Design and Technology: Product Design (9252) | How materials are used in products

Materials in Products: The Designer's Choice

Welcome to this essential chapter on How Materials Are Used in Products! Think of a designer as a chef. A great chef knows exactly which ingredient (material) to use for the perfect dish (product). This chapter is all about learning the technical reasons behind those material choices.
Don't worry if some of the terms sound technical—we’ll break them down using simple examples you see every day. Understanding this is key to being a brilliant Product Designer!

1. The Four Pillars of Material Selection

When a designer chooses a material, they are balancing many different requirements set out in the design brief. It’s rarely just about what looks good. It’s about suitability!

Key Selection Criteria:

• Functionality (The 'Must Do'): The material must be able to perform its primary task.
  Example: If you are designing a boat hull, the material must be waterproof and resistant to corrosion.
• Aesthetics (The Look and Feel): This covers how the product looks, feels, and sounds. Materials contribute heavily to the product’s perceived value and appeal.
  Example: Expensive jewellery often uses precious metals (gold, silver) for their high lustre and inherent value.
• Cost and Availability (The Budget): Is the material affordable? Is it easy to source in large quantities? High-end materials like titanium may offer amazing properties, but they increase the final price significantly.
  Quick Tip: Designers often try to achieve a desired aesthetic using cheaper substitutes (e.g., using polished plastic to mimic metal).
• Environmental and Ethical Impact (Sustainability): How the material is sourced, processed, and disposed of is crucial. Designers often prioritise renewable materials (wood) or materials that are easily recycled (aluminum).

Key Takeaway: Material choice is a trade-off. You might sacrifice low cost for high strength, or vice versa.

2. Defining 'Usability': Understanding Material Properties

To know how a material is used, we must know how it behaves under stress. These behaviors are called Properties. We categorize these into two main types: Mechanical Properties (how it reacts to force) and Physical Properties (its natural state).

2.1. Crucial Mechanical Properties (How Materials Deal with Force)

These properties determine if a product will last, bend, or snap when used.

1. Strength: The ability to withstand force before failure.

• Tensile Strength: How much the material can be pulled (stretched) before breaking. (Think of a rope being pulled.)
• Compressive Strength: How much the material can be pushed (squashed) before failure. (Think of the legs supporting a heavy table.)

2. Hardness: The ability of a material to resist scratching, abrasion, or indentation.

• Real-World Analogy: A diamond is incredibly hard, which is why it can cut glass. Hard materials are essential for tools and protective surfaces.

3. Toughness: The ability of a material to absorb energy and withstand impact without fracturing (snapping).

• Don’t confuse Hardness and Toughness! A material can be hard but brittle (like glass or concrete), meaning it resists scratching but shatters easily on impact. Tough materials (like rubber or mild steel) can absorb shock.

4. Elasticity: The ability of a material to return to its original shape after a force is removed.

• Example: Rubber bands, springs, and memory foam all rely on high elasticity.

5. Plasticity: The opposite of elasticity. The ability to permanently change shape without cracking when a force is applied (essential for moulding, drawing, or bending).

6. Ductility: The ability to be stretched or drawn out into a thin wire. This is a crucial property for electrical wiring (copper is very ductile).

Memory Aid (Tough vs. Hard):
Tough materials take a punch (absorb impact). Hard materials resist a scratch (resist surface damage).

2.2. Essential Physical Properties (Natural Characteristics)

These properties relate to heat, electricity, density, and melting points.

• Electrical Conductivity: How well a material allows electricity to flow through it. Conductors (metals) are used for wiring; insulators (plastics, ceramics) are used for casings and protection.
• Thermal Conductivity: How well a material transfers heat. High conductors (aluminum) are used for saucepan bases; low conductors (wood, most polymers) are used for handles and insulation.
• Density: The mass of a material per unit volume. Products requiring lightness (aircraft parts, sports gear) use low-density materials like carbon fibre or aluminum alloys.
• Corrosion/Degradation Resistance: The ability to resist breakdown from environmental factors (rust from water, UV damage from the sun, or rotting). Essential for outdoor products.

3. Material Choice Dictates Manufacturing Process

The way a material behaves (its properties) determines how it must be shaped and joined. A designer must always choose a material that can be processed using available, cost-effective methods. This is known as workability.

The Link Between Property and Process:

1. Workability and Cutting/Shaping:

• Materials with high Hardness and Toughness (like tool steel) are difficult to cut and require specialised machinery (CNC milling, laser cutting) and slow speeds.
• Softer materials (like pine wood or low-density polymers) are easy to cut, drill, and sand using basic hand tools or standard workshop equipment.

2. Plasticity and Forming:

• Materials with high Plasticity (like thermoplastics or malleable metals) are perfect for forming processes like vacuum forming, blow moulding, or casting, as they hold a new shape permanently when cooled.
• Did You Know? Thermosetting polymers cannot be melted and reformed once cured, so they are generally cast or moulded using compression moulding, rather than injection moulding.

3. Joining Suitability:

• The material dictates the best joining method. Metals are often welded (using high heat) or soldered. Wood and some polymers are typically glued or joined using mechanical fixings (screws/bolts).

Common Mistake to Avoid: A struggling student might think a material is 'strong' enough simply because it is metal. However, cast iron is strong under compression but very brittle (low toughness), making it unsuitable for products that might receive sudden impacts, like a hammer head!

4. Enhancing and Protecting Materials: Finishes

Often, the material in its raw state is not ready for use. A designer applies a finish to modify the material's surface for two main reasons: protection and aesthetics.

Reasons for Applying a Finish:

1. Protection (Extending Lifespan):

• Corrosion Resistance: Metals like steel will rust quickly when exposed to moisture. Finishes like painting, galvanising (zinc coating), or electroplating create a barrier that prevents corrosion.
• Weathering and UV Resistance: Outdoor wood furniture requires varnish or oil to prevent moisture absorption, warping, and degradation caused by sunlight.
• Wear Resistance: Hard coatings can be applied to tools to increase their surface hardness and reduce wear during repeated use.

2. Aesthetics (Improving Appeal):

• Finishes change the colour, texture, and lustre (shine) of a material.
  Examples: Stains on wood to change the colour, polishing metals for a reflective shine, or textured powder coatings on steel bike frames for grip and a modern look.

Step-by-Step Example: Finishing a Steel Component

1. Preparation: The steel component must be cleaned, degreased, and potentially sanded to ensure the finish sticks properly.
2. Application (Protection): A primer is often applied first (like a base coat for protection against rust).
3. Application (Aesthetics/Final): The final layer is added (e.g., paint, lacquer, or powder coating) to give the desired colour and texture.
4. Curing: The finish is dried or baked to ensure maximum durability.

Key Takeaway: The chosen finish must be appropriate for both the material and the intended environment (e.g., an indoor finish won't work outdoors).