Flashcards

DT revision

Aidan Magee English 140 cards

Cards in this deck (140)

1PlasticityThe ability of a material to return to its original shape after the deforming shape has been removed.
2DuctilityThe ability of a material to be drawn or stretched
3HardnessThe ability of a material to withstand indentation, abrasion or stretching
4BrittlenessThe tendency of a material to fracture under Stress
5MalleabilityThe ability of a metal to be deformed by compression without being torn or cracked
6Aesthetic propertiesThe sensory qualities of a material
7Functional propertiesThe qualities of a material must possess in order to be fit for purpose, for example the correct weight, size, etc..
8Mechanical propertiesA material's reaction to physical forces, e.g. strength, plasticity, ductility, hardness, brittleness, malleability, etc..
9Ferrous• Metals that contain mainly ferrite or iron
• (steel which is made up of iron with various amounts of carbon)
• Occasionally ferrous metals have small amounts of other substances added to them to enhance their properties.
• Will rust
• Magnetic.
10White Cast Iron• Brittle
• Hard
• Not easily worked
• Cannot be machined
• Used in heavy machinery
• 1.7-2.9% carbon content
11Cast Iron• Brittle
• Will shatter or break if dropped
• Has high thermal conductivity
• Used in car brakes and cookware
• Ideal in situations where heat might be an issue.
• Impossible to weld
12Grey Cast Iron• More useful than cast iron
• Can be cast into intracate shapes
• Used on components such as tail stocks on lathes
• Corrosion resistant
• Used in cast iron cookware, disk brakes and machine components because of its high thermal conductivity
• 2.5-4% carbon content
13Mild SteelSteel is alloy of carbon. The more carbon added the harder it becomes.
• Ductile
• Malleable
• Tough
• Has high tensile strength
• Cannot be heat treated (except case hardening)
• Rusts (can be protected by galvanizong with zinc or thermoplastic)
14Carbon Steel• Can be heat treated to alter properties
• Has many engineering applications
• Versatile
• Can be cut, shaped or machined
• Major disadvantage is rusting (can be galvanised or painted to prevent this)
15Medium carbon steel• 0.30 – 0.70% carbon content
• Harder than mild steel
• Less ductile
• Less malleable
• Used for garden tools and springs
16High Carbon steel• 0.70 - 1.40% carbon content
• Properties can be improved by heat treating
• Used in hammer heads, drills and cutting tools.
17Non-ferrous• Metals which contain no iron, such as aluminium, tin and copper.
• Do not rust
• Are not magnetic
18Aluminium (purest form)• Pure metal
• Soft
• Malleable
• Conducts heat and electricity well
• Useless as enginerring material in purest form
19Aluminium• Lightweight
• Soft
• Malleable
• Good conductor
• Difficult to weld
• Cracks under stress
• Requires constant annealling when being worked
• Doesnt withstand loads well
• Melting point 650C
• Used in aircraft components, engine components and castings
20Aluminium 2• Aluminium is always alloyed to improve its properties
• When polished and shone aluminium s shine will disappear after a short period of time because an oxide layer forms
• This protects the aluminum from oxidation and allows it to be used outdoors
21Copper• Easily cut and machined
• Very malleable
• Ductile
• Good conductor of heat and electricity
• Easily machined
• Corrosion resistant
• Can be worked cold but does work harden
• As it is work hardened it becomes harder to work with, eventually cracks appear and it can break. This can be rfeversed by annealing
• Can be joined via hard/soft soldering
• Used for electrical cables, central heating, printing circuits, pipes.
• Melting point 1100C
22Zinc• Easily worked
• Has an oxide layer which prevents oxidation
• Corrosion resistant
• Used in the galvanisation process to protect steel from rusting
• Used in products such as buckets, water tanks and car bodies to prevent rust
• Used as an element in solder fluxes
• Used in die casting
• Becomes brittle when worked
• Used in batteries, die casting and galvanising
• Melting point 420C
23Alloys• Metals that have been formed by mixing two or more metalsand occasionally other elements in order to produce metals withenhanced properties.
• An example is stainless steel which is an alloy of steel and chromium. Adding chromium to the steel makes it less prone to rusting.
24Stainless steel• Steel alone when leftuncoated will oxidise (rust). One way of preventing this is to alloy it with another metal.
• Stainless steel is an alloy of steel, chromium and nickel.
• Corrosion resistant
• Expensive
• Hard to cut
• Used for kitchen utensils, medical tools and chemical and nuclear industries
25Duralumin• Alloy of Aluminium, copper and manganese
• Lightweight and strong
• Age hardens it
• Malleable
• Ductile
• Easily machined
• Work hardens
• Used in the aviation and automobile industries
26Brass• Alloy of copper and zinc
• Corrosion resistant
• Harder than copper but can easily be joined using hard and soft soldering
• It has good heat and electrical conductivbity
• Casts well
• Easy to machine
• Susceptible to cracking
• Needs to be annealed constantly
• Used in central heating valves, electrical components, ships propellers and plumbing fittings.
27ThermoplasticA thermoplastic is a material that, once produced, can be formed using heat, into a variety of shapes using different forming techniques. e.g. injection moulding or blow moulding.
• Thermoplastics can be reheated, softened, shaped, reshaped and cooled many times over.
• They can be recovered and recycled easily.
• Thermoplastics - Made up of long chains of molecules held together by small cross links. The polymer chains are held together by mutual attraction called Van der Waals forces.
• When a thermoplastic is heated, the bonds between the chains weaken and become pliable. This means that the plastic can be shaped and formed. Once the heat is removed & the plastic cools down the chains reposition and the plastic becomes hard. This means that they can be heated and shaped many times.
28Acrylic• Stiff
• Hard
• Durable
• Can be easily scratched
• Good electrical insulator
• Brittle and can break
• Scratches easily
• Splinters easily
• Used for lighting, CD cases, car lights and baths
29High Density polyethylene (HDPE)• Good electrical insulator
• Chemical resistant
• Impact resistant
• Flexible
• Colour tends to fade over time
• Can break under stress
• Used for water tanks, pipes, buckets and bowls.
30Low Density polyethylene (LDPE)• Good electrical insulator
• Chemical resistant
• Flexible
• Colour tends to fade over time
• Can break under stress
• Used for washing up liquid bottles
• Dustbin sacks
• Cable insulation
• Packaging film
31Polyethylene terephthalate (PET)• Good alcohol and oil barrier
• Chemical resistant
• High impact resistance
• High tensile strength
• Can discolour
• When used in containers for foodstuffs needs to be treated to prevent taste problems
• Fizzy drinks bottles
32Polyvinyl chloride (PVC)• Good chemical resistance
• Weather resistant
• Stiff
• Tough
• Hard
• Lightweight
• Can become brittle over time
• Ultraviolet light causes brittleness
• Used in electrical wiring insulation, Pipes and guttering , Floor covering
33Polypropylene (PP)• Light, hard
• Chemical/impact resistant
• Ultraviolet causes
degradation
• Oxidation causes
problems during
manufacture
• Medical syringes, Carpets, Kitchenware
34Compressed PS• Light, hard, stiff, brittle,
low impact strength
• Weak
• Ignites easily
• Used in CD cases, Water tanks, fridge linings
35Expanded PS• Buoyant, lightweight,
good insulator
• Crumbles and breaks
• Easily ignites
Used for Packaging and Insulation and displays
36ABS (Acrylonitrile butadiene styrene)• Chemical resistant
• Hard & Tough
• UV causes degradation
• Used for Mobile phone casings and Safety helmets
37Thermosetting• Thermosetting plastics - Unlike thermoplastics, thermosetting plastics once formed cannot be reheated and changed. The molecules in thermosetting plastics link side-toside and end-to-end. This linking is referred to as covalent bonding and the result is a very rigid structure.
• Thermosetting plastics on the other hand are produced by mixing two components, a resin and a catalyst, together. These are usually in the form of liquids or pastes. Whilst they are apart they remain a liquid or paste but as soon as they are mixed together a chemical reaction occurs and the mixture becomes hard.
• Unlike thermoplastics, thermosetting plastics, once shaped cannot be heated and reshaped.
• Thermosetting plastic are therefore harder to recycle.
38Thermosetting Plastics 2• Produced by mixing a
resin and a catalyst
together, which are usually
in the form of liquids or
pastes.
• Chemical reaction occurs
when mixed together.
• Once shaped, cannot be
heated and reshaped.
• Difficult to recycle.
• The molecules in thermosetting link side to side and end to end
• This linking is referred to as covalent bonding and the result is a very rigid structure
39Epoxy resin• Corrosion resistant
• Electrical resistant
• Good bond qualities
• Health problems
• Can cause Allergic reactions
• Used for Adhesives, Paints and coatings and Electronics
40Urea formaldehyde• Strong
• Hard
• Brittle
• Heat resistant
•Can emit toxic vapors during manufacturing process
•Electrical fittings
• Domestics appliances
41Polyester Resin• Good electrical insulator
• Heat resistant
• Brittle
• Can crack
• Used for Glass reinforced boats and Garden furniture
42Hardwoods• Hardwoods - Not necessarily hard. (Balsa wood for example is physically very soft but it is technically a hard wood.)
• Hardwoods come from bread-leaved trees whose seeds are enclosed. Common hardwood trees include oak, mahogany and beech, hardwood trees usually grow in warmer climates and take on average 80 - 100 years to reach maturity. Due to the relatively long time they take to grow, hardwoods tend to be more expensive than softwoods. Very often hardwoods come from inaccessible places and this also adds to the cost.
• Added to this, there is also an environmental issue. If a tree takes 100years to mature it takes a long time to replace. For this reason there is concern about the overharvesting of hardwoods.
• They produce tough, strong timber and often have a close grain.
43Oak• Strong, hard, tough
• Works well
• Durable
• Expensive and heavy
• Prone to splitting
• Can be physically hard
• Used for high quality furniture, construction and garden furniture
44Mahogany• Easy to work
• Durable
• Finishes well
• Grain can be variable
• Prone to warping
• Physical hardness varies
• Used in Furniture, Veneers and Floorboards
45Beech• Physically hard, tough
• Polishes well
• Prone to warping
• Not suitable outside
• Difficult to work
• Workshop benches, School desks
and Furniture
46Softwoods• Softwoods - Not necessarily physically soft. (A plank of pine can feel physically hard as a plank of oak!)
• Softwood is the wood that comes from cone-bearing conifer trees. They have needles rather than leaves.
• Examples of softwoods are Scots pine (red deal), Parana pine and whitewood.
• Softwoods grow quicker than hardwoods. On average they take 30years to mature and can be produced in plantations where they can be forested and replanted.
• As a result of careful planning, in particular by the Forestry Commission in the UK, softwood is a managed resource. As a consequence, softwoods tend to be cheaper to buy than hardwoods.
• As a rule, softwoods are easier to work than hardwoods.
47PineStraight grain
• Easy to work
• Knots can make working
difficult
• Comes from conebearing
(conifer) trees
• Grow quickly (30 years)
• Cheaper than hardwoods
•Used in Construction, Roof joists and Floorboards and Furniture
48Composites• If two or more materials are combined together by some kind of bonding, a composite material is created. The resulting composite often has improved mechanical, functional and aesthetic properties when compared to the original materials from which it was made.
• They tend to have excellent strength-to-weight ratios and are useful for many projects.
49Glass Reinforced Plastic (GRP)• GRP - Glass reinforced plastics - Is a composite material that is manufactured from thermosetting plastic resin that has been reinforced using very fine glass. This glass comes in the form of either matting or in strips.
• Resin on its own is relatively strong when it comes to compressive strength but weak in tensile strength.
• By adding glass matting to the resin, the tensile strength of the final product can be considerably improved. In fact, GRP can be as strong as steel.
50Manufacturing a product in GRPManufacturing a product in GRP
• Stage 1 - A high-quality mould is prepared. This is the 'negative' of the product being produced.
• Stage 2 - A release agent is sprayed onto the mould. If not done, the final product will not be able to be removed from the mould.
• Stage 3 - A gel coat is applied to the mould. This is a thin layer of special resin that will form the outer skin of the final product. This will end up being a shiny layer & will be coloured by adding a pigment to the gel coat.
• Stage 4 - Alternative layers of resin plus catalyst and glass matting are placed in the mould. It is important that the resin is worked well into the matting to ensure the best finish. usually in an item like a fibreglass canoe, there should be about 6 layers of glass matting fused with resin.
• Stage 5 - Once the 'laying up' process has been completed, the work is left to cure over night and then it can be gently eased out of the mould.
51Glass Reinforced Plastic (GRP) 2• Can be as strong as steel
• Good strength-weight
ratio
• Resistant to corrosion
• Prone to osmosis (water
seeps through and
delaminates the hull)
• Resin and catalyst give
off harmful toxic fumes.
• Thermosetting resin
reinforced with very fine
glass, resin is strong
(compressed) not good
tensile strength and is
brittle, adding glass
matting improves this.
• Car bodies
• Boat hulls
Gloves must be worn and must be carried out in well ventilated room
52Carbon Fibre• Can take very heavy load
• Extremely strong, far
stronger than GRP
• Excellent properties allround
• Carbon fibre composites,
which can take tensile
loads are set onto a
polymer matrix able to take
compressive loads.
Together they make an
incredible tough material.
• Aircraft
• Sports Equipment
• Racing car manufacture
53Medium Density Fibreboard (MDF)• Can be laminated to
improve strength/
aesthetics
• Is easily workable
• No danger of splitting/
warping due to no grain
• Produces dust when
worked - which is irritating
towards the skin, nose and throat. Dust extraction should be used.
• Can be very heavy
•Made from wood chips from wood waste which are heated and
pressurised, then the pulp
is adding with synthetic
resins that bond the
material together, making it
uniform in thickness with a
fine texture. After cooling, the sheet material is trimmed.
Used for Furniture (with formica)
• Worktops
• Flat pack
54ChipboardChipboard - Wood particles are glued together under heat & pressure. Results in a rigid board, with a relatively smooth surface. If wet can swell and break down.
• Very cheap
• Easily workable
• Can become waterlogged
and swell
• Unattractive
Same process as MDF,comes in normal, medium, and high-density forms.Most common is normal density.
Same uses as MDF.
55LaminateA material that is produced by bonding together two or more layers of material. Very stable. Do not warp or misshape. Can be easier to work than wood.
56PlywoodPlywood - Manufactured from layers of veneers bonded together with the grain direction at 90 degrees to the sheet of veneer above and below it. Odd no. of sheets.
•Very strong and stable
• Doesn’t warp/distort
• Relatively cheap
• If damp, the the layers delaminate and come apart
• Marine ply, which is more expensive is waterproof.
Veneers are obtained by the rotary
cut process of timber.
Used in Flooring/construction
• Flat pack furniture
• Schools workshops
57BlockboardManufactured by softwood strips 25mm wide positioned edge-to-edge, it is then covered with an attractive veneer such as beech on either side of the sheet, it is then glued together with water based glues and subject to heat and pressure, therefore making it suitable indoors.
• Good resistance to
warping/distorting
• Strong and durable
same uses as plywood
58Makeup of Blockboard and Plywood
59Thermo-Ceramics 1Thermo-ceramics - used in specialist engineering situations. Their internal structure makes them extremely hard and very stable at very high temperatures. Used in places where stability and strength at high temp. are necessary. e.g. turbine blades in jet engines, turbo chargers in racing cars.
60Thermo-Ceramics 2• Extremely hard
• Very stable at high temps
• Very strong at high temps
• Superior to ceramics
• Brittle, break when dropped
• If they are imperfections in the material, it can break/crack
• Very expensive
They are advanced ceramic materials that are used in high temperature surroundings. They are produced by combining ceramic and metallic powders by sintering. The powders are subject to heat and pressure in a die
until the particles bond.
• Used for Turbine blades in jet
engines, Turbo chargers in racing
cars.
61Tinted glass and Photochromic glassGlass that automatically darkens when exposed to ultraviolet light & then reverts to when light has gone. Used in spectacles.
• Automatically darkens when exposed to UV light, returns clear when light reduces
• Reversible process
Glass is impregnated with minute silver halide particles, which reacts to light, is encapsulated and sealed within the glass. Used for specs
62Solar PanelsPhotovoltaic cells, constructed from silicon (with impurities) have two layers: when exposed to light one layer becomes electron rich while the other is electron deficient, therefore a current is produced which can then be tapped into via contacts.Unfortunately voltage produced is very small.
• Extremely inefficient and
uneconomical
• Limited applications as the environment must be in sunny areas that receive plenty of light
• Useful in remote places (marine buoys..etc) where mains power is not readily available.
• Marine buoys, ships,remote railway signalling
• Medicals in developing
countries
• Domestic housing
63Liquid Crystal displaysLiquid crystals are organic, carbon based compounds that are have both liquid and solid characteristics, because of the molecular arrangement, when voltage applied, on which light falls, the crystal goes dark.
• Ultra flat screens
• Very high resolution
• Can harness millions of colours
• Images produced are inferior to cathode-ray televisions and screens
• Do not require much power
Used for Portable devices (phones..etc)
• Computers
• TVs
64Electroluminescent lightingElectroluminescent lighting - Converts electrical energy into light by applying a voltage across electrodes. An organic phosphor is sandwiched between two conductors and, as the electric current is applied, it rapidly charges phosphor crystals, which emit radiation in the form of visible light. Extremely low fuel consumption. Used for LCD displays e.g. blue glow on a digital watch. Used in advertising to produce displays and posters with high visual impact.
• Very low power consumption
• Organic phosphor materials have a limited life span
• LCD backlighting
• Billboards
• Watch backlights
65Shape Memory Alloys (SMA)• A material that can be deformed having had an outside stimulus and will revert to its origional shape when the stimulus is removed
• The stimulus is sometimes heat which is sometimes powered by electrical input
• Others react to light such as photochromatic pigments
• Some react to pressure (such as quartz)
• Nitinol, alloy of nickel and titanium can be programmed to a certain length or shape at a set temperature, as the temperature increases - the nitinol will bend or contract until the heat source is removed, at which it will return to it’s original shape.
• Can be repeated millions of times
• Expensive to produce
• Difficult to machine
• Not very strong
• Used in • Air conditioning • Fire alarms • Hydraulic systems • Hot water systems
66Reactive GlassGlass that goes dark when receives an impulse from the impregnated silver
halide particles.
• Rapid transition from clear to dark.
•Very effective at what they do.
Used in • Welding masks
• Privacy glass
67Photochromic paintPaints that contain pigments that change colour instantly when stimulated with UV, when the light source is removed it returns to it’s original colour
• Reversible process
• Almost instant transition of colour
• Can create stunning pigment changes
Used in • Security markers
• UV warning sensors
• Art
68Quantum tunnelling composites (QTCs)A smart material that when stretched, compressed, twisted goes from being an electrical insulator (relaxed) to an electrical conductor (Activated), allowing current through, sometimes very high currents. As the strain increases, the material will conduct more electricity.
• Instant transition of property
• Proportional properties: Strain and conduction
• Can be used millions of
times non-stop
Used for • Power tools
• Robots
• Textile industry
69Nuts and Screw threads• Nuts are usually manufactured from mild steel or med carbon steel
• Advantage of nuts and bolts is that they can be easily undone allowing components to be replaced or repaired.
• The diameter of a bolt is always in mm and is sold in standard or stock sizes
• The most commonly used thread is the ISO metric thread (root angle 60 degrees)
• Others have different angles (British Standard Whitworth threads – 55 degrees)
• The other measurement you need to know is the pitch
• The pitch is the distance a bolt or screw will travel through one full revolution
70V thread 1
71V thread 2• Generates a lot of friction/locks in place.
• Can be used with readily available standard components e.g.
nuts.
72Screwthread
73Acme thread
74Acme Thread 2• Strength / transmits large forces.
• Applies force in both directions.
• Allows a disengaging facility / easy engagement
75Buttress Thread
76Buttress thread 2• Applies force in one direction only.
• Facilitates quick release systems / easy engagement.
77Specialist Nuts• Where vibration is an issue there is a danger that it could cause some nuts to come loose. In these cases lock nuts are used
• Lock nuts might have split pins put through them or nylon inserts which lock the nut as it is being tightened
• It is often necessary to screw a thread into a hole to allow a machine screw to be screwed into it or onto a rod so a nut can be screwed onto it
78Cutting threads on a rod 1• A thread can be cut by hand or by using a metalworking lathe
• The quickest and most common way to put thread on a bar is to cut it by hand
• The tools required are a die and a die stock holder
• It is important the size of the die matches the size of the bar ie 10m die on 10mm bar
• Dies are manufactured from high speed steel which is harder than mild steel so it will cut a thread on mild steel quite easily
79Cutting threads on a rod 2• Firstly, the end of the bar that is to be thread needs to be slightly chamfered with a file. This will help the die to go onto the bar.
• The die then needs to be screwed onto the bar.
• The biggest problem is making sure that the die goes onto the work squarely. If this is not done a 'drunken thread' is produced. This means that any nut screwed onto the bar will not be at right angles to the bar and will appear wobbly on the bar.
• One method of ensuring that the de is on the bar squarely is to use the tailstock of a centre lathe.
• Set the work up in the chuck on the lathe and place the die between the work and the tailstock and, by hand, turn the work until the die just begins to cut. As the axes of the lathe and the tailstock are at 90" to each other, the die must go on at the correct angle.
• Once the die has started to cut the diestock should be gently turned half a turn clockwise and then a quarter of a turn anticlockwise to break off the swad.
• As with cutting an external thread, some lubrication is again necessary.
80Cutting threads on a rod 3
81Cutting threads in holes 1• The correct term for putting a thread into a hole is 'tapping.
• The first consideration when tapping a hole is that the hole into which the thread is to be cut must be the correct size.
• The tapping hole diameter is determined by subtracting the depth of the thread from the outside diameter of the bolt or machine screw.
• For example, to produce a thread in a hole a 5mmm bolt could screw into a drill with a diameter of 4.2mm would be required. This would mean that the depth of thread would be 08mm.
• The tools required to cut the thread are 'taps and a tap wrench.
• There are three types of tap, the taper tap. the intermediate tap and the plug or bottoming tap, and each tap is used at different stages of cuing the thread.
82Cutting threads in holes 2• Once the hole is drilled the first tap. the taper is planted into the hole and using a tap wrench the thread is carefully cut
• The wrench and tap must be slowly turned through half a turn clockwise and then a quarter of a turn anticlockwise to break off the swarf.
• The tap will gradually work through the Piece of metal Until it appears on the other side.
• During this process some lubrication should be applied This lubrication traditionally hasbeen tallow, but any grease or oil will work.
• This process is repeated with the intermediate tap and then &nay with the plug or bottoming tap. Each tap takes out a little more material from the hole until the thread is completed.
• One of the most important things to remember when tapping a hole is that the three taps must be at a right angle to the metal. If this is not done. when the thread is completed. any screw put into the hole will go in at an angle and appear wobbly when a is screwed in
83Cutting threads in holes 3• Taps can be fragile and Snap very easily
• If a tap breaks in a piece of work it is often very difficult to remove it from the hole.
• The most difficult holes to put a thread in are 'blind holes” , holes that do not go right through the metal
• If you are not careful it is easy to keep tuning the tap wrench into the blind hole and snap the tap
84Cutting threads in holes 4
85Spacers & washers• Sometimes used in machinery.
• Used in situations where components need to be separated on a shaft, such as on a bicycle gears where it is sometimes necessary to put a spacer to separate the gears.
• Come in various materials e.g. HDPE, nylon, steel.
• Can also be used as spacers, anti-vibration devices and locking devices.
86Screws• Often used as part of a temporary joint.
• Machine screws used for engineering and woodscrews used for wood.
87Machine ScrewsParallel sides with standard threads cut into them.
Usually manufactured from carbon steel and are mass produced.
Come with a variety of different heads or tops. Most common are countersunk (which allow them to fit flush with the material) heads and cheese heads (which sits above the metal into which it has been screwed).
88Cheesehead screw
89Wood screws• Classified first by shape of screw head and secondly by length of screw itself.
• Three types of head; Countersunk head (allow flush surface), raised head (Head is slightly domed and round head (Rests on top of the surface of wood).
• Pilot hole should be used to avoid splitting the wood.
90Raised head screw
91Round head screw
92Rivets• Are permanent joints in metals. There are two kinds of rivets, solid rivets and pop rivets. Solid rivets are manufactured from soft iron because they need to be ductile and easy to work as they have to be hammered into shape.
• Pop rivets are usually manufactured from aluminium and, instead of being hammered into shape, are fixed into place using a pop rivet gun.
• Examples: Countersunk rivet, snap rivet, flat rivet, pop rivet.
93Rivets 2
94Rivets
95Pop Rivet
96Gears 1Gears
Gear wheels are one part of a mechanical system that when linked together can have a number of applications. Essentially, they are used to transmit rotary motion in various ways. Gears can be used to:
• Change direction of rotary motion.
• Change spindle speeds.
• Transmit motion through 90 degrees.
The shape of a gear tooth is in fact a mathematical curve called an involute.
If one gear was bigger than the other, the rotational speed would be changed between each gear.
If both gears were required to turn in the same direction an extra gear called an idlerwould be placed between the input and output gears. An idler can be of any size.
For more complex tasks, a compound gear train is used. This involves separate gear trains that mesh together. Can significantly increase or decrease the number of possible rotational speeds.
97Gears 2
98Gear velocity ratio
99Spur GearUsed in • Simple gearboxes • Clothes dryers • Alarm clocks
• Speeds can be increased or decreased
• Direction of rotation can be changed
100Spur gear 2
101Bevel and mitre• Can have shafts at 90degrees
• Different sizes of gears can change speeds
• Commonly seen on hand drills
102Bevel and mitre 2
103Worm and wheel• Transmit force and motion through 90degrees
• Reduction in rotational speed possible
• Used in food mixers
104Rack and pinion• Used to change rotary motion into linear motion
• Used in pillar drills
• Used in steering mechanisms in cars
105Rack and pinion 2
106BearingsBearings are used to reduce friction and decrease the wear of materials at their joints e.g. where a rotating shaft is being supported, so the bearings reduce friction and allow shafts to spin more efficiently.
107Plain bearingsIn its simplest form, can be a support that holds a rotating shaft. To reduce the wear of the support, a sleeve of a bearing material is used. This is called a bush. Most common material for bushes is bronze which is 90% copper and 10% tin. The disadvantage of using a bush is that they wear out over time and have to be removed and replaced. An advantage of using sintered ceramics in bearings is that they are porous and if saturated with oil soak up the oil and thus provide lubrication for the bearing.
108Journal BearingsJournal bearings - The main difference is that, instead of having a bush insert, it has a layer of grease, or oil, between the rotating shaft and support. The theory is that the layer of grease, or oil, is very thick and therefore the shaft never actually comes in contact with the support. In order to keep this type of bearing working efficiently, it is important that regular servicing is undertaken and the grease is kept to the correct level. To top up the oil or grease, it is fed into the bearing under pressure through a small hole.
109Plain bearing
110Journal Bearing
111Ball Bearing
112FollowersCams are usually used in machines where, in some part of that machine, rotary motion needs to be changed into reciprocating linear motion. They come in a wide range of sizes and shapes, all of which are designed for specific tasks.
Each type of these movements requires a different cam profile (followers that move around the cams). The most common are:
• Flat -(flat disc or block) - Lots of friction. Cannot follow hollow contours.
• Knife -(pointed end) - Provides the most accurate conversion of movement. Can be used to follow hollow contours.
• Roller -(round wheel) - Least friction. Cannot be used to follow hollow contours. Most expensive.
113Followers 2
114CamsVarious types of cams and their characteristics:
Pear-shaped cam - Used in control inlet and outlet valves in engines. Symmetrically shaped so rise and fall times are identical.
Eccentric or circular cams - Simplest type of cam as based on an off-centre circular disc. Smooth rise and fall. Constant acceleration and retardation. Used in fuel pumps.
Heart-shaped cams - Symmetrical cams that generate continuous motion. Used in sewing machines and to wind relay coils and motor windings.
Snail cams - Generate output with uniform acceleration and retardation.
115Cams 2There are 3 types of movement that can be created by cams
Uniform velocity
simple harmonic motion
uniform acceleration and retardation
cams are used to change one type of motion into another IE rotary into reciprocating linear motion
116Pear shaped
117Eccentric
118Hearth shaped
119Snail
120Scale of productionOne off - 1
Batch 100s - 1000s
Continous - hundreds of thousands
Mass - Hundreds of thousands - millions
121One offOne-off - Referred to as job production and relates to 'tailor-made', bespoke or customised solutions. A key feature is a single, often high-cost product that is manufactured to a client's specification. This kind of one-off product may be relatively high-cost payment for unique features, more expensive or exclusive materials and time-consuming handcrafted production.
• SMALL SPECIALIST COMPANIES.
• -A SKILLED WORKFORCE - SPECIALIST SKILLS eg. ENGINEERING.
• -SPECIALIST MATERIALS OFTEN REQUIRED eg. SPECIALIST MODELLING MATERIALS.
• -HIGH QUALITY PRODUCTS MANUFACTURED.
• -FINAL PRODUCTS OFTEN EXPENSIVE DUE LEVEL OF SKILL REQUIRED TO MANUFACTURE THEM AND COST OF SPECIALIST MATERIALS.
• -A HIGH STANDARD OF QUALITY CONTROL
• -PRODUCTS MANUFACTURED FOR AS SPECIALIST MARKET / CLIENTELE.
• Used for PROTOTYPES
• SPECIALIST MODELS
• HANDMADE ITEMS
• SPECIALIST ENGINEERING
• ONE OFFS
122Batch• Involves manufacture of products in specified, predetermined 'batches', which can vary from 10's to 1000's.
• A key feature is flexibility of tooling, machinery and workforce to enable a fast turnaround, so production can be quickly adapted to manufacture a different product, depending on demand.
• Batch production often makes use of flexible manufacturing systems (FMS) to enable companies to be competitive and effective.
• The use of CIM (computer-integrated systems) involving automated machinery enables production 'downtime' to be kept to a minimum.
• Lower unit cost than one-off production.
• Scale of buying materials enable cost savings and identical batches of consistently high-quality products are manufactured at competitive costs.
123Mass production• Makes use of efficient automated manufacturing processes and a largely unskilled workforce.
• Mass-produced products are designed to follow mass market trends, so the product appeals to a wide national and international target market.
• Product planning and QC in production enables manufacture of identical products.
• Production costs are kept as low as possible so the product will provide value for money.
124Continuous• Used to manufacture standardised mass-produced products that meet everyday mass-market demand.
• The production of blow-moulded fizzy drinks bottle, for example, necessitates 24-7 to satisfy customer demands for soft drinks.
• This type of production is highly automated and uses machines that can run continuously for long periods of time with breaks only for routine maintenance.
125Scale of Production
126Preperation of sand casting mould• Sand casting is the process where molten metal is poured into a tend mead that contains a cavity of the desired shape of an object or component.
• Once the metal has toldified the sand is bicker open and the product or component is removed. 7he first step in sand casting is to make a mould in sand using a pattern. A pattern, usually manufactied from wood a medium density fibreboard (MDR. is a replica of the object that is so be cast. It is identical to the finished product apart from the fact that it is slightty oversized to allow for the contraction of metal as it coots down.
• The mrity of patterns are made in two parts They are cut down the centre line and are held together using dowels. Using split patterns allows MO sides of a sand mould to be created and complex casting to be produced.
• Pattern making for casting requires great skit TM pattern mat be designed with sloping sides so that it can be easily removed from the mould *About demagog the walls of sand. It must have no undercuts or sharp edges and any corners must be finished off with fillet radii
127Sand casting 1• Molten metal is poured/forced into a sand mould with a cavity where the metal fills;
• Firstly, a mould is produced by green sand (or Petrabond) with a pattern inside to create the cavity for the metal (usually in two parts, to create a complex shape) (usually made from MDF) that is slightly oversized to allow for contraction.
• The pattern is covered with parting powder (to stop it sticking) and then compact facing sand and the drag is filled with backing sand.
• The cope and drag are placed on top of one another, the sprue pins are locked in place; this is where the metal will enter the cavity, (runner) and how the air is released (riser). Gates are cut and a hollow is cut where the metal will flow into the sprue pins.
• The mould is clamped and enclosed, the metal is heated in a crucible in a furnace until it is molten, then it is fluxed and degassed (removing impurities and bubbles) before being poured. The metal is then poured slowly into the mould until the riser becomes occupied with metal.
128Sand casting 2The metal is then left to cool and solidify, when ready, the mould is opened and the component removed and fettled (runner/risers/waste cut off with hacksaw).
• Green sand must be thoroughly dried before the metal is poured to prevent an explosion.
129Sand casting 3
130Sand casting advantages• Produces extremely high quality metal components
• Mould can be reused (unless made from Petrabond)
• Is a very time-consuming, therefore not suitable for mass production, and is dangerous process
• Pattern making requires highly skilled craftsman
• Requires many different parts processes before actually casting the metal.
• Can be a cheap process; but is labour intensive.
131Sand casting 4Materials used• Ferrous metals
• Aluminium
• Magnesium
• Brass
• Bronze
Uses • Machinery component
• Engine parts
• Mechanical pieces
• 70% of all metal components are made from sand casting.
• Caterpillar tracks
132Die Casting 1Pressure die casting: forcing the molten metal in the mould via an Archimedean spiral.
Gravity die casting: molten metal flows into the cavity under the influence of gravity.
Pressure die casting: Dies are reusable moulds made from high-speed steel. The metal is forced into the die under hydraulic pressure.
• Firstly, the mould is sprayed with lubricant to control the temperature and ease the removal of the component,
• molten metal is then shot into the mould,
• once filled the pressure is maintained until it has solidified and cooled.
• It is then removed by ejector pins, the gates, runners and risers are cut off.
133Die Casting advantages• High volume process suitable for mass production
• It is highly automated
• Produces very high quality castings.
• Unlike sand casting, it cannot be done in schools.
• Produces good surface finish
• Good control over mould temperature during process
• Elements such as screw threads can be including in the casting.
134Die casting 3Metals used Non Ferrous metals:
• Zinc
• Aluminium
• Copper
• lead
Uses • Engine blocks
• Large components
• Same as sand casting but not as complex
• Taps
• Model cars
135Milling / routing 1• It is a process of cutting away material, it can be CNC, and it works by the piece of work being fed through a rotating cutter.
• Routing is for wood; milling is for metal; and is usually used for cutting slots into material.
• The work must be securely fastened to the bench and the rotary speed and the speed the work travels through the cutter are closely controlled.
136Milling/Routing advantages• Very neat and tidy process
• Depth of groove can be customised
• Relatively quick and inexpensive process
• Suitable for any production method as the initial setup costs aren’t too high.
137Milling/routing• Soft, easily machined, malleable metals such as aluminium.
• Grooves for shelving units
138How milling is done (metal)• Block clamped to table / clamped in machine vice (1)
• Cutter selected / fitted into chuck / collet / onto
mandrel (1)
• Table manoeuvred into position (1)
• Appropriate speed / feed selected (1)
• Cutter rotates (1)
• Block fed into cutter (1)
• References to up milling / down milling (1)
• Several small cuts taken (1)
• Cutting fluid applied (1)
139Milling machine
140Drilling• Process of making holes using a rotating cutting cutting tool operated by a hand drill or drilling machine
• Most common type is twist drill
• Two types – parallel shank and taper shank
• Parallel held by chuck and taper held by friction
• Drill bits have grooves along them to remove swarf (waste material)
• When cutting , cutting fluids or lube should be used to keep drill cool and efficient