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
General casting diagram and labels
flask core core print mold cavity draft taper riser gating system sprue parting line drag cope
Sand casting vs Investment casting Materials Weight Thickness 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
