Metals All metals belong to one of these two groups. Ferrous metals are metals, which are mainly made of iron with small amounts of other metals or elements added in order to give the correct properties. Almost all ferrous metals are magnetic and can be picked up with a magnet. These metals rust or oxidise if not treated as they contain iron. Non-Ferrous metals are those metals, which do not contain iron. These metals are not magnetic and cannot be attracted by a magnet. Examples of these are aluminium, copper, lead, zinc and tin. These metals do not oxidise as they do not contain iron.

Pure metals and alloys All metals fall into two categories. They can either be pure metals or alloys. A pure metal consists of a single element, which means that it is a metal only having one type of atom in it. The most commonly used pure metals are aluminium, copper, iron, lead, zinc, tin, silver and gold. An alloy is a mixture of two or more pure elements. Pure metals sometimes lack certain required properties. To create these properties a number of these pure metals are combined together. Pure aluminium is rarely used because it is too soft. It is normally mixed with other metals, which produce aluminium alloys that are even stronger than mild steel, are resistant to corrosion but still retain the lightness of aluminium.

Structure

Name the metal?

Mild steel. It is used for general structural work for example girders, nuts, bolts, screws, car body panels and non-cutting tools. If mild steel is coated in tin it is called ‘Tin plate’. If mild steel is coated in zinc it is called ‘Galvanised sheet’.

Name the metal?

Aluminium. It is used to make car bodies, cooking utensils, engine cylinder heads, window frames, insulation, foil food wrapping and boats. mixed with copper to make an alloy. This alloy is much stronger than pure aluminium.

Name the metal?

Medium carbon steel. It is used to also make garden tools, axles and shafts.

Name the metal?

High Carbon Steel (tool steel)

Material TypeUses Properties Mild steelFerrous metal Nails, screws, nuts and bolts, girders, car bodies Tough, malleable, high tensile strength, easily joined, poor resistance to corrosion, general-purpose metal. BrassNon- ferrous metal Ornaments, boat fittings, castings. Corrosion resistant, polishes well. Hard, easily joined, good conductor of heat and electricity. CopperNon- ferrous metal Hot water storage cylinders, central heating pipes, electrical wires, copper clad electronics boards Good conductor of heat and electricity, corrosion resistant, easily joined, polishes well, solders and brazes well, expensive to buy. Stainless steel Alloy Sinks, cutlery, dishes, teapots Hard and tough, resists wear, corrosion resistant, difficult to cut and file. AluminiumNon- ferrous metal Kitchen cooking utensils, pans, packaging, cans, window frames High strength to weight ratio, light, soft, difficult to join, good conductor of heat and electricity, corrosion-resistant, polishes well.

Electroplating Zinc – exterior use (galvanised) Nickel – interior use

Metal Casting Metal Forming Metal Machining Metal Fabrication

The Mould in Casting Contains cavity whose geometry determines part shape Actual size and shape of cavity must be slightly oversized to allow for shrinkage of metal during solidification and cooling Moulds are made of a variety of materials, including sand, plaster, ceramic, and metal

Two forms of mold: open mould, simply a container in the shape of the desired part; and closed mould, in which the mold geometry is more complex and requires a gating system (passageway) leading into the cavity

Two forms of mold: open mould, simply a container in the shape of the desired part; and closed mould, in which the mold geometry is more complex and requires a gating system (passageway) leading into the cavity

Sand casting mould

Investment Casting

Die Casting

Issues melting temperature (1100 C for Cast Iron; 550 C for Al) surface finish from sand casting cycle times between gravity & pressure diecasting use of pressure & steel tools to form complex & precision details

Metal Forming

Process Classification Bulk Deformation Process Sheet Metalworking Material Behaviour in Metal Forming Flow Stress Temperature in Metal Forming

Rolling - compression process to reduce the thickness of a slab by a pair of rolls. Forging - compression process performing between a set of opposing dies. Extrusion - compression process sqeezing metal flow a die opening. Drawing - pulling a wire or bar through a die opening.

Bulk Metal Forming Rolling Forging ExtrusionDrawing

Extrusion

Drawing

Pressing

Sheet Metalworking Forming on metal sheets, strips, and coils. The process is normally a cold working process using a set of punch and die. Bending - straining of a metal sheet to form an angle bend. Drawing - forming a sheet into a hollow or concave shape. Shearing - not a forming process but a cutting process.

Sheet Metalworking

Temperature in Metalworking Cold working –Pros better accuracy better surface finish strain hardening increases strength and hardness grain flow during deformation provides directional properties no heating is needed –Cons higher forces and power are required surface should be cleansed ductility and strain-hardening limits the extent of forming

Temperature in Metalworking Hot working - Deformation at temperature above recrystallization temperature typically between 0.5T m to 0.75T m –Pros larger deformation possible lower forces and power forming of room temperature low ductility material is possible isotropic properties resulted from process no work hardening