Manufacturing Process Encyclopaedia

Water jet cutting
Other names / variants: Hydrodynamic machining, Abrasive jet cutting

• Jet cutting (or hydrodynamic machining) has been widely used in the food industry for a long time, but more recently it being taken up by general engineering manufacturers.
• The basic process is very simple – a concentrated jet of fluid at almost supersonic velocity is directed at the workpiece which literally ‘blasts’ the material out of the cut.
• In the food industry, oil is used which provides a hygienic means of cutting.
• In metal cutting, fine abrasives in water are used – steel up to 100mm thick can be cut
this way.
• All though the process is quite slow, sheets can often be stacked up and several cut at once.
• The primary advantage for metal cutting is that the process generates very little heat, so the material is not affected in any way.

Process details

Abrasive jet machining
An abrasive jet uses water that is pressurized up to 40,000 pounds per square inch (psi) and then forced through a small sapphire orifice at 2500 feet per second, or about two and half times the speed of sound. Abrasive (often garnet) is then pulled into this high-speed stream of water and mixed with the water in a long ceramic mixing tube. A stream of abrasive laden water moving at 1000 feet per second exits the ceramic tube. This jet of water and abrasive is then directed at the material to be machined. The jet drags the abrasive through the material in a curved path and the resulting centrifugal forces on the
particles press them against the work piece. The cutting action is a grinding process where the forces and motions are provided by water, rather than a solid grinding wheel.

Materials and shapes
• Abrasive waterjets can machine a wide range of thicknesses and materials, including metals, plastics, glass, and ceramics.
• Materials cut by the abrasive jet have a smooth, satin-like cut edge, similar to a fine sandblasted finish.
• Little heat in machining process.

Vacuum forming
Other names / variants: Thermoforming

Almost the opposite of blow moulding - with sucking instead of blowing! As a result, the two processes are useful for different types of shape, although both can only produce parts with thin walls. This process is more properly called thermoforming and relies on the sudden drop in strength and stiffness of thermoplastics above a certain temperature.

Materials and shapes
Only suitable for thermoplastics and some polymer foams. Shapes should have constant section thickness and not 'curve-back' on themselves. Parts cannot have holes or openings. Surface texture good, but fine detail in mould cannot be copied. Suction holes in mould need to be small to avoid leaving a mark on the product. Near-net-shape, but often leaves some waste material that needs trimming (and is difficult to recycle).

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 cheap enough to use in a school workshop. 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 - 1000 parts. With fully automated systems, only becomes economically viable for batches over 10,000.

Typical products
Advertising signs, bath panels, washing-up bowls, packaging.
Turning is unusual amongst the machining processes in that it is usually the workpiece that moves, whilst the cutting tool remains stationary. Lathes in metalwork shops usually have single point cutting tools. Lathes in woodwork shops often have tools with simple shapes to make turning of complicated shapes more simple. Lathes in industrial woodworking have large, intricate cutting tools, capable of shaping a complicated piece with only a few inserts of the tool.

Materials and shapes
• Woods and metals are the most commonly turned materials, although difficulties arise with the high-strength metals.
• It is possible, but unusual, to turn polymers. Rigid polymer foams are sometimes turned when producing models for prototypes.
• Turning is usually used to produce parts with radial symmetry (i.e. based on a cylinder).
• It is possible to produce other shapes, e.g. a helix or screw thread, by turning the part slowly and moving the cutting head at a constant rate.
• Wood is the most commonly turned material, as it is easy to produce a wide variety of aesthetic
• The use of dedicated lathes for metal turning is rare on an industrial scale, except for
• Where metal turning is required industrially, it is usually done as part of the function of a
machining centre.
• Wood turning for mass production uses dedicated tooling to dramatically increase production
rates and hence reduce costs.
Typical products
• Chair legs
• bowls
• candlesticks
• large threaded shafts
Transformation hardening
Other names / variants: Laser hardening, Induction hardening, Flame hardening
Transformation hardening is often used in addition to carburising or nitriding, and is primarily used to
improve the mechanical properties of the surfaces of steel components. There are many ways to
"transform" the surface microstructure, but all of them involve heating of the surface followed by a
rapid quench (either in oil or water, or by a "self-quench" because the bulk of the component will still
be cold).
• Flame hardening uses a flame gun to provide the heating. It is inexpensive and flexible;
however it is quite slow, difficult to control accurately and not easily automated. Only external
surfaces can be treated.
• Induction hardening works by placing the component in a high-frequency magnetic field. This
"induces" a current in the surface and so heats it rapidly. It can be used to uniformly treat large
components such as the rolls for a rolling mill. Although this process is expensive and requires
some dedicated tooling, it is easily automated and can be applied accurately – e.g. to just the
teeth on a gear cog.
• Laser hardening works by focusing a laser beam on to the surface to provide very rapid
heating. As a result, a self-quench is usually sufficient. The equipment is very expensive and not
economic for large surfaces, but automation is straightforward and very precise control can be
Surface treatment (generic)
Related processes in this database include: Case hardening, Transformation hardening, Surface
coating Peening
Surface treatment processes apply primarily, but not exclusively to metals. After a component has been
formed and finished (e.g. by grinding), it may still not have acceptable surface properties. There are 4
main reasons why the surface properties may need altering:
1. Improve wear resistance.
2. Improve corrosion resistance.
3. Improve fatigue resistance.
4. Change the aesthetic appearance.
There are various ways these aims can be achieved:
• Coating the surface in a new material - e.g. painting, electroplating
• Altering the surface chemistry/microstructure – e.g. carburising, transformation hardening
• Changing the mechanical properties of the surface – e.g. shot peening, planishing.
Surface coating (generic)
Other names / variants: Chemical vapour deposition (CVD), Physical vapour deposition (PVD),
Painting, Varnishing, Electroplating
By applying a surface coat of a different material, dramatic changes in the surface properties are
possible. Normally the materials used for the coats are too expensive, or have the wrong bulk properties
to use for the whole components. There are several ways to coat the surface of a component:
• Painting / varnishing. Commonly used to provide corrosion resistance for woods, but also
widely used for metals. Relatively inexpensive and flexible.
• Electroplating is a relatively inexpensive way of providing a surface coat, although it relies on
the component being a good conductor and only certain coats are possible.
• Physical vapour deposition (PVD) or sputtering works by "shooting" a fine spray of droplets
at the component. It is mainly used for metals and ceramics. Although very expensive, it can
provide excellent surface properties for high-performance drill bits etc.
• Chemical vapour deposition (CVD) is similar to PVD, but the surface is formed by a chemical
reaction with a special gas rather than using a spray.
Soldering and brazing
Soldering and brazing differ from welding because only the filler melts, not the materials that are
joined. Soldering differs from brazing by the melting temperature of the filler alloy - this is usually
below 450oC for soldering and above 450oC for brazing. Soldering using lead-tin alloys was the first
hot joining process, used as far back as 4000BC.
Materials and shapes
Brazing is usually used for joining metals, and especially where the parts are not of the same material.
Most geometries are possible; however, good join alignment is essential to achieving a strong joint.
Mechanical cleaning or the use of flux is needed to give good joint strength. The strength of the joint is
also dependent on good design. Because of the low melting point of the filler, soldered joints have
limited use at high temperatures. Also, the joints are usually not strong and therefore not used in loadbearing
situations. Soldering aluminium and stainless steel is difficult because of their strong oxide
Equipment is generally low cost, except where automation is used. The need for good joint alignment
usually means fixtures are required, adding to the cost. Wave soldering is the most economic means of
soldering large batches of printed circuit boards.
Typical products
Plumbing, electrical circuits
Sintering and HIPing
There are 2 main types of sintering: with pressure (hot pressing or pressure sintering) and without
pressure (pressureless sintering). A variant used for 3D shapes is called hot isostatic pressing (HIPing)
Much of the research in powder processing is to obtain good quality powder, as this helps to achieve a
good quality component.
Materials and shapes
Mostly used for small (<2kg) components. Dominant method of producing ceramic components. For
non-HIPing, sides must be parallel to allow ejection of part. HIPing can work with complex 3D shapes.
Very good dimensional accuracy (near net-shape process) with 100% material utilisation.
The machinery is expensive, and can cost well over £100,000 for HIPing. The dies are dedicated,
expensive (£5,000+) and need to be replaced after about ten thousand uses. They can take several
weeks to manufacture, so prototype testing is slow. The production rate is dominated by the sintering
stage and is therefore quite slow (2-20 per hour). Because there is little competition, can be economic
for small batches (1,000+) - although still not cheap!
Typical products
cutting tool tips, spark plugs, electrical insulators
Sheet forming
Sheet metal forming (also called pressworking) is among the most important metalworking processes.
It is used in the manufacture of a wide range products as there are many different forming operations
including blanking, drawing, pressing and bending. Sheet metal is produced by rolling and is generally
coiled prior to forming. Parts made this way and subsequently mechanically fastened are said to be
Materials and shapes
Sheets are usually less than 6 mm thick. Dominant material used is mild steel. 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 die
design and quality. 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.
Primarily used when near-net-shape 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. Production rates with automated equipment can be very high (drinks
cans can be produced at almost a 1000 a minute).
Typical products
Cans, washing machine cases, car body panels, kitchen utensils, hubcaps, metal desks.
Sand casting
Other names / variants: green sand casting
• Sand casting is the oldest form of casting and has been used for millennia.
• It is still widely used today and in the US alone about 15,000,000 tonnes of metal are cast every
• Although almost any sand can be used, a mixture of synthetic sand, clay and water, called green
sand, is preferred by most foundries.
Materials and shapes
• Most metals can be cast, the limit is the melting temperature - the higher it is, the greater the
• 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 etc. can also greatly add to the cost of the
finished product.
• Porosity can be a problem leaving parts that are prone to cracking.
• The basic equipment cost is low - from £500 to £3,000; automation and higher temperature
furnaces can increase this a lot. Dies can be cheap, but take some time to make.
• The limit on the production rate is usually the cooling. Small parts can be produced at several an
hour - large parts can take hours or even days to cool fully.
• The labour intensive nature of the process mean it is usually only economic for small batches,
although dedicated automation can increase this to 10,000+.
Typical products
• Engine blocks
• cylinder heads
• pump housings
• machine tool bases
• ship propellers
Rotational moulding
Other names / variants: Rotomolding
• Think of a large polymer product, and the chances are it is made by rotational moulding.
• This versatile process is surprisingly inexpensive and is used to make a wide range of everyday
• The main disadvantage is the low production rate which usually limits it to smaller batches.
Process details
Stage 1: Plastic is introduced to a mould in powder form up to the mass required for the required
Stage 2: The mould is then closed and passed into an oven chamber. The mould is then heated
externally to a temperature typically between 220°C and 400°C and is rotated around both vertical and
horizontal axes.
Stage 3: As the mould rotates, the inner surface passes through the mass of powder at the bottom of the
mould. As the mould heats up, the powder begins to melt and adhere to the inner surface of the mould.
The mould continues to rotate in the presence of heat and more plastic melts and builds up to produce
an even layer over the surface of the mould. The mould is then withdrawn from the oven whilst still
rotating and moved into a cooling chamber.
Stage 4: Cool air is directed at the mould and in some cases water jets are used to cool the mould.
When the plastic inside the mould has become solid, the mould can be removed from the cooling
chamber. The plastic component is then removed from the mould and allowed to finish the cooling
process unrestricted by the mould.
Materials and shapes
• Mainly for thermoplastics (especially polyethylene), but some thermosets can be used.
• Used to produce containers and similar hollow products with uniform thin sections.
• Tanks up to 4m across can be made this way; wall thicknesses as low as 0.4 mm are possible.
• Products are near-net-shape and rarely need further finishing.
• Parts do not have to have circular cross-section.
• The surface finish depends on the quality of the die surface; it is possible to include surface
detail such as logos.
• Metal or polymer inserts can be moulded-in during processing.
• All material is used in the product so there is no scrap.
• Parts with large openings may be produced in pairs in a single mould and separated after
removal, or through use of insulation in mould.
• The plastic is formed without pressure or centrifugal force and as such has no moulded in
• 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 cheap - between 1 & 10 thousand pounds.
• The long cycle times usually limit economic batch sizes to between 500 and 10,000.
Typical products
• buckets
• plastic footballs
• dustbins
• oil drums
• storage tanks
• traffic cones
Other names / variants: tandem mill, reversing mill
Rolling was first used in the 1500s. The basic operation is a bit like flattening dough with a rolling pin.
Rolling is unusual in that it is primarily used for making stock items rather than making finished
components. Over 90% of worked metals are processed at some point by rolling.
Process details
Reversing mill
• In a reversing mill, 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.
• Reversing mills are used for making thick sections such as slabs or large I-beams. In practice,
there do not need to be many separate ‘dies’ (as is shown here) if the operator can move the
rolls closer together between passes.
Tandem mill
• In a tandem mill, a hot slab is passed through a series of flat rolls.
• Each of the rolls reduces the thickness slightly, until the desired thickness is reached. If the final
sheet is not too thick it can be ‘coiled-up’ while it is still hot.
• Tandem mills are mainly used for producing plate and sheet. In practice, 5 or more rolls in
series can be used – in which case the material coming out the end can be going very fast!
Materials and shapes
• For flat sections, ingots over 1m wide are reduced to plates (usually 6mm-300mm), sheet
(0.1mm - 6mm) or foil (about 0.008mm).
• Shaped sections (such as rails and I beams) up to 300 mm across are made using a series of
shaped rolls.
• Specialised forms of rolling can be used to make large rings.
• Hot rolling has poor dimensional tolerance and leaves a poor surface finish.
• Cold rolling can improve these and also improve mechanical properties, but only for small
reductions in thickness.
• 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 products
I-beams, rails, sheets, plates, foil
Rapid prototyping (generic)
Other names / variants: Stereo-lithography, Selective laser sintering (SLS)
Prototyping is the making of a test component before full manufacture begins. These prototypes
provide an important means of assessing a design in a "hands-on" way. Conventionally, prototyping
was performed by machining the component from a solid block. With the advent of CAD/CAM and
CNC machining, this approach has greatly speeded up – but "rapid" prototyping techniques are even
faster. They all work by building-up thin layers in sequence to produce the whole component.
Recent trends in rapid prototyping include:
• The techniques are now being used with scanning techniques to produce exact replicas of
delicate objects such as antique carvings.
• Rapid mould development (rapid tooling), where prototypes produced by one of these
techniques is coated and can be used directly for injection moulding dies etc.
• Making shapes not possible any other way – e.g. custom jewellery, ‘sculptures’ etc.
Powder metal forming
Other names / variants: Sintering, HIPping, Reaction bonding
• One of the first uses for powder metal forming was the manufacture of tungsten filaments for
light bulbs. Advances in the technology mean even structural parts for aircraft (e.g. landing
gear) can be made this way.
• Much of the research in powder forming is to obtain good quality powder, as this helps to
achieve a good quality component.
• Pressureless sintering involves only heat. It can be used for any shape.
• Pressure sintering involves heat and axial pressure, but can only be used for 2D components.
• HIPping (hot isostatic pressing) is a variant used for 3D shapes; it uses a foil bag and a
hydrostatic pressure chamber.
• Reaction bonding involves using a binder (so it can be moulded like plasticine) which is later
burnt off; it can used for most shapes.
Materials and shapes
• Possible sizes range from balls in ball point pens up to 25kg.
• Mostly used for small (<2kg) complex components that are difficult to make from solid stock or
where uniform properties are desired.
• All metals can be processed this way, though extra care is required for some which burn or
oxidise easily.
• Sides must be parallel to allow ejection of part.
• Very good dimensional accuracy (near net-shape process) with 100% material utilisation.
• There can be problems with porosity – although sometimes this can be beneficial (e.g. filter,
• The machinery is expensive, and can cost well over £100,000.
• The dies are dedicated, expensive (£5,000+) and need to be replaced after about ten thousand
uses. They can take several weeks to manufacture, mean prototype testing is slow.
• The production rate is dominated by the sintering stage and is therefore quite slow (2-20 per
• Tends only to be economic for large batches (50,000+) or processing high-strength alloys.
Typical products
• small gears
• magnets
• cutting tool tips
• light bulb filaments
• aircraft landing gear
• bearings (porous)
• filters
Polymer shaping (generic)
Related processes in this database include: Injection moulding, vacuum forming, blow moulding,
rotational moulding,, extrusion (polymers), compression moulding
• The biggest mistake with forming polymers is to design the products the same way as metal
products - it took 20-30 years from the introduction of polymer forming for many manufacturers
to use them well. For instance, because of the comparatively low strength and stiffness of most
polymers, "ribbing" is often incorporated into the design – this will have an effect on which
processes can be used.
• Generally, polymer products are formed near-net-shape and do not require further finishing.
This "one-stop" processing gives polymer processing a cost advantage over metal processing.
• Polymer processing basically splits into those suitable for thermosets and those suitable for
thermoplastics, although care must be taken over toxic fumes for both.
Polymer extrusion
Unlike metal extrusion, polymer extrusion is a continuous process. A useful variation of the process
called co-extrusion can be used (for example, to coat wires in-line for electrical cables). Polymer
extrusion is sometimes used as a 'melter' for feeding other shaping processes such as injection
moulding or blow moulding.
Materials and shapes
Mainly used for thermoplastics, but can be used with rubbers 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. Near-net-shape process, only the ends of
the extrusion are wasted.
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
Channels, pipes, sheet, architectural mouldings, cables, coated wires.
Other names / variants: Shot peening
• Peening is only used for metals.
• All metals can have their strength improved by ‘working’ them – i.e. deforming them past the
elastic limit. Peening only does this to the surface, by firing ‘shot’ (like small ball-bearings) at
it. This can result in greatly improved fatigue resistance (useful for components which undergo
cyclic loading such as turbine blades).
• Peening is flexible and relatively inexpensive unless significant automation is used.
• Peening can also be used for shaping thin sheets – but this isn’t a surface treatment!
Milling will be familiar to anyone with experience of a metal workshop. The machines used
industrially can be extremely sophisticated - the cutting head is often able to twist and turn in many
directions! As well as being used for many small products suitable for school workshops, milling has
been used for large scale items such as aeroplane wings and tanks!
Materials and 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.
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
Finishing surfaces (e.g. top of engine block), wooden furniture, architectural mouldings
Metal shaping (generic)
Related processes in this database include: Forging, Die Casting, Lost Wax Casting, Sand Casting,
Extrusion (metal), Rolling, Sheet forming
Bulk metal shaping is generally done near-net-shape by forging or casting although further finishing
work is usually required. However, it does reduce the material wasted by machining and is usually
much faster. For many components, casting and forging are in direct competition and there is often no
easy way to decide which is the better choice; both are usually undertaken by specialist companies
(foundries and forges respectively).
There are a variety of sheet forming processes suitable for metals less than 6mm thick, and in general
all products based on sheet will be made using one of these processes. Sheet is made by rolling, which
is also used to produce most large stock items held by material suppliers and a few final products such
as I-beams.
Extrusion is also used to produce some stock items with constant cross-section, such as tubes, and
some finished items, such as window frames.
Metal extrusion
• Metal extrusion was developed in the late 18th century for making lead pipe. The basic process
of forcing a round billet through a shaped die is still used today.
• Modern variants can produce clad products in one go - e.g. copper clad with silver.
• Wire drawing is related to extrusion but is used for smaller (round) sections and the metal is
pulled through the die rather than pushed.
Materials and shapes
• Mainly used with the softer metals, e.g. aluminium, copper, zinc.
• Generally speaking, the softer the metal, the more intricate the shapes that can be made.
• Useful for long thin parts with constant cross-section.
• Possible cross-sections are usually 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.
• 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 £1000 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 5-10metres/minute are possible.
• Usually only economic for several thousand metres +
Typical products
• Tubing
• aluminium window frames
• railings
• trims
• wires
Mechanical fastening
Other names / variants: rivets, snap-fits, screws, bolts, nuts
Related processes in this database include: Joining (generic)
Mechanical joining falls into two distinct groups: fasteners and integral joints. Examples of fasteners
include: nuts and bolts, screws, pins and rivets; examples of integral joints include: seams, crimps,
snap-fits and shrink-fits.
Some form of mechanical joining needs to be used where products need to be taken apart 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.
Materials and shapes
• Virtually any material in any shape can be joined by mechanical fastening - given enough
• 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.
• Can be economic for any batch size from one-offs to mass production (with or without
• 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
• 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.
Mechanical cutting
Other names / variants: Sawing, hacksaws, bandsaws, circular saws
One way of splitting a workpiece in two is to plastically press a shape out of it, such as with blanking.
This entry deals with splitting a workpiece in two by removing a thin slice of material by mechanical
means (the other main approach is removal by intense heat). These processes are usually called
"sawing" and include: hacksaws, bandsaws, circular saws and friction saws.
Other specialist cutting processes include gear cutters.
Materials and shapes
• Generally speaking, sawing is only for straight line cuts all the way through a workpiece.
• Some sawing processes are capable of producing curves, and some can be used for cutting
• In general, wood and metals are easily cut - although the higher the strength of the metal the
greater the rate of wear on the cutting teeth.
• Polymers can be cut, but care must be taken to avoid any melting.
• Glass can be cut by "score-and-snap" techniques.
• Composites are not usually cut (other than edge trimming) after forming as it can have a serious
impact on the mechanical properties.
• If possible, avoid cutting! A surprising number of designs involve a cutting process followed by
a joining process. Although this can be more economical than making in one-piece, it is not
usually the case.
• The main use for cutting is to reduce stock items (usually from rolling or extrusion) to the
correct length.
• For thin workpieces (up to 6mm), mechanical cutting competes with sheet process such as
• For thicker workpieces, new processes such as plasma-arc, water jet and lasers are becoming
competitive because of their greater flexibility.
Typical products
• I-beams
• window frames
• joists
• architectural mouldings
Machining (generic)
Related processes in this database include: drilling, milling, turning, mechanical cutting, grinding,
Machining is one of the most widely used types of process found in industry, particularly for metals.
There are many variants including milling, grinding and drilling — all share the common feature of
removing material with some form of cutting tool.
As it can be expensive, extensive machining of a product is limited to trials or low volume products. It
should be kept to a minimum for high volume products and so is not used for most consumer items.
Industrially, milling, turning and drilling are often combined in CNC machining centres which can
produce a wide variety of shapes at high speeds. These machines can contain over 200 different cutting
tools, which are automatically replaced as they wear out.
It is possible (but unusual) to machine polymers – care must be taken as they can melt. In addition,
machining polymers usually leaves a rough finish (they are normally smooth after moulding).
Mechanical cutting is a type of "machining" used to separate parts – the most commonly know
processes are saws.
Lost wax casting
Other names / variants: Investment casting
• Some form of lost wax casting has been used since 4000BC.
• It is now mainly used for medium size batches where good quality is required.
• The fine dust and harmful fumes require careful control of the workplace to avoid health
problems for operators.
Materials and shapes
• Suitable for most metals, leaving a good surface finish which usually does not require further
finishing steps.
• Best for small complex-shape parts, but can be used for parts from 5g to 100kg.
• Not much metal scrap, and it can be easily recycled. Wax can be re-used but ceramic coating
must be disposed of carefully.
• The production cycle is slow: usually only 1-5 castings can be made an hour, depending on the
size. Assembling lots of patterns on one tree can help in achieving a reasonable production rate.
• The basic cost of the equipment can be as little as £1,000, although automated kit can be a lot
more. The cost of the patterns is usually only a few hundred pounds, but they can take several
weeks to make.
• Although the setup costs are low, the low manual production rate means that only batch sizes of
up to 50 are economic; this can rise to a few thousand if automated.
Typical products
• Jewellery
• dental implants
• hip replacements
• valves
• wind instrument keys
Laser processing (generic)
Although lasers are often thought of as "sci-fi", they are a surprisingly versatile tool in manufacturing
and can be used for:
• Cutting of most metals (up to 30mm thick) and woods. Over 75% of lasers are currently used
for sheet metal cutting as they can provide accurate cuts at high speeds. Because there is no
contact, it doesn’t matter how hard the material is and there is no tool wear.
• Welding of most metals up to 20mm thick without the need for a filler. They can also be used
for high speed spot welding (used for Gillette razors).
• Drilling of burr-free precision holes with no further finishing required. A common application
is the cooling holes in turbine blades – it can be over 20x faster than competing techniques.
• Surface hardening of steel component - see transformation hardening for further details.
Other applications include paint removal and rapid prototyping. Industrial lasers start at about
£100,000, but because they are very flexible and easily automated they can often prove cost-effective
Joining (generic)
Related processes in this database include: Welding, Brazing, Adhesive bonding, Mechanical
• It is unusual for a product to be made in one-piece – almost all products consist of components
which must be joined in some way.
• The most familiar joining processes are probably mechanical fasteners and adhesives and, as a
result, designers often think they understand these the best. However, mechanical fastenings
such as snap-fits are often over looked and modern adhesives are greatly under-rated because
they are thought of as "just glue".
• In addition to these processes, there are a variety of "hot processes" such as welding and
brazing which can often provide stronger and more economic joints for metal parts.
• The one thing which is key for all the processes is to design the joint for the process, and not to
design the joint before deciding on the process – a good joint for welding can be disastrous for
adhesive bonding, and vice-versa.
• Joints are often a source of weakness in failure – they are very important in design.
Injection moulding
Essentially, injection moulding is die-casting for polymers. It is normally automated and used for high
speed, high volume production where component quality does not need to be high - over 50% of
polymer parts are produced this way.
The mark left by the ejector pin can often be seen on cheap mouldings. To increase the shapes possible,
sophisticated dies with moving and unscrewing inserts are used.
Injection moulding machine
[Pictures courtesy of Withersdale Plastics Ltd.]
Materials and shapes
• Thermoplastics dominate, but can also be used for thermosets, rubbers, polymer foams and
short-fibre composites.
• Can make intricate shapes, though not suitable for thick sections.
• Typical part sizes are 100-600g, although parts up to 25kg can be made at great expense.
• Parts generally do not require finishing, although parts for feeders etc. may require removal.
• A wide variety of surface finishes and embosses can easily be incorporated into the die design.
• Thermoplastic scrap is easily recycled, but other materials must be disposed of carefully.
• To reduce costs, several parts are often moulded together on a "tree-like" structure; parts can
then be separated after moulding.
• The cycle time is limited by solidification time and time to open and close the mould.
Production rates from 1-20 parts/minute are readily achievable.
• Capital cost for machines are from £10,000 - £100,000 and dies can cost between £1,000 and
• Injection moulding is only economic for batches of 10,000 - 100,000 or more and so is usually
Typical products
• toys,
• model-making kits,
• handles,
• food containers,
• cups,
• electrical and plumbing fittings
Grinding / Polishing
The basic principle of grinding is similar to that of using sand paper to smooth wood. Where it is used
it will be the final finishing operation, with the possible exception of painting. Although grinding
wheels (which can be up to 2m!) are commonly found in industry, they are being replaced by abrasive
belts. Unusually for a mechanical process, grinding usually works best with harder materials, rather
than softer materials.
Materials and shapes
Grinding and polishing are finishing operations used where great dimensional accuracy or a good
surface finish are required. Polishing often produces a lustrous surface finish - this is due to softening
and smearing of the surface from the frictional heating. Primarily used with metals and ceramics.
Although grinding does remove material, almost none of this can be recycled.
On an industrial scale, the wear on grinding equipment is significant and this adds greatly to the cost.
The variable wear on a grinding wheel makes control of automated equipment more difficult and hence
expensive. The production rate depends on the level of finish required - the limiting factor is usually
the overall cost. As with the other machining processes, grinding and polishing should be avoided if at
all possible
Glass forming
Sheet glass is produced by drawing, rolling, and floating. Drawing is also used to produce fibres, rods
and tubes.
Discrete glass products (e.g. bottles) are made by blowing, pressing and casting.
All these processes begin with molten glass (which looks like red-hot thick syrup). A further process,
called sagging, is useful for products with shallow curves (e.g. plates) or light embossings.
Materials and shapes
• There are over 750 types of glass, but they can all basically be formed in the same ways.
• Drawing and rolling give a rough finish which normally needs grinding and polishing. Float
glass has a smooth surface.
• A variant of drawing is used to make rods and tubes.
• Blowing is used to produce hollow thin-walled items; it is similar to blow moulding of
thermoplastics. The surface finish is acceptable for most applications.
• Pressing produces parts with greater dimensional accuracy, but cannot be used for items with
thin walls or inward curves.
• Production rates and costs strongly depend on the type of process and the size of component.
• The different processes are generally suited to different shapes, so there tends to be little
• Blowing of light bulbs takes place on expensive fully automated equipment, but over 1000
bulbs per minute can be formed.
• Fibre optics can be drawn at speeds of up to 500m/s.
Typical products
• table tops
• bottles
• vases
• television tubes
• windows
• headlights
• light bulbs
• mirrors
• dishes
• optical fibres
Friction welding
Welding is commonly thought of as a process where material is melted - this type of process is more
properly called fusion welding. However, there is another type of welding process, called hot welding,
where the material is heated until it softens but does not melt. Friction welding falls into the latter
category - the heating is provided by the rubbing of the parts to be joined (at speeds which can be up to
Materials and 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).
• Solid bars up to 100mm can be joined and pipes up to 250mm.
• Good joint quality depends on good alignment of parts and timing of the final forging together.
• 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.
• Competitive with adhesives for polymers for the geometries it can do, especially for a large
number of joints.
• Removal of flash (if required) adds to the cost.
Typical products
• pipes
• studs
Other names / variants: ring-rolling, open-die forging, closed-die forging, drop forging
Related processes in this database include: metal extrusion
• Forging is probably the oldest metalworking process - dating back to at least 5000BC.
• It has advanced a long way from its "blacksmith" image and today there are many hi-tech
variants that compete mainly with the casting processes.
• Although forging can take place "cold", the component is usually heated to reduce the forces
• The forging action can be extremely noisy!
• Impression Die Forging - also called closed die forging, presses metal between 2 dies that
contain a precut profile of the desired part.
• Cold Forging - includes bending, cold drawing, cold heading, coining, extrusions and more, to
yield a diverse range of part shapes. The temperature of metals being cold forged may range
from room temperature to several hundred degrees.
• Open Die Forging is performed between flat dies with no precut profiles is the dies. Movement
of the work piece is the key to this method. Larger parts over 20 tonnes and 10 metres in length
can be hammered or pressed into shape this way.
• Seamless Rolled Ring Forging is typically performed by punching a hole in a thick, round
piece of metal (creating a donut shape), and then rolling and squeezing (or in some cases,
pounding) the donut into a thin ring. Ring diameters can be anywhere from a few inches to 30
Process details
Closed-die forging
A heated blank is placed between 2 halves of a die
A single compressive stroke squeezes the blank into the die to form the part. In hammer or drop forging this happens
by dropping the top of the mould from a height. An alternative is to squeeze the moulds together using hydraulic
Once the die halves have separated, the part can be ejected immediately using an ejector pin.
The waste material, flash, is removed later.
Materials and shapes
• Any metal can be forged, provided the blank is hot enough (( 60% of the melting temperature).
• Typical possible 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.
• Any waste material squeezed between the die halves, called flash, is readily recycled.
• 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
Typical products
• Spanners
• pedal cranks
• gear blanks
• valve bodies
• hand tools
• crankshafts
• coins
Other names / variants: Trepanning
One of the most common of the machining processes - as there are few other ways to produce a deep
circular hole. One of the biggest challenges to the drill designer is how to remove the waste material
out of the hole at the same time as getting the cutting fluid into the hole. Large shallow holes are made
by trepanning, where a disc is removed rather than all the material.
Materials and shapes
• Almost any material can be drilled, although difficulties arise with very brittle materials (e.g.
ceramics) and very hard materials (e.g. tool steel).
• Drilling is used for making circular holes, dimensional accuracy can be improved by subsequent
reaming or boring.
• Holes from 0.5 mm to 50mm are commonly drilled - although the design of the drill bit will
vary quite a lot!
• Drilling is often used to complete parts that have been formed by a near-net-shape process (e.g.
casting or forging) as precision holes are difficult to form with these processes.
• Threaded holes are made by first drilling a cylindrical hole and then "tapping" with a threaded
cutting tool.
• It is normal to try to reduce the amount of drilling required in a component by careful design -
but when an accurate hole is required, drilling has little competition.
• Where drilling is required industrially, it is usually done either as part of the function of a
machining centre, or in a dedicated drill set with multiple heads so that all the holes can be
made simultaneously
Die casting
Other names / variants: ferro-die casting
• Developed in the early 1900s, this is the most common of the casting processes that use a
permanent mould.
• It is used for high volume products, of which small zinc die-cast toys (e.g. "Matchbox" cars) are
probably the most widely known.
• Very small components like zipper teeth can be made at over 20,000 an hour!
Ferro-die is used for high melting point materials such as steels. It uses higher melting point ferrous
alloys for the die materials and is more expensive.
Materials and shapes
• Mostly used for low melting point alloys such as aluminium, zinc and copper. In general only
small parts are made, but it can be used for components up to 25kg.
• 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.
• The machinery is expensive, and can cost well over £100,000.
• Dies cost many thousand pounds and need to be replaced after a few hundred thousand uses.
They 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 only economic for batches of 100,000+
Typical products
• Small toys e.g. cars/soldiers
• hand tools
• disc drive chassis
• motor casings
• carburettors
Compression moulding
Essentially, this process is forging for polymers - although only one 'hit' is possible. Mainly used for
thermosets and rubbers in mid-size batches as injection moulding is cheaper for thermoplastics. With
thermosets, the chemical reaction provides most of the heat, so little extra energy is required.
Materials and shapes
Mainly used for thermosets, although rubbers, some thermoplastics and chopped-fibre composites can
be formed this way. Limited to simple shapes, although a wider variety is possible with rubbers as they
can be more easily removed from the mould. Possible part size range from 10mm up to 1m. Waste
material, called flash, needs to be removed after moulding and is not readily recycled.
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. The
low production rate means that it is only usually economic for batch sizes in the tens of thousands.
Typical products
Dishes, handles, caps, electrical components.
Composite shaping (generic)
The unique structure of reinforced plastics requires special processes to shape them into useful
products. Although some of the polymer forming processes can be used (when the fibres are chopped
and mixed in a polymer), there are special processes which are specific to composites containing long,
continuous fibres (such as CFRP) – it is these that are discussed here. Many of the polymer resins used
can give off toxic fumes, so precautions have to be taken to protect operators from the adverse effects.
Design issues include:
• Avoiding sharp changes in section
• Orienting fibres where possible to improve mechanical properties
• Forming as close as possible to finished shape; drilling holes can dramatically reduce strength
A few years ago, fibreglass Formula 1 car bodies needed to be replaced after every race. New carbon
fibre and precision forming techniques mean that these bodies can now last all season.
Composite forming
Other names / variants: Hand lay-up, Resin transfer moulding (RTM), Spray-up, Pultrusion
The basic aim of all composite forming techniques is to mix a resin with a reinforcement (which may
be as woven mat, long fibres or chopped fibres) to produce the desired shape. This may be done by
using prepregs or performed in-situ. A variety of processes exist for various shapes and scales of
Materials and 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 - these can be reduced by
using vacuum bagging.
• A variant of compression moulding, called resin transfer moulding (RTM), can be used to
make complex parts or where greater dimensional accuracy is required.
• Hollow parts can be made by filament winding which can produce parts with optimised
mechanical properties.
• Fibres, tapes and mats are produced by processes called pultrusion and continuous laminating;
these can also be used to produce prepregs (composite tapes and mats with resin that has not yet
• 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
• 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, RTM and filament winding can be automated, so are usually used for mass
• The wear on the dies from the fibres is significant in RTM, and they may need to be replaced
after every few thousand injections.
Typical products
Boat hulls, propeller blades, baths, water tanks, structural cables, rocket noses, turbine blades, golf
clubs, tennis racquets, bicycle frames
Ceramic shaping (generic)
Related processes in this database include: glass moulding, sintering, HIPping
There are several ceramic forming processes, although most of them are specific to individual materials
such as throwing for pottery, casting for concrete and slip casting for porcelain.
Because ceramics only melt at very high temperatures, most forming of “engineering ceramics” (like
alumina) is based on using dry powder or "bound" powder which can be moulded; at the dominant
method of forming engineering ceramics is sintering. An exception to this general rule is glass
forming, since glass softens sufficiently for it to be moulded.
Case hardening
Other names / variants: Carburising, Nitriding
Carburising and nitriding are both forms of case hardening and are primarily used to improve the
mechanical properties of the surfaces of steel components. The component to be treated is put into a
special gas atmosphere (gas carburising) at a high temperature. The process works by altering the
surface chemistry because of the diffusion of gas into the solid.
The process is quite slow because it depends on diffusion, so it is normally automated by using a
conveyor belt. It is also possible to use certain liquids (liquid carburising) which speed up the diffusion
so cycle times are shorter.
The main advantages of these processes are:
• only simple equipment is required and no dedicated tooling,
• and any shape can be treated, as long as the gas has a passage to the surface,
• large components can be treated in one go
the main disadvantages are:
• relatively slow,
• not easy to transform only parts of the surface
Blow moulding
Blow moulding is most commonly a batch process used to produce simple drinks bottles. Clever design
of the blank allows the screw top and base of bottles to be thicker than the walls.
Materials and shapes
• Used for simple, thin-walled, hollow products - mainly bottles
• Used with thermoplastics, mainly PET.
• Good, smooth surface finish can be readily achieved.
• Depending on how the hollow blank (parison) is made, scrap can be negligible.
• There is a variant which is continuous and used to produce thin-walled tubes which can be slit
to make cling-film or plastic bags.
• The production speed is limited by opening and closing the mould, so automation is normally
• Production rates from a few hundred to a few thousand per hour can be achieved.
• The tooling and machines are moderately expensive (£10,000 - £100,000).
• Moulds may need to be replaced after about 100,000 uses.
• Only used for high volume products with batch sizes of 100,000+.
Typical products
Bottles and containers up to 0.5 litre
Arc welding
Other names / variants: MMA, TIG, MIG, spot welding, seam welding
• 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.
• There are other more specialist arc welding processes such as spot welding or seam welding
which work without a filler.
• Safety precautions must be taken to protect the welder from the bright arc and the noxious
• Good welding requires a lot of skill, and in industry a welder must have special qualifications.
Materials and 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.
• 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.
• MIG and TIG are available as manual processes, but they are often automated to improve
quality and production rate.
• For joining thick metals, arc welding has few serious competitors.
• Where reliable joints are essential (e.g. aeroplane wings) mechanical fasteners such as rivets are
used instead of welding.
• Joining of sheet (e.g. car body panels) is usually more economic by other welding processes
such as spot welding.
Typical products
• Car bodies
• ships
• oil rigs
• pipelines
• pressure vessels
Adhesive bonding
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.
Materials and 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 solution is to design interlocking joints and combine with another form
of mechanical joining.
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.