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Manufacturing Concept
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  Metal shaping (generic) Overview Bulk metal shaping is generally done near-net-shape by forging  or casting  although further finishing work is usually required. However, it does reduce the material wasted by machining and is usually much faster. For many components, casting and forging are in direct competition and there is often no easy way to decide which is the  better choice; both are usually undertaken by specialist companies foundries and forges respectively!. here are a variety of sheet forming  processes suitable for metals less than #mm thick, and in general all products  based on sheet will be made using one of these processes. $heet is made by rolling, which is also used to produce most large stock items held by material suppliers and a few final products such as %-beams. Extrusion  is also used to produce some stock items with constant cross-section, such as tubes, and some finished items, such as window frames. Die casting Overview ã &eveloped in the early '())s, this is the most common of the casting processes that use a permanent mould. ã %t is used for high volume products, of which small *inc die-cast toys e.g. +atchbo+ cars! are probably the most widely known. ã ery small components like *ipper teeth can be made at over /),))) an hour0 Variants: Ferro-die  is used for high melting point materials such as steels. %t uses higher melting point ferrous alloys for the die materials and is more epensive Materials and shapes ã ostly used for low melting point alloys such as aluminium, *inc and copper. %n general only small parts are made, but it can be used for components up to /1kg. ã 2omple parts can be made with good dimensional accuracy and surface detail. ã 3 draft taper! angle has to be incorporated to alloy easy e4ection of the part. ã 5arts are left with good mechanical surface properties. ã 64ector pin marks are often visible Economics ã he machinery is epensive, and can cost well over 7')),))). ã &ies cost many thousand pounds and need to be replaced after a few hundred thousand uses. hey can take several weeks to manufacture, mean prototype testing is slow. ã he production rate depends on how long the part takes to cool before it can be e4ected. his can give rates of 1))8 parts per hour in normal conditions. ã Because of the high capital cost, the process is only economic for batches of ')),)))8 !pical products ã $mall toys e.g. cars9soldiers ã hand tools ã disc drive chassis ã motor casings ã carburettors  Forging Overview ã Forging is probably the oldest metalworking process - dating back to at least 1)))B2. ã %t has advanced a long way from its +blacksmith+ image and today there are many hi-tech variants that compete mainly with the casting processes. ã 3lthough forging can take place +cold+, the component is usually heated to reduce the forces required. ã he forging action can be etremely noisy0 Variants ã mpression Die Forging  - also called closed die forging , presses metal between / dies that contain a  precut profile of the desired part. ã #old Forging  - includes bending, cold drawing, cold heading, coining, etrusions and more, to yield a diverse range of part shapes. he temperature of metals being cold forged may range from room temperature to several hundred degrees. ã Open Die Forging  is performed between flat dies with no precut profiles is the dies. ovement of the work piece is the key to this method. :arger parts over /) tonnes and ') metres in length can be hammered or pressed into shape this way. ã $eamless %olled %ing Forging  is typically performed by punching a hole in a thick, round piece of metal creating a donut shape!, and then rolling and squee*ing or in some cases, pounding! the donut into a thin ring. ing diameters can be anywhere from a few inches to <) feet. &rocess details#losed-die forging ' heated lan is placed etween * halves of a die' single compressive stroe s+uee,es the lan into the die to form the part n hammer   or drop forging   this happens ! dropping the top of the mould from a height 'n alternative is to s+uee,e the moulds together using h!draulic pressure  Materials and shapes ã 3ny metal can be forged, provided the blank is hot enough  #)= of the melting temperature!. ã ypical possible si*es for closed dies range from ')g to ')kg, depending on compleity. ã he part is left with good surface and mechanical properties, although cold-forging can perform even  better. ã 2omple parts can be formed using a series of forging dies with increasing levels of detail. ã 3 draft taper! angle has to be incorporated to allow easy removal of the part. ã 3ny waste material squee*ed between the die halves, called flash, is readily recycled. Economics ã 5roduction rate is limited by the insertion and removal of the blank, so some form of automation is often used.  ã 3s a result, machines can cost 7')),)))8, but can produce many parts a minute if small!. ã 3s both the machines and the dedicated dies are costly, production runs in ecess of 1),))) are often needed to produce small parts economically. ã :arge parts can be produced economically at smaller batch si*es, because there is less competition !pical products ã $panners ã  pedal cranks ã gear blanks ã valve bodies ã hand tools ã crankshafts ã coins .ins ã he Forging %ndustry 3ssociation has a guide to forging processes. ã he 3 6 pro4ect have a video clip of hot rolling in action. requires eal5layer    ! ã he $cience useum has an animation. .ost wax casting Overview ã $ome form of lost wa casting has been used since >)))B2. ã %t is now mainly used for medium si*e batches where good quality is required. ã he fine dust and harmful fumes require careful control of the workplace to avoid health problems for operators. Materials and shapes ã $uitable for most metals, leaving a good surface finish which usually does not require further finishing steps. ã Best for small comple-shape parts, but can be used for parts from 1g to '))kg. ã  ?ot much metal scrap, and it can be easily recycled. @a can be re-used but ceramic coating must be disposed of carefully. Economics ã he production cycle is slowA usually only '-1 castings can be made an hour, depending on the si*e. 3ssembling lots of patterns on one tree can help in achieving a reasonable production rate. ã he basic cost of the equipment can be as little as 7',))), although automated kit can be a lot more. he cost of the patterns is usually only a few hundred pounds, but they can take several weeks to make. ã 3lthough the setup costs are low, the low manual production rate means that only batch si*es of up to 1) are economic; this can rise to a few thousand if automated. !pical products ã ewellery ã dental implants ã hip replacements ã valves ã wind instrument keys
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