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GCSE Resistant Materials - Unit

2 - Knowledge and

Understanding Revision Guide

(June 2013 paper)

Note: Please do not just rely on reading only through

this guide to pass your test

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Keywords

CAD – Computer aided design

CAM – Computer aided manufacture

CNC – Computer Numerical control e.g. computer controller router / lathe

Rapid Prototyping – This is when computers and machines are used to develop a model very

quickly. CAD drawings are fed from the computer to the machine and a model will be developed.

E.g. 3D printing

Aesthetics – The appearance / looks of the product

Anthropometrics – The study of human measurements

Ergonomics – The interaction between the end user and the product.

Ferrous Metal – Contains iron and will rust

Non-ferrous Metal- Does not contain any iron whatsoever

Thermosetting plastics – Can only be heated and moulded into a shape once.

Thermoplastics – Can be reheated and reshaped several times. Like the plastic used in vacuum

formers

Alloy – Substances that contain two or more metals and sometimes other elements to improve

their properties

Annealing - Annealing is a heat process whereby a metal is heated to a specific temperature /colour and then allowed to cool slowly. This softens the metal which means it can be cut and shaped more easily

Wasting -Shaping by wasting means cutting away material to leave the desired shape. It gets its name

because the material which is removed is usually thrown away. Shaping by wasting can be done on

any type of material.

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Plastics - Vacuum Forming

Used to form/shape thin plastic, usually plastics such as; polythene, High impact polystyrene (HIPS), and perspex.

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Plastics – Injection Molding

Materials such as polystyrene, nylon, polypropylene and polythene can be used in a process

called injection molding. These are thermoplastics - this means when they are heated and then

pressured in a mold they can be formed into different shapes.

Advantages

Very accurate components can be manufactured

Complex shaped components can be manufactured

Excellent for use in mass production

Disadvantages

Would not really be used in short production runs

Very expensive to make the molds / purchase the machinery = expensive start up costs

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Plastics – Blow Moulding

Blow moulding a shape is a common industrial process. The example shown below is of the production of a

plastic bottle. The plastics normally used in this process are; polythene, PVC and polypropylene.

The process is similar to injection moulding and extrusion.

1. The plastic is fed in granular form into a 'hopper' that stores it.

2. A large thread is turned by a motor which feeds the granules through a heated section.

3. In this heated section the granules melt and become a liquid and the liquid is fed into a mould.

4. Air is forced into the mould which forces the plastic to the sides, giving the shape of the bottle.

5. The mould is then cooled and is removed.

Plastics – Extrusion

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Materials such as polystyrene, nylon, polypropylene and polythene can be used in a process called extrusion. These are thermoplastics - this means when they are heated and then pressured in a mould they can be formed into different shapes and sections

A machine used to extrude materials is very similar to the injection moulding machine. A motor

turns a thread which feeds granules of plastic through a heater. The granules melt into a liquid

which is forced through a die, forming a long 'tube like' shape. The extrusion is then cooled and

forms a solid shape. The shape of the die determines the shape of the tube.

The animation below shows a close up of the steel die. The hole in its centre is a hexagon. This

means that the fluid plastic forms a hexagonal section when it is forced through the hole. Dies can

be manufactured to almost any section / shape, including tubes.

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Plastics – Strip Heater / Line Bender

Plastics such as acrylic can be formed (shaped) in different ways. One of the most popular methods of shaping plastic

materials like acrylic is to fold (bend) it on a ‘strip heater’, at different angles. An example of a strip heater is shown

below. A heating element extends along the length of the strip heater and gives off intense heat when it is turned

on.

Metals – Die Casting

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Overview

Die casting is a metal casting process that is characterized by forcing molten metal under high

pressure into a mold cavity. Due to the costs involved in purchasing machinery and producing the

molds used in the production of die casting it is usually associated with mass produced products.

Die cast components are characterized as having a good surface finish and good quality control.

Advantages

Fast Production

Thinner walls are achievable when compared to investment casting (0.6mm -0.8mm)

Wide range of possible shapes

Simplified assembly (external threads can be cast, or holes cored to internal tap drill size)

Good finish (1 μm - 2.5 μm) (depending on purpose not all parts will require extra finishing)

Disadvantages

High initial cost (Cost of molds and machine set up) A large production volume is required to make the process cost effective Die casting is limited to high fluidity metals (Zinc, Aluminium, Magnesium, Copper, Lead

and Tin)

The Process

Die casting first requires the creation of a steel mold (called a ‘die’) of the part to be cast, these

molds once created are fitted to the die casting machine and injected under pressure with the

desired molten metal or alloy of choice. There are two methods of injection, these being hot

chamber and cold chamber

Metals – Sand Casting

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Overview

Sand casting, the most widely used casting process, utilizes expendable sand molds to form

complex metal parts that can be made of nearly any alloy.

The sand mold must be destroyed in order to remove the part, called the casting, sand casting

typically has a low production rate. The sand casting process involves the use of a furnace, metal,

pattern, and sand mold. The metal is melted in the furnace and then ladled and poured into the

cavity of the sand mold, which is formed by the pattern. The sand mold separates along a parting

line and the solidified casting can be removed. The steps in this process are described in greater

detail in the next section.

Advantages

Can produce very large parts

Can form complex shapes

Many material options

Low tooling and equipment cost

Scrap can be recycled

Short lead time possible

Disadvantages

Poor material strength

High porosity possible

Poor surface finish and tolerance

Secondary machining often required

Low production rate

High labour cost

Plastics – Thermosetting and Thermoplastics Overview

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Thermosetting Plastic Examples

Many adhesives (glues) are thermosetting plastics. A good example is ‘Araldite’ which is an epoxy resin that hardens when a second chemical is added (a catalyst). It will bond most materials including woods and metals as well as some plastics.

Polyurethane. This forms the basis of many paints and varnishes because it is very tough and has water resistant qualities.

Melamine Formaldehyde. Used in the production of plastic laminates because of its smooth surface and hygienic qualities. It is also used in electrical plugs and sockets because it can be cast and it is an excellent insulator.

Urea Formaldehyde (UF): Urea Formaldehyde has physical properties of high hardness and high toughness, making it suitable for strong, knock-resistant electrical fittings. It is also scratch resistant and a very good electrical insulator, making electrical fittings manufactured from this polymer safe to use.

Polyester resins. If resins are combined with a material such as fibre glass the result is a very tough material that can resist impact. This type of material is known as a glass reinforced plastic (GRP) and is used in car body repairs, sailing boats, corrugated sheet because of its lightness, toughness and resistance to water.

Thermoplastics Examples

These plastics possess a common property, they soften when heated and are often used in schools to vacuum form shapes. Usually, when heated and formed into a shape - if reheated they return to their original shape.

Acrylic. (Known also as PERSPEX) This is the most common plastic in a school workshop. It is purchased usually in the form of sheets and comes in a range of colours. It can be translucent (e.g. smoked), transparent or opaque. It is resistant to most acids and weather conditions.

Polythene. Can be moulded into almost any form due to its excellent moulding qualities. Used for the production of bottles, bowls, toys, tube etc... It is available in large sheets. There are two types: High density which is rigid and hard, and low density which is tough and flexible. Machine parts are generally made from high density polystyrene whilst bottles are made from the low density polystyrene.

Polyvinyl Chloride. Better known as PVC. It is a tough material which can be purchased as a hard material or alternatively a flexible form. It can be welded or bonded with an adhesive. It has a range of uses including water pipes, raincoats, long play records, coating on electrical wires and many more.

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Hardwoods

Hardwoods are usually have broad leaves and are deciduous (lose their leaves) Distinguished from softwoods by the structure of the grain They are generally more expensive than softwoods as they take longer to grow

.

Hardwood Apperance Properties Uses

Oak

Very strong, tough, durable.

Furniture, veneers, doors, fences

Beech

Close grain works and finishes well, Hard and strong but not durable outdoors

Wood floor in your house Functional furniture, tools, toys

Mahogany

Hard and Strong but not easy to finish. Expensive Indoor work only

Expensive furniture, veneers

Teak

Very durable, Fire resistant, but quickly blunts tools

Fine furniture, chairs, tables, shop fronts

Balsa

Very light and very soft, but strong for its weight

Model making, life belts, rafts

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Softwood

Usually evergreen trees (Do not lose their leaves) Grow fast therefore cheaper. Often used as construction material as trees grow tall and straight giving long

planks of wood

Softwood Apperance Properties Uses

European redwood

Quite strong, Lots of knots, durable when preserved. cheap

General woodwork, cupboards, shelves, roofs.

Stika Spruce

Tough, easily worked, straight grain. cheap

Indoor work only, low cost furniture

Parana pine

Tough with fine grain, prone to twisting

General woodwork, fitted furniture

Douglas fir

Strong, needs protection outdoors

Furniture, plywood, doors, windows. (Xmas trees)

Red cedar

Soft and weak. Very durable against weather, insects and rot

Weather boarding

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Manmade Boards

Some of the advantages of manmade boards can be listed as being:

Available in large sizes

Do not have knots / imperfections in the wood

Man made boards often made use of waste materials. For example saw dust is use to make MDF and hardboard. The saw dust is held together with a glue.

Man made boards are often used as cheap alternatives to real woods.

Man made boards do not look as expensive as real woods.

Man made boards are often cover with a thin layer of real wood to improve their appearance (Veneered).

BLOCKBOARD - This is built up with a core of softwood strips bonded together with adhesive and covered with a sheet of plywood on either side. Used as a building material and for furniture manufacture including fitted kitchens / bedrooms.

CHIPBOARD - This is made up of small chips of wood bonded together with resin and formed into sheets by compression. It is not as strong as plywood and block board but it is not expensive. Chipboard is often covered with a plastic laminate or wood veneer and used in furniture.

HARDBOARD - This is made from wood fibres that have been pulped. The pulp is put under pressure until the fibres bond to produce a tough board that is smooth on one side and rough on the other. It is not as strong as the other boards.

PLYWOOD - This is made from veneers (plies) of timber with each grain layer being at right angles to each other and bonded together by resin and pressure. A number of grades are available, designed to suit a variety of situations. 1. Marine plywood that is moisture resistant. 2. Weather and boil proof plywood. 3. Boil resistant plywood. 4. Interior plywood.

MEDIUM DENSITY FIBRE BOARD (MDF) - A quality board, relatively cheap. This board is

composed of fine wood dust and resin pressed into a board. This material can be worked, shaped

and machined easily. Paint can be applied to it without the need for an undercoat or primer. Used

in the building and furniture trades.

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Flat pack furniture

Overview

Flat-pack is the term associated with modern furniture.

This type of product is normally delivered in pieces, inside a flat package.

It can be assembled in the home. Instructions are supplied but some customers complain

that they are difficult to follow.

Advantages to the manufacturers

Fabrication is expensive for the manufacturer.

Costs are reduced if the customer assembles the products.

Flat-pack products are easier to transport than assembled products. They may be transported in larger quantities in a single journey

CAM is used to manufacture most flat-pack furniture. The set up costs may be expensive but it saves the manufacturer money in the long-term.

Flat-pack furniture is generally less expensive than permanently jointed timber furniture.

Advantages to the retailers

Flat-pack furniture takes up less space. Examples of a product line may be placed on the

shop floor but the rest are stacked.

Storage space on the shop floor is expensive to a retailer.

The regular shapes of packaging allow more products to be stacked.

Advantages to the customers

Customers can easily take the flat-pack product home themselves and do not have to wait

for delivery.

Large pieces of furniture may be carried through narrow doors whilst in a flat-pack state.

Customers moving home may easily disassemble and transport their furniture.

Customers may choose from a range of surface tops, textures, colours and carcasses.

Companies may specialise in manufacturing individual, made to measure, flat-pack

bedrooms, home offices and kitchens.

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Metal Processes

Name - Tap and Die

Description – Cuts a thread on a piece of round metal.

Name – Pop Riveting

Description – Used to permanently attach two pieces of material together. You overlap the two pieces of material and drill a hole Only way you can remove is by drilling out

Name – Brazing

Description – Heat is applied to attach two pieces of metal together. Both pieces of metal must be clean / filed Flux is used to again help clean and the brazing solder rod attach to the metal surface Uses a lot more heat than plumbers soldering Blocks can be positioned to help focus heat

Name – Tin Snips

Description – Basically scissors for cutting metal Will leave sharp edges sometimes which you would need to file to remove

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Bluetooth

Bluetooth is a wireless technology for exchanging data over short

distances.

Using a special radio frequency to transmit data, it creates a short range network. It is very secure and can connect up to eight devices (items of electronic equipment) at the same time. The chip can be plugged into items such as computers, digital cameras, mobile phones and faxes.

The name ’Bluetooth’ reflects the Scandinavian origins of the technology. It is named after a 10th century Danish viking, King Harald Blåtand (translating as 'Bluetooth' in English).

He united and controlled Denmark and Norway, hence the association of uniting devices through Bluetooth. Legend has it that he liked eating blueberries - so much that his teeth became stained with the colour of the fruit, giving rise to his name!

Wi-Fi

Wi-Fi s a popular technology that allows an electronic device to exchange data wirelessly (using radio waves) over a computer network, including high-speed Internet connections.

A device that can use Wi-Fi (such as a personal computer, video-game console, smartphone, tablet, or digital audio player) can connect to a network resource such as the Internet via a wireless network access point.

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Shaping by wasting

Shaping by wasting means cutting away material to leave the desired shape. It gets its name because the material

which is removed is usually thrown away. Shaping by wasting can be done on any type of material.

Shaping by wasting which can be done by hand

Process Wood Metal Plastics

Cutting straight lines Tenon saw (dovetail saw for fine work)

Hacksaw (junior hacksaw for small work) Hacksaw (junior hacksaw for small work)

Cutting curved lines Coping saw (fret saw for fine work) Abra saw (piercing saw for fine work). Tin snips can be used on thin sheet metal

Abra saw (piercing saw for fine work). A coping saw can also be used

Trimming cut edges to a straight line

Jack plane or smoothing plane Flat or hand file Flat or hand file

Trimming cut edges to a curved line

Spokeshave or rasp Round or half round file Round or half round file

Cutting grooves and slots

Tenon saw to cut sides, then wood chisel or coping saw

Drill holes at ends, then use abra saw Drill holes at ends, then use abra saw or piercing saw

Machine wasting

Almost any wasting technique can be mechanised.

Common machines used for shaping by wasting

Process Wood Metal Plastics

Cutting curved lines Jig saw, either fixed or portable, with suitable blade. Band saw (teachers only)

Bench mounted Jig saw (with suitable blade). Band saw (teachers only)

Jig saw, either fixed or portable, with suitable blade. Band saw (teachers only)

Making holes Drilling machine and suitable drill bits Drilling machine and twist drills Drilling machine and twist drills

Creating round shapes of different diameters

Wood turning lathe Metal turning lathe Metal turning lathe

Cutting grooves and slots Hand router or Computer Numerical Control (CNC) milling machine

Vertical milling machine or CNC milling machine

Vertical milling machine or CNC milling machine

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Measuring Tools

Name – Micrometer

Description –

The micrometer is a precision measuring instrument, used by engineers.

You first of all read the sleeve measurement. You then read the thimble measurement In the example opposite the reading is 17mm

Vernier Caliper

Description -

The Vernier Caliper is a precision instrument that can be used to measure internal and external distances extremely accurately