A level DT aqa Technical principles

compressive strength

the ability to withstand being crushed or shortened by pushing forces

tensile strength

The ability to resist stretching or pulling forces

Bending strength

The ability to resist forces that may bend the material

shear strength

the ability to resist sliding forces on a parallel plane

Torsional strength

The ability to withstand twisting forces from applied torque or torsion

Hardness

The ability to resist abrasive wear such as scratching, surface indentation or cutting

Toughness

The ability to absorb impact force without fracture

Plasticity

The ability to be permanently deformed and retain the deformed shape

Ductility

The ability to be drawn out under tension, reducing the cross sectional area without cracking

Malleability

The ability to withstand deformation by compression without cracking

Elasticity

The ability to be deformed and then return to the original shape when the force is removed

Density

The mass of the material in a standard volume of space

Mechanical Properties

How a material reacts to an external force

physical properties

The actual make-up or structure of the material

Fusibility

The ability of the material to be fused or converted from a solid to a liquid or molten state, usually by heat. Good fusibility is an essential property for a metal being cast

Magnetism

The natural force between objects that causes the material to attract iron or steels

Corrosion Resistance

The ability of the material to withstand environmental attack and decay

electrical conductor

Allows the flow of electrical current through the material. A good conductor gives very little resistance to the flow of charge

electrical insulator

Does not allow the flow of electricity through the material

Thermal conductor

Allows the transfer of heat energy through the material

Thermal insulator

Prevents the transfer of heat through the material

thermal expansion

The increase in material volume in response to a heat input

opaque

Prevents light from traveling through

translucent

allows light through but diffuses the light so that the objects appear blurred

Transparent

allows light to pass through easily

Modern material

a material developed through the invention of new or improved processes, for example, as a result of man-made materials or human intervention. They do not react to external change

Example of modern materials

Kevlar, metal clay (PMC) and high density modelling foam

Simple workshop tests

Use basic tools and equipment

Industrial tests

Usually carried out in a lab with specific testing machinery, using standardised test pieces of materials

Rockwell Hardness Test

Preload applied to the material using a diamond indented which breaks through just the surface of the material. Diamond is used because it does not deform under load. An additional load is then applied to the test material and held for a predetermined length of time. The load is released and the distance between the preload and the applied load is measured

Brinell Test

A hardness test performed by pressing a steel ball of standard hardness into a surface by a standard pressure. The diameter of the indent in the surface is measured

Vickers pyramid hardness test

Used for very hard materials. Uses a diamond square-based pyramid to indent the surface of a material. A microscope is used to measure the size of the indent

Non-destructive Testing

The product is not destroyed during testing. It finds defects in the material

2 standard non destructive tests

Ultrasonic and x-ray

Kevlar

Features- aramid fibers with high cut-and heat- resultant properties

Uses- body armour, cut-proof gloves and aprons, aerospace applications

Metal clay (PMC)

Features- made up of fine metal particles. Works like ceramic clay, easily mouldable, easy to shape and form, sets hard once fired with a klin or butane torch. In expensive compared to solid metals like silver

Uses- Jewelry, decorative items, small sculptures

High density modelling foam

Features- lightweight, easy to work using traditional woodworking tools, sands easily

Temporary fasteners

used where a permanent joining method is not required, or in situations where a product may need to be disassembled or accessed for repair

self-tapping screws

Used for joining thin sheet metal. A pilot hole is drilled through the metal parts to be joined. As the screw is screwed in it cuts its own thread, which holds the screw in place

machine screws

A type of bolt where the thread is the whole length of the shaft, used to join thicker pieces of metal such as inspection covers on motor or gear housings. The top part to be joined will have a clearance hole larger than the thread on the bolt. The bolt goes through this and is screwed into a threaded hole in the second piece. Machine screws are often tightened with a spanner or Allen key

Nut and bolt

Similar like machine screws but they go all the way through both pieces of metal. A bit is tightened on to the end to keep the pieces together

Milling

The work to be machined is clamped on to the table of the machine. The table can then in run left or right, forwards or backwards and up or down to cut slots, sharp edges or thread holes

Turning

This is carried out on a centre lathe. Work such as a bar can be held in a rotating chuck and machined to reduce the diameter, square the end, thread and drill. Can be done manually or using CNC. Machined by cutting tools held in a tool post which can be moved in and out

Flame cutting

This method uses oxy-acetylene gas and a special flame cutting torch to deliver a very intense and focused flame above 3500 degrees. It is used to cut low carbon and alloy steel plate. Has an additional jet of oxygen to intensify the flame and pierce the metal. However, it is difficult to maintain in a parallel line with high levels of tolerance

Plasma cutting

Super-heated ionised gas that is electrically conductive. It will use conductive gas to transfer the energy from the power supply to a conductive material such as a steel plate. The heat generated by the plasma can be as high as 28,000 degrees which quickly burns through the material and blows it away. The resulting cut is fast and clean

Laser cutting (metal)

Used for precision cutting metals. Uses the power from a high powered laser beam that is directed through optics. The laser head contains a lens that focuses the laser into a fine beam for cutting and engraving. Laser beams usually have a very fine tolerance. It is more accurate and uses less energy but cannot fit to the same thickness of material like plasma cutting

Punching/stamping

The process uses CNC machines that stamp out sections of sheet material. Uses the shearing action on a sheet of metal placed between an upper tool and a lower tool. Suitable for small and medium size production runs and is normally used for processing matels from 0.5mm to 6mm thickness

Dovetail Joint

Used for drawers due to multi-directional strength

Comb joint

Used for box construction

Housing joint

Used for framework construction, cabinets and shelving

A half lap joint

For simple frames or boxes

A dowel joint

Typically used in flat-pack furniture (bookcase or wardrobe)

mortise and tenon joint

Frame constructions for tables, chairs

Knock down fittings (KDF)

Used to manufacture flat-pack furniture. They are relatively easy to use with a limited number of simple tools

Modesty blocks

Small rigid polymer blocks. They have modulded holes that take screws that are used to join the block panels and could be used on cupboards and storage units

Barrel nuts and bolts

Cross dowel fitted into one of the pieces being joined. Bolt inserted through other piece and tightened into cross dowel. They are often used in bed frames

Cam lock connectors

Metal dowel is screwed into one of the pieces. The Cam is fitted into a pre-drilled hole connecting to the dowel. When rotated the collar of the dowel locks into the cam and as you screw is pulled tightly together. They are used in flat-pack furniture such as bookshelves

wood screws

Used for screwing two pieces of wood together where the thread is needed only at the bottom. The top part is drilled with a clearance hole that the screw simply pushes through. The bottom piece of the wood has a pilot hole so that the thread bites into the timber

coach bolt

Used to join wood prices together. Under the domed head of the bolt is a square piece that digs into the wood when tightened, preventing the bolt from rotating. They are used for fitting door locks or in street furniture such as wooden benches

Lamination

Bonds materials together. Uses wood veneers or thin manufactured boards which can be glued together and bent over a former so that when dry the form a thick board in the shape of the former. Held while drying by clamps or a vacuum bag

Steam bending

combined heat and steam make strips of wood pliable so they can be shaped over a former

wood is placed into a steam box where it will absorb the steam

wood is then bent over a former and clamped to it until it dries

Quicker than laminating and is less wasteful and laminating involves waiting for the glue to dry

Turning methods

Turning between centers- used to machine a spindle such as chair legs

Turning on a faceplate- used to machine items such as domes or bowls

Turning in a chunk-used to grip the item while it is machined

Milling (process)

Used for small-sized, basic jobs such as a rough prototype or roughing out a small hole or channel

Doesn't have as large a work area as CNC routers

They can be operated manually or CNC

Routering

- used to machine slots and holes in wood, or to make decorative 'mouldings' on the edges, e.g a table top

- can be manual plunge routers or CNC

Polyvinyl acetate (PVA)

Water-based adhesive used to bond most woods and wood-based materials together

Not usually a waterproof adhesive

Can be used for furniture and other wooden products

Contact adhesive

used for bonding large areas such as sheet material

Join the same or different materials together

The two surfaces to be joined are coated in contact adhesive and left for 10 mins or until the adhesive feels tacky

UV hardening adhesive

clear liquid that quickly 'cures' to form a bond when exposed to UV (ultraviolet) light

Contains photo initiator which means that as it absorbs the UV light wavelength, it begins to cure and set to a solid bond

Used to join metal, glass and polymers

Excess can be wiped away with a cloth prior to being exposed to UV light

Solvent cement

Most commonly a clear liquid called dichloromethane, which softens the polymer surfaces allowing them to fuse together

Can be used in the plumbing industry to bond non-pressure pipes made from ABS or PVC together

Epoxy resin

Used to join dissimilar materials e.g. any material to any material. It is a two-part adhesive supplied as resin and hardener.

Jigs and fixtures

Often used to ensure that parts or components can be made repeatedly, more quickly and accidentally

A jig holds the work and guides the tool, eliminating the need to repeatedly mark out

A fixture is something that holds the work in a given position while a manufacturing process takes place

Why are finishes used

-prevent material from absorbing moisture

-protect against decay or corrosion

-protect against insect attack

-enhance the appearance of the final product

lamination via encapsulation

A desktop laminator and the sheet of paper is encapsulated by a polymer pouch or film roll

Lamination via surface coating

Liquid lamination (for signage) or film lamination (menu cards)

Embossing

Creates a raised design on the surface of the paper or card to give a visual and tactile effect

Debossing

produces an imprinted depression that sits below the surface of paper or card

Varnishing, UV varnishing and spot varnishing

Clear, non-pigmented ink used on pre-coated papers and boards to enhance the colour, as well as offer some protection against dirt, fingerprints and water

UV varnishing

-provides a very smooth finish, usually high gloss or matt, and abrasion and chemical resistant.

-applied to a sheet via a set of rollers, then passed under UV light to cure

Spot varnishing

applied in specific areas or spots rather than to the whole surface area

Foil blocking

Heat and pressure applied to a metallic paper (foil) to create areas of depth and texture to add aesthetic impact

Screen printing

Can be carried out in a workshop with minimal set-up costs due to the use of basic screens and printing inks

The screen has open areas for the ink to pass through

A different screen is required for each colour

Quite a slow process with a high cost per product

Used for small print run items such as posters

flexographic printing

- flexography, offset lithography and digital printing use a four colour process: cyan, magenta, yellow ad key (black)

- the 4 colours are printed on top of one another in various quantities on to the substrate surface to create the print colour required

- colours must line up exactly to ensure a non blurry image

- flexographic printing is a simple process, the least expensive of the printing processes due to fast-drying water-based inks

- its used for products such as newspapers, comics, catalogues, folding packaging cartons, labels, carrier bags and continuous-pattern products such as wallpaper and gift wrap

Advantages of flexographic printing

-high print speed

- ideally suited for long runs

- prints on wide variety of substrate materials

- low cost of equipment and consumables

- low maintenance

Disadvantages of flexographic printing

The cost of the printing plates is relatively high, but they last for millions of print runs

Takes a large amount of substrate to set up the job; excess material may be wasted

Time consuming to change for any alterations to the print content

Offset lithographic printing

Extremely versatile printing process capable of producing on colour (single roller), 5 colour, (CMYK, metallic, varnishing, spot varnishing and duplex (both sides printed) on a ten-roller machine)

Used for printing medium and long print runs of products such as books

Advantages of lithographic printing

Consistently high image quality

Suited to higher volume print runs of 1000 or more

Quick and easy production of printing plates

Long life of printing plates because they only come into contact with printing blanket which is much softer and less abrasive than substrate

Disadvantages of lithographic printing

Expensive set-up and running costs for small quantities

Digital printing

- widely utilised resource for printing products, due to its high speed and efficiency

- digital printers produce full colour, highly detailed print runs with the option for printing promotional materials such as business flyers and business cards

It is ideal for mass cutsomisation, such as printing of specific names on drink cans because of the fast-drying inks

Polymer finishing

polymers are self finishing materials because they require no additional finishing process once manufactured

Overmouldings

Modelling a second polymer over specific parts of a product

TPE (thermoplastic elastomer) is often used

Overmouldings provide areas of grip or texture

Can highlight different colours for different component parts on products

two injection moulding moulds

- one mould for the product and one mould for grip areas

- product is injection moulded, then placedcinto a second mould where the overmoulding polymer is injection-moulded on to the body

twin shot injection moulding

- the injection moulding machine has a mould designed to produce the product in one cycle

- the mould has two separate component cavities and can be rotated through 180 so they line up with the twin injection points

- a very fast continuous cycle process

Acrylic spray paints

- additional finishes are sometimes applied to enhance aesthetics or improve product function

- acrylic paint is a fast drying, water soluble paint that becomes water resistant when dry

- it improves aesthetics and can provide additional protection against the effects of UV light and weathering

- often used for mass customisation, particularly in the automotive industry, such as colour coding bumpers and wing mirrors on cars

- items could be pigmented, but is impractical and not cost effective for the manufacturer to keep changing the granules on an injection moulder to produces small numbers of differently coloured components

Adding pigments (polymer)

The addition of pigments to the polymer provides colour

Can be added during the manufacturing process or manufacture of the polymer stock form

Smart pigments such as thermochromic can be added in the same way

Pigments can be added to gel coats

For example, kitchen chopping boards

Metal finishing

- most metals (except steel) have an oxide layer, which provides some barrier against environmental effects

- steels (except stainless) have an oxide layer which is porous, allowing moisture to penetrate the metal, leading to rust

- the porous oxide layers continue to allow moisture to penetrate, leading to layers of crumbling rust

cathodic protection

A method used to control the rate of corrosion by: making the metal the cathode of an electrochemical cell; the anode is a sacrificial metal. The anode corrodes while the base metal is protected

The main use is to protect steel structures buried in soil or immersed in waters like pipelines

Impressed current

- component to be protected must be connected to electrical power supply

- impressed direct current flows from an inert electrode through any liquid to the component to be protected

For example, a burrried pipeline receives direct current from an electrode burried in the ground

sacrificial anode

Uses a sacrificial metal to protect the metal product value. A more electrochemically active material is wrapped around or joined to the less active metal to provide resistance to corrosion

Wood finishing

Prevent the wood from absorbing moisture

Protect aginast decay

Protect against insect attack

Enhance the appearance of the final product

One-Off/Bespoke Production

Refers to unique, individually designed and manufactured products such as a wedding cake, a luxury cruise ship

It is expensive and requires a complex production

More skilled workers required

Customised to clients need

Batch production

Efficient and cost effective manufacture by using simultaneous manufacturing processes. For example, pottery,wooden furniture, electric guitars

Jigs, fixtures and CNC machines facilitate more accurate and faster production of parts