Lec 2 Flashcards
Basic disposable mould casting process
- Solid Material
- Melted and heated to temp
- Molten material poured into a mould cavity
- 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
- Pattern of final casting (wood/plastic/metal)
- Mould in sand using pattern
- Molten material poured in
- Left to solidify
- 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
- Master pattern created (could be CAD)
- Pattern makes steel die (milled or cast) - master die maybe machined directly (low melting point wood/metal
- Die produces sacrificial replica in wax
- Dipped in ceramic investment material or placed in flask wax poured around it
- Left to harden - creates mould
- Wax pattern melted poured out
- Mould preheated filled with molten material
- Mould broken away
investment casting steps large productions runs
- Master die created
- 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 - Attached to common wax sprue and runner system using heated tools and melted wax
- First coasting applied - cluster dipped or invested into slurry of finely ground ceramic refractory material (thin layer)
- 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) - Left to harden, wax pattern melted or dissolved
- pre heat 550 - 1100 oC
- Pour in metal
- Mould broken casting removed
- 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 preheat molten metal poured in cools vibrations mould broken
