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AQA DT: Product

Design (3D-Design)

Plastics:

What is a plastic?

A Group of materials made up of long chains of molecules.

There are three different types of plastics; thermoplastics (Can be reheated

and reshaped), thermosets (Become permanently rigid), elastomers (have good

elasticity).

General Properties

·

Good electrical/thermal insulators

·

Good strength to weight ratio

·

Generally, good atmospheric and chemical

resistance

Thermoplatics

ABS

High Impact strength, good toughness/strength, Scratch resistant,

lightweight and durable

Kitchen products, mobile phone cases, toys, some car parts and

domestic products.

PVC

Good Chemical resistance, good resistance to weathering, rigid, tough

and lightweight

Flexible hoses, cable insulation

HDPE

High Density, good stiffness, good chemical resistance

Crates, Bottles, buckets and bowls

LDPE

Lightweight, low stiffness and rigidity and good chemical resistance.

Detergent bottles, toys and carrier bags

Thermosets

Epoxy Resins

High strength when reinforced with fibres, good chemical and wear

resistance

Surface coating, adhesives

Melamine Formaldehyde

Rigid, Good strength and hardness, scratch resistant, can be

coloured.

Tableware, decorative laminates for work surface

Polyester Resin

Rigid, Brittle, good heat and chemical resistance.

Casting, glass re-in forced plastics.

Urea Formaldehyde

Rigid, hard, good strength, brittle, heat resistant, good electrical

insulator.

Electrical fittings, adhesive.

Plastic Additives

Fillers

Used to bulk the plastic. Normally cheaper than plastic so reduces

costs.

Flame Retardant

Used to reduce risk of combustion. Put in foam to fill up cushions.

Anti-Static Agent

Reduces chances of build-up of static charge. Put in carpet.

Plasticiser

Helps the flow of plastic when being moulded. Make the product less

brittle.

Stabilisers

Make plastic more resistant against UV.

Biodegradable Plastics

PHA’s and PHB’s are biodegradable natural plastics produced

by bacteria. PHA can also be known as Biopol, has a wide range of uses in the area

of medicine (e.g. Screws, bone plates and as slow-release medication) which as

PHB is more used in the packaging area.

Oxo-Degradable Polymers have additives to promote short

degradation times. It does by breaking down into powder because of heat oxygen

and moisture which makes it easier to digest by microorganism.

Photo-Degradable Polymers will break down when in contact

with UV light.

Plastic Production

Methods

·

Injection Moulding

·

Blow Moulding

·

Rotary Moulding

·

Thermoforming

·

Vacuum Forming

·

Calendaring

·

Line Bending

·

Compression Moulding

International Symbols of

Polymers

Composite Materials:

What is a Composite

Material?

Composites are produced by mixing two or more different

materials together. There are different types of composite materials; Fibre

reinforced composites (Glass Fibre, Carbon Fibres…), particle based composites

(Cermet’s, filament reinforced ceramics, tarmac, concrete...) and sheet-based

composites (Plywood, Chipboard…).

Range of Man Made

Boards

Plywood

Backs of furniture, can be flexible for producing curves

Block Wood

Generally used for table tops and furniture carcasses

Chipboard

Knockdown Furniture, Usually veneered

MDF

Furniture sides and pattern for casting

Particle-Based

composite materials

·

Concrete: It is made out of aggregates sand and

cement. Concrete is thoroughly mixed while dry then water is added. Once cast

the concrete is left to harden.

·

Cermets: These are a mixture of both metal and

ceramics particles (e.g. Tungsten Carbide – cutting tools as it keeps it edge

very well)

Metals:

Types of Metals

Metals can be classed as either ferrous (contains iron so

magnet and rusts) or non-ferrous (doesn’t contain iron). Then you can separate

them into alloys (a mixture of two or more metals) or non-alloy.

Ferrous metals

Cast-iron

Hard skin with soft core, strong

under compression but cannot be bent or forged.

It is used for heavy crushing machinery,

car brakes discs and vice or machine

parts

Stainless steel

Hard and tough but very good resistance to corrosion.

It is used for sinks, cutlery, work surfaces dishes.

High speed steel

Very hard, resistant to friction and can be sharpened by

grinding.

It is used lathe cutting tools, drills and milling tools.

Non-ferrous

metals

Aluminium

It is strong for its weight. Light, soft and ductile. Good

conductor of

heat and electricity. Difficult to join

It is used for kitchen foils, cooking pans

and window frames. It is non-toxic and

polishes well.

Zinc

It is very weak and heavy. Resists

corrosion but very difficult to work. Often used to electro

plate and hot dip ferrous product.

It is used for galvanising products to

protect from rusting, for example,

roofing, crash barrier and fencing. It is a greyish silver.

Gold

It is a precious metal that is

extremely malleable and ductile.

Highly resistant to corrosion.

It is used for jewellery, gold leaf, ornaments, electrical

contact. Look at book for

last detail.

Alloys

Brass

Heavy, quite hard and gold in

colour. Easily machined and joined by soldering.

It is used for castings, garden ornaments, taps and valves. More

zinc and makes it harder than copper.

Bronze

It is a reddish yellow, harder than

brass, corrosion resistant and casts well.

It is used for bearings and gears,

architectural fittings, cast sculptures/statues.

Work Hardening

and Heat Treatment

Work Hardening occurs when a material is cold worked by, for

example, bending, rolling, hammering and drawing.

Heat treatments

·

Annealing: Heating a metal to a temperature where crystals grow.

Then let the metal cool

down very slowly. It is used to

reverse the internal stresses.

·

Hardening: Heat up a metal then quench it. This results in the

hardening of the metal as the crystals don’t have enough time to go back their original

shape causing internal stress.

·

Tempering: This is the process done after hardening. If not done

some metals may be too

brittle. This is done by heating the

metal once again and then leaving it to cool slowly

helping the atoms relax a little.

·

Age Hardening: This is the process of leaving a metal to cool down

slowly.

·

Case Hardening: This is the process of hardening metals by soaking

them in carbon rich

material. It produces a metal with a soft core but hard

shell perfect for gears….

Metal Processes

·

Blanking and piercing are shearing processes in

which a punch and die are used to modify webs. The tooling and processes are

the same between the two,

only the terminology is different: in blanking the

punched out piece is used and called a blank; in piercing the punched out piece is scrap.

·

Plasma Cutting uses an electric arc and compressed

air to cut through a metal.