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Engineering > Trials Study > Flashcards

Trials Study Flashcards

1
Q

Precipitation Hardening

A

Mostly for Al alloys,
1. Heat and soak to make a homogenous structure
2. Quench to retain uniform structure
3. Heat to slightly elevated temp, disperse precipitate throughout structure

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2
Q

Heat Treatment Types (6)

A
  1. Annealing (Process and full)
  2. Precipitation hardening
  3. Normalising
  4. Tempering
  5. Spheroidising
  6. Austempering
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3
Q

Normalising

A

Heat to austenitic region (above UCT), then cooled in still air
- finer grain structure then annealing, thus stronger

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4
Q

Process Annealing

A

Less that 0.3%C, heated to 550-650 (below UCT). Cooled in still air
Releaves stress from cold working or deformation
Unstressed ferrite, stressed pearlite

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5
Q

Full annealing

A

Heat to above UCT, (hypo-eutectoid or eutectoid), then cool slowly in furnace. Large, equaxied grains of unstressed pearlite and ferrite.

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6
Q

Spheroidising

A

Medium to high carbon steels
Heat steel to around 650-700, soak (slightly below UCT). Slowly cool
- forms spheres of cementite (easier to machine then lamellar pearlite)
- improved ductility, malleability

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7
Q

Hardening Process

A

Heating transforms to austenite (BCC-FCC). Quenching does not give it enough time to react, and so: Cannot transform to BCC, remains trapped in between as BCT (MARTENSITE) (>0.3%C)
- hard yet brittle

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8
Q

Tempering

A

Used to make tempered martensite from acicular martensite. (DIAGRAM: needles to needles with smudges)
- reduced hardness slightly, increases toughness.

Heat below UCT. Harder then annealed or normalised steels.

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9
Q

Austempering

A

Forms Banite, small cementite particles in a ferrite matrix.
- similar properties to tempered marten., yet more resiliant

Austenitic steel quenched to 400, soaked till uniform temp, then quenched to room temp.

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10
Q

Banite

A

Forms when quenching slightly slower to form martensite, some cementite forms. Even slower = pearlite.

Particles of cementite in a ferrite matrix.

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11
Q

Testing Types

A
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12
Q

Hardness Tests (4)

A
  1. Brinell
  2. Vickers
  3. Rockwell
  4. Shore Scleroscope
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13
Q
  1. Brinell
A
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14
Q

Manufacturing Processes:

A
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15
Q

Wire Drawing

A

Drawn through successively smaller diameter dies
OR
Put in tension and stetched by running it around progessively faster winding drums

  • usually process annealed during to relieve stressed from cold working
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16
Q

Surface hardening types

A
  1. Case Hardening (carburising)
  2. Nitriding
  3. Flame hardening
  4. Induction hardening
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17
Q

Surface Hardening Pros and Cons

A

Hardness of outside with toughness of inside

Makes further heat treating difficult.

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18
Q

Case Hardening

A

Heating and soaking in a carbon rich atmosphere: carbon diffuses into surface

CONS: further heat treatment is difficult

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19
Q

Nitriding

A

Specific steel alloy is heated in furnace with gaseous nitrogen (from decomposition of material e.g. ammonia): soaked for long time.
- reacts with Al, Cr, of V

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20
Q

Nitriding Pros and cons

A

Pros: corrosion resistance, high hardness in core, keeps hardness up to 500.
BUT
More costly setup, only specific alloys, if heated beyond 500 properties lost.

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21
Q

Flame Hardening

A

Flame applied to steel above 0.4%C in localised area then quenched. Martensite formed on surface.

  • Mechanised with a single assembly (waterjet follows flame holder)
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22
Q

Induction Hardening

A

Same idea as flame, but uses electromagnetic induction.

  • uses induction coil, then current is turned off and quenched.
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23
Q

3 ways to alter steels

A
  1. Carbon Content
  2. Heat treating
  3. Alloying
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24
Q

Ferritic manufacturing processes

A
  1. Forging
  2. Rolling (hot and cold)
  3. Casting
  4. Extrusion
    5.Powder forming
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25
Q

Manufacturing types

A
  1. Forming
  2. Casting
  3. Molding
  4. Joining
  5. Machining
  6. Additive
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26
Q

Forming Process and types

A

Mostly metals, done by applying force to PLASTICALLY DEFORM
1. Forging
2. Extruding
3. Drawing
4. Rolling

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27
Q

Forging

A

Applying force to plastically deform.

Grain flow follows the shape of the metal and is not interrupted: improves strength

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28
Q

Hot vs Cold Rolling

A

Hot: heated above recrystallisation temperature: structure will be unstressed, equiaxed grains.
LESS dimensionally accurate, poor surface finish
More ductile and malleable

Cold: below recryst: elongated grains
harder and increased strength with work hardening. Requires more force: stronger, more expensive machinery required.

29
Q

Rolling: description and pros/cons

A

Passed through successive rollers that produce a smaller thickness.
Pros: automated, better mechanical properties

CONS:
Simple shapes, high tooling cost

30
Q

Casting

A

Pouring of molten metal into a die, then cooing
- primary shaping process: often needs further manufacturing for good finish

31
Q

Casting types

A
  1. Die Casting (pressure + gravity) - low melting point metals
  2. Sand Casting
  3. Investment/lost wax casting
32
Q

Pressure Die Casting

A

Molten metal is poured into a chamber and forced into a reusable die using a ram. This is then cooled and removed.

33
Q

Pressure Die Casting Pros and cons

A

Pros: good for low melting point metals
Good surface finish
Denser casting then with gravity
Reusable die
Good for high production runs

Cons: needs excess equiptment for ferritic metals
Expensive set up

34
Q

Gravity Die casting + pros and cons

A

Molten metal poured into die using gravity

Pros: cheaper then sand casting in long production runs
Good surface finish
Tight tolerances

CONS:
- high set up cost

35
Q

Sand Casting

A

Sand with a binder

Temporary mold is made by separating drag in cope in two halves, then imprinting with pattern.
They are rejoined, molten metal is added.
Once cooled, it is removed and sand is reused

  • pins are used to make runner and riser: runner allows excess material to flow in as it contracts.
36
Q

Investment/lost Wax Casting Pros and Cons

A

High tolerances, good surface finish

Expensive (single-use mold) and time consuming

37
Q

Sand Casting pros and cons

A

Pros: low cost
Good final grain structure
Can do large and complex parts

Cons:
single-use mold: expensive for large production runs
Poor surface finish and dimensional accuracy: further machining required.

38
Q

Investment/lost Wax Casting

A
  1. Temporary mold made out of wax: “tree”
  2. Dipped in ceramic slurry
  3. Wax melted out, molten metal poured in
  4. Once cooled, ceramic is shaken off
  5. Individual parts removed from tree.
39
Q

Powder Forming/Power metallurgy

A

Metal is ground made into powder form, then blended with lubricants and mixed with desired compositions.

Then pressed into a mold: pressure compoacts particles together.
- then sintered together in a furnace to make a homogenous grain structure.

40
Q

Casting Pros and Cons

A

Can have uneven grain structure due to cooling: increase stresses.

41
Q

Extrusion

A

Metal is forced using a ram through a die: constant cross section. HOT WORKING PROCESS

Direct and indirect extrusion

42
Q

Extrusion pros and cons

A

good surface finish
tight tolerances

BUT
Only good for 2D shapes

43
Q

Powder metallurgy products (4)

A
  1. Poros metals: use deliberately larger powder sizes. Good for self-lubricating items e.g. bike suspension, electrical motor bearings
  2. Complex articles
  3. products difficult to machine
  4. composites
44
Q

Powder Metallurgy pros and cons

A

Pros: good to make things otherwise to hard to make.

Cons:
Limited shapes
Expensive set-up
Final product less strong as normally produced

45
Q

Machining processes

A

Drilling, turning, reaming, et.c

  • removing material via a tool (usually secondary process)
    Metals, plastics and composites
46
Q

Joining types

A
  1. Welding
  2. Riveting
  3. Bolting
  4. Soldering
  5. Fastening
47
Q

Welding process + Pros and cons

A

Using extremely high heat to fuse metal parts together: melts base metal.

Pros:
Less preparation
Stronger and more rigit
Less maintenance then riveted joints
Less corrosion (riveting, etc subject to galvanic corrosion)
Less equipment then riveting

Cons:
Subject to warping under heat and metal fatigue
Stress corrosion can occur
Some metals need special treatment before welding
Needs specialisation
Stress cracking can occur at HAZ

48
Q

Bolting Pros and Cons

A

Pros:
Easy to use if holes made during construction
Less equipment needed

Cons:
drilling accuracy needed
Holes weaken beams
Differential aeration corrosion
Can loosen under vibrations

49
Q

Riveting Pros and cons

A

Pros:
Not subject to vibration: thus more used for planes and transport craft.

Cons:
Time consuming to install and remove then bolting
Limited loads
Weaker then welding

50
Q

Hooke’s law

A

Stress is proportional to strain

51
Q

Bronze

A

Copper and tin

52
Q

aluminium

A
53
Q

Copper

A
54
Q

Brass

A

Copper and zinc

55
Q

Glass manufacturing processes

A
  1. Lamination
  2. Toughened
  3. Annealed
56
Q

Toughened glass

A

Glass is heated, outer surfaces cooled at a greater rate and contracts
- outside in compression: must overcome compressive force first before applying tensile load.

57
Q

Thermoset plastics and types

A

Undergo a chemical change when heat is applied: non-reversable
1. Epoxy resins
2. Silicone
3. Polyeutherane
4. Polyester

58
Q

Thermoplastics and types

A

Weak Van Der Waal’s forces
1. Polyethylene
2. Polystyrene
3. PTFE
4. Acrylic
5. Polypropylene
6. PVC
7. ABS

59
Q

Rubber

A

Natural polymer, can be vulcanised by adding sulpher and heating to 150: adds cross links
- more rigid but still flexible

60
Q

Polymer Manufacturing

A
  1. Molding (injection, rotational)
  2. Extruding
  3. Thermoforming
  4. Calendaring
61
Q

Injection molding

A

Done on polymers
Similar to investment casting but small pellets added into a hopper, forced through a barrel with a screw which heats up an melts until it is forced into mold.

62
Q
A
63
Q

Composite manufacturing

A
64
Q

Guided media + pros and cons

A

Guided: transmission media that carries signals with a conductor e.g. fibre optic cables: has a PHYSICAL LINK
- short distance, but expensive for long distance/weird terrain

65
Q

3 Guided media types

A
  1. Twisted pair cable
  2. Coaxial
  3. Fibre optical
66
Q

Geotextiles

A

Fabric that lets through liquids but blocks solids e.g. road surfaces, retaining walls

67
Q

True Stress

A

Final stress at failure: use FINAL diameter (vs. engineering stress, use original diameter)

68
Q
A

Engineering (10 decks)

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