Welcome to the World of Product Design: Selecting Materials and Components

Hello future designer! This chapter is one of the most important parts of the whole course. Why? Because the materials and components you choose are the very DNA of your product. If you pick the wrong material, even the most brilliant idea will fail.

Don't worry if this seems tricky at first. We will break down the selection process into simple, manageable steps. By the end of this, you’ll be able to justify exactly why you chose plastic over metal, or a screw over a bolt!


Section 1: The Six Core Factors in Material Selection

When a designer selects a material for a product, they must balance many competing demands. It’s like trying to find a perfect combination of strength, beauty, and low price. We can group these considerations into six key factors.

To help you remember these crucial points, think of the mnemonic: F. A. C. E. M. A. (Though we'll mix the order slightly to make the categories clearer!)

1. Function and Fitness for Purpose

The material must be able to do the job it was designed for. This is called Fitness for Purpose. If the material cannot function correctly, the product is useless.

  • The Job: What stresses and environments will the material face? Will it carry weight, resist heat, or be constantly exposed to water?
  • Example: A kettle handle must be made of a material that is a poor thermal conductor (like plastic or Bakelite) so you don't burn your hand. A material that conducts heat well (like copper) would be completely unsuitable for this function.
  • Key Consideration: The material choice directly affects the safety and effectiveness of the product.

2. Aesthetics and Sensory Factors

Aesthetics simply means how the product looks and feels. How a product appeals to our senses is critical for sales and user satisfaction.

  • Visuals: Colour, texture, reflectivity (shiny or matte?), and finish are all aesthetic choices. (Example: A luxury wooden desk feels warm and inviting, while a stainless steel counter feels clean and modern.)
  • Sensory Appeal: This includes feel (smooth, rough, soft), smell (some materials like certain woods or leather have distinct smells), and even sound (the 'clunk' of a car door vs. the 'thud' of a cheap toy).

Did you know? Designers often use contrasting materials (like smooth glass and rough wood) to enhance the overall aesthetic appeal and make the product more interesting.

3. Cost and Budget

Money matters! The designer must work within a set budget. Choosing an expensive material will significantly increase the final selling price.

When considering cost, you must look beyond just the price of the raw material:

  • Material Cost: Is it a cheap, common material (like mild steel) or an expensive, rare material (like titanium)?
  • Processing Cost: How difficult is it to shape and finish? Some materials are cheap but require complex, expensive machinery to process (e.g., carbon fibre).
  • Maintenance Cost: Does the material need expensive upkeep? Wood needs varnish or treatment, but plastic often requires zero maintenance.

4. Availability and Maintenance

Availability (Can we get it?)

If a material is difficult or slow to source, it can cause huge delays in manufacture. Designers prefer readily available, standard stock forms (like standard sheets or rods) that can be easily bought in bulk.

Maintenance (How do we look after it?)

The user must know how to maintain the product. Materials that require little maintenance (like sealed plastics or anodised aluminium) are often preferred for consumer goods. Materials that rust or degrade quickly require high maintenance.

5. Environmental Impact and Sustainability

Modern design requires us to think about the planet. Designers must choose materials and manufacturing processes that are as gentle on the environment as possible. This is known as Sustainable Design.

The simplest way to remember sustainable choices is through the 6 Rs:

  1. Rethink: Could a completely different material or process be used?
  2. Refuse: Refuse to use harmful materials (like toxic paints or unsustainable woods).
  3. Reduce: Use less material overall (lightweight design).
  4. Reuse: Design products so parts can be used again for a different purpose.
  5. Recycle: Use materials that can be broken down and turned into new products (e.g., PET plastic).
  6. Repair: Design products that are easy to fix rather than throw away.

Quick Review Box: The Selection Checklist

Function (Does it work?) | Aesthetics (Does it look good?) | Cost (Can we afford it?) | Environment (Is it sustainable?) | Maintenance (Is it easy to look after?) | Availability (Can we source it easily?)


Section 2: Material Properties – What We Measure

To ensure a material meets the Function requirement, we need to understand its specific properties. These properties determine how the material behaves under stress, heat, or moisture.

1. Mechanical Properties (How materials react to force)

These properties describe the material’s ability to withstand pushing, pulling, bending, and impacts.

  • Strength: The ability to withstand external forces (load) without breaking. (Example: Steel is stronger than foam.)
  • Hardness: The ability to resist scratching, abrasion, and indentation. Think of diamonds being very hard.
  • Toughness: The ability to absorb impact energy without fracturing or cracking. Tough materials bend or dent instead of shattering. (Example: A car bumper needs high toughness.)
  • Malleability: The ability to be permanently pressed, hammered, or rolled into new shapes without cracking (e.g., rolling dough). This is important for forming metals into thin sheets.
  • Ductility: The ability to be stretched, pulled, or drawn out into a thin wire. This is crucial for making electrical cables.
  • Elasticity: The ability of a material to return to its original shape after the force causing the deformation is removed (like a rubber band).

Common Mistake Alert! Don't confuse Strength (resistance to breaking) with Hardness (resistance to scratching). A ceramic tile is very hard, but if you drop it, it has low toughness and breaks easily.

2. Physical Properties (Intrinsic characteristics)

These are characteristics that do not involve applying force, but affect how the material interacts with energy, heat, and weight.

  • Density: How heavy a material is relative to its size (mass per unit volume). High-density materials (like lead) are heavy; low-density materials (like expanded foam) are light.
  • Melting Point: The temperature at which a material turns from a solid to a liquid. Critical for materials used near heat sources (like ovens or engines).
  • Electrical Conductivity: How easily electricity can pass through a material. Good conductors (metals like copper) are used for wires; poor conductors (insulators like rubber) are used for safety covers.
  • Thermal Conductivity: How easily heat can pass through a material. Conductors (metals) move heat quickly; insulators (wood, foam) slow heat transfer.
  • Corrosion Resistance: The ability of a material to resist chemical breakdown, especially from moisture, air, or acids (e.g., stainless steel resists rusting).

3. Aesthetic Properties (Appearance and Feel)

These properties directly relate to the Aesthetic factors discussed earlier.

  • Colour: Can be inherent (like the grain of wood) or added (via paint or dye).
  • Texture: The surface quality – smooth, rough, matte, or glossy.
  • Finish: The final coating or treatment applied (e.g., polish, veneer, powder coating). This also protects the material from environmental damage.

Section 3: Selecting Standard Components

Designers don't always have to invent every single part of a product. Many parts—like screws, hinges, and batteries—are already perfectly designed and manufactured in huge quantities. These are called Standard Components.

Why Use Standard Components?

Using standard parts is almost always the smart choice because it offers several benefits:

  1. Cost-Effective: They are made in huge volumes (mass produced), making them very cheap to buy.
  2. Reliability: They have been tested and proven to work, ensuring consistent quality.
  3. Availability: They are readily available from suppliers, speeding up manufacturing time.
  4. Maintenance and Repair: If a part breaks, a standard replacement can be easily found and fitted by the user (e.g., changing a AA battery or tightening a standard screw).

Examples of Standard Components

1. Temporary Fixings and Fasteners

These allow the product to be disassembled for maintenance or recycling.

  • Screws and Bolts: Available in standard thread sizes (e.g., M8, M10).
  • Nuts and Washers: Used to distribute load and secure bolts.
  • Knobs and Handles: Often standardised in size and mounting holes.
2. Permanent Fixings

Used when disassembly is not required or is difficult (though not as common in sustainable design).

  • Rivets: Used to permanently join sheet materials (e.g., aerospace).
  • Adhesives: Standard glues and resins, chosen based on the materials being joined.
3. Mechanisms and Motion Control

These components facilitate movement or control energy.

  • Hinges and Runners: Allow doors or drawers to open smoothly.
  • Wheels and Castors: Enable movement (e.g., on office chairs or shopping trolleys).
  • Gears and Pulleys: Used to transmit force or change the speed of rotation.

Key Takeaway: Choosing a component means matching its size, material, and tolerance (accuracy of manufacture) to the specific job it needs to perform. For instance, a hinge for a heavy door needs to be robust (strong, tough material) with thick, accurate metal.