EXAM REVISION. Metal Properties and Processes

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1 EXAM REVISION Metal Properties and Processes

2 Metals 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.

3 Alloys 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.

4 Properties 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.

5 Ferrous Metals Take a note

6 Ferrous Metals 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

7 Name Composition Properties and Working Characteristic These metals contain Iron! Uses Cast Iron Iron+3.5% Carbon Brittle/Hard skin Machine Tools, vices Mild Steel Iron+0.35% Carbon Malleable/ductile, uniform texture High Carbon Steel Iron+ up to 1.5% Carbon Malleable/ductile, can be hardened or tempered. Nuts, bolts, screws, tubes, grinders, car bodies Cutting knives, files, drills, saws, knives, hammers, taps and dies

8 Non-Ferrous Metals Take a note

9 Non-Ferrous Metals 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)

10 Non-Ferrous Metals Take a note Name Composition Properties and working characteristics Aluminium Pure metal produced Good strength to weight ratio, casts easily Copper Pure metal Ductile/malleable, low melting point, expensive Tin Pure metal Heavy/soft, low melting point Lead Pure metal Heavy/soft/weak, ductile/malleable, low melting point, can be cast Zinc Pure metal Weak, difficult to work Uses Window frames, pots and pans Central heating pipes, electric wiring/cable, jewellery Bearings, solder, coating sheet steel Roof flashing, solder Galvanising

11 Metal Processes Take a note

12 Metal Turning Take a note y7zfg

13 Turning 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

14 Milling Take a note

15 Milling 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. Vertical Milling Machine Horizontal Milling Machine

16 Milling Slot Cutter Slot Straddle Milling

17 Milling Dovetail Slot Angled Face Dovetail Cutter Angle Cutter

18 Milling T-Slot Tee Slot Cutter Flat Surface Slab Cutter

19 Die Casting Take a note e8d4

20 Die Casting 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.

21 Die Casting 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. cavity release die fixed pattern molten metal injection piston 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.

22 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.

23 Press Forming Take a note

24 Press Forming 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

25 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.

26 Sand Casting Take a note

27 Sand Casting 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.

28 Sand Casting sprue pins runner riser pattern cope drag 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. gates

29 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.

30 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.

31 Piercing and Blanking Take a note

32 Piercing and Blanking 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.

33 Piercing and Blanking The Process Punch Stripper Ram Metal Strip Die 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. Bolster plate Blank falling through die and bolster plate

34 Progressive Piercing and Blanking Ram Blanking punch Scrap Stop Die Pilot The Process Finished Washer Piercing punch Metal Strip Metal Strip Stripper 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.

35 Piercing and Blanking 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.

36 Drop Forging Take a note

37 PRESSURE PRESSURE Drop Forging 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. 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. Top Die Billet Bottom Die Ram Anvil Flash 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.

38 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.

39 Joining Materials Take a note

40 Joining Materials 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.

41 Joining Materials Knock-down Fittings 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 RIGID JOINT TWO BLOCK FITTING

42 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

43 Joining Materials Welding 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.

44 Joining Materials Spot Welding The metal is heated and fused together between two copper electrodes. Used on thin gauge mild steel, e.g. car bodies

45 Joining Materials Riveting 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

46 Joining Materials Pop 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 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.

47 Joining Materials Bolts 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.

48 Joining Materials Screws 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