Materials & Industrial Processes · 2018-02-05 · metal ingot between two massive rolls or dies. In hot rolling the metal ingot is heated to around 2/3 of its meting point and forced

Higher Design & Manufacture

Manufacturing Processes

Duncanrig Secondary School

Content

Section A: Manufacturing Processes

Introduction 1

Material Preparation

Extrusion (metal) 2 Extrusion (polymer) 3 Rolling (metal) 4

Spindle moulding (wood) 5

Material Processing

Injection moulding (polymer) 6 Rotational moulding (polymer) 7

Blow moulding (polymer) 8 Compression moulding (polymer) 9 Mould & Die Design 10 Vacuum forming (polymer) 11 Sand casting (metal) 12

Die casting (metal) 13 Forging (metal) 14 Drop forging (metal) 15 Press-forming (metal) 16 Drawing (metal) 16 Piercing & Blanking (metal) 17 Spinning (metal) 18 Turning (wood, metal & polymer) 19 & 20 Milling (metal & polymer) 21 Routing (wood) 22 Laminating (timber) 23

Laminating (polymer) 24

Assembly Processes

Adhesive Bonding (all materials) 25 Welding (metal & polymer) 26 & 27 Riveting (metal & polymer) 28 Mechanical fastenings (all materials) 29 Knock-down fittings (wood) 29

Finishing Processes

Aqua Transfer Printing (all materials) 30 Powder coating (metal) 30 Varnishing & Lacquering (all materials) 31

Painting (all materials) 32 Anodising (aluminium & titanium) 32 Galvanizing (steel) 33 Finishing Summary Table 33

Industrial Processes: Summary Table 34

Section B: Rapid Design & Manufacture

Computer Aided Design (CAD) 35 Computer Aided Manufacture (CAM) 36 Computer Numerical Control (CNC) 36 Rapid Prototyping (RP) 37 Sterolithography (SLA) 37 Selective Laser Sintering (SLS) 38 Fused Deposition Modelling (FDM) 38 3D printing 38 Rapid Tooling 39

Section C: Manufacturing Systems

Introduction 40 Production Planning 40 Flowchart 40 Process chart 40 Gantt chart 40 Concurrent Engineering 41 Just-in-Time (JIT) 42

Quality Assurance (QA) & Control (QC) 42 One-off production 43 Mass production 43 Batch production 44 Line production 44 Continuous (flow) production 45 Cell production 45 Sub-contracting & Outsourcing 45

Duncanrig Secondary School - Manufacturing Processes 1

SECTION A: MANUFACTURING PROCESSES Introduction

The choice of which manufacturing process is most suitable depends upon; material, shape, size, degree of accuracy, surface finish, unit cost and most critically the number of components to be made – the batch size.

Manufacturing processes can be grouped into a number of broad families:

Material Preparation (converting raw materials into standard stock sizes):

Extrusion (metal & polymer)

Rolling (metal)

Spindle moulding (wood)

Material Processing (giving the component its final form):

Injection moulding (polymer)

Rotational moulding (polymer)

Blow moulding (polymer)

Compression moulding (polymer)

Vacuum forming (polymer)

Sand casting (metal)

Die casting (metal)

Drop forging (metal)

Forging (metal)

Pressing (metal)

Stamping (metal)

Piercing (metal)

Blanking (metal)

Turning (wood, metal & polymer)

Milling (metal & polymer)

Routing (wood)

Laminating (timber & polymer)

Assembly Processes (bring together the component to complete the product):

Adhesive (wood, metal & polymer)

Arc welding (metal)

Spot welding (metal)

Heat welding (polymers)

Riveting (metal & polymer)

Mechanical Fastenings (wood, metal & polymer)

Finishing Processes (enhancing and protecting the product’s component parts):

Varnish (wood)

Lacquering (metal)

Powder coating (metal)

Aqua Transfer printing (metal & polymer)

Painting (wood & metal)

Galvanizing (metal)

Anodising (metal)


Material Preparation: Metal Extrusion

The extrusion of metal is used to produce long straight lengths of material with a uniform cross-sectional shape. The cross-sections possible include solid round, L and T shapes, tube or complicated irregular hollow shapes.

Extrusion can be likened to squeezing tooth paste out of a tube – long lengths of material are formed in the same cross sectional shape as the tube opening. Common metals that are extruded include aluminium, copper, magnesium, steel, and stainless steel.

Extrusion involves squeezing a hot metal billet inside a closed cavity with a shaped opening formed by a die using either a mechanical or hydraulic press.

Extrusion often minimises the need for secondary machining, but it does not give the same dimensional accuracy or surface finish as a machined part. However, this process can produce a wide variety of cross-sections that are hard to produce cost-effectively using other methods. Minimum thickness of steel is about 3 mm, whereas with aluminium and magnesium this can be extruded to about 1mm.

Cold extrusion can be used for most materials -subject to the design of robust enough tooling that can withstand the stresses. Examples of the metals that can be extruded are lead, tin, aluminium alloys, copper, titanium, vanadium and steels. Examples of parts that are cold extruded include collapsible tubes, aluminium cans, cylinders, gear blanks. The advantages of cold extrusion include, no oxidation, good mechanical properties due to the cold working, and a good surface finish.

Metal Extrusion: features

Materials & shapes: Mainly used with the softer metals, e.g. aluminium, copper, zinc. In general, the softer the metal, the more intricate the shapes that can be made. Useful for long thin parts with a constant cross-section. Possible cross-sections are usually limited to less than 100mm across. Dimensional tolerance and surface finish may be poor with hot extrusion. Cold extrusion is possible for some metals giving better properties.

Economics: Although extrusion appears to be a continuous process, it is really a batch process as it needs to be interrupted to load new billets. Typical machine prices are in excess of £50,000. Dies can cost upwards of £1,000 to make (depending on size), but a lot more to design well. More frequent die replacement is needed for higher strength metals. Production rates from 5-10 metres/minute are possible. Usually only economic for a batch size of 1,000 – 1,000,000 metres.

Typical products: metals such as aluminium, copper, magnesium, steel, and stainless steel are extruded to form window frames, tubing, building and car trim, aircraft parts, railings & wires. Extrusion can be used to form 1 – 1,000kg lengths to an accuracy of 0.2 - 2mm.

Dies showing the detailing possible when

extruding lengths of metal

A selection of just some of the

possible extrusion shapes

A length of aluminium window frame being

cold extruded


Material Preparation: Polymer Extrusion

Polymer extrusion is used to produce long lengths of plastic with a uniform cross-sectional shape. Extrusion can be likened to squeezing toothpaste out a tube and it is commonly used with thermoplastics, such as: polyvinyl chloride (PVC), polyethylene (PE) and polypropylene (PP).

Polymer granules are placed in a feed hopper and then moved through a heater using a screw feed. When in the plastic state the polymer is forced at high pressure through a die with the required profile to produce long lengths with a uniform cross section. The extruded component is cooled as it leaves the die cavity. Unlike metal extrusion, polymer extrusion is a continuous process and can produce unlimited lengths of the component. A useful variation of the process, called co-extrusion, is used to coat wires in-line for electrical cables.

Polymer Extrusion: features

Materials & shapes: Mainly used for thermoplastics, but can be used with elastomers and some thermosets. Complex shapes with constant cross-section can be easily formed. Because of shrinkage, die design can be difficult (and hence expensive) if good dimensional accuracy is required. It produces a finished component with no waste that requires no further finishing.

Economics: The cost of the machines is high - well over £50,000. Die design can be expensive; the actual dies usually cost a few thousand pounds to produce and need replacing after 10-100km of extrusion. Depending on size, parts can be extruded at rates from 1-60m/minute. Because of the high costs, it is usually only economic to produce lengths over 10km - although there is little competition for many of the possible shapes.

Typical products: Polymers formed into channels, pipes, sheet, architectural mouldings, cables, coated wires. These can be formed continuously with the economic batch size of 1,000 – 1,000,000 is typical.

A PVC pipe being cooled with water as it leaves the

die cavity.

A selection of some of the forms possible when

extruding polymers

Commercial extrusion of PVC water pipes


Material Preparation: Rolling

Rolling is an alternative to metal extrusion and it is used to produce long lengths of straight material with a uniform external cross-section. Rolling cannot, however, be used to form hollow components. Rolling is a very common process and is used to form 90% of all stock sized steel by squeezing the metal ingot between two massive rolls or dies.

In hot rolling the metal ingot is heated to around 2/3 of its meting point and forced through a series of roller dies that progressively form the profile. This produces components with particularly good mechanical properties because the metal grain reforms to the rolled profile as the material cools. This leaves hot rolled material relatively soft with a surface layer of oxide (called black bar in the case of hot rolled mild steel).

Cold rolling produces good dimensional accuracy, an oxide free surface finish and a work hardened surface making the metal strong. Often hot rolling is first used to shape the metal and cold rolling (or drawing) is then used to finish the material and work harden the surface. Metal Rolling: features

Materials & Shape: a hot ingot in moved back and forth through a set of connected die rolls. Each roll gets closer the final shape; the last pass will finish the rolled shape. Rolling can be used to make thick sections such as slabs or large I-beams. In practice, there do not need to be many separate ‘dies’ if the operator can move the rolls closer together between passes.

Economics: For making stock items, rolling has few competitors. For this reason, it is usually performed by the foundries before passing on to customers for further processing. For long shaped sections, rolling is the only viable option for larger cross sections - for smaller cross section extrusion may be more economic. Machines can cost millions of pounds. Typical economic batch sizes 10,000 – 1,000,000

Typical products: metal I-beams, rails, sheets, plates, foil with a low shape complexity. Typical weight range 0.1 – 100kg with the minimum thickness of 0.2mm.

A selection of rolled steel components

A selection of cold rolled steel components with a good surface finish and dimensional accuracy

Rolling machine set up to produce rectangular bar or

sheet.


Material Preparation: Spindle Moulding

Spindle moulders are used for cutting shaped profiles along lengths of wood to form such things as skirting boards, decorative mouldings and window frames.

The spindle moulder consists of a cutter block that rotates at high speed on a vertical spindle protruding through a hole in the worktable. Adjustable fences guide the work past the cutter block. A large variety of off-the-shelf shaped cutting tools are available for all the common profiles.

Spindle Moulding: features

Materials & Shape: it is possible to mould a wide variety of different profiles along the length of timber or manufactured board. Specialised or one-off moulding cutters can be produced inexpensively by grinding a tool to the required profile, although these cutters tend to have a much shorter life span than the off-the-shelf tools manufactured from high speed steel. It is only possible to mould external profiles, no internal detail such as holes or slots can be machined.

Economics: commercially standard stock profiles are mass produced. The low capital costs of a spindle mould mean that even small to medium sized companies can produce specialised moulding for one-off or low volume batch jobs.

Typical products: skirting boards, decking, dado and picture rails with a low shape complexity.

Stock sized spindle moulded lengths of MDF

Small volume or one-off batches are possible with the timber boards being manually fed into the spindle moulder

High volume batches are produced on automated spindle moulder


A selection of some polymer products made

by injection moulding

An ABS car dashboard being manually removed from an injection moulder

Material Processing: Injection Moulding

Injection moulding is the most commonly used polymer forming process. It is used to produce components to a high degree of accuracy with a very fine surface detail, something that cannot be achieved by any other moulding processes. It is typically used for thermoplastics (polythene, polystyrene, ABS, nylon, PVC, polypropylene etc) although it can also be used with certain thermosets.

The thermoplastic in the form of granules, or the liquid thermoset, is heat softened and then injected into a shaped metal die mould where it is cooled. When the die is opened, the component is automatically ejected. This is a perfect copy of the mould with all its intricate detail such as texture, text, holes and very fine detail.

Injection Moulding: feature

Materials & shapes: injection moulding is the best way to mass-produce small, precise, polymer components with complex shapes. The surface finish is excellent; texture, pattern and fine detail reproduce well. Thermoplastics dominate, but it can also be used for thermosets and elastomers. It is unsuitable for thick sections with typical part sizes of 100-600g, although items up to 25kg can be made but at great expense. Injection moulded parts generally do not require finishing, although parts for feeders etc. may require removal. Thermoplastic scrap is easily recycled, but other materials must be disposed of carefully.

Economics: to reduce costs, several parts are often moulded together on a "tree-like" structure; parts can then be separated after moulding. Economical batch size can vary between 10,000 – 1,000,000 units.

Typical products: polymer toys, model-making kits, handles, food containers, cups, electrical and plumbing fittings to a maximum weight of 25kg and minimum wall thickness of 0.3 – 10mm.


Material Processing: Rotational Moulding

Think of a large hollow polymer product and the chances are that it has been made by rotational moulding. This versatile process is surprisingly inexpensive and is used to make a wide range of everyday products including medical goods, consumer items, agricultural and garden equipment, automotive and transportation components. Its main disadvantage is the low production rate which usually limits it to smaller batches.

Rotational moulding is used with thermoplastic and elastomers, although certain thermosets may be formed using this process. However, Polythene is by far the most common material used and accounts for 85% of all rotational moulded products.

Overview of rotational moulding: A hollow mould is filled with a thermoplastic powder and then rotated about the horizontal and vertical axis in an oven until the polymer coats the inside of the mould. The mould is then cooled and the part removed:

Rotational Moulding: features

Materials & Shape: mainly for thermoplastics (especially polyethylene), but some thermosets can be used. It is used to produce hollow products with uniform thin sections as low as 2.5mm thick and in size up to 4m across. The moulded products do not need to be circular (or symmetrical) in cross-section and no further finishing after forming. It is possible to include surface details such as logos or even incorporate metal inserts into the component although the low pressure limits the possible sharpness of the detailing. There is no waste as all material is used.

Economics: cycle time is limited by heat conduction out of the mould, so increases dramatically for larger wall thicknesses. Thin walled products can be produced at almost 1 a minute, whereas thick walled products might be as few as 3 per hour. Although the tooling is dedicated, the moulds are usually quite cheap. Equipment is relatively inexpensive (£1,000 to £20,000). The long cycle times usually limit economic batch sizes to between 100 and 10,000.

Typical products: polymer buckets, plastic footballs, dustbins, storage tanks, traffic cones with a maximum weight of 50kg and minimum wall thickness of 2.5 - 6mm.

A selection of large

hollow product made by rotational moulding.

A rotational moulder showing the

potential size of the products that can be formed.


Material Processing: Blow Moulding

Blow moulding is used to manufacture hollow thermoplastic products such as bottles and containers from polythene, PVC, polypropylene or PET. It is a fast process with very little waste and suits automation, however, the high cost of the die mould means that it is only suitable for high volume runs.

A hollow plastic tube is extruded and placed between the two halves of a shaped mould die. The die is closed sealing the bottom end of the tube and air under pressure is blown into the tube forcing the thermoplastic material against the side of the mould. Once cool, the die is opened, the component is ejected and the cycle begins again.

Blow Moulding: features

Materials & Shape: blow moulding is used for simple, thin-walled, hollow products - mainly bottles with thermoplastics, particularly PET and polythene. It produces a good, smooth surface finish and the fine detailing such as the bottle thread can be moulded. Depending on how the hollow blank (parison) is made, scrap can be negligible.

Economics: The production rate is 100–2500 components/hour. The tooling and machines are moderately expensive (£10,000 - £100,000) and moulds may need to be replaced after about 100,000 uses. Blow moulding can be economically used for batch sizes of 1,000 – 10,000,000.

The flexibility of the process is limited by dedicated dies and there are short set-up and tool change over times. Full automation of the process is viable and blow moulding is well suited to high volume production. Extrusion blow moulding allows a continuous operation but increases the waste material as the complexity of the mould also increases; material utilisation is generally good. Although some trimming is required the cost is minimal. Typical Products: thermoplastic bottles and hollow components with a maximum weight of 300g and a minimum wall thickness of 0.4 to 3mm.

A selection of the

thermoplastic product made by blow moulding

The fully automated blow moulding of thermoplastic bottles used for fabric conditioner.

Note the large amount of flash caused by the high production rate. This excess material will need to be trimmed off before the bottles can be filled.


Material Processing: Compression Moulding

Compression moulding is mainly used to form thermosets and elastomers in mid-size batches (injection moulding is less expensive for thermoplastics). With thermosets the chemical reaction provides most of the energy and little extra heat is required to cure the polymer.

The thermoset liquid and hardener are placed in a heated mould. The die is closed creating sufficient pressure to force the polymer into the shape of the mould. After the polymer has had time to cure, the die is opened and the component is ejected from the mould.

Compression Moulding: features

Materials & Shape: this process is mainly used for thermosets, although rubbers, some thermoplastics (polypropylene) and chopped-fibre composites can be formed this way. Complexity of the mould design is relatively limited to simple forms as moulding can only be in one plane, although a wider variety is possible with rubbers as they can be more easily removed from the mould. Holes, inserts, threads, bosses, ribs and lettering are possible. Although it is not common, thin sections are possible with a good cavity design. Components have a section range 0.8–13mm and max weight 20kg. Waste material, called flash, needs to be removed after moulding and is not readily recycled. Compression moulded components do not have sprue gates as the material was not injected.

Economics: cycle time is limited by heat transfer, or curing time and is usually over 1 minute. Production rate can be increased by using multiple cavity moulds. Equipment cost is low compared to similar processes - about £10,000 - £50,000. Die cost a few thousand pounds, and need replacing after 10-50,000 uses. This makes the overall cost moderate to high and with the low production rate (20 to 140 components per hour) compression moulding is only usually economic for batch sizes of between 5,000 – 1,000,000.

Typical Products: polymer dishes, pot handles, caps, electrical components and other heat resistant products or items made from elastomers such as rubber. Maximum component weight of 20kg is possible and a minimum thickness of 1.2-25mm.

A compression moulded rubber component being manually removed from

a die after curing

The polymer placed in the mould and heated. The die is closed forcing the polymer to fill the mould. It is left to cure and then the die is opened and the component is removed.


Material Processing: Mould & Die Design

The high tooling cost involved in the manufacture of a new die mould from special alloy steel, with its automatic ejection and water cooling, makes it only suitable for higher volume batches where the die can be used to produce thousands of identical components at a very low unit cost.

Modern dies moulds feature a number of interchangeable parts which can be altered or replaced if the component has to be changed without requiring an entirely new die to be made. There are a number of features on a product that indicate that it has been moulded:

Split lines: around the product showing where the different parts of the die mould met.

Sprue gate: showing where the plastic was injected into the mould.

Ejector pins: will leave small round marks on the inside of the component as it is ejected from the die.

Webs: added to stiffen and strengthen the component due to the limited thickness of the material.

Boss: moulded to the component to allow the product to be screwed together.

Draft: wall sides are tapered to allow the component to be ejected from the die mould.

Corner fillets: internal corners rounded to avoid weakening the component.

Uniform wall thickness: to avoid sudden changes in size which interrupt the flow of polymer and weaken the moulding.

Injection moulding die

Ejector pin marks

Sprue gate

Web

Boss

Draft

Fillet


Material Processing: Vacuum Forming

Vacuum forming involves heating a polymer sheet until soft and then sucking it over a shaped mould until cool. This process is only suitable for thermoplastic polymers and it is in effect the opposite forming process to blow moulding - with sucking instead of blowing.

Vacuum Forming is an inexpensive technique that can be used for one-off or low volume batches (with wooden moulds) or volume production runs (more expensive cast metal moulds).

Vacuum Forming: features

Materials & shapes: only suitable for thermoplastics and some elastomer foams. Shapes should have constant section thickness and not 'curve-back' on themselves. Parts cannot have holes or openings. Surface texture produced is good, but fine detail in mould cannot be copied. Suction holes in the mould need to be small to avoid leaving a mark on the product. Some further processing is required to complete the component as the surplus material must be trimmed off and this waste cannot be easily recycled.

Economics: the vacuum forming cycle time is limited by heating and cooling of the sheet. Normally cycle times of 5+ units a minute can be achieved. Production rate can be increased by multi-part moulds, although extra trimming will be required. Manual equipment is inexpensive; making it suitable for one-off or low volume batches, however fully automated equipment can cost over £250,000. Moulds are usually aluminium (although wood can be used for small-scale production) and so relatively inexpensive. Manual systems viable from 1 – 1,000 parts while fully automated systems, only becomes economically viable for batches over 10,000.

Typical products: thermoplastic advertising signs, bath tubs and panels, washing-up bowls, open plastic containers, food containers, packaging with a material thickness of 0.25 – 6mm. Economic batch size 10-100,000.

The thermoplastic sheet is clamped tightly in the vacuum former and

then heated until soft.

The former is forced up through the centre of the soft plastic and then the vacuum pump is switched to

suck it tightly around mould.

The formed plastic sheet is removed once cool and the excess material is cut off.

A selection of vacuum formed food thermoplastic food containers

An automated vacuum former capable of volume production of

thermoplastic components


Material Processing: Sand Casting

Sand casting involves pouring molten metal (aluminium, cast iron, brass) into a shaped impression, called a mould, made in sand.

The mould is made inside a two-part box, called a cope and drag, by packing sand around a shaped pattern. The pattern can be made from expanded polystyrene (investment casting), modelling clay, or more commonly painted hardwood. The sides of the pattern must be tapered (draft) to allow it to be removed from the sand and all corners must be rounded (filleted) to prevent stress lines forming in the metal as it cools.

The pattern is placed in the drag and fine sand is sieved and packed around. The drag is then turned over and the cope attached. Sprue pins are inserted and the sand is packed around. The pattern and sprue pins are removed leaving the mould cavity. The box is then reassembled and ready to receive the molten metal.

The molten metal is poured in through one of the sprue pin holes (runner) and as the mould fills up the gases escape via the second hole (riser). When cooled the cast object can be broken out of the sand mould.

The patterns used for sand casting are relatively cheap and easy to produce but the surface texture of the cast component tends to be poor and may require further machining or finishing. Casting does allow complex shapes to be manufactured that could not be produced in any other way.

Sand Casting: features

Materials & Shape: most metals can be cast but this process is most commonly used to form products out of aluminium, bronze, brass or cast iron. There is almost no limit to the size of a sand casting - casings over 5m wide are routinely made (e.g. ship propellers). Most shapes can be made, but the surface often has a characteristic rough finish which may need machining. Removing the extra material left from risers/gates can also greatly add to the cost of the finished product.

Economics: the basic equipment cost is low - from £500 to £3,000, however, automation and higher temperature furnaces can increase this price considerably. The limit on the production rate depends on the metals cooling time. Small parts can be produced at several per hour - large parts can take hours or even days to fully cool. The labour intensive nature of the process mean it is usually only economic for small batches but with automation the volume can be viable between 1 – 100,000 units.

Typical Products: aluminium, cast iron, brass, bronze item including engine parts, plumbing fittings, pump housings, machine tool bases, ship propellers and decorative items. The weight of product can vary from 0.3kg to 1,000kg and the minimum thickness of 5-100mm.

A turbine mould being prepared in before casting.

This features a sand core used to produce hollow shapes within the metal casting.

A selection of sand cast metal components. They all feature rounded corners (fillets), stiffening webs and

tapering sides.

A bronze church bell being cast.

Note that the sand mould has been reinforced with steel rings.


Material Processing: Die Casting

Die-casting is a highly automated process used in the mass production of aluminium, magnesium or zinc alloy components where a high degree of accuracy and excellent surface finish is required. Die-casting is used to produce items such as toy cars, military models, pencil sharpeners, car parts and camera bodies.

The molten metal is forced into the shaped water-cooled die mould where it rapidly solidifies and is then ejected. Very little finishing is required other than removal of the sprue gate and any flashes caused by leakage of material where the dies meet.

Die Casting: features

Materials & Shape: die casting is mostly used for low melting point alloys such as aluminium, zinc and magnesium. In general only small parts are made, but it can be used for components up to 20kg. Complex parts can be made with good dimensional accuracy and surface detail. A draft (taper) angle has to be incorporated to alloy easy ejection of the part. Parts are left with good mechanical surface properties. Ejector pin marks are often visible.

Economics: die casting equipment is expensive, and can cost well over £100,000 while the dies cost many thousand pounds. Dies require replacing after a few hundred thousand uses and this can take several weeks to manufacture, mean prototype testing is slow. The production rate depends on how long the part takes to cool before it can be ejected. This can give rates of 500+ parts per hour in normal conditions. Because of the high capital cost, the process is typically used for batches of 100,000+, although it may be economical for volumes between 5,000 –1,000,000 units.

Typical products: aluminium, zinc or magnesium alloy small toys e.g. cars/soldiers, hand tools, disc drive chassis, motor casings, carburettors. The weight of product can vary from 0.05kg to 20kg with a medium to high shape complexity and an accuracy of 0.15-0.5mm.

Die cast zinc engineering components.

A robotic arm used in an automated factory to remove components

after die casting.


Material Processing: Forging

The forging involves heating metal, to 60% of its melting temperature, and then hammering into the required shape. Forging is a skilled and labour intensive process that is only really suitable for one-off or low volume batch production.

Just about any metal can be forged, some of the most common include: carbon, alloy and stainless steels; very hard tool steels; aluminium; titanium; brass and copper; and high-temperature alloys which contain cobalt, nickel or molybdenum. Hot forging refines the grain structure and improves physical properties (such as strength, ductility and toughness) of the metal. The forging process can create parts that are stronger than those manufactured by any other metalworking process. This is why forgings are almost always used where reliability and human safety are critical. But you rarely see forgings, as they are normally component parts contained inside airplanes, automobiles, tractors, ships, oil drilling equipment and engines.

Forging: features

Materials & shape: any metal can be forged. The forged component is left with mechanical properties however an oxide layer forms on the surface and this usually requires further processing before finishing. One-off or very low volume batches can be forged manually by a skilled blacksmith using a hammer and anvil but for larger batches powered hammers and jigs may be used to speed up production and ensure uniformity in the component.

Economics: production rate is limited by the insertion and removal of the blank, so some form of automation is often used. As a result, machines can cost £100,000+, but can produce many parts a minute (if small). As both the machines and the dedicated dies are costly, production runs in excess of 50,000 are often needed to produce small parts economically. Large parts can be produced economically at smaller batch sizes, because there is less competition.

Typical products: metal wrought iron work including fences, gates and decorative furniture, high stressed mechanical parts such as aircraft components, chains and hand tools.

A selection of

hand forged steel components

A powered hammer being used to forge a steel engine components


Material Processing: Drop Forging

Drop forging of metal is the volume production version of hand forging. The process involves repeatedly stamping the hot metal between a punch and die using a hydraulically power hammer until the component shape as been formed.

Drop Forging: features

Materials & shapes: any metal can be forged, provided it is hot enough (60% of the melting temperature). Typical sizes for closed dies range from 10g to 10kg, depending on complexity. The part is left with good surface and mechanical properties, although cold-forging can perform even better. Complex parts can be formed using a series of forging dies with increasing levels of detail. A draft (taper) angle has to be incorporated to allow easy removal of the part. Drop forging leaves a parting line and flash (waste metal squeezed out between the die halves) on the component. The flash waste has to be removed to finish the component although this metal is recycled.

Economics: production rate is limited by the insertion and removal of the blank, so some form of automation is often used. As a result, machines can cost £100,000+, but can produce many parts a minute (if small). As both the machines and the dedicated dies are costly, production runs in excess of 50,000 are often needed to produce small parts economically. Large parts can be produced economically at smaller batch sizes, because there is less competition.

Typical products: metal spanners, pedal cranks, gear blanks, valve bodies, engine components with a typical economic batch size of 10,000 – 1,000,000 units.

A selection dropped forged

steel components

The stages in forming a typical metal

component by drop forging

Drop forging used to form a steel axle for a railway carriage.

Hand finishing the flashing on a drop forged crank shaft for the diesel engine


Material Processing: Presswork – Press-Forming

Presswork is the generic term applied to the cold working of sheet metal with shaped presses. Pressworking is among the most important metalworking processes. It is used in the manufacture a wide range of sheet metal products using processes such as blanking, piercing, drawing, stamping, pressing, spinning and bending.

Press-forming is used to produce 3D products from thin sheet metal. Examples of such items are kettles, baking tins, tubular furniture, car bodies and aircraft frames.

The dies used in press forming are expensive to produce and have to be able to with stand the many hundreds of tonnes loading exerted by the hydraulic press. The die press is made of two parts that allow for the thickness of the metal. Components start out as flat sheets, which are then blanked out, to the required shape. The large force is then used to press the blank into the required form.

Material Processing: Presswork – Drawing

The process of drawing is the main process in the production of three-dimensional curved pressings e.g. drinks cans, gas cylinders, and bullet casings.

The sheet material (blank) is placed on a shaped die, which has a highly finished surface and lubricated to minimise friction. A punch is then forced into the material, drawing it down to form the object. The depth, which can be drawn in one punch, depends on the type of material, its tensile strength and the tool design.

A selection of just some of the sheet metal product made by

press forming

A press-forming machine used to

produce simple bends on sheet metal used on building cladding

A complex 3D shape press-formed in stainless steel

The stages of drawing a drinks can


Material Processing: Presswork – Piercing & Blanking

Blanking is the process of stamping out the external shape in sheet metal.

Piercing involves punching internal shaped hole(s) in the sheet metal blank.

These two presswork processes are usually carried out at the same time when a large number of identical items are required. These processes are similar and work by passing a length of sheet metal from a coil or roll between a hardened steel punch and matching die. The punch is forced through the strip and shears the metal on the die. The shape is formed immediately in one press. This process is automated by passing the metal strip through by the exact amount on every stroke. Bicycle chains and jewellery chain links are examples of products made in this way.

A simple steel spanner for use with flat-packed furniture

is produced by blanking

A bicycle sprocket is made in one operation by blanking (outer shape)

and piercing (internal detailing)

A high speed blanking & piercing pressed use in high

volume batch production of sheet metal products

The die and punch, waste material and the blanked sheet steel component


Material Processing: Presswork – Spinning

Spinning is a simple process used to form symmetrical hollow objects such as bowls or vases out of sheet metal.

The metal blank is pushed against a rotating wooden former using the lathe tailstock. A forming tool is used like a lever to wrap the metal blank against the former. The uneven edge is then machined off.

Presswork: features

Materials & shape: mild steel less than 6 mm thick is the most common press formed material. Blanking (shearing) is used to cut parts for subsequent processing, sheet is shaped with bending (1-D) and drawing (2-D), pressing contains elements of all three. Surface finish is usually good, but this is dependent on good quality die design. A wide variety of shapes can be made, but die design must account for the elastic 'springback' of the sheet after forming. Some scrap is always produced and cannot be directly recycled.

Economics: primarily used when near-net-shape (finished form) processes are impractical in terms of time or materials e.g. for car body panels. Simple manual equipment can cost only a few thousand pounds, but is only used for prototyping and small batches as the production rates are low. Automated tooling (which can be expensive) is usually dedicated to individual components, so is normally only used for long production runs in order to be cost-effective. Economic batch size 25,000-250,000 with automated production rate being very high (drinks cans can be produced at almost a 1,000 a minute).

Typical products: sheet metal from 0.2-6mm thick in products such as cans, washing machine cases, car body panels, kitchen utensils, hubcaps, metal desks etc.

A sheet metal lampshade being formed by spinning

A selection of the sheet metal product that are manufactured

by spinning

Mild steel car body panels: blanked, pierced and press

formed ready to be spot welded together


Material Processing: Wood Turning

Woodturning is the process used to form round or cylindrical timber objects on a lathe.

There are two methods of turning, between centres and faceplate turning. Turning between centres is used to produce long cylindrical items such as table legs. Turning with a faceplate is used to produce items such as bowls or bases. As the timber rotates, special shaped chisels are used to remove the waste using a cutting or scraping action. When mass-producing a product, like turned staircase spindles, the process is automated. Traditional this was done on a copying lathe where an inexpensive plywood profile was used to repeat the shape however; these have been phased out in favour of CNC (Computer Numerically Controlled) lathes which convert a CAD (Computer Aided Drawing) file into a set of control instructions which automatically operate the cutting tool. This helps to ensure accuracy, reduce the lead-time between the design and manufacture, allows small batch production to be automated and increases productivity by machining the items quickly again and again.

Wood turning: features

Materials & shape: most timbers can be turned into circular and cylindrical forms. Turning produces a good quality surface although the product will require some form of finishing in order to protect and enhance the timber. The turning process involves the removal of timber to form the product and hence this process produces unusable waste material.

Economics: primarily used to produce finished components. Manual turning is used for one-off or small batch production while copying or CNC machines are used for larger volumes. Basic manual lathes can cost less than £1,000 while CNC equipment £10,000+.

Typical products: solid timber cylindrical products such as stair spindles and newel posts, tool handles, bowls, vases, table and chair legs and rails etc.

A CNC wood lathe used to automatically turn component

using the CAD information

A selection of timber product produced by wood turning

A copying lathe using a plywood profile to repeatedly turn identical pine table legs

A mahogany table with four identical legs machined on a

CNC wood lathe

A pine staircase with the spindles machined on a CNC

wood lathe


Material Processing: Metal Turning

Metal turning lathe is used to form cylindrical or conical shapes in metal and some types of plastic.

The material is held firmly in a rotating chuck while a shaped cutting tool removes the waste using a simple wedging action. A variety of processes can be carried out on the lathe for example turning cylinders, creating texture (knurling), accurate drilling and threading.

When mass-producing a component the turning process is automated. This machining is carried out automatically using a CNC (Computer Numerically Controlled) lathe which converts a CAD (Computer Aided Drawing) file into a set of control instructions for the cutting tool. This helps to ensure accuracy, reduce the lead-time between the design and manufacture, allows small batch production to be automated and increases productivity by machining the items quickly again and again.

Metal turning: features

Materials & shape: most metals and certain polymers can be turned into circular and cylindrical forms. Turning produces a good quality surface. The turning process involves the removal of material to form the component and hence this process produces waste which is difficult to recycle.

Economics: turning is primarily used to produce finished components rather than products. Manual turning is used for one-off or small batch production while a CNC machines are used for larger volumes. Basic manual lathes can cost less than £1,000 while CNC equipment £10,000+.

Typical products: metal products such as engineering components, bolts etc.

A selection of the components machined on a metal turning

lathe

A CNC metal lathe used to automatically produce

components. Note the ejector chute to remove the machined

components.

A CNC metal lathe machining a steel billet into a component

A cast aluminium alloy piston with

the end machined on a CNC metal lathe before fitting in the

motorcycle engine


Material Processing: Milling

Milling is a machining process used to remove waste metal or polymer in order to produce 3D forms out of solid block.

The material is securely clamped to the machine table and then the whole assembly is fed across a rotating multi toothed cutter to shape the component. The machines used industrially can be extremely sophisticated - the cutting head is often able to twist and turn in many directions!

When mass-producing a component the milling process is automated. This machining is carried out automatically using a CNC (Computer Numerically Controlled) mill which converts a CAD (Computer Aided Drawing) file into a set of control instructions for the cutting tool. This helps to ensure accuracy, reduce the lead-time between the design and manufacture, allows small batch production to be automated and increases productivity by machining the items quickly again and again. Milling: features Materials & shapes: almost any material can be milled, although difficulties arise with very brittle materials (e.g. ceramics) and very hard materials (e.g. tool steel). Milling is used in metals primarily to shape parts by cutting edges, slots or grooves. It is often used to complete parts that have been formed by a near-net-shape process (e.g. casting or forging). Milling is unusual for wooden products, although variants such as routing can be used to form grooves and mouldings. Economics: milling machines vary in price from £1,000 to £1,000,000. Milling is generally a very slow way to produce a component - but it can be economic for prototyping or small batches. High speed machining centres are used where the accuracy of milling is required to finish a component. The cost of milling on a commercial scale is often a balance between higher speed and longer tool-life. Typical products: metal or polymer components formed from a solid billet of the material or used to finish casting (e.g. top of engine block).

A selection of milled metal components showing the level of detailing possible

A manual milling machine used for one-off or low volume batch

production A boat’s propeller being

milled out of solid brass as an alternative to casting

A CNC milling machine which uses the CAD drawing to generate the control

program for the movement of the

cutting tools

Titanium golf putter machined on a CNC

mill


Material Processing: Routing

A router is a versatile piece of equipment which can perform a variety of different tasks. It may be used to:

Cut detailed profiles along the length of a wooden board similar to a spindle moulder;

Form intricate joints for furniture using a jig to guide the cutter;

Act as an engraver for 3D lettering or other sign writing applications;

Cut detailed 3D shapes out of a range of sheet materials similar to a milling machine.

In its least expensive form the hand operated power router it can be used to produce groove, housings, rebates and moulding in manufactured board or solid timber. The hand router consists of a powerful high-speed electric motor with a chuck which can hold a wide variety of shaped tungsten carbide cutters. Industrial CNC (computer numerical control) routers have the motor and cutter mounted on moveable arms operated by computer. This technology allows the manufacturer to convert CAD (computer aided drawing) files automatically into control programs for the router which can shape, groove, pierce, or even form text in the timber.

Routing: features

Materials & shapes: traditionally routers are used on timber and manufactured board, especially MDF which has excellent machining characteristics; however, modern CNC equipment can be used on most sheet material including polymers and soft metals such as aluminium. A router can be used to cut grooves or rebates, form joints such as the mitre used to join kitchen work surfaces, machine intricate 3D shapes and to pierce and engrave the surface of the material.

Economics: routers vary considerable in price from a few hundred pounds for a hand operated power tool to a large scale CNC machine costing tens of thousands of pounds. Routing is generally a very slow way to produce a component - but it can be economic for prototyping or small batches. Power tool routers are generally used by tradesmen for one-off or low volume batches while large CNC routers are economical for medium sized batches. Routing involves removing waste material to form the component and this cannot be easily recycled.

Typical products: manufactured board or solid timber or sheet polymer or softer metals used to for small to medium batches of components such as panelled doors, wood joints, engraving, decorative mouldings, piercing and lettering for sign writers etc.

A selection of routed components showing the level of detailing possible

A jig used to router a traditional dovetail joint for the low volume

batch of pine box A range of sheet materials

formed using a CNC router by a sign writer

A guitar being machined out of a solid board of mahogany

using a CNC router

A selection of tipped cutters

for a hand power router

A shape pierced out of sheet

aluminium on a CNC router


Material Processing: Laminating

Laminating is the process of building up a component or product out of a number of layers. Laminating can be used with manufactured board, timber or polymers to produce shapes and sizes that would not be possible to manufacture otherwise.

Glue laminating (glulam) of timber is used to produce curved and straight beams or structures. Glulam components available off-the-shelf in a range of standard cross section and lengths of 10, 12 and 15 metres but it is also possible for these beams to be made to low volume batches for specific projects.

When forming curves the timber is first softened using chemicals, microwave irradiation, or steam boiling, although steam boiling is the simplest and cheapest method and it takes 1 hour per 25mm thickness. The softened timber is then bent around former mould using clamps or a hydraulic press. Bending is more economical than machining a curve because there is no waste and the end product is stronger and less vulnerable to breakage.

Laminating Wood: features

Materials & shapes: solid softwood timbers and plywood are traditionally laminated. Standard cross-sections and lengths are available off-the-shelf but custom made beams or structural components can be manufactured. These are all tested and given a British Standard institute (BSi) rating guaranteeing their strength. Laminated timber can be used for roof and floor beams, columns, and rafters in almost any type of structure where it offers a low cost, attractive alternative to steel. The wood can be fire proofed, pressure treated with preservatives or finishes.

Economics: off-the-shelf stock is inexpensive and the standard length allow for road delivery. Since wood is a renewable resource, glulam is an ecologically attractive alternative to steel and concrete (it takes ten times more energy to make a steel beam than to make an equivalent laminated timber beam).

Typical products: glulam is used extensively in the construction industry for building beams, columns while steam bending of solid and laminated timber is used in furniture making, traditional boat building and sports equipment.

Laminated pine building joists

Curved laminated pine roof

A solid ash chair back being bent around a former after

steaming The steamed timber is clamped

around a former overnight

Laminated and steam bent

building beams

Laminated and steam bent tennis rackets


Material Processing: Laminating Composites

Laminating involves building up layers of thin plastic sheet over a simple shaped mould.

Typically, laminating is used to form Glass Fibre Reinforced Plastic (GFRP) or Carbon Fibre Reinforced Plastic (CFRP). Here woven fibre matting is soaked with thermosetting polyester resin and laid-up in the mould. Once cured the shaped composite has an excellent strength to weight ratio.

For low volume or one-off production hand lay-up is used. This is particularly suited for products that are medium to large in size, with simple shapes, requiring only one smooth finished surface.

For a large batches volume spray-up moulding is used. Parts produced by spray-up include boat hulls, swimming pools, bus roofs, reinforced acrylic bathtubs etc. The process consists of simultaneously spraying onto the mould, chopped glass strands and the resin. After spraying onto the mould hand rolling is used to flatten or compact the mixture well onto the mould and, as far as possible, eliminate air bubbles.

Laminating Composites: features

Materials & shapes: hand lay-up is perhaps the most familiar process. It can be used for components of virtually any size, but usually simple shapes. Similar shapes can be made by spray-up, which is faster but more expensive. Both process can suffer from quality problems - using vacuum bagging to suck the material tightly against the mould walls can reduce these issues.

Economics: there are few composite forming processes, and the decision of which to use is normally determined first by shape and type of fibre (chopped or continuous), and then by volume of production. In general, composite forming is more expensive than in other material classes. This is primarily because of the slow production rate due to the curing time of the resins. Hand lay-up equipment can cost under £100, but good quality moulds can cost significantly more and have a lead time of several weeks. It is useful for prototyping or where only a few parts are required. Spray-up can be automated and so is usually used for mass production.

Typical products: GFRP and CFRP are used for boat hulls, propeller blades, baths, water tanks, structural cables, rocket noses, turbine blades, golf clubs, tennis racquets, bicycle frames etc.

Laminated glass fibre reinforced plastic (GFRP)

garden pond

Spray-up moulding of glass fibre reinforced plastic (GFRP)

A laminated Carbon fibre hull on a Swedish stealth patrol boat


Assembly Processes: Adhesive Bonding

Glues allow a wide variety of different materials to be quickly and easily joined. Once cured, this permanent fixing method will often have a greater strength than that of the actual material it is joining. Adhesive bonding was first used for load-bearing joints for aircraft in World War II. Significant advances have been made in the technology since then, but it has still to be widely used industrially for metals.

Adhesives are available in many forms including: liquids, pastes, powders, tapes and films. Adhesive bonding is often combined with mechanical joining - 'super glue' was first used to prevent nuts on machinery shaking loose.

Adhesive bonding is a widely used joining process in the fabrication of engineering products. It forms an essential part of the laminating process in multi-material sandwich structures and it is also used for structural connections between multi-material components. Adhesive bonding is achieved by placing a 'liquid' or semi-liquid material between the components to wet the joint surfaces. Solidification of the liquid, usually by chemical reaction, then provides the joint strength.

Adhesive Bonding: features

Materials & shapes: any materials can be joined, although some may require special surface preparation. Especially useful for joining different materials or very thin materials. The mechanical properties of adhesive joints can be very good, but they usually have poor resistance to 'peeling'. The strength also deteriorates with temperature and is rarely useful above 100-2500C. Adhesive joints can provide additional benefits as well as joining, including: sealing, insulation, corrosion protection and vibration damping. Correct design of the joint is essential for it to be strong. One method is to increase the area, so lap joints are better than butt joints; another

Economics: equipment costs (unless automation is required) can be low, although the cost of the adhesives themselves can be significant. Where good joint quality is essential, special equipment such as fixtures, presses and ovens are required which can significantly add to the cost. The production rate is often limited by the curing time, which can range from a few seconds to many hours (think of 'super glue' and 'araldite' as common household examples).

Typical products: car mirrors, brake linings, helicopter blades, laminated glass, packaging etc.

A selection of different configurations used in

adhesive bonding of materials

The very large composite deck structure weighing 7 tonnes is attached to the aluminium deck by adhesive bonding


Assembly Processes: Welding (metal)

Welding is a permanent way of joining metal components and this technique is used with 70% of the all the steel produced in the UK. Welding applications range from largest structures to the micro joining of electronic circuits.

There are several types of arc welding - MMA (Manual Metal Arc) is probably the most well known. Automated arc processes include TIG (Tungsten Inert Gas) and MIG (Metal Inert Gas). All arc processes use a filler to join the two pieces - in MMA and MIG the filler also serves as the electrode which makes the electric arc. In manual arc welding, a welding rod is struck over the surface of the metal and then just lifted off. The electrical current jumps across the gap and carries the molten steel from the rod to form the weld. At the same time the flux covering on the welding rod forms a protective skin over the weld which can be chipped off when the weld cools. Safety precautions must be taken to protect the welder from the bright arc and the noxious fumes. Good welding requires a lot of skill, and in industry a welder must have special qualifications.

There are other more specialist arc welding processes such as spot welding or seam welding which are used on sheet steel and work without a filler. They rely on the electrical current melting the two surfaces together and forming the weld

Manual Metal Arc (MMA) Welding: features

Materials & shapes: although many metals can be joined with MMA, it is most commonly used for steel. Other materials, such as aluminium, are usually joined by more sophisticated arc welding processes (e.g. MIG, TIG). MMA is portable and so suitable for repair or on-site work. Thin plates may require only one pass for a successful join. For thicker plates, multiple passes may be required to fill the gap. For thin plates, the edges may be square. For greater thicknesses, the edges need to be bevelled to allow the gap to be filled more easily. In the area that has been affected by heat, the properties of the material may change greatly.

Economics: the cost of MMA equipment can be less than £100. However, the production rate is slow so it is only economic for one-off jobs, repair work and difficult access situations.

Typical products: metal components such as car bodies, ships, oil rigs, pipelines, pressure vessels.

A 200 tonne steel water cooler assembled by arc welding

Manual Arc welding of steel

Manual and automated spot welder used on sheet steel products such as car body panels

Seam welding where two round copper electrodes roll along the edge forming the weld. This technique is limited to products where the

electrodes can follow the outside profile such as in the sheet steel fuel tank for a car

Laser spot welding is used to join the 3 stainless steel razor blades with 13 welds in a cycle time of

1 second

Titanium bike frame TIG welded together


Polycarbonate lens ultrasonically welded onto the ABS body

Assembly Processes: Polymer Welding

There are three main types of welding used with thermoplastic polymers; ultra sonic, friction and laser welding.

Ultrasonic welding involves the use of high frequency sound energy to melt the thermoplastic at the joint. Parts to be joined are held together under pressure and are then subjected to ultrasonic vibrations. When ultrasonic vibrations stop, the molten material solidifies and a weld is achieved. The resultant joint strength approaches that of the parent material; with proper part and joint design, hermetic seals are possible. Ultrasonic welding allows fast, clean assembly without the use of consumables. Since ultrasonic welding is very fast (weld times are typically less than 1 second) and easily automated, it is a widely used technique in mass production.

Friction welding is a technique in which the heat needed to melt the material is generated by pressing one of the parts to be joined against the other and rapidly vibrating it. The heat generated by the resulting friction melts the material (either thermoplastic or metal) in 2-3 seconds. The vibration is then stopped and the parts are aligned, and held together under pressure until a solid bond is formed. Such bonds are permanent, and have a strength approaching that of the parent material.

Lasers are a versatile tool which can be used in welding, cutting, engraving, marking, drilling and polishing of polymers and metal. Lasers are non-contact, zero-wear and are capable of precisely delivering enormous amounts of energy to specific, highly localised areas. Because plastics melt at low temperatures and vaporize very easily, only a small amount of heat input is needed to make the surface of the plastics slightly fluid. In fact, the influence required for laser welding is far lower than is needed for any other plastics application

Friction Welding: features

Materials & shapes: usually, at least one of the parts to be joined must be circular - this can be solid or hollow. One of the materials to be joined must soften before melting. Used to join different materials to each other (e.g. polymers to metals).

Economics: basic equipment costs around £10,000, but automation can increase this significantly. Most suited economically to joining pipes and attaching studs. For similar metals, competitive with arc welding for the geometries it can do. But because of the capital cost, it is not competitive where only a small number of joints are required.

Typical products: thermoplastic and metal components such as pipes, two-part bumper, fuel tanks, fuel pumps, expansion vessels, instrument panels, air channels, parcel shelves, inner door panels, spectacle frames, motor saw housings, heating valves etc.

Friction welding a steel stud onto a plate by placing it in a drill and rotating at high

speed

A laser was used to cut, engrave and weld the polymer

pendant

The principles of friction welding

Polymer welded onto the titanium frame


Assembly Processes: Riveting

Riveting is an old established technique which is used to permanently join materials together. Traditionally riveting was solely a manual technique where a hole is drilled through the materials, the rivet is inserted and then hammered until it expanded and joined the pieces together. On large engineering projects such as shipbuilding and civil engineering, the steel rivets were heated to red hot and then formed with a pneumatic or hydraulic hammer (this has been replaced by welding or bolting). Today riveting usually involves pop or self-piercing riveting. Self-piercing riveting is a one-step joining technique suitable for ductile metal and polymers up to a maximum thickness of 10mm. As it relies on a mechanical interlock to form the permanent join and it can be used on materials and combinations of materials where, for instance, spot welding is difficult or even impossible. Self-piercing riveting involves driving a pipe shaped steel rivet with plane solid head into the two layers of the materials using a pneumatic gun. The rivet makes its own hole and joins the parts together in one moment. Self-Piercing Riveting: features

Materials & shapes: self-piercing riveting is a simple; one-step joining technique that relies on the mechanical interlock to join sheet materials together up to a maximum of 10mm in total thickness. The nature of the process means that only ductile non-brittle sheets can be joined using this technique. The pipe shaped steel rivet is forced through the surface of the two materials joining them together. It offers a good fatigue performance, often better than spot welds and can be used for many different combinations of materials. Joining of more than two sheets is possible.

Economics: it is a fast process which can readily be automated for large batch production. Unlike welding there are no fumes or heat produced and little noise emission. There is little or no damage caused to pre-finished materials and the tooling has a long life (20,000 joints are possible without maintenance). Typical products: ductile sheet metal and polymer components such as automotive, heating, ventilation and building industries, for pre-painted steels for white goods, and for joining aluminium used for road signs.

A hot steel rivet being formed by a pneumatic hammer

Pop riveting is used to join thin pieces of metal or polymer. The pop rivet has two parts; the pin and the rivet. The pop rivet pliers are used to pull the pin through the rivet and as this happens the rivet is deformed so that it joins the pieces together. This process is used on thin metal or plastic where the joint does not have to be very strong and it is ideal for situations were access can only be gained from one side such as in heating and ventilation ducting and air frame construction. Pop riveting is a relatively slow technique which does not lend itself to large batch production due to the need to pre-drill holes before forming the rivet.

Pop rivets and an air operated pop rivet gun used to join sheet aluminium to an

aircraft wing

A robotic arm with a self-piercing riveter used for high volume production

A cut through a self-piercing rivet showing clearly how it joins the sheets together


A selection of just some mechanical fastenings available

A nut and bolts allowing a semi-permanent joining of a wide range of materials. Bought inexpensively off-the-shelf from specialised

manufacturers

Cam KD fitting allowing flat-packed furniture to be easily assembled at home

by the purchaser using just a screwdriver.

Assembly Processes: Mechanical Fastenings & Knock-down fittings

Bolts, screws and patent fixings are a semi-permanent way to assemble a range of different material components. These are bought ‘off-the-shelf’ from specialised manufactures and come in a variety of different forms. They allow products to be assembled on a semi-permanent basis using simple tools like a screwdriver or spanner. Some form of mechanical joining needs to be used where products need to dismantled

during their normal life, e.g. where repair or maintenance is likely. With the move towards efficient recycling, there is likely to be increased use of mechanical fastening.

Most modern furniture comes flat-packed for ease of transport and to keep costs down. Knock-down (KD) fitting have been developed to allow furniture to be assembled at home with just a few simple tools.

There are hundreds of different types of KD fittings produced by specialist manufactures, for example a carcass could be formed with nylon corner blocks or bloc-joint fittings. Much furniture is sold in flat packs. This makes it easy to transport and store. The customer then has to assemble it at home. Box joints are formed with corner blocks or bloc-joint fittings. Usually these are made from a plastic (often nylon).

Mechanical Fastenings: features

Materials & shapes: virtually any material in any shape can be joined by mechanical fastening - given enough ingenuity! Practical limitations come from being able to form holes - this limits the options for ceramics and composites. Snap-fit joints are especially suitable for low stiffness materials like polymers. Especially good for joining different materials (e.g. composite to metal). Joint quality is reliable and readily determined, given sufficient operator skill. However, mechanical joining usually reduces fatigue life. Essential where two parts will move relative to each other (e.g. hinges for doors). The non-permanence of many fasteners is useful for products that may need repair/maintenance or need access to the interior. Economics: can be economic for any batch size from one-offs to mass production (with or without automation). Ease of mechanical joining (especially with snap fits) means low skilled workers can be used. For fasteners, there can be a significant stock cost in ordering and keeping track of so many components! By far the dominant means of joining parts. Competes with welding for thick metallic sections where a permanent joint is needed. Competes with adhesives for polymers and woods where a permanent joint is needed.


Finishing Processes: Aqua Transfer Printing

Aqua transfer printing (cubic printing) is a decorative finish which is ideal for complex 3D shaped polymers, metals and other materials. The finish uses a printed film to cover the product which can have a range of natural and abstract patterns including wood grain, marbling, leather, textures and abstract designs.

Aqua transfer printing is an immersion process used to provide the product with an eye-popping finish. During the manufacturing process, a printed water-soluble film is set on the surface of water. The film dissolves in the water, leaving the decorative inks floating on the surface, similar to a film of grease. As the product is immersed, the ink film is evenly applied to the piece by the static water pressure. After drying, the parts are coated with a clear protective lacquer. Aqua transfer printing is used in the automotive industry to create mock-timber dashboards and mobile phone fashion covers are also printed the same way.

Finishing Processes: Powder Coating

Powder coating is a finishing process suitable for metal, wood and polymers. It is a dry finishing process which has the advantage that unlike paint it contains no solvents and as a result it is environmentally friendly with up to 98% of the material used due to the recoverable and reusable capabilities of the powder. In addition, powder coatings provide excellent wrap-around coverage and are easily applied. Compared with liquid sprayed coatings, powder coatings can result in a thicker, single coat film build. Finally, the cured coating has an extremely durable finish that adheres well to the component and provides a superior coating hardness along with increased resistance to scratching, impact damage, stains, and chemicals. The process is usually set up as part of a line production where the components are attached to a moving overhead conveyor where an electrostatic charge is applied. The powder is charged with opposite polarity and is sprayed onto the components. The charged powder particles are attracted to and stick on the surface of the components. The components then move into an Ultraviolet (UV) oven where the powder completely melts and flows out within 2 minutes and finally cures under UV exposure within seconds.

Aqua transfer printing used to

apply the decorative finish to the body panels of the Smart car

Electrostatically charged powder attracted to the

oppositely charged component.

The cured powder coated component move

out of the UV oven on the overhead conveyor

Smeg mild steel fridge powder finished in a

range of colours


Finishing Processes: Varnish & Lacquering

Varnish is a clear or coloured finish applied to timber and manufactured board products to protect and improve appearance while lacquering is a clear finish applied to metals and polymers to prevent tarnishing and scratching.

Varnishing is made up of a combination of oils and resins in any number of variations. Varnishes are typically classified as either oil, synthetic or spirit varnish.

Oil varnish can further broken down into three groupings based on the amount of oil in their make-up: short-oil, medium-oil, and long-oil varnishes. Short-oil varnish dries to a high hardness and can be rubbed to a high gloss sheen, making it a good choice for the fine finisher. Long-oil varnishes resist wear-and-tear best, so they are good for outdoor work and boats. Medium-oil varnishes have a combination of the short-oil and long-oil qualities.

Synthetic varnish is a man-made finish that is the most versatile of the varnishes. Polyurethane varnish is the most common used today. It dries reasonably fast and very tough (it is the most scratch-resistant of the varnishes).

Spirit varnish is made of a solution of natural gum resin. Shellac is the most common gum resin and this comes from shell of the Lac beetle in India.

The application of the varnish depends upon the size and batch volume of the product or component. Small volume production can be finished by manually with the wood sanded by hand with power tools and two or three coats of varnish applied by brush or spray. For volume production the components may be pre-finished by the material supplier using a fully automated system. Here rotating spraying gun technique is used to produce perfectly uniform finish. The process is completed with a water suction unit and mat conveyors for the recovery and the re-use of the varnish before the components are passes through an in-line ultraviolet (UV) oven which rapidly cure the varnish.

Line production and finishing of kitchen doors. This automated process involves the sanding, spraying and drying of the wooden components

Vacuum cleaner casing spray lacquered on by a robotic arm as it moves along a conveyor belt


Finishing Processes: Painting

Paint is a decorative and protective finish suitable for wood, metals and polymers. Paint can be applied manually by brush or roller; however, these are usually unsuitable for anything other than one-off production. Batch production usually involves applying the paint by spraying. Here the aim is for high transfer efficiency. That is to ensure that a high percentage of paint actually ends up on the product and not lost in overspray. The higher the efficiency, the less coating that is wasted. Factors affecting transfer efficiency include spray equipment type, size and shape of the component, coating type, skill level of the spray operator, air velocity, atomisation air pressure, fluid flow rate and fan size.

Paint is not a particularly environmentally friendly process with the amount of waste material, the nature of certain solvents used to carry the paint pigments and the fine paint spry which is dangerous when inhaled. Depending on the application the paint finish may have to be re-applied every few years and hence it is not always the maintenance free option.

If the entire product is not to be painted then the unfinished areas have to be thoroughly masked.

Finishing Processes: Anodising

The anodising process, performed on aluminium and titanium usually for protection and cosmetic purposes, builds up both on the surface as well as into the metal. The finishing layers are durable and abrasion resistant and can be made in different colours (silver, brass, gold, red, violet, green, blue and black) depending on the chemicals used. The anodised parts are quite durable and do not tarnish and maintain their cosmetic appearance for a long period of time.

The aluminium or titanium component being anodised is placed in an electrolyte (commonly of sulphuric acid) solution and used as the anode. When an electrical current is passed through the solution, oxidation takes place and a protective scratch resistant oxide layer forms on the surface.

Industrial finishing of components using

spray painting

Anodised aluminium pipes being removed from the electrolytic tank

A selection of aluminium products finished by colour anodising

Anodised titanium motorbike exhausts


Finishing Processes: Galvanizing

Galvanizing is a surface finish applied to steel products by immersing them in molten zinc. The zinc coating protects the surface against corrosion by shielding the steel from the moisture in the atmosphere and if the surface is damaged the zinc provides sacrificial protection and prevents rusting.

No other protective coating for steel provides the long life, durability and predictable performance of galvanizing. The hot dip galvanizing process is adaptable to coating nearly all types of fabricated and non-fabricated products such as wire, tanks, crash barriers, hand rails, sheets, strip, pipes and tubes, fittings, hardware, wire cloth, hollow-ware, and structural assemblies.

Finishing Process: Summary Table

Finish Type Application Typical Material Uses

Varnish Hand brushed for small batches or sprayed for the best quality finish.

Most timber and certain manufactured boards.

Interior and exterior woodwork, furniture, boats

Vegetable Oil Hand applied with a cloth rubber used on timber which is used with food stuffs

Beech and other close gained timber.

Wooden spoons, bread and chopping boards

Creosote This exterior finish is brushed or sprayed on.

Soft or hardwood used for rough exterior work

Garden sheds and fences

Stain Appling a colour finish to timber sprayed or brushed onto the surface

Hard and softwoods. Timber toys, furniture

Paint Covering with a layer of paint. Protection lost when scratched

Inexpensive softwoods, man-made boards & steel

Interior and exterior wood, large steel structures - ships

Dip Coating Polymer coating used to protect metal component.

Generally used on mild steel products

Wire fridge and dishwasher shelves. Insulation on tools

Tinplating Coating with a layer of tin. Protection lost when scratched

Mild steel sheet covered with tin on both sides

Food and drinks cans

Galvanising Coating with a layer of zinc. Protects even when scratched

Mild steel Bins, crash barriers, step hand rails, car body panels.

Anodising A protective and decorative colour finish produced by electrolysis.

Aluminium and titanium Pots and cooking utensils, bike components.

Chrome plating Coating with a layer of chromium. Protection lost when scratched

Steel, brass, copper Pipes and decorative work. Cheap alternative to stainless steel.

Aqua transfer printing

Paint film is dissolved in water and the product is immersed taking the pattern.

Mainly metal and polymers Telephone cases, wood effect dashboards.

Powder coating Covering with a layer of plastic to produce a tough scratch resistant finish

Wood (mainly MDF), metal and polymers.

Electrical and office equipment

Galvanised steel bins being removed from the liquid zinc

Galvanised steel crash barriers

require no further finish for

years of rust free service

Small steel components like nails are galvanised by dipping into zinc

held in a wire basket


MANUFACTURING PROCESSES: SUMMARY TABLE

W

oo

d P

roc

es

se

s

Process Production

Volume Unit Cost Typical Materials Typical Products Identifying Features

Wood Turning Low - medium Medium Hard & softwoods Furniture, stair parts Cylindrical symmetrical timber products

Routing Low - medium Low MDF, hard & softwoods furniture Wood goods with circular machine marks

Spindle moulding Low - medium Low Timbers & MDF Skirting boards, picture & dado

rails Wooden lengths with uniform cross section with no

internal detail possible

Laminating Low - medium Medium Softwoods Glulam roof beams Thick wood beams (some bent) made up of a series of

timber strips glued together

Knock Down Joints Low - medium Low Manufactured boards Flat-pack furniture Pre-drilled holes on board

Finishing Low - high Medium All materials Most wood & metal products and

some polymer goods Clear or coloured surface that protects and enhances

the product

Me

tal

Pro

ces

se

s

Metal Turning Low - medium Low Any, but mainly steel Engineering parts Cylindrical symmetrical metal parts

Milling Low - medium Medium Metal and polymers Engineering parts Crisp metal parts with square internal corners and

circular machine marks

Sand Casting Low - medium Medium Aluminium, brass, cast

iron Metal engine parts, plumbing

fittings Metal parts with rounded internal corners and a grainy

finish with webs and bosses around holes

Die Casting Medium - high Low Aluminium, zinc & magnesium alloys

DVD chassis, model toys, engine parts

Small fine detailed metal castings with split lines, flash and ejector pin marks.

Forging Hand: low Drop: med

Hand: med Drop: med

Most metals but mainly steel alloys

Wrought iron furniture, railings, engine parts, tools

Metal goods with a poor finish: split lines, & flash (drop forged) and hammer marks

Extrusion (metal) Medium - high Low Aluminium, copper, steel,

stainless steel Tubing, window frames, channels

Metal lengths with uniform cross section requiring no further finishing

Piercing & Blanking Medium - high Low Sheet metal mainly steel Metal cans, electrical casings Sheet metal with shear marks at the edges and holes,

thinning of the metal at bends.

Arc Welding (MMA) Low - medium Low Steel (aluminium, stainless

steel & titanium with MIG/TIG)

Permanently joining steel products – buildings etc

Rippled mound running along the joined pieces.

Spot Welding Low - medium Low Sheet steel Car body panels Sheet steel goods with circular marks

Riveting Low - medium Low /med Sheet material White goods Round (some hollow) heads at the join

Bolting & Threading Low - medium Low Most materials Items that require maintenance Hexagonal or slotted head

Adhesives Low - high Medium Most materials Permanently joining materials Little but dissimilar materials joined possible indicates

the use of glue

Po

lym

er

Pro

ces

se

s Injection moulding Medium - high Low

Thermoplastics some thermosets & elastomers

Electrical casings, containers, plumbing items

Small, precise, polymer components with fine detailing, thin walls including injector sprue and ejector pin marks

Rotational moulding Low - medium Medium Thermoplastics (mainly

PE) and some thermosets All large polymer goods - wheely

bins, tanks, buoys Large polymers items with no injection marks but with

join lines and flash

Extrusion (plastic) Medium - high Low Thermoplastics – PVC, PE

and PP Pipes, cables, window frames

Lengths of polymer with uniform cross section requiring no further finishing

Vacuum forming Low - medium Low Thermoplastics – ABS,

PA, PC, PS Fridge liners, baths, food

packaging Thermoplastic sheet with tapered sides, no fine

detailing and trimmed outer edge

Blow moulding Medium - high Low Thermoplastics – PE, PP,

PET Hollow bottles and containers Hollow polymer goods with join lines and flash

Laminating Low - medium High Carbon or glass fibre Sports goods, cars, boats One smooth side (next to mould) and one rough side

with the fibre visible

Compression moulding

Medium - high Medium Thermoset & elastomers Electrical fittings, pot handles and

dishes Thermoset goods with no injection sprue but may have

split lines with flash and ejector pin marks


SECTION B: RAPID DESIGN & MANUFACTURE

Computer Aided Design (CAD)

Over the last 20 years the computer has replaced the drawing board as the means of producing detailed 2D working drawing.

Computer Aided Drawing (CAD) offers many advantages to the designer:

• Drawing mistakes can be easily corrected. • Library of standard components or details can be created and then used again and again. • Commands like mirror image and copy, allow components to be rapidly drawn. • Dimensioning and scaling can be added. • The size and shape of all or part of a drawing can be altered. • Drawings held electronically can be stored, retrieved, displayed, E-mailed and printed as and

when required. Recently with the advent of more powerful computer systems, industry has moved away from 2D CAD to use 3D CAD modelling software.

3D Modelling software offers all the benefits of 2D CAD but has additional advantages to the designer:

• 3D images can be rotated and rendered to appear lifelike. These images can be used for advertising and to allow the client and/or customer to comment on aesthetics.

• 3D models can automatically generate 2D orthographic views. • Individual 3D components can be assembled on screen to check if the product will actually fit

together. • 3D computer models can be automatically converted into physical models using a Rapid

Prototyping (RP) process. • Products can be tested more quickly. • Costly mistakes in design or production can be avoided • Reduce the lead time for new product introduction.


CAM (Computer Aided Manufacture)

Computer Aided Manufacture (CAM) allows complicated products or components to be manufactured very accurately and at speed using Computer Numerical Controlled (CNC) machines. These machines often perform many different operations and allow components to be cut, shaped, turned, drilled and milled, while all the operator has to do is to change the material and maintain the tools. The introduction of CAM systems has greatly reduced the lead-time; that is the time between design and selling of the product.

CNC (Computer Numerical Control)

Almost all manufacturing companies have changed over from manual to Computer Numerical Controlled (CNC) versions of lathes and milling machines etc. This enables components to be design on a Computer Aided Drawing (CAD) system and then automatically converted into a Computer Aided Manufacture (CAM) program for the control of the CNC machine. This software program will control the entire process and allow the machine to produce identical components quickly and accurately:

Numerical controlled machines such as lathes, mills, drills and punch presses, have their movements and functions controlled by a programmed set of numbers. Once the computer has been programmed automatically from the CAD file, the machine tool will perform the set of functions over and over again to produce many identical components.

Advantages of CNC Disadvantages of CNC

Consistent accuracy Initial machine cost Increased productivity Maintenance and servicing costs Less operator involvement Installation costs Complex shapes easy to machine Operator training Tooling costs reduced Component rejection reduced Uniformity of product Can operate unattended

CNC laser cutting sheet steel plate for a ships hull

CNC router cutting a shape on a timber board

CNC milling machine forming an aluminium part

CNC lathe forming a steel part


Rapid Prototyping (RP)

Traditional engineering relies on removing material to manufacture a component; it is a subtractive process. For example, a Computer Numerically Control (CNC) milling machine will cut a component out from a solid block of metal. Rapid Prototyping (RP), by contrast, adds material layer after layer until a engineering prototype model of the component has been produced. This layering enables complex forms to be generated in one piece that would otherwise be impossible to model. Why Rapid Prototyping (RP)?

• Product designers prefer to have a physical model to see, feel and test rather than just a line drawing or computer image;

• Complex forms can be manufactured in one piece which may be impossible to make otherwise;

• RP enables exceptionally accurate models to be made from Computer Aided Drawing (CAD) files in a much shorter time than conventional methods would permit;

• The process itself reduces waste, as unused materials can be recycled;

• Certain RP methods allow the model to be used as a master for production of injection moulding dies.

How much does RP cost?

The prices listed below allow the alternatives to RP to be compared:

• RP machines £15,000 to £350,000

• Laser cutters £9,000 to £17,000

• CNC milling machines/routers £1,600 to £15,000

• 3D scanners £900 to £6,000

The cost to produce a RP model depends on size and complexity, but is in the range of £150 to £400 and is limited to components / products that fit within the standard envelope (A4 box). It is predicted however, that within the next five years that certain RP equipment will cost less than £10,000.

There are a range of different Rapid Prototyping (RP) machines but each is computer controlled and produces an engineering prototype out of a series of layers in minimum lead time, hours rather than days or weeks, based on a CAD model of the component/product.

Stereolithography Apparatus (SLA)

This was the first RP process developed and is currently the most popular although it is very expensive to buy and run. The engineering component shape is etched by a laser in the tank of photo-sensitive resin layer by layer as the supporting table is lowered after each layer is formed.

Material: Cured photo-polymer resin Envelope: 500 x 500 x 550 mm Speed: Relatively slow. Surface finish and accuracy: Usually very good (+/-0.1mm), allowing parts to be used as masters for forming dies etc. Practicality and durability of model: Good, but brittle. Uses: Detailed models well down the design process, which may then be used to manufacture patterns. Costs: High purchasing and running costs makes this process very expensive and hence is becoming less popular.

SLA equipment

Injection moulding die

design modelled on SLA


Selective Laser Sintering (SLS) A layer of polymer coated metal powder is spread onto a table. The laser etches out the component’s shape and bonds the powder together to form the layer. The table is lowered and another layer of powder is added and the process repeats until the finished component is produced. The end product can be porous and may require infiltration to give strength and improve surface finish.

Material: metal, polymers and ceramics Envelope: 380 x 330 x 450 mm Speed: Medium level of performance. Surface finish and accuracy: Surface finish is rough, but accuracy is good. Uses: Models made in metal are realistic and may be strong enough to be used for evaluative tests.

Fused Deposition Modelling (FDM) This process is likened to icing a cake with the piping bag squeezed and extruding a line of icing. In FDM the machine’s nozzle is heated and it extrudes a fine filament of ABS, which then sets after it has bonded on to the layer beneath. The nozzle moves in the X–Y axis and the table which the model is built on moves down in the Z axis.

Material: ABS Envelope: 250 x 250 x 400 mm Speed: Slow, common to take 24 to 48 hours. Surface finish and accuracy: very good, accurate 0.2mm. Practicality and durability of model: Strength is good. ABS is a commonly used

plastic, which is chosen for its impact and scratch resistant properties. Uses: Models are functional and can be tested fully for evaluation purposes. Possible to use it for one-offs as end product is made in a suitable material. Costs: Machines: £80,000 to £120,000. Models, per item: commonly £450.

3D Printing This is now the most popular form of RP due to it low cost. Here a layer of powder is spread over a table and a printer-type inkjet then passes over the powder spraying a water-based adhesive. This bonds the powder together into the desired shape. The table lowers slightly, another layer of powder is deposited and the process repeats itself until the 3D model is built up. Overhangs are supported by the unbonded powder beneath. Upon completion the unused powder is removed by vacuum cleaning, leaving the model. The models are porous at this stage, and must be infiltrated to give them more strength.

Material: plaster or corn-starch treated to stiffen it. Envelope: 210 x 210 x 300 mm. Speed: The world’s fastest method, with the capability of building layers at 50 mm vertical per hour. Surface finish and accuracy: Accurate to 0.5mm with Corn-starch produces a rough surface finish. Practicality and durability of model: Models tend to be weak compared to FDM.

Uses: Good for concept models, and development work, but unsuitable for pre-production work. Costs: Machine: £25,000 for the machine. Model costs about £150.

SLS equipment

Injection moulding die which is impregnated before being

used for to produce the part

An ABS prototype of a component modelled

with FDM

Human skulls copied on a MRI

scanner and modelled on a 3D printer


Rapid Tooling

One of the greatest challenge facing manufacturers is how to transfer a fully working RP model into something which can be manufactured in quantity. This usually involves a large scale investment in tooling and can create long delays to the lead time. The term Rapid Tooling (RT) refers to the use of the RP model to produce a moulding tool suitable for mass production. There are a number of RT techniques which can be used with RP models:

LaserForm Rapid Tooling This rapid tooling techniques uses Selective Laser Sintering (SLS) with the base material which is a mix of steel and polymer powder particles. The laser fuses the polymer and the metal particles together layer on top of layer. The finished component, called the green part, is then placed in an oven and infiltrated with bronze. This burns out the polymer binder and completes the sintering of the steel powder particles. The resultant mould can then be machined to cater for channels, ejector pins, gates etc for injection moulding. The end result is a very strong mould which can be used to produce up to 100,000 copies.

Vacuum Casting Rapid Tooling This is the most common RT process because of its simplicity and low cost. A master is formed in an RP system, normally Sterolithography (SLA). This master is then suspended in a mould box and liquid silicone rubber is poured over it under zero pressure in a vacuum. The solidified rubber mould is cut open, the master is removed and gates and runners are carved out. The mould is reassembled and placed in the vacuum chamber. Once the air has been removed a polyurethane resin is poured into the mould. This produces a copy which closely represents the final product. The main drawbacks with Vacuum Casting of Rapid Tooling is that the moulds have a short life, normally 30 copies, before the silicone degrades and that the silicone itself is relatively expensive to buy and is not reusable.

Rapid Design & Manufacture: Summary

These processes include:

• Computer Aided Design (CAD);

• Computer Aided Manufacture (CAM) with Computer Numerically Controlled (CNC) machines used to removing material;

• Rapid Prototyping (RP) where accurate and complicated 3D models are created by adding material;

• Rapid Tooling (RT) where moulds and dies are produced from RP models. These processes are used by industry to:

• Reduce the lead time between design and manufacture • Ensure that components and products are thoroughly tested before going forward for final

manufacture • Reduce costly mistakes and ensure that the design is “right first time” • Allow products to be visualised and evaluated early in the design process.

Laser formed die mould


SECTION C: MANUFACTURING SYSTEMS

Introduction Product designers must know about the characteristics of a range materials and manufacturing processes before they can recommend what is best for a particular product. As part of this consideration a Product Designer must also think about the volume of production, equipment and expertise available and how the manufacturer will organise:

• the movement of material and resources;

• the production process;

• the assembly of the product.

Production Planning

Production planning deals with the task of defining how a product is made. There are a number of different techniques used to assist in the planning for the production of a new product. Each of these techniques has different advantages but their purpose is the same, to allow a project to be planned and analysed in order to ensure that the production is as fast and efficient as possible: Flowchart: graphically showing the stages in the production: Process chart: the scientific analysis of the production looking at the processes, movement, storage and quality assurance of the production:

Gantt chart: a time line based approach where key personnel and / or processes are outlined:

Broiler2.50

= Operation; = Transport; = Inspect; D = Delay; = Storage

TOTALS3.153.5

Place in Finish Rack.05.5

Assemble Order.20

Obtain Buns, Lettuce, etc..10.5

Temporary Storage.15

Transfer to Rack.051.0

Visual Inspection.05

Transfer to Broiler.051.5

Meat Patty in Storage-

Process Description

Chart Symbols

Time (Mins)

Dist. metre

Broiler2.50

= Operation; = Transport; = Inspect; D = Delay; = Storage

TOTALS3.153.5

Place in Finish Rack.05.5

Assemble Order.20

Obtain Buns, Lettuce, etc..10.5

Temporary Storage.15

Transfer to Rack.051.0

Visual Inspection.05

Transfer to Broiler.051.5

Meat Patty in Storage-

Process Description

Chart Symbols

Time (Mins)

Dist. metre

Ⅾ

Ⅾ

Ⅾ

Ⅾ

Ⅾ

Ⅾ

Ⅾ

ⅮⅮ

Ⅾ

2 4 1 - 2

Ⅾ

Ⅾ

Ⅾ

Ⅾ

Ⅾ

Ⅾ

Ⅾ

ⅮⅮ

Ⅾ

Ⅾ

Ⅾ

Ⅾ

Ⅾ

Ⅾ

Ⅾ

ⅮⅮ

Ⅾ

2 4 1 - 2

Customer

Sales

Production

control

Plant A

Warehouse

Plant B

Transport

Order

Product

Process

Order

Print

Extrude

Receive

product

Wait

Move

Wait Wait Wait

Move

Ord

er

Ord

er

WIP

WIP

WIP

WIP

Pro

du

ct

Pro

du

ct

Pro

du

ct

12 days 1 day 1 day 1 day 1 day13 days 4 days 10 days 9 days

52 days

Customer

Sales

Production

control

Plant A

Warehouse

Plant B

Transport

Order

Product

Process

Order

Print

Extrude

Receive

product

Wait

Move

Wait Wait Wait

Move

Ord

er

Ord

er

WIP

WIP

WIP

WIP

Pro

du

ct

Pro

du

ct

Pro

du

ct


Customer

Sales

Production

control

Plant A

Warehouse

Plant B

Transport

Order

Product

Process

Order

Print

Extrude

Receive

product

Wait

Move

Wait Wait Wait

Move

Ord

er

Ord

er

WIP

WIP

WIP

WIP

Pro

du

ct

Pro

du

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Pro

du

ct


52 days


Concurrent Engineering

One of the major goals of manufacturing industry is to reduce the lead-time, that is, the time between the decision to build the product to its actual manufacture. If this time can be kept as short as possible the company will be able to quickly respond to changes in the marketplace and maximise its sales.

Traditionally consecutive or over-the-wall engineering was used:

This process was very slow and often meant that an original design became degraded as it passed through a series of separate departments. It either arrived too late or unsuited to the target market.

In order to reduce the lead time most companies now use concurrent or simultaneous engineering. This brings together all the different specialists (marketing, design, production, quality assurance, sales, accountants etc) in a team to work at the same time on the same project. Concurrent engineering requires departments to work closely together, overlapping the steps in the development and manufacturing which saves time and increases efficiency:

SalesDistributionQuality

Control

ManufactureDesignResearch

Product Planning

Survey Research

Idea development

Planning for Manufacture

Testing

Consumer trials

Advertising & promotions Planning

Time

SalesDistributionQuality

Control

ManufactureDesignResearch SalesDistributionQuality

Control

ManufactureDesignResearch

Product Planning

Survey Research

Idea development

Planning for Manufacture

Testing

Consumer trials

Advertising & promotions Planning

TimeTime


Just In Time (JIT) Production

Just In Time (JIT) or lean production was developed in Japan during the 1980s. Its aim is to reduce the amount of stock kept and to ensure that the product is made in the exact quantity to satisfy the demand at any given time.

Firms using the JIT have less capital tied up in raw materials, carry less stock and require less storage space. The manufacturer need only start production once they have received an order and so they have no stockpiles of finished goods waiting to be sold.

JIT requires a good relationship between the manufacturer and their suppliers. Suppliers have to be flexible and able to respond immediately to manufacturers’ demands. For example, the computer manufacturer Dell, because of its market share can insist that all component suppliers will guarantee delivery within 2 hours of a customer placing an order.

The goal of any JIT production system is to achieve the five zeros:

• Zero stock • Zero lead time • Zero defects • Zero breakdowns • Zero paperwork

These five zeros are almost impossible to achieve but they are targets to aim at. In practice, companies carry a small amount of stock usually enough for a few days production. However, they rely on fast, frequent and flexible delivery systems which can respond to their changing order books.

Quality Assurance (QA) & Quality Control (QC)

With the increased use of JIT production, with its emphasis on zero defects, many companies are adopting quality assurance (QA) in place of the traditional quality control (QC).

Many people are confused about the difference between quality assurance and quality control. They are closely related, but they are different concepts.

• Quality assurance: an ongoing set of activities designed to ensure that the production process meets its objectives;

• Quality control: a set of activities that test and evaluate the product with the intention to find defects.

The difference is that QA is process oriented and focuses on building in quality....and hence preventing defects. While QC is product oriented and focuses on testing for quality....and hence detecting defects.

So quality assurance makes sure you are doing the right things, the right way; while quality control makes sure the results of what you have done are what you expected. If a company gets the QA correct then, unlike QC, there will be no waste as faults will be rectified before defective products are produced.

Quality Control (QC) it is too late the product has already been made!


One-Off Production

One-off production is a time consuming and expensive way to produce a product. It is most suited to large, complex, one-off products such as found in civil engineering, aerospace, ship-building or original hand crafted items. One-off production does have the advantage that the product can be designed and made to suit the exact needs of the client because each product will have its own particular specification.

In one-off production:

• the product is sold and paid for as soon, or even during, its manufacture;

• all design and development costs have to be covered by the income from the single sale;

• a highly skilled workforce is required;

• the low production rate result in very high unit costs.

Mass Production

Mass-production is used to produce standardised products extremely quickly and very cheaply using dedicated machines and moving assembly lines with an unskilled and semi-skilled workforce in large factories.

Despite mass production being cost effective and a good way to make things in bulk, it has the disadvantage that it can take a very long time to stop the process and alter the product. Mass production thrived in the early half of the 20th century where there was stable demand and little product variety.

At its peak, Henry Fords "any-color-as-long-as-it’s-black" Model T car, which was the first mass produced consumer item, had a 57% market share. However, despite its very low price of $245, it eventually lost its market position when competitors offered colour paint and other options. Ford was slow to respond (mostly because mass production’s key to success, hard tooling, labour specialisation, and economies of scale) prevented it from offering variety or adapting quickly to emerging trends.

The one-off reception desk for the Scottish Parliament designed by David Colwell and made out of sycamore and oak cost £88000 in 2004

The mass production of Ford’s model

T car kept costs very low but the system is very inflexible and cannot

alter quickly to respond to changes in the market place


Batch Production

Batch production is used to manufacture a number of identical products or components as a group in a set period of time.

Batch production allows the manufacturer to quickly respond to market demand by changing the product being made. For example, a car manufacturer may make a batch of 8,000 convertibles in the early spring to meet the summer demand. Here all 8,000 chassis will be spot welded in the jig for convertibles, then painted before finally going on to assemble line where the engine and interior are added. Once this batch has been manufactured the company may go on to assemble another specialised batch or return to producing their normal salon car.

Batch production where the one operation is completed on a number of units, before they are then passed on to the next stage, has the advantage that it allows for flexibility in the workforce and a quick response to changes in the market place.

Line Production

Line production is used to manufacture the product through a continuous process. Raw material enters the production line and operations are performed on it in sequence until it goes out as a finished product.

Individual work stations are arranged according to the sequence of operations necessary to complete the product. The equipment and work force are dedicated to a particular process on the product line.

Line production is suitable for mass production and it has the advantage of a very high production rate. The disadvantage of line production is that there is a very high initial investment cost in the specialised tools and machines. It tends to be inflexible and while it can be used for batch production it may be difficult to produce great variations on the original product without redesigning the line. Line balancing can also be difficult in order to ensure that each stage or process takes an equal length of time and help ensure the smooth movement of the product along the production line.

A bakery using batch production to produce morning rolls for the

market place each day

Line production of generators


Flow (Continuous) Production

Flow or continuous production is used in large-scale volume output where the degree of standardisation is great and the demand for the product is consistent and long lasting. Flow production tends to be highly capital-intensive and the process is often continuous often over 24 hours and 7 days a week.

On these production or assembly lines the very high cost of specialised equipment, including automated control systems, keep production rates extremely high and brings unit cost down to a very low level.

Flow production is dedicated to a single product and no batch production is possible. This system is used extensively by the food industry.

Cell Production

Cell or lean production is a relatively new approach to organising a manufacturing system. It is closely associated with Just-In-Time (JIT) production.

The system groups the manufacturing and assembly processes into a number of cells. Each cell has a team of workers who will carryout a range of different tasks involving multi-machine working and who take responsibility for efficiency and quality assurance within their cell. Typically the cell layout is U-shaped which keeps all the different operations compact with no unnecessary movement of materials or personnel.

Cell production involves concurrent engineering where each different cell is working on a separate process at the same time. The output from each cell is brought together at the assembly cell where the different parts are combined to form the finished product. Cell production provides a fast, flexible and efficient manufacturing system which is suitable for small and large volume batches. If planned correctly it will optimise resources and yield the best products, with zero defects, in the fastest manner and at the lowest cost.

Sub-contracting & Outsourcing

A sub-contractor is a person or company which provides goods or services to the manufacturer. Unlike an employee, an independent contractor does not work regularly for the company. Some of the advantages of using sub-contractors include;

• they have specialised knowledge and skills that the manufacturer does not have; • they are brought in only when they are need at key stages in the development of a product; • they are only paid when they are working on the project and receive no holiday or sick pay; • if time is critical then more sub-contractors may be employed to finish the task quickly; • they can free up the manufacturers workforce to do other tasks.

Outsourcing, such as purchasing off-the-shelf standard components, involves transferring control of the manufacture of components, to another supplier. This transfer of control means that the specialised supplier decides how the part will be manufactured and the company which buys this service/product just specifies what the part has to do. Outsourcing is popular for two main reasons:

• the economies of scale that bring down unit costs dramatically when very high volumes of production and sales are achieved;

• companies tend to concentrate on specialised fields where they have the expertise, equipment and personnel to produce the product.

Flow production used by bottling

plants

Cell production with its typical

U-shaped design

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Documents

Materials & Industrial Processes · 2018-02-05 · metal ingot between two massive rolls or dies. In hot rolling the metal ingot is heated to around 2/3 of its meting point and forced