Design and Manufacture National 4/5 Commercial Manufacturing Processes

Injection Moulding Video Injection moulding Injection Moulding is a process which allows large quantities of plastic components to be made quickly. Thermoplastic granules are heated until they soften. Then the material is forced under pressure into a mould. When cooled, the mould is opened and a component, which is the exact shape of the cavity is taken out. Injection Moulding is one of the most important industrial processes in the mass production of plastic goods. The cost of producing the moulds can be very high, therefore it is necessary to manufacture and sell large quantities of the product being manufactured to recover costs. The Process A feed hopper if filled with thermoplastic granules. A rotational screw mechanism passes the granules through a heater. The heater causes the granules to plasticise. The soft plastic is injected into the mould where it is cooled. The mould is opened automatically. The finished component is ejected. No further finishing is required. The quality of the product is identical to the surface of the mould. Uses Components produced by injection moulding vary from golf tees, spoons, wash basins, buckets, airfix models to product casings.

Identifying Features Ejection pin marks on the inside of the product Mould split Lines Injection mark (sprue pin) Advantages Large quantities of identical plastic components can be made quickly High quality surface finish Complex accurate shapes can be produced Strengthening ribs and webs can be included Disadvantages High tooling cost Expensive set up costs/costs of machinery

Rotational Moulding Video Rotational Moulding Rotational moulding is a method of creating medium to large sized hollow components from plastics. It involves melting plastic inside a closed mould which is rotated so the plastic coats the inside of mould. The plastic is then cooled and solidifies in the shape of the mould. Stage 1 At this stage the liquid plastic is poured into the mould. The mould is then sealed and the process of rotating it begins.   Stage 2 This stage shows the plastic being heated as it is rotated around the mould. The heated plastic coats the inside wall of the mould.   liquid plastic mould Stage 3 The completed plastic mould is now cooled before ejection from the mould.   Stage 4 The moulded shape is ejected from the mould. The picture here shows a hollow sphere.  

Identifying Features Mould split Lines Uniform wall thickness No joining processes evident Advantages Large, identical plastic components can be made quickly Good quality surface finish Strengthening ribs and webs can be included Disadvantages High tooling cost Expensive set up costs/costs of machinery

Vacuum Forming Video Vacuum Forming In Vacuum Forming, a sheet of thermoplastic is held in a clamp and is heated until it is soft and flexible. Air is sucked out from underneath the sheet so that air pressure pulls the sheet down onto a specially made mould. This process enables thermoplastics to be formed into complicated shapes such as packaging, masks, storage trays and seed trays. Stage 1 The first stage of vacuum forming is to clamp the sheet across the top of the machine and heat it until the plastic is soft and flexible. This can be judged by watching the material, which will start to sag under its own weight when soft. If touched with a stick it will feel soft and rubbery.   platform raised Stage 2 The pattern is then raised up to meet the hot soft plastic.   air sucked out Stage 3 At this stage the air has been sucked out from beneath the plastic pulling it onto the pattern.   formed plastic Stage 4 The final stage is to remove the pattern from the plastic leaving the finished article.  

Air holes- for removing air from around the mould Identifying Features Rounded Corners – The pattern should have rounded corners and not sharp edges so that the plastic does not rip or tear as it forms round the pattern. Tapered Edges - The pattern should have tapered edges or sloping sides so that the pattern can be easily removed from the plastic after forming. Internal curves – The pattern should not have internal curves as these cause folds in the plastic to occur during the forming process. Air holes- for removing air from around the mould Advantages Repeatable Low cost Disadvantages Limited Strength Stretching and tearing can occur in plastic Pattern with rounded corners and sloping/tapered sides.

Extrusion Video This process can be compared to squeezing toothpaste from a tube. It is a continuous process used to produce both solid and hollow products that have a constant cross-section. Extrusion can be used to produce products such as gutters, window frames and electrical trunking.

Identifying Features Uniform profile along it’s length Available in long lengths Advantages Continuous Process High production volumes Low cost per meter Many types of raw materials are suitable Disadvantages Limited complexity of parts Uniform cross-sectional shape only

Die Casting Video This process is the equivalent of the plastic process of ‘injection moulding’, where molten material is forced into a mould (die) to cool and set. The dies used are made of special alloy steel and are very expensive to produce, being made in sections for easy removal of the components. The high operating costs make this process viable for high-volume production or ‘mass production’ where accuracy of shape, size and surface finish is essential. Process A measure of molten metal is poured into the charge chamber. An injection piston then forces the metal into a water-cooled die through a system of sprues and runners. The metal solidifies rapidly and the casting is removed, complete with its sprues and runners. Video 2

Uses Engine casings, toy cars, pencil sharpeners etc. This pencil sharpener has been ‘die cast’. It has ejector pin marks on each corner.

Identifying Features Mould split Lines Injection mark (sprue pin) Ejector pin marks Advantages Repeatability High quality surface finish Complex accurate shapes can be produced Strengthening ribs and webs can be included Disadvantages High tooling cost Expensive set up costs/costs of machinery

Sand Casting Video Uses This is the most frequently used metal casting process. ‘Green’ foundry sand is a blend of silica grains, clay and water. Oil-bound sand gives good results but is difficult to reconstitute (re-use). The quality of the casting depends on the quality of the pattern, which is normally made of 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. Uses Engine parts, machine tables, tools and tool handles, stoves, taps, propellers

Identifying Features Simple components which can be solid or hollow Rough texture May show signs of shrinkage Can be used with a wide variety of metals Advantages Low cost Repeatable Relatively easy to carry out Disadvantages Low quality surface finish Parts may require secondary processing

Press Forming Video 2 Video Uses Pans Kettles Kitchen sinks Car bodies 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 the thickness of the material being formed. The machining of these dies is a specialised skill as they are complicated and therefore time-consuming and expensive to produce. Uses Pans Kettles Kitchen sinks Car bodies Aircraft panels Process A blank is cut out to the required size. The blank is placed in a press. The product is formed using immense force. (1 thousand tonnes are required to manipulate 3.5mm thick steel plate.) Video 2

Identifying Features Uniform thickness sheet material Bending and forming to increase strength Advantages Repeatable Relatively easy to carry out Can produce a wide range of strong products Disadvantages Set up costs of machines is high Limited material thickness

Centre Lathe Turning Video Centre lathes are used to make cylindrical components from metals and plastic materials. The process is called turning – never use the term lathing. The principle of turning is straightforward. Work is held firmly and is rotated whilst a single-point cutting tool, located in the tool post, cuts the work using the familiar wedge-cutting action. The shape of the work produced depends upon the path taken by the tool, the two principle shapes being cylindrical and flat, produced by parallel turning and facing. Centre lathes, like the one shown have four main elements: lathe bed – very rigid and usually made from cast iron. The bed keeps the other parts in alignment. headstock – containing the gearbox, controls and the means of holding the work, most commonly a 3-jaw or 4-jaw chuck. tail stock – for location of drills and drill chucks and for supporting long work. saddle – travels along the bed and carries a cross slide upon which is mounted the tool post. Centre lathe

Uses Bike hubs, engine parts, door handles, bolts, screws Identifying Features Can be manual or computer controlled Cylindrical components Advantages Highly accurate High quality surface finish Relatively easy to carry out Disadvantages Skilled process Parts may require secondary processing

Traditional Woodworking Joints Video Found in traditional carpentry and joinery, using hand tool and basic machinery. Advantages Used for high quality products Aesthetically pleasing Can be strong and durable, so products will have a long lifespan Disadvantages Time consuming Easy to make errors

Knock-down fittings/CNC Video Knock down fittings are commonly used in flat pack furniture, in particular by brands such as Ikea. Advantages Low cost Quick to assemble Repeatable No skill required to build products Allows products to be dismantled CNC machining reduces human error and is highly accurate Disadvantages Perceived as being low quality High set-up costs of machines

Laminating Industrial Laminating for Buildings- video 1 Laminating Furniture- video 2 This method of shaping wood involves building up a curved form with layers (‘lamina’). The layers may be thin veneers, thicker constructional veneers or saw-cut strips. They are assembled so that the grain of each layer is running in the same direction, following the curve (unlike plywood which has interlocking grain). The layers are glued together with a strong adhesive and are sandwiched between the waxed faces of a former or a jig using cramp pressure. The layers bend to the shape of the jig and ‘set’ together. Advantages Low cost Can be used to create complex curves Strong Repeatable Disadvantages Time consuming Relatively difficult to carry out