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MEC130 > Disposable Mould Casting > Flashcards

Disposable Mould Casting Flashcards

1
Q

What do we want from a casting?

A

Strength
Shape
Cost effective

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2
Q

What are a few characteristics of a good cast?

A

As dense as possible, no bubbles.
No secondary inclusions
As pure material as possible

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3
Q

Define casting

A

The process when molten material is poured and solidified in a mould

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4
Q

What should the mould do?

A

Form the desired product shape
Release the cast at the end of the process
Form the best quality product

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5
Q

Terminology - What is the parting line?

A

The interface that separates the Cope and the Drag

Often found on the cast itself

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6
Q

Terminology - What is the Cope?

A

The top part of a mould
(think covering)
Shape

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7
Q

Terminology - What is the Drag?

A

The bottom part of a mould
(frame, thing that is dragged)
Shape

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8
Q

Terminology - What is the Flask?

A

A rigid metal/wood frame that holds the entire moulding assembly
Shape

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9
Q

Terminology - What is the Pouring Cup?

A

The entrance for molten material

Shape

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10
Q

Terminology - What is the Sprue?

A

A channel used to deliver molten material

Shape

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11
Q

What do we want the pouring cup and sprue to do?

A

Deliver molten material to the cavity as quickly as possible
If mould hasn’t been designed and insulated properly, molten material will solidify in the sprue.
Other option is the material will solidify just outside of the sprue, and will start to cause turbulence or disruption to the flow

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12
Q

Terminology - What is the Gating System?

A

A channel used to deliver molten material to mould cavity

Quality

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13
Q

Terminology - What is the Riser?

A

An extra void (which is part of the Gating System) created to be filled with molten material
Quality

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14
Q

What is the purpose of the Riser?

A

Deliver molten material when the material in the cavity starts to shrink
Release

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15
Q

Terminology - What is the Mould Cavity?

A

A space to be filled with molten material

Shape

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16
Q

Terminology - What is the Core?

A

A sand or metal shape used to produce an internal feature of a casting
Shape

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17
Q

Terminology - What is the Draft?

A

Taper on a casting that permits the casting to be withdrawn from the mould
Release

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18
Q

Terminology - What is the Core Print?

A

An area used to locate and support the core within a mould

Shape

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19
Q

When would you use disposable mould casting?

A

Unique geometry that has to be made

Or when a small enough number of parts need to be made that no other production means would justify it

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20
Q

What is the basic process for sand casting?

A

Uses a pattern of the final casting, produces a mould based on that pattern using sand, molten material is poured into the mould,molten material is left to solidify, mould is then broken to extract the finished casting

21
Q

Sand Casting - What is the pattern?

A

A replica of the object to be cast.

Used to form the mould cavity

22
Q

Sand Casting - What are the 2 main groups of patterns?

A

Loose and Gated

23
Q

Sand Casting - What is a loose pattern?

A

Cheap, made from wood, plastic, metal alloys

Can be made in one or more pieces, depending on the complexity of the moulding

24
Q

Sand Casting - What is a gated pattern?

A

More expensive to make, made from aluminium or cast iron
Designed to incorporate the gating system and core print
Time saved in operation warrants the cost of mounting
Used to produce large batches of small castings

25
Q

Sand Casting - What must be considered when designing the mould?

A

The weight of the component, the effect of pouring (must be able to resist the erosive action of pouring), the temperature of the molten metal, clean removal of the casting, trapped gases must be able to escape

26
Q

Sand Casting - What are the main objectives of the gating system?

A

A continuous and uniform flow of metal into the mould cavity without turbulence
To form a reservoir of molten metal which feeds the casting as shrinking takes place
To protect the metal from oxidation

27
Q

Sand Casting - What are the applications?

A

Pipelines, valves, heavy machinery, industrial tooling including pressure-containing components
Transport - railway wheels, engine crankshafts

28
Q

Sand Casting - Advantages

A

Low cost
Almost all engineering metals & polymers can be cast
No limit on maximum weight and thickness
Able to produce complex shapes

29
Q

Sand Casting - Disadvantages

A

High porosity
Rough surface finish
Low dimensional accuracy

30
Q

What is the basic process for investment casting?

A

Uses a pattern that is a modified replica of the product, pattern is used to make a steel die, die produces a sacrificial replica of the product using wax, replica dipped into ceramic investment material or placed into a flask and material is poured around it, left to harden creating a mould, wax replica is melted and poured out of the mould, mould is pre-heated and filled with molten metal, mould is broken away from finished product

31
Q

Investment Casting - What is the pattern, what is it made from and how is it made?

A

A modified replica of the desired product
Made from metal, wood, wax, plastic or resin
Rapid prototyping machine

32
Q

Investment Casting - How is the die made?

A

Produce a master die from the master pattern
The die is made from low MP material such as metal, steel or wood
Steel dies may be machined directly, eliminating pattern making

33
Q

Investment Casting - How is a wax pattern made?

A

Molten wax poured into a master die or injected under pressure and allowed to harden, plastic and frozen mercury can also be used as pattern material, when cores are required they can be made from soluble wax and ceramic
Soluble Wax Cores are dissolved from the patterns prior to investment coating
Ceramic Cores remain as part of the wax pattern and are removed from the casting during cleaning

34
Q

Investment Casting - How are the patterns assembled?

A

Assembled onto a common wax sprue

Individual patterns are attached to a central sprue and a runner system by means of heated tools and melted wax

35
Q

Investment Casting - Describe the initial coating process

A

Cluster is dipped into a watery slurry of finely ground ceramic refractory material.
A thin layer of investment material is deposited onto the cluster to ensure a smooth surface and good detail in the final product

36
Q

Investment Casting - Describe the final coating process

A

Either: the cluster is re-dipped into the watery slurry with a layer of sand and allowed to dry, then repeated until the coating is in the desired thickness (ranging between 5-15mm)
Or: The coated cluster is placed upside down in a flask, then liquid investment material is poured around it, the flask is then vibrated to allow the entrapped air to escape

37
Q

Investment Casting - Describe the hardening and removal process

A

Investment is left to harden, pattern is then melted or dissolved and removed from the mould, moulds are placed upside down in an oven to melt the wax and allow other residue to vaporise

38
Q

Investment Casting - Describe the pouring process

A

In preparation for pouring, moulds are heated up to 550-1100 C. This ensures complete removal of wax material, cures moulds to give added strength, allow molten metal to retain its heat and flow readily into all thin sections, provide dimensional control as mould and metal shrink together during cooling.
Pour molten metal and allow it to solidify

39
Q

Investment Casting - Describe the removal process

A

Castings are removed by breaking the mould material, techniques used include mechanical vibration and high-pressure water, castings are then removed from the sprue and gate stubs are ground off

40
Q

Investment Casting - What are the applications?

A

Mechanical components such as gears, valves, precision housings.
Titanium aircraft-engine and structural airframe
Bio-engineering components

41
Q

Investment Casting - What are the advantages

A 
Excellent surface finish
High dimensional accuracy
Almost unlimited intricacy
Most metals can be cast
No flash or parting line concerns
42
Q

Investment Casting - What are the disadvantages

A

Costly pattern and moulds
High labour cost
Time consuming

43
Q

Sand vs Investment - Material cast?

A

Sand: All
Inv: All

44
Q

Sand vs Investment - Weight?

A

Sand: 0.005kg - no limit
Inv: 0.005kg - 100kg +

45
Q

Sand vs Investment - Thickness?

A

Sand: 3mm - no limit
Inv: 1mm - 75mm

46
Q

Sand vs Investment - Surface finsish?

A

Sand: 5mm - 25mm
Inv: 1mm - 3mm

47
Q

Sand vs Investment - Shape Complexity? (1 best, 5 worst)

A

Sand: 1-2
Inv: 1

48
Q

Sand vs Investment - Dimensional accuracy (1 best, 5 worst)

A

Sand: 3
Inv: 1

49
Q

Sand vs Investment - Porosity (1 best, 5 worst)

A

Sand: 4
Inv: 3

MEC130 (8 decks)

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