3. 1 proccesses, techniques and specialist tools Flashcards
Heat treatments:
3.1a
hardening and tempering
case hardening
annealing
normalising
hardening and tempering
3.1a
The piece of work will
need to be first hardened to allow it to take the pressure of the work, but then tempered to remove the brittleness.
define heat treatments:
3.1a
Heat treatments is the term given to the process of heating and cooling metal in a controlled manner, to alter its properties in order to obtain certain desired characteristics
Hardening and tempering
step 1- harden the steel
step2- temper the steel
3.1a
step 1
Heat gradually until red hot
Plunge into cold water
Steel becomes hard and brittle
step 2
Clean using emery cloth until shiny
Reheat slowly and carefully
A thin line of oxide will appear and change colour with heat
Stop at the colour associated with the product
Quench in water
case hardening
3.1a
This technique is used for steels with low carbon content. Carbon is added to the outer surface of the steel, to a depth of approximately 0.03mm. One advantage of this method of hardening steel is that the inner core is left untouched and so still processes
properties such as flexibility and are still relatively soft.
annealing
3.1a
Annealing is a heat process whereby a metal is heated to a specific temperature /colour and then allowed to cool slowly. This softens the metal which means it can be cut and shaped more easily.
Mild steel is heated to a red heat and allowed
to cool slowly.
Aluminium- The flame should be held at a distance
to the aluminium so that it gives generalised heating to the metal. Rub soap on to the surface
of the aluminium and then heat it on the brazing hearth. It takes only a short time for the soap to turn black.
normalising
3.1a
Normalising is a process that is undertaken on ferrous metals that have become hardened, in order to return them to their original unhardened state. The steel is heated until cherry red, 900°C and then allowed to cool in the air.
which process applies to which material?
heat treatment
tempering
case hardening
mild steel aluminium high carbon steel steel copper
3.1a
Heat treatment
aluminium
steel
copper
tempering
high carbon steel
case hardening
mild steel
why carry out alloying?
3.1b
Pure metals are rarely used in manufacturing because they are too soft. Usually, other elements are added to the molten metal so that the resulting solid is harder and has other desirable properties.
alloy examples include:
1
2
3
3.1b
Stainless steel - 87% carbon steel for strength and rigidity and 13% chromium for resistance to wear and corrosion.
Duralumin – 93.5% aluminium for strength and lightness, 4.4% copper for strength, 1.5% magnesium and 0.6%
manganese.
Brass – 65% copper and 35% zinc
printing methods
3.1c
offset printing lithography
flexography
screen printing
gravure
offset lithography
3.1c
Principle:
Oil and water
don’t mix
Products: Posters Books Newspapers Packaging Brochures
flexography
3.1c
Principle - Relief printing (raised surface)
Products – Carton board containers Plastic bags Wrappers
screen printing
3.1c
Principle -
Stencil method
Products – Posters PoS displays T-Shirts Signage
Gravure
3.1c
Principle -
Intaglio printing
(engraved
surface)
Products – Labels Vinyl flooring Magazines Postage stamps
offset lithography
proccess
3.1c
Printing plate made from flexible aluminium Plate fixed to plate cylinder Rollers apply water – water is repelled from the image areas Ink is applied – ink is repelled by the water and adheres to the dry image areas Print transferred to a rubber blanket cylinder to avoid the paper getting wet. Blanket cylinder absorbs the water and picks up the ink Ink transferred to the paper Repeat for CMYK
flexography
proccess
3.1c
A plastic or rubber plate is made with a
raised surface for the image areas
Plate fixed to plate cylinder
A fountain roller is submerged in the ink
An anilox roller and doctor blade produce
an even distribution of ink
This is then transferred to the printing
plate
Then pressed onto the printed surface
Repeat for CMYK
screen printing
proccess
3.1c
A wooden or aluminium screen has a finely woven fabric stretched over it The non-image areas are blanked out using a photo-emulsion Place screen over the material to be printed on to Ink is applied to the screen A squeegee is used to push the ink through the screen onto the material Repeat for CMYK
Gravure
proccess
3.1c
Produce a digitally engraved copper plate cylinder Plate cylinder is partially submerged in the ink fountain The recessed cells are filled with ink A doctor blade scrapes the cylinder, removing the ink from the non-recessed areas An impression cylinder is then used to press the paper onto the plate cylinder. Repeat for CMYK
offset lithography
pros and cons
3.1c
Pros Good quality Inexpensive Wide range of surfaces High speed Widely available
Cons Colour variation due to ink and water Paper can get wet Expensive set up costs Only flat prints
flexography
pros and cons
3.1c
pros
High speed
Fast drying
cons Difficult for fine detail Colour may be inconsistent Set up costs high
screen printing
pros and cons
3.1c
pros Easy to produce stencils Print onto any surface Good for short runs Can produce large volumes
cons Can be hard to produce fine detail Longer drying times
Gravure
pros and cons
3.1c
pros
Consistent colour
High speed
High quality
cons Expensive plates Only long runs Can see the dots printed Very expensive set up costs
Casting methods
3.1f
sand casting
investment casting
die casting
resin casting
plaster of paris casting
sand casting
products
advantages
disadvantages
3.1f
Products:
Engine block
Garden furniture
Advantages: Inexpensive Complex shapes can be produced Large components can be made
Disadvantages: Sand moulds can only be used once Surface finish not always good Labour intensive Slow production rates
incestment casting
products
advantages
disadvantages
3.1f
Products:
Mechanical parts
Fan blades
Advantages: Excellent surface finish High dimensional accuracy Extremely intricate parts are castable Almost any metal can be cast No flash or parting lines
Disadvantages: Overall cost, especially for short-run productions. Specialized equipment Many operations to make a mould It can be difficult to cast objects requiring cores. Usually limited to small casting Requires longer production cycles compared to other casting processes.
die casting
products
advantages
disadvantages
3.1f
Products:
Traditional toy cars
Engine parts
Advantages: High dimensional accuracy is achievable Fast Production Thinner walls are achievable when compared to investment casting (0.6mm -0.8mm) Wide range of possible shapes Good finish
Disadvantages: Castings must be smaller than 600mm and the thickest wall section should be kept below 13mm High initial cost (Cost of moulds and machine set up) A large production volume is required to make the process cost effective
resin casting
products
advantages
disadvantages
3.1f
Products:
Industrial prototypes
Dentistry
Model making
Advantages: Cheaper moulds than injection moulding Resin casting enables the casting of intricate designs Can be casted or painted in any desired colour
Disadvantages: Drying time Not good for batch/mass production
plaster of paris casting
products
advantages
disadvantages
3.1f
Products: Lock components Gears Valves Fittings Tooling Ornaments
Advantages: Excellent surface finish Good dimensional accuracy Produces minimal scrap material
Disadvantages: can only be used with non-ferrous materials The used plaster cannot be reused. Metal cools more slowly than in a sand mould
sand casting
process
3.1f
Make a two part wooden pattern (replica of the product to
be made) – the pattern must have sloping sides so it can be
removed from the sand. It should have rounded edges and
no undercuts. This is then often finished with gloss paint.
Prepare the sand – it needs sieving to remove any lumps.
The mould in sand casting is produced in two open boxes
called the ‘cope’ and the ‘drag’.
The drag (bottom half) – turn this mould upside down and
place half the pattern face down in the centre.
Sand is then packed around the pattern.
Ram the sand down and levelled off.
Turn the drag over and place on the cope.
Place the second part of the pattern onto the first half.
Place the sprue pins into the sand – this is where the molten
metal is poured in.
Fill the cope with sand.
Remove the sprue pins.
Carefully separate the cope and drag.
Remove the pattern.
Re-assemble the cope and drag.
Pour molten metal into the sprue pin holes.
The metal is allowed to cool and solidifies.
Cope and drag is separated, the sand is broken up and the
product is removed.
The product now requires ‘fettling’ to remove excess metal
from the process.
investment casting
process
3.1f
The first step in investment casting is to manufacture the wax
pattern for the process – Since the pattern is destroyed in the
process, one will be needed for each casting to be made.
When producing parts in any quantity, a mould from which
to manufacture patterns will be desired. The mould to create
wax patterns may be cast or machined from aluminium.
Since the mould does not need to be opened, castings of
very complex geometry can be manufactured.
Several wax patterns may be combined for a single casting.
Or as often the case, many wax patterns may be connected
and poured together producing many castings in a single
process. This is done by attaching the wax patterns to a wax
bar, the bar serves as a central sprue.
A ceramic pouring cup is attached to the end of the bar. This
arrangement is called a tree, denoting the similarity of
casting patterns on the central runner beam to branches on
a tree.
The pattern is then dipped in a ceramic slurry. A ceramic
layer is obtained over the surface of the pattern. The pattern
is then repeatedly dipped into the slurry to increase the
thickness of the ceramic coat.
Once the refractory coat over the pattern is thick enough, it
is allowed to dry in air in order to harden.
The hardened ceramic mould is turned upside down and
heated to a temperature of around 90°C-175°C. This causes
the wax to flow out of the mould, leaving the cavity for the
metal casting.
The ceramic mould is then heated to around 550°C-1100°C.
This will further strengthen the mould.
Molten metal is then poured while the mould is still hot.
The casting is allowed to set as the solidification process
takes place.
Break the ceramic mould from the investment casting and
cutting the parts from the tree.
die casting
process
3.1f
Clamping - The first step is the preparation and clamping of the two halves of the die. Each die
half is first cleaned from the previous injection and then lubricated to facilitate the ejection of the
next part. After lubrication, the two die halves, which are attached inside the die casting machine,
are closed and securely clamped together. Sufficient force must be applied to the die to keep it
securely closed while the metal is injected.
Injection - The molten metal, which is maintained at a set temperature in the furnace, is next
transferred into a chamber where it can be injected into the die. The method of transferring the
molten metal is dependent upon the type of die casting machine, whether a hot chamber or
cold chamber machine is being used. Once transferred, the molten metal is injected at high
pressures into the die. Typical injection pressure ranges from 1,000 to 20,000 psi. This pressure
holds the molten metal in the dies during solidification. The amount of metal that is injected into
the die is referred to as the shot. The injection time is the time required for the molten metal to
fill all of the channels and cavities in the die. This time is very short, typically less than 0.1 seconds,
in order to prevent early solidification of any one part of the metal.
Cooling - The molten metal that is injected into the die will begin to cool and solidify once it
enters the die cavity. When the entire cavity is filled and the molten metal solidifies, the final
shape of the casting is formed. The die cannot be opened until the cooling time has elapsed and
the casting is solidified.
Ejection - After the predetermined cooling time has passed, the die halves can be opened and
an ejection mechanism can push the casting out of the die cavity. The ejection mechanism must
apply some force to eject the part because during cooling the part shrinks and adheres to the
die. Once the casting is ejected, the die can be clamped shut for the next injection.
Trimming - During cooling, the material in the channels of the die will solidify attached to the
casting. This excess material, along with any flash that has occurred, must be trimmed from the
casting either manually via cutting or sawing, or using a trimming press. The scrap material that
results from this trimming is either discarded or can be reused in the die casting process.
resin casting
process
3.1f
Produce a pattern of the object you would like to produce
a resin casting of.
Spray the pattern with the separating agent. This will help
to later remove the model from the mould. Allow to dry.
Suspend the pattern in a container with sealed sides
Pour silicon into the container half the way up the pattern
Allow to set
Apply a layer of silicon separation cream
Pour the rest of the silicon over the top half of the pattern
Allow to set
Remove the silicon and separate the two halves
Remove the pattern
In the example shown here the model maker pours resin
into the two halves separately. Letting the first half fully set
before pouring the second and placing the first set mould
over the top of the wet second half.
You can place a sprue inside with the pattern to allow the
resin to be poured into the mould in one go.
You can see the sprue holes on the right hand side of this
mould.
After removing the resin cast, you will need to clean the
model to remove any excess resin from the process.
plaster of paris casting
process
3.1f
Similar to sand casting except the moulding material is plaster of Paris instead of sand
Make a pattern in the shape of the product you require. The pattern is usually made from metal.
Spray a thin film of parting compound to prevent the plaster from sticking to the pattern.
Mix the plaster. The plaster is not pure plaster of Paris, but rather has additives to improve green
strength, dry strength, permeability, and castability.
The plaster is then poured over the pattern and the unit shaken so that the plaster fills any small
features.
The plaster sets, usually in about 15 minutes, and the pattern is removed.
The mould is then baked, between 120 °C and 260 °C, to remove any excess water.
The dried mould is then assembled, preheated, and the metal poured.
The metal solidifies.
The plaster is broken from the cast part.
Machining methods
3.1e
milling/ routing
drilling
turning
stamping/ pressing
Milling
3.1e
Milling is the process of cutting away metal, by feeding a
piece of work past a rotating cutter.
A vertical milling machine is used to shape metals such
as mild steel and aluminium.
drilling
3.1e
Drilling is the process of making holes by using a
rotating cutting tool that is either secured in either a
hand operated drill or drilling machine.
drill bits
3.1e
Flat bits – deep
holes in wood
Forstner bits –
flat bottom
holes in wood
Auger bits –
deep holes using
a brace
Countersink bits
– angled sides
for screws
Hole saw – large
diamtre holes
Tank cutters –
circular cutters
for metal
turning
method
-turning
3.1e
The work on a lathe turns. On a metalworking lathe
the cutting tools are securely fixed, whilst on
woodworking lathe, the cutting tools are held in the
hand and are rested on a tool rest.
On a metalwork lathe, work is held in a chuck and on
a woodworking lathe the material is usually secured
to a faceplate or turned between centres.
turning
method
-centre drilling
3.1e
Centre drilling is when the lathe I used to drill a hole
in the end of a rod or bar. It is the work which rotates in the chuck
with the drill help securely in the tailstock.
turning
- screw threads
3. 1e
Screw threads can be cut using a
centre lathe. They are cut from a from
a bar to produce the correct thread
profile.
turning
- knurling
3.1e
Knurling is a manufacturing process, typically conducted on a lathe, whereby a pattern of straight, angled or crossed lines is cut or rolled into the material
turing
- parting off
3.1e
Parting is the operation of cutting a
piece off by slicing a groove all the
way through it with a special parting
tool.
stamping/ pressing
3.1e
Stamping (also known as pressing) is the process of placing flat
sheet metal in either blank or coil form into a stamping press
where a tool and die surface forms the metal into a net shape.
laminaton
3.1f
Lamination is where a material has been produced by gluing together thin sheets, or veneers, to make up that material.
Lamination can also be used for shaping material. This is where strips of veneer are glued together and clamped in a
former. When the glue has dried the work is removed and it retains the shape of the former.
most common laminate materials
3.1f
lamin board (5-7 mm strips)
block coard (upto 25mm strips)
plywood
moulding methods
3.1g
injection moulding
blow moulding (pre-form)
blow moulding (parison)
vacuum forming
extrusion
rotational moulding
injection moulding
products
pros
cons
Casings for electrical products Packaging Toys
pros Good for mass production Low unit costs for high volume Precision moulding Surface texture can be added to the mould
cons High set up costs Expensive moulds to design and make
blow moulding (pre-form) products
pros
cons
plastic bottles
pros Intricate shapes Hollow shapes Thin walls to reduce weight and cost Good for mass production
cons High set up costs Expensive moulds to design and make
vacuum forming
products
pros
cons
Products: Yoghurt pots Blister packs Chocolate box inserts Packaging
pros Good for batch production Inexpensive Relatively easy to make the moulds
cons Accurate mould design needed to prevent webbing Large amounts of waste material produced
extrusion
products
pros
cons
drain pipes
tubes
pros Continuous High production volumes Low cost per unit Limited complexity of parts
cons
Uniform cross-
sectional shape
only
rotational moulding
products
pros
cons
Buckets
Footballs
Oil drums
Traffic comes
pros The investment in equipment and tooling is less than vacuum forming and blow moulding. No seams Uniform wall thickness Metal inserts can be added to the mould
cons
Lower volume
production
Labour intensive
blow moulding (parison) products
pros
cons
plastic bottles
pros Intricate shapes Hollow shapes Thin walls to reduce weight and cost Good for mass production
cons High set up costs Expensive moulds to design and make
