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MECHENG 236 > Metal Forming Processes > Flashcards

Metal Forming Processes Flashcards

1
Q

What is the process of sand casting?

A

Process involves pouring molten metal into the sand mould, solidification, then removal of the casting.

Examples include engine blocks

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2
Q

What are the advantages of sand casting?

A
  • Relatively inexpensive
  • Ability to product large components
  • Can cast ferrous and non-ferrous parts
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3
Q

What are the disadvantages of sand casting?

A
  • Lower degree of accuracy
  • Can be difficult to sand-cast components with predetermined size and weight specs
  • Rough surface
  • High surface hardness (can be useful), however cutting tools can get worn down quickly
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4
Q

What is shell moulding?

A
  • Process in which the mould is a thin hardened shell of sand mixed in thermosetting binder, backed and reinforced by another material.
  • Only useful for parts under 10kg
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5
Q

Whare are the advantages of shell moulding?

A
  • Good surface finish
  • High dimensional accuracy
  • Further machining usually unneccesary
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6
Q

Whare are the disadvantages of shell moulding?

A
  • Metal patterns are expensive
  • Thermosetting binder increases costs
  • Resin-sand mixture is non-recyclable
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7
Q

What is the process of die casting?

A

Metal is injected into a mould under high pressure

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8
Q

What are the two types of die casting?

A

Cold chamber and hot chamber (used for metals with low melting pt and high fluidity)

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9
Q

What are the advantages of die casting?

A
  • Close size and shape tolerances
  • Dimensional consistency and uniformity
  • Reduced need for post-casting machining
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10
Q

What are the disadvantages of die casting?

A
  • High tooling costs
  • Economical in only very large quantities (only used where quantity of parts justifies the high tooling cost).
  • Can be difficult to ensure mechanical properties of a die cast component; they are not recommended to serve as structural components.
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11
Q

What is centrifugal casting

A
  • Mould is spun and molten metal is poured in

- Action of centrifugal force improves homogeneity, consistency and accuracy of casting

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12
Q

What are the advantages of centrifugal casting?

A
  • High production rate
  • Suitable for ferrous/non-ferrous
  • Soundness and cleanliness of casting
  • Able to produce large parts
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13
Q

What is the main disadvantage of centrifugal casting?

A
  • Casting shape is limited to cylindrical forms
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14
Q

What is the process of investment casting?

A

A wax pattern of the final part is made and dipped in a refractory slurry, which forms the mould. The coating is dried and repeatedly dipped in the slurry to increase thickness. The wax is then melted away in an oven and the metal cast.

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15
Q

What are the advantages of investment casting?

A
  • Parts do not require further machining

- Can produce highly complicated geometries and high precision

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16
Q

What are the disadvantages of investment casting?

A
  • More expensive
17
Q

What is full mould/lost foam casting?

A

Lost foam is similar to Investment, or lost wax, in that the medium, or pattern device, is expendable (usually polystyrene), they melt or evaporate away, leaving the cast part.

Process can make complex shapes, however costs of materials can be high due to expendable nature.

18
Q

What is powder metallurgy?

A

It is the process of compressing fine metal powders and then sintering the compact.

19
Q

What are the advantages of power metallurgy?

A
  • Near perfect shapes with close tolerances
  • Parts can be made from high melting pt metals
  • High productions rates, low unit costs
  • Can produce complicated forms with uniform microstructure
  • Can produce parts with specific physical and mechanical properties
  • Ability to impregnate other materials
  • Makes use of 100% of the raw material
20
Q

What are the disadvantages of power metallurgy?

A
  • Cost of production for power is high
  • Somewhat limited shapes
  • Health and safety issues
  • Tooling is expensive
  • Parts have relatively low ductility and strength
21
Q

What are the four design considerations with regards to powder metallurgy?

A
  • Length to width ratio must not be too large because it will leave the middle of the part with a lower density
  • Re-entrant grooves, reverse tapers and lateral holes cannot be moulded into the compact due to the nature of the ejection and thus must be machined seperately
  • Bevels require feather edged tools which are fragile and easily fractured
  • Abrupt changes in section should be avoided as they are stress raisers which lead to crack formation.
22
Q

What is spark discharge machining?

A

Electrical discharge machining, also known as spark machining, spark eroding, burning, die sinking, wire burning or wire erosion, is a manufacturing process whereby a desired shape is obtained by using electrical discharges.

23
Q

What does EDM stand for?

A

Electrical discharge machining

24
Q

What is Conventional Ram EDM?

A

It is a process whereby the electrode is shaped like the cavity desired.

Dielectric fluid is used in all operations - it acts as a coolant, spark conductor and a flushing medium.

25
Q

What is Travelling Wire EDM?

A

TWEDM uses a wire electrode to perform straight cuts.

26
Q

What is forging?

A

It is the plastic working of metal by means of compressive forces acting locally on a section of the part

27
Q

What is Open Die Hammer Forging?

A
  • Utilises a heavy mechanical stamp to impart repeated blws onto the hot metal
  • Used for large components
  • Mechanical manipulators are often required to turn the workpiece
  • Slow, not suitable for large scale production
28
Q

What is Impression Die Dropped Forging?

A
  • Half of the mould is on the anvil, half on the stamp
  • A hot metal blank is placed on the anvil and hammering ensues
  • Hammering pressure causes blank to fill cavity
  • Often takes several steps
29
Q

What are the advantages of impression die forging?

A
  • Favourable fiber structure can be obtained to increase strength and fatigue resistance
  • Process produces a fine grain structure and eliminates voids in the material
  • Forgings generally have a high strength to weight ratio compared to cast parts
30
Q

What is Upset Forging?

A
  • It is a process for increasing the diameter of the end of a central portion of the bar of metal by compressing its length
  • Commonly used to forge heads on bolts etc.
31
Q

What is extruding?

A
  • Long, straight metal parts can be produced by squezzing metal through a cavity using a mechanical/hydraulic press.
  • Produces compressive and shear forces but no tensile forces, which makes high deformation possible without tearing the metal.
  • Not of the same dimensional accuracy or surface finish as machined parts
  • Able to produce complex cross sections at a high production rate
32
Q

What is cold extrusion?

A
  • Carried out at room temp
  • No oxidation
  • Good mechanical properties
  • Good surface finish
33
Q

What is hot extrusion?

A
  • Carried out at high temperatures

- Good lubrication necessary

34
Q

What is Impact Extrusion?

A
  • Use of a heavy mechanical press

- Punch forces the blank into the cavity at high velocity and mechanical force produces shape

35
Q

What are the advantages of impact extrusion?

A
  • Simple, economical
  • High prod rate
  • Low cost
  • Good surface finish
36
Q

What are the disadvantages of impact extrusion?

A
  • Tooling wear rate is high
  • Can only apply to soft metals
  • Difficult to lubricate

MECHENG 236 (14 decks)

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