Cambridge IGCSE Design and Technology: Student Book

Contents Section 1 Product Design............................................. 6 1·1 Getting started........................................................8 1·2 Design ideas and techniques.......................... 20 1·3 Making..................................................................... 36 1·4 Evaluation............................................................... 48 1·5 Health and safety................................................. 55 1·6 Use of technology............................................... 63 1·7 Design and Technology in society................. 72 1·8 Product design application.............................. 78 1·9 Environment and sustainability...................101

Section 2 Graphic Products..................................... 108 2·1 Formal drawing techniques...........................110 2·2 Sectional views, exploded drawings and assembly drawings...........................................115 2·3 Freehand drawing.............................................120 2·4 Drawing basic shapes......................................122 2·5 Developments....................................................127 2·6 Enlarging and reducing...................................130 2·7 Instruments and drafting aids......................134 2·8 Layout and planning........................................136 2·9 Presentation........................................................139 2·10 Data graphics...................................................144 2·11 Reprographics..................................................148 2·12 Materials and modelling..............................150 2·13 ICT.........................................................................156 2·14 Manufacture of graphic products.............159

Section 3 Resistant Materials.................................. 164

Section 4 Systems and Control.............................. 228 4·1 Systems.................................................................230 4·2 Structures.............................................................233 4·2·1 Basic concepts.........................................233 4·2·2 Types of frame structure members....237 4·2·3 Strengthening frame structures.......240 4·2·4 Nature of structural members...........242 4·2·5 Applied loads and reactions..............245 4·2·6 Moments...................................................248 4·2·7 Materials....................................................251 4·2·8 Testing........................................................253 4·2·9 Joints in structures................................255 4·2·10 Forces.......................................................258 4·3 Mechanisms.........................................................265 4·3·1 Basic concepts.........................................265 4·3·2 Conversion of motion...........................273 4·3·3 Transmission of motion.......................281 4·3·4 Energy........................................................292 4·3·5 Bearings and lubrication.....................295 4·4 Electronics............................................................299 4·4·1 Basic concepts.........................................299 4·4·2 Circuit building techniques................305 4·4·3 Switches....................................................311 4·4·4 Resistors....................................................316 4·4·5 Transistors.................................................320 4·4·6 Diodes........................................................323 4·4·7 Transducers..............................................326 4·4·8 Capacitors.................................................328 4·4·9 Time delay circuits.................................330 4·4·10 L ogic gates and operational amplifiers................................................335

Section 5 The Project................................................ 344 Glossary........................................................................359 Index..............................................................................366 Acknowledgements.................................................373

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3·1 Types of materials..............................................166 3·2 Smart and modern materials........................170 3·3 Plastics...................................................................173 3·4 Wood......................................................................177 3·5 Composites .........................................................184 3·6 Metals....................................................................188 3·7 Preparation of materials .................................195 3·8 Setting and marking out.................................199 3·9 Shaping.................................................................204

3·10 Joining and assembly....................................210 3·11 Finishes...............................................................222

Contents

Introduction.....................................................................4

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This section will help you to develop a broad understanding of the materials, techniques, tools, equipment, methods and processes used with resistant materials. Specifically, it aims to support you as you develop your understanding of both the physical and working properties of a range of woods, metals and plastics.

This section is designed to help you to relate your understanding directly to the processes associated with designing and making, so that you are able to apply relevant skills, knowledge and understanding effectively. This is so that following analysis, based on evidence, you can make sound judgements and decisions in relation to material and process choices, in order to plan and carry out work safely and effectively.

You will develop your awareness of the different types of material, including smart and modern materials, and their associated physical working properties. You will learn key terms and understand the processes involved to accurately set and mark out material. You will also learn the correct techniques and be aware of the manufacturing processes involved in shaping, joining and finishing different materials.

startIng poInts • What materials are available?

• What are composite materials?

• How do you decide which type of material is best to use?

• Which tools and equipment are available to cut, shape and join different types of material?

• Which tools and equipment do you use to mark and set out material?

• How do you decide which tools and equipment to use to cut and shape material?

• How do you decide which is the best type of finish to use?

• What is PPE equipment and why is it important to know how to use it?

seCtIon Contents

3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11

Types of materials Smart and modern materials Plastics Wood Composites Metals Preparation of materials Setting and marking out Shaping Joining and assembly Finishes

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3

Resistant Materials

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3·1 Types of materials LEARNING OBJECTIVES By the end of this section you should: ✓✓understand the common physical and working properties of materials ✓✓understand the common factors that should be considered when selecting materials that are fit for purpose.

Why do I need to know about the properties of materials?

Designers, technologists and engineers need to know the properties of materials to inform their selection of suitable materials in order to meet the requirements of a product design specification. Two key concepts are critical in relation to your knowledge of materials: • how materials are classified, so that you have knowledge of a broad range of materials to choose from when designing, and are not restricted to the materials that you have used • what the properties of materials are, how they add functionality or make a product aesthetically pleasing, and how they can be worked.

Categories of materials A basic understanding of categories or types of materials can help you classify and select the materials most appropriate for your design needs. This can help you to take a methodical approach to materials and help when interacting with materials databases. The most common materials are woods, metals and plastics, and composites. The terms smart or modern materials are often used to describe manufactured materials with particular properties, which often react to environmental conditions. These are described in detail in unit 3.2. It is also worth noting that textiles are a classification of materials and, while these might be labelled as ‘compliant’ rather than ‘resistant’ materials, some materials can be produced in both a textiles (or fabric) and a solid form, such as the polymer nylon which may be used for garments and engineered mechanical components.

Woods

Natural

Manufactured

Metals

Ferrous

Plastics

Non-ferrous

Composites

Thermoforming

Smart and Modern

Thermosetting

∆∆A classification table of materials

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Materials

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Working properties Each working property has a technical definition describing how a material behaves when being worked or shaped (see unit 3.9). The most common working properties are: • strength: the ability to withstand a constant external force without failing • hardness: the ability to resist wear-and-tear, scratching and dents; usually related to surfaces • toughness: the ability to withstand blows or momentary shocks (live forces) • durability: the ability to resist wear, such as weathering, over time • elasticity: the ability to bend and then to return to its original shape/ size • plasticity: the ability to permanently change shape or form, which applies to materials other than polymers • malleability: the ability to permanently change shape, in all directions, while retaining integrity • ductility: the ability to change shape by stretching along its length without snapping.

3·1 Types of materials

Physical Properties Physical properties are a major factor when selecting materials for specific users, purposes and conditions. Each physical property describes how a material behaves under specific conditions. Common physical properties are: • mechanical: how a material will react to physical forces, such as how some materials become brittle when repeatedly bent or flexed • electrical: a material’s conductive properties including insulation and resistance, such as how a screwdriver’s polymer handle (insulator) protects the user from electic shocks through the tip (conductor) • chemical: how a material reacts to other chemicals, such as how metals oxidise when exposed (for example, ferrous metals rusting) • thermal: how a material responds at different temperatures, such as freezing/melting and boiling points, such as the temperature ranges where thermoforming plastics can be shaped • magnetic: most ferrous (containing iron) materials are attracted to magnets or can be magnetised, such as the use of magnetic catches for keeping doors closed • permeability: the degree to which liquids or gases can pass through a material, such as woods that have been varnished having low permeability to liquids and water resistance • aesthetic: the visual sensory properties of the surface/form of a material, such as colour and shine • tactile: the touch or sensory properties of a material, such as texture.

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Selecting materials When selecting appropriate materials for a product it is important to get the design specification right. It is essential to identify the requirements for the user, function or conditions that a product will be exposed to. Once a specification has been drafted, the required physical and working properties can be identified and used to search a materials database or table. For example, a specification for a garden chair might state that the product must be durable for use outdoors in all seasons, with minimum maintenance.

TOP tip

A common mistake is to rely only on materials that you know and have used before.

Understanding how materials are classified, what their properties are, and how to select them will lead to more functional and appealing products. When making a prototype (working model/product to test a concept) you might use the materials that are most readily available. However, when writing a manufacturing specification for production, alternative materials should be selected to optimise the efficiency of a commercially viable product, in relation to the cost of manufacture, marketability or functionality.

SKILLS ACTIVITY Choose a product that you use often and sketch or photograph it. List the materials that you can see. If you are unsure what materials have been used, look in units 3.3 to 3.7 of this book, or go online and investigate the product. Manufacturers’ websites often list the materials used. Now select one of the materials that you have identified and list the properties for which it was selected. Give reasons why you think this was the case, including functional, aesthetic, financial and manufacturing factors.

Modern mobile phones and devices are designed around touch screens.

Currently most of these devices use special screens that sense electronic charge. Therefore, the glass used needs to have specific properties that enable input from your finger to be picked up by the sensors built into the screen, alongside the visual display. In addition to this the material used needs to be highly transparent, avoid glare and be tough enough to resist normal day-to-day use. The glass used in these devices is designed by material scientists to have particular properties and differs from that used, for example, in windows or spectacles. This is a good example of how important it is that designers, technologists and engineers have a sound knowledge of the properties of materials, so that they can select the most appropriate materials to meet the functional, aesthetic, financial and manufacturing requirements of a product.

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Resistant Materials

DESIGN IN ACTION

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KNOWLEDGE CHECK Design a folding worksurface that could be used by a teenager when doing homework.

1. Communicate your idea using an annotated sketch.

(4) 2. Identify all materials used in your design and list the specific physical and working properties which make them suitable.

(6)

Reflective Log

Think of a product that you have made recently. Write a brief evaluation of the product, focusing on the properties of materials, using these prompt questions:

• What materials did you use?

• Why did you use these materials?

• Would alternative materials be more appropriate if you were to batch or mass manufacture the product? Why do you think this? Make reference to properties of materials.

Key Terms

force: a power that produces strain on a material and that changes its shape, or has the potential to change its shape. There are five forces that act on materials: compression, tension, torsion, sheer and bending.

physical property: an observable or measurable characteristic of a material, for instance strength or density

prototype: a working model, in the early stages of development, which, through testing against the specification, is used to help refine the product before beginning final or larger scale production

stiffness: resistance to forces of bending or torsion stress or strain: a force created by pressure on an object or material, that has the potential to damage it by changing its shape

working property: the way a material behaves when being worked or shaped or while being used

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3·1 Types of materials

within a product. Working properties determine the tools or processes that will be used when making or manufacturing and how a product will function.

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3·2 Smart and modern materials LEARNING OBJECTIVES By the end of this section you should: ✓✓be aware of a range of ‘smart and modern materials’, including thermochromic materials; polymorph; shape memory alloy (SMA); shape memory polymer ✓✓understand the key properties of common ‘smart and modern materials’.

What are smart and modern materials?

‘Smart and modern materials’ is an umbrella term for a wide variety of materials whose properties alter depending on environmental conditions, such as light, temperature or movement. These materials are designed and manufactured through scientific discoveries, where materials are engineered or altered so that they perform a particular function. They react independently, which is why they are known as ‘smart’, and some appear to have a ‘memory’: for example, deforming and returning to their original shape/structure under certain conditions, such as heat from an electrical current (shape memory alloys and the effect of heat on shape memory polymers).

Modern materials also include those manufactured by making changes to the structure at molecular level or using nanoparticles, such as the super strong graphene or hydrophobic surfaces that repel water. Some smart and modern materials are inspired by nature; this is called biomimicry.

Smart and modern materials have numerous applications in health and medicine. A ‘stent’ is a small mesh tube, made from a shape memory alloy, which is inserted into damaged blood vessels to strengthen or keep them from collapsing. The stent is inserted cold and expands into the desired size with the patient’s body heat.

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DESIGN IN ACTION

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Properties

Uses

Shape Memory Alloy (SMA) or nitinol

An alloy composed of nickel and titanium, which will (a) when deformed (bent), return to its original shape when heated beyond 90°C and (b) contract when an electric current is passed through it.

SMAs are used in stents, which are tubes inserted into damaged blood vessels. They are inserted cold and expand to the correct size in response to the patient’s body temperature, strengthening the blood vessel. SMAs are also used in some spectacle frames or in dentures.

Shape Memory Polymer (SMP)

A variety of polymer (plastics), which deform in response to an external stimulus, such as when an electric voltage is applied or there is a change in temperature.

Potential uses for SMPs are valves or pumps for liquids where mechanical components are not desirable.

Thermochromic inks

Materials with these properties change colour in response to changes in temperature.

Commonly used in forehead thermometer strips and in the food industry to indicate the temperature of a packaged food product.

Photochromic inks

Materials with these properties change colour in response to changes in light level, including ultraviolet (UV) or infrared (IR).

Light reacting sunglasses or spectacles, which darken in response to UV light.

Lenticular sheet

An embossed polymer sheet with optical properties which make a surface appear deeper. There are different kinds of lenticular patterns, which can be used to make images appear to flicker or move.

Can be used to provide visual/ aesthetic interest to a surface, such as the illusion of depth, and 3D effects.

Polymorph

Polymorph is available in small pellets which fuse when heated to 62°C and can be moulded, resulting in a tough polymer.

Can be used by designers and engineers to prototype difficult shapes, such as components, joints and handles.

Smart grease

A viscous gel which will uniformly control the movement between two friction surfaces.

Can be used to dampen movement on volume control knobs, slowing down and smoothing the rotation.

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3·2 Smart and modern materials

Examples of Smart and modern materials There are many different materials that can be classed as being smart or modern. Some common examples are shown in the table below.

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SKILLS ACTIVITY Investigate different kinds of smart and modern materials and create a table containing the following information.

• Find out more about the properties of some of these materials and their potential uses and applications.

• Find and give details of a product on the market that utilises smart materials.

KNOWLEDGE CHECK 1. Explain how a smart and modern material differs from a natural material.

2. Describe the properties of a smart and modern material and give examples of how these could be used to add functionality to a product.

(2) (4)

Key

Terms biomimicry: an approach to innovation and design that takes inspiration from how nature

solves problems. Materials developed using biomimicry include polymers with adhesive properties inspired by a gecko’s feet and fabrics with streamlining properties inspired by shark skin.

memory: the property by which a material returns to its original shape under specific environmental conditions, such as ambient temperature or heat from an electrical current

nanoparticles: nanoparticles are between 1 and 1000 nanometers (10–9) m, and materials where the structure has been engineered at the nanoscale can have unique properties. For example, graphene (comprised of carbon sheets with the thickness of a single atom) has over 200 times the strength of steel, gram for gram. Nanomaterials is the name given to materials manufactured at the molecular level to provide specific properties.

polymer: a substance comprised of large molecules made up of simple molecules of the same kind.

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Plastics such as acrylic and polythene are the most commonly recognised polymers, but polymers exist in nature; for example silk, wool and cellulose.

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