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MEC130 2 4 8 10 15 > Lec 2 > Flashcards

Flashcards in Lec 2 Deck (17)
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Basic disposable mould casting process

1. Solid Material
2. Melted and heated to temp
3. Molten material poured into a mould cavity
4. Solid Material formed into desirable shape


Sand casting vs Investment casting

Sand casting - Heavy large shapes any material small batches
Investment casting - Better Quality and Accurate


Sand Casting adv and disadv

Low cost, any material, no max weight or thickness, complex shapes
High porosity bubbles poor surface finish - additional machining, low dimensional accuracy, slow cooling process - weaker parts


Sand casting diagram

Bottom board, runner, riser, sand, core, in gate


Sand casting 5 steps

1. Pattern of final casting (wood/plastic/metal)
2. Mould in sand using pattern
3. Molten material poured in
4. Left to solidify
5. Mould broken part extracted (further finish maybe req)


Loose pattern vs gated pattern

Loose = cheap wood plastic metal alloys, just runner and riser, one or more pieces depending of complexity of cast
Gated = More expensive aluminium cast iron, gating system incorporated, larger batches - saves time in operation warrants additional cost


Things to consider when producing mould x 5

resist erosive action of pouring
temp of molten metal
trapped gases must be able to escape (riser)
weight of component
clean removal of casting from mould


What does a gating system do

Ensures continuous uniform flow - reduces bubbles no turbulence
reservoir of molten material - part cools therefore contracts
protects metal from oxidation


8 steps of investment casting (lost wax casting) no tree small production runs

1. Master pattern created (could be CAD)
2. Pattern makes steel die (milled or cast) - master die maybe machined directly (low melting point wood/metal
3. Die produces sacrificial replica in wax
4. Dipped in ceramic investment material or placed in flask wax poured around it
5. Left to harden - creates mould
6. Wax pattern melted poured out
7. Mould preheated filled with molten material
8. Mould broken away


investment casting steps large productions runs

1. Master die created
2. Wax injected at pressure/poured into master die creates wax pattern
(if core req soluble wax core - dissolves from pattern prior to investment coasting or ceramic core remain part of fixing removed from cast during cleaning
3. Attached to common wax sprue and runner system using heated tools and melted wax
4. First coasting applied - cluster dipped or invested into slurry of finely ground ceramic refractory material (thin layer)
5. Redipped into slurry with sand leave to dry repeat until 5 -15mm
OR placed upside down in flask, investment material poured around and vibrated (so air can escape)
6. Left to harden, wax pattern melted or dissolved
7. pre heat 550 - 1100 oC
8. Pour in metal
9. Mould broken casting removed
10. Sprue and gate ground off


Why pre heat investment mould

Ensure wax completely removed
Adds strength to mould
Molten material retains heat flows into all sections
Dimensional control - mould and metal shrink together


How is the mould broken in investment casting

Mechanical vibration or high pressure water


What is investment casting used for

Gears titanium aircraft - engine structural frame
bio engineering components - hip replacements


Adv and Disadv of Investment casting

Excellent surface finish
high dimensional acc
unlimited intricacy
most metals
but costly pattern and moulds
high labour
time consuming - EXPENSIVE


Diagram of investment casting

Steel die -> wax pattern
multiple parts attached to wax runner
mould dipped in wet ceramic slurry - repeat thicker and thicker
heat remove wax harden mould
molten metal poured in cools
vibrations mould broken


General casting diagram and labels

core print
mold cavity
draft taper
gating system
parting line


Sand casting vs Investment casting
surface finish
shape complexity *
Dim accuracy *
Porosity *
* 1 best 5 worst

sand vs investment
Material all - all
Weight(kg) 0.05 to infinity - 0.005 to 100
thickness(mm) 3 to infinity - 1 to 75
surface finish (microns) 5 to 25 - 1 to 3
shape complexity 1 to 2 - 1
dim acc 3 - 1
porosity 4 - 3