FabLab Academy 2012

Manchester Lab

David Forgham-Bailey

Week 8: molding_casting composites

Hardware: Roland Modela

Weekly Assignment: 

I decided to make an eyeball unit for my final project. We were restricted to milling a wax block, then using this to form a silicone mould, from which the final 3D shape will be cast.
I designed a two part mould which will produce a silicone mould  (2 part - with registration lugs and pouring/filling spout -

Narrative:   having produced the .stl file the milling path is made my Modela Player. The wax block is first cut to make the top face flat and tool zeroed. Next path is the roughing out - leave enough work for a final cut with a round nose tool. Finishing cut is final path - this will determine the quality of the finished item.


Machine Settings:



External Links:

Course Notes:

Similar to 3D printing but better finish and quicker - Good for short production run - not good for parts within parts -
Injection - sprue/runner/gate/vent/partition line/flashing
insert casting - place object in mould before casting
vacuum - blow - inflate - bottles - flexible - start with rigid material then use flexible - need mould release - make part and bend mould to demould
machinable wax - high temp wax - remelt and reuse - melt shavings from machining  - remelt and reuse - Good Surface finish
low temp wax - good for transferring - make mould from other objects
rigid foam - building material - use on ShopBot - glue sheets together for deeper mould - not good finish due to granular foam use Gesso to seal then sand.
alginate gel - non toxic - one shot use - good for body casts
urethane rubber - plastic - stick to each other - v stretchy -
silicone - not as stretchy - completely inert - will not stick
PDMS - Latex - avoid - cures by drying - takes many coats - take long time
thermoplastic - fluid when heated - thermoset - needs heat to cure

Drystone - fancy plaster - adds polymer matrix to strengthen - quick dry
Hydro Stone - mix of portland cement and plaster takes a little longer - cheap $30 - 50lb - waste is just rock - good starting point low viscosity -
metal powder  -  ceramic powder - low temp alloys - glass can be moulded - food -

additives - fibres - add strength - -fillers - add other characteristics - glass spheres for bulk - other s for conductivity/density/flexibility/colour/etc

Beware - if water is added to eurothane plastic it will foam -
mixing - mix well
deairing - removes bubles - avoid getting bubbles in first place - vacuum chamber - residue
when stirring use shear - you have 10-15 mins to work and have bubbles removed - filling pour slowly - tilt mould so vent on top design mould for vent to work correctly
curing 150 degC - silicone use desk lamp to elevate temp - exothermic - gets hot when curing
demould - taper - release agent - washing up liquid - shelf life 6-12 mths will not cur if too old - Keep container ring clean - will not open if cures in place
safety - materil safety data sheet - disposable gloves - ventilation - protection - can make you sensitive to the material

weekly project use - silicone rubber - hydrostone - drystone - 3D toolpath - depth of cut must be possible with selected tool - what is the cut depth of the tool?
Rough cut in layers to remove material - finish cut follows surface of the part - tool overlap -
flat end mill for flat surfaces - ball end for round surfaces -

Composites - strong compression - not good in tension - composite makes tension good - epoxy/carbon fibre - toxic - concrete/rebar - -adobe -
friendly composites - fabris with matrix - epoxy eurothane - needs ventilation - oat building uses all materials - processes - compaction infusion - 50/50 volume fraction
open mould - 1 side - *.png good at preserving dimensions