and Working Properties

Depending on the product, you might need a material that is:

• Durable: Can it withstand wear and tear over time? (e.g., Stainless steel for kitchen sinks).
• Tough: Can it take a sudden impact without breaking? (e.g., HIPS for toys).
• Malleable: Can it be hammered or pressed into shape? (e.g., Aluminium for drink cans).
• An Insulator: Does it stop heat or electricity? (e.g., Urea formaldehyde for electrical sockets).

Quick Tip: If a question asks you to "justify" a material, always link a property to a function. For example: "I chose copper for the wires because it is an excellent conductor of electricity, which allows the circuit to function."

2. Factors Influencing Selection

It’s not just about strength! Designers have to balance many different factors when picking materials and components.

Aesthetic Factors

This is all about how the product looks and feels. Consider form, colour, and texture. Example: A luxury watch might use oak or stainless steel because they look high-quality and "expensive" to the consumer.

Environmental and Ethical Factors

Modern designers must think about the "Green Design" of their products:

• Life Cycle Analysis (LCA): Looking at the environmental impact from "cradle to grave" (extracting raw materials to eventual disposal).
• Sustainability: Can the material be replaced? (e.g., Pine trees grow faster than Oak).
• Recycling and Reusing: Is it easy to take apart and recycle? (e.g., Using thermoplastics like Acrylic which can be melted down and reshaped).
• Fair Trade: Ensuring the people who produced the materials were paid a fair wage and worked in safe conditions.

Economic Factors (Cost)

Cost is a huge part of the real world. Designers must work within a budget. Some material prices change constantly, such as the London Metal Exchange price for metals or the global oil price for polymers. Choosing a cheaper material like Pine instead of Mahogany might be necessary to keep the product affordable for the customer.

3. Selecting Components

Components are the "ready-made" parts you add to a product, like screws, hinges, or LEDs. Instead of making every single tiny part, designers use standardised components.

Why use standardised components?

• Consistency: A \( \text{5 mm} \) screw will always fit a \( \text{5 mm} \) hole.
• Cost: They are much cheaper to buy in bulk than making them yourself.
• Ease of repair: If an LDR (Light Dependent Resistor) breaks in a nightlight, the consumer can easily find a replacement part with the same tolerance and rating.

4. Justifying Manufacturing Processes

Once you have the material, how will you shape it? You need to justify your choice of process based on the scale of production.

One-off Production: Making a single, unique item (like a wedding cake or a custom piece of furniture). Justification: High skill level needed, but no expensive moulds or machinery required.

Batch Production: Making a specific number of items (like 50 wooden chairs). Justification: Uses jigs and templates to ensure all items are the same without the massive cost of a full factory line.

Mass Production: Making thousands of the same item (like plastic bottles). Justification: Uses automation and CAM (Computer-Aided Manufacturing) to lower the cost per item, even though the setup cost is very high.

Continuous Production: Running 24/7 for millions of items (like copier paper). Justification: Highest efficiency and lowest cost for extremely high-demand products.

5. The "Selection & Justification" Checklist

Don't worry if this seems like a lot to remember! When you are asked to justify a choice in your exam, just run through this "ACCESS FM" style thinking (but focused on selection):

• Function: Does the material do the job?
• Cost: Is it in the budget?
• Environment: Is it sustainable/recyclable?
• Availability: Can I buy it in the stock forms (e.g., sheets, tubes, or reels) that I need?
• Scale: Is the process right for how many I am making?

6. Math Skills in Selection

In the exam, you might need to calculate how much material to buy. Always remember your units!

• Linear measurements: Usually in millimetres \( (\text{mm}) \).
• Area: \( \text{Length} \times \text{Width} \).
• Waste: You might need to calculate how much material is wasted during a process. For example, if you need \( \text{10 m} \) of fabric but \( \text{10\%} \) is wasted: \( 10 \times 1.10 = 11 \text{ m total} \).

Key Takeaway: Justifying is simply giving a "because." "I selected Aluminium for the ladder because it has a high strength-to-weight ratio, making the ladder strong enough to hold a person but light enough to carry."