EXAM

REVISION Metal Properties and

Processes

Metals for the major portion of the earths elements.

They can be found combined with other elements as minerals which are mined in various ways.

Metal ‘ores’ are processed using different methods depending on the ore.

Gold is the only metal found in its pure state.

Other metals are found chemically combined with other elements in the form of oxides or sulphates.

Metals are categorised as Ferrous and Non-Ferrous.

Metals

These are mixtures of metals and/or other elements combined together.

Ferrous alloys range from plain carbon steels, with 98% iron, to high alloy steels, with up to 50% of other elements.

All other metals are non-ferrous and can be subdivided into light, heavy and refractory (heat resistant) alloys.

Ferrous alloys, particularly steels, form 90% of the world’s total metal usage. This is because of their low cost and versatility which is brought about hardening and tempering.

Alloys

Elasticity Ability to return to shape after deformation.

Toughness Ability to withstand sudden loading (impact resistant).

Brittleness Ability to be snapped easily.

Malleability Ability to be hammered into shape without fracturing.

Hardness Resistance to wear or indentation

Ductility Ability to be stretched (drawn) to a reduced cross-section.

Properties

Ferrous Metals Take a note

Iron is the basis of ALL ferrous alloys. Pure iron is of little practical use as a material. Ferrous metals all contain iron and in addition will contain other elements in varying quantities. The principle element which is mixed with IRON is CARBON. The percentage of carbon which is added to the iron will produce alloys of varying properties

It is important to know the properties of the various grades of steel so that you can select the right one to suit a particular application and method of manufacture.

Steel (alloy of iron and carbon) with a low carbon content will tend to be quite soft e.g. Black bar. Steel with a high carbon content will tend to be very hard and brittle e.g. tool steel

Cutting Tools

Car Bodies

Ferrous Metals

These metals contain Iron!

Name Composition Properties and Working

Characteristic

Uses

Cast Iron Iron+3.5% Carbon Brittle/Hard skin Machine Tools,

vices

Mild Steel Iron+0.35% Carbon Malleable/ductile,

uniform texture

Nuts, bolts, screws,

tubes, grinders, car

bodies

High Carbon

Steel

Iron+ up to 1.5%

Carbon

Malleable/ductile, can

be hardened or

tempered.

Cutting knives,

files, drills, saws,

knives, hammers,

taps and dies

Non-Ferrous Metals

Take a note

The group of metals does not contain iron and therefore will withstand moist

conditions. Common examples are:

-copper, aluminium, tin and lead

-precious metals such as gold and silver

-metals used in small amounts (mercury, platinum, chromium)

-’new’ metals (vanadium, niobium, zircoium).

Aluminium

Aluminium is the Earth’s most plentiful metal. Aluminium’s lightness and strength make it

the most widely used non-ferrous.

Other Non-ferrous Alloys

Other common non-ferrous alloys include:

-brass (copper and zinc)

-bronze (cooper and tin)

-soft solders (lead and tin)

Non-Ferrous Metals

Name Composition Properties andworkingcharacteristics

Uses

Aluminium Pure metalproduced

Good strength toweight ratio, castseasily

Window frames,pots and pans

Copper Pure metal Ductile/malleable,low melting point,expensive

Central heatingpipes, electricwiring/cable,jewellery

Tin Pure metal Heavy/soft, lowmelting point

Bearings, solder,coating sheet steel

Lead Pure metal Heavy/soft/weak,ductile/malleable,low melting point,can be cast

Roof flashing,solder

Zinc Pure metal Weak, difficult towork

Galvanising

Non-Ferrous Metals Take a note

Metal Processes Take a note

Metal Turning Take a note

https://www.youtube.com/watch?v=7LMOml

y7zfg

Turning is the production of cylindrical components using a centre lathe. The

material is held firmly in a rotating chuck whilst a cutting tool is brought towards

it to create the required shape. A variety of processes can be carried out on

the lathe for example turning cylinders, creating texture (knurling), accurate

drilling and threading

Turning

Milling Take a note

Milling machines are powerful pieces of equipment which use rotating multi

toothed cutters to shape the material. There are two types of milling machine,

horizontal and vertical. The machines are named by the position of the cutting

tool in relation to the workpiece. Milling machines can be used as side and

face cutters and can also be used to cut slots in the material.

Milling consists of machining metal by using rotating cutters which have a

number of cutting edges. These tools are known as milling cutters.

Horizontal Milling Machine Vertical Milling Machine

Milling

Slot Cutter

Slot

Straddle Milling

Milling

Dovetail Slot

Dovetail Cutter

Angle Cutter

Angled Face

Milling

Flat Surface

Slab Cutter

T-Slot

Tee Slot Cutter

Milling

Die Casting

https://www.youtube.com/watch?v=LH8B3i6

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Take a note

Where large quantities of quality castings are required in industry, the moulds

(‘dies’)need to be permanent. These special, alloy moulds are costly to produce

because they are made in sections for easy removal of the components. The high

operating costs involved make this process economically viable for high volume

mass production where accuracy of shape, size and surface finish is essential.

Gravity Castings

Molten metal is poured into the cavity under its own weight. This produces sound,

dense castings with mechanical properties superior to pressure casting (since metal

enters the mould with less turbulence). This process also traps less gas than

pressure casting does, leading to less porosity.

Die Casting

die

fixed pattern

injection piston

molten metal

release

cavity

‘Hot’ chamber and ‘cold’ chamber processes are used. In both processes molten

metal is forced into a metal die by a hydraulic ram. Thin section and complex

shapes with fine detail are possible.

1. A measure of molten metal is

poured into the charge chamber.

2. An injection piston then forces the

metal into a water-cooled die through

a system of sprues and runners.

3. The metal solidifies rapidly and the

casting is removed, complete with its

sprues and runners.

Die Casting

Materials

Materials used in this process include low melting temperature alloys, lead, zinc,

aluminium and brass alloys.

Identifying Features

Section hair lines, ejector pin marks, flashes caused by leakage left on internal

surfaces (these do not interfere with performance or appearance), and sprue and

runner marks.

Die Casting

Press Forming Take a note

Press forming involves squeezing sheet metal between two matched metal moulds

(dies). This gives a very strong, shell-like structure. One die is the mirror image of

the other, apart from an allowance for he thickness of the material being formed.

The machining of these dies is a specialised skill. They can be complicated and

therefore difficult and time consuming to make. This makes them very expensive to

produce.

The Process

The sheet metal component starts out as a flat sheet or strip

1 A blank is cut to the required size.

2 The blank is placed in a press.

3 The product is formed using immense force.

The complete forming process may take several additional stages of

operations to form, draw (stretch) and pierce the material into its final shape

Press Forming

Materials

Sheet metals; various steels, aluminium alloys, brass, copper

Identifying Features

Sudden directional changes, i.e. sharp edges and deep draws, are avoided to minimise

overstretching the walls of the product. Different operations, e.g flanges, ribs, piercing,

can be identified.

Uses

Products used in many everyday activities are easily identifiable. These range from pans,

kettles and stainless steel kitchen sinks to car bodies and aircraft panels.

Press Forming

Sand Casting Take a note

Sand casting is the most frequently used metal casting process. ‘Green, foundry

sand is a blend of silica grains, clay and water. The term ‘green’ describes the

damp quality which bonds the sand together. Oil-bound sand gives excellent

results but is relatively expensive and difficult to reconstitute. There is an

element of waste involved as the sand that is in contact with the hot metal will

burn. This burned sand needs to be scraped out and disposed of.

The quality of the casting produced depends on the quality of the pattern. These

are normally made in wood. The pattern requires radiused corners, drafted

sides and a good surface finish. The sand mould is produced around the

pattern, which is removed to leave a cavity. Molten metal is poured into the

mould and solidifies. When cold, the mould is broken up to retrieve the casting.

Sand Casting

pattern

sprue pins

cope

drag

gates

riser runner

1. Place the pattern centrally in the drag.

2. Pack sand around the pattern.

3. Turn the drag over and attach the cope.

4. Insert sprue pins and pack sand around them.

5. Remove the sprue pins.

6. Split the moulding box and cut ‘gates’.

7. Remove the pattern to leave a cavity.

8. Reassemble the cope so that the mould is ready to receive the molten metal.

9. Pour the molten metal into the runner. The melt fills the mould and exits, along with

any gases, via the riser.

Sand Casting

Materials

Iron, aluminium and non-ferrous alloys are most widely used in sand casting. Exceptions

include refractory (able to withstand high temperatures) metals such as titanium. Precious

metals e.g. gold lend themselves to casting.

Identifying Features

Complex 3-D components. Mainly solid but internal shapes can be produced using cores.

Thin sections are difficult to mould. Surface texture can be poor. Draft angles, fillets,

rounded corners and strengthening webs will be evident and will echo the pattern

requirements. Other recognisable features include bosses and porous surface textures.

Fettle marks, due to the removal of runners and risers, may be visible.

Uses

Casting is a versatile process using the material properties in the manufacture of engine

parts, tools and decorative jewellery. Multiple mould patterns decrease production time

thus lowering production costs.

Sand Casting

Casting in Aluminium

The main reason for casting an object is that the shape of the object is such

that it would make matching either very difficult or too expensive.

There are many ways in which an object can be cast, but there are only two

ways which are suitable for use in the school workshop.

1. Gravity feed casting

2. Investment casting.

The main difference being that gravity feed casting uses a wooden pattern

and so can be used for large numbers, where as investment casting uses

either a wax or a polystyrene pattern and therefore only be used once. Both

these methods come into the category of Green sand moulding, which gets

its name not from the colour of the sand, but because the sand is damp.

Casting

Piercing and

Blanking Take a note

Piercing and blanking are essentially the same process, involving the stamping of

shapes out of sheet metal or metal strip. The differences in the process simply

depend on which bit of metal is to be kept: in piercing a shaped hole is made in the

metal, whereas in blanking a shape is stamped out of the metal and then used.

The Process

punch

strip

die

Piercing

The punch and die are shown here

in the closed position. Notice how

the punch fits into the die but does

not enter it, stopping instead as

soon as the metal has been cut.

Accurate alignment of the two is

essential.

Piercing and Blanking

Blanking

The main components used for blanking in

mass production are a punch, a die and a

stripper plate. The stripper plate prevents

the metal ‘riding up’ the die on its upward

travel. The die is attached to the main press

by means of a bolster plate. The punch is

attached to a movable ram.

Blank falling through die

and bolster plate

Bolster plate

Die

Ram

Metal Strip

Punch

Stripper

Piercing and Blanking

The Process

Progressive Piercing and Blanking

Many products requires to be both pierced and blanked.

This is often done in the same press by first piercing the

metal, and then moving it along to another die and

blanking out the desired shape. This process is called

progressive piercing and blanking.

1 The metal strip is fed into the first die.

2 A hole is pierced in the metal on the first stroke of the

ram.

3 The ram rises and metal is moved into position over

the blanking die.

4 Accurate alignment is essential here.

5 The punch descends and the completed component (

in this case a washer) is blanked from the metal strip. At

the same time a hole is pierced in the next washer.

6 Piercing is normally done before blanking, as this

minimises the risk of fracturing the metal.

Metal Strip Finished Washer

Metal Strip

Stripper

Piercing punch

Die

Stop

Scrap

Ram

Blanking

punch

Pilot

Progressive Piercing and Blanking

The Process

Materials

Most types of metals can be pierced and blanked in sheet or strip form. The metal is

normally annealed first so as to minimise the risk of fracture or tearing.

Identifying Features

A sheared surface will show two distinct areas of deformation and fracture. With the

correct clearance angles in the punch, this can be minimised to give a reasonably smooth

edge which will require no further finishing.

Uses

Uses of piercing and blanking include component parts for a variety of tool and products.

Often products made from sheet metal that have been press formed are pierced to give a

decorative finish.

Piercing and Blanking

Drop Forging Take a note

Impression-die drop forging is an industrial process used in the production of high quality, strong metal components or products. The main advantages are that components can be accurately repeated using specially shaped dies to control the flow of metal; the need for highly skilled craftsmen is thus eliminated.

PR

ES

SU

RE

PR

ES

SU

RE

Anvil

Ram

Top Die

Bottom Die

Billet Flash

The Process The die used are very expensive to produce. High alloy steels are required to prevent heat loss

which causes them to wear too quickly under impact loads.

1. A hot metal billet is placed between the

dies.

2. The hot metal is forced into the cavity

using a power driven hammer. (Note that the

process may take more than one operation using a

succession of dies.)

3.Excess metal is squeezed out forming a

flashing around the parting line of the two

dies. The amount of flashing is determined

by die wear and the quantity of excess

metal.

4. When the forging is complete the flash is

removed using a trimming die.

Drop Forging

Materials Most metals are in alloy form are suited to the drop forging process. Alloy steels and copper alloys are most

common.

Identifying Features The function of the product may indicate that drop forging is the most appropriate process for manufacture, i.e. the

product or certain parts of the product may require compressive or tensile force to be used. Strength to weight

ratio is a consideration. Visually there may well be evidence of flashing and flash removal around the edges of

the product. Quality products may have undergone further finishing to eliminate visual evidence of die parting

lines.

Uses Drop forging metal increases its strength. The grain structure of the metal is changed to follow the outer contour of

the component. This provides greater scope for the design of high quality metal products. Examples range from

hand tools such as spanners and plumbing fittings to high quality cutlery and domestic appliances.

Drop Forging

Joining Materials Take a note

The manufacture of most products requires joining together of materials. Part

of the designer’s role is to select the most appropriate method.

Permanent joining methods include adhesives, arc welding, fitted joints,

riveting, spot welding.

Non-permanent methods include nuts, bolts and screws.

Joining Materials

Mechanical knock down fixings are generally used on square cut butt joints on

manufactured boards. No glue is required but accurately drilled holes are essential.

Knock-down fixings (fixings) make assembly straight forward and have the added

advantage that dismantling a product is possible.

PLASTIC CORNER

BLOCK

TWO BLOCK

FITTING

RIGID JOINT

Joining Materials Knock-down Fittings

Knock-down fittings are those that can be put together easily, normally using only a

screw driver, a drill, a mallet/hammer and other basic tools. They are temporary

joints although many are used to permanently join together items such as cabinets

and other pieces of furniture that are purchased in a flat pack

CAM LOCKS

SCAN FITTINGS

Joining Materials

Knock-down Fittings

Soldering, brazing and welding techniques are used mainly to join metals. Some

thermoplastics can also be joined in this way.

Arc Welding

Heat is obtained by an electric arc via a transformer. One lead is attached to the work

and the other to a grip holder a welding rod. An arc is formed when the end of the

rod is brought near the work. The heat melts the parent metal and the filler rod

together. The rod is coated with flux to prevent oxidation.

Joining Materials Welding

The metal is heated and fused together between two copper electrodes. Used on thin

gauge mild steel, e.g. car bodies

Joining Materials Spot Welding

There are two methods. The traditional method uses soft iron, aluminium or copper for

snap, countersunk and flat head rivets in conjunction with a hammer and rivet ‘set’.

1

.

2

. 3

.

4

.

5

.

Joining Materials Riveting

Where the use of a hammer is to be avoided, controlled pressure is applied to a ‘pop

rivet’ using a pop-riveting ‘gun’. Also used for ‘blind’ riveting.

1. 2. 3.

The two pieces of

plastic or aluminium

are drilled to a size

slightly larger than the

rivet

The pop rivet is passed

through both holes in the

sheet plastic /

aluminium.

The rivet pliers are pushed on to the pin of the

rivet and the handles are pulled together. As

this happens the pin head is pulled into the

rivet and the end of the rivet is expanded.

Eventually the pin will break off leaving the

rivet permanently fixed in position holding the

two pieces of plastic / aluminium together.

Joining Materials Pop Riveting

The screw thread has the advantage of enabling items to be taken apart for inspection

or maintenance purposes. Nuts, bolts and set screws can be obtained in various

forms. There are numerous designs of spanners for use with square- and

hexagonal-headed nuts and bolts, just as there are keys for socket screws.

Joining Materials Bolts

Screws are used to fasten together boards, panels and fittings such as hinges and

brackets. Pieces can be taken apart and reassembled without damage. Screwdrivers

are available in a variety of blade types, e.g. slot and pozidrive. Effort in driving screws

home can be minimised by using electrically powered ‘screw guns’

Joining Materials Screws