Week 13. Molding and Casting
This week we are learning about molding and casting.
group assignment:(linke here)
review the safety data sheets for each of your molding and casting materials,
then make and compare test casts with each of them
compare mold making processes
individual assignment:
design a mold around the process you'll be using,produce it with a smooth surface finish that
does not show the production process toolpath,
and use it to cast parts
extra credit: use more then two mold parts
Molding and Casting
This week I decided to use the rotocasting machine we built during machine building week. My intention was to mould some small chocolate bunny figurines using the rotocasting process. My initial plan was to 3D print a mould and vacuum form the mould to rotationally cast the parts. However, I did not have any food-safe materials for vacuum forming - which I only realised after already printing the moulds. So I decided to then 3D print a tool in PETG and cast a mould using Smooth-On Sorta-Clear 40, a food-safe silicone. Below is the process I followed.
Vacuum Forming
3D modelling the part and adjusting the model in Meshmixer to change the ears to a more suitable shape for rotational casting.
Making a low-poly version of the model by decimating the mesh in Meshmixer.
Exporting the mesh from Meshmixer and importing into Autodesk Fusion.
Splitting the part in Autodesk Fusion and adding a base for vacuum casting with registration band around the edge.
Export to Prusa Slicer to slice for 3D printing.
As we would be vacuum casting, I decided to use 0 walls, 0 top layers and 0 bottom layers.
I split the top part off the model to make the infill more dense - 70% gyroid infill.
The lower part was 50% gyroid infill.
This would allow the vacuum moulding to pull the plastic to the surface of the mould.
I exported the model from Prusa Slicer to be printed on the Prusa MK3S+ printer.
Three to four coats of Mould Release 200 were applied to the printed parts, allowing a few minutes drying time between coats.
The mould was then placed in the Vacuum Forming machiene and dropped the platform.
Material added and clamped in place.
Timer was set and the heater was turned on and brought over the material to be heated.
During heating, air can be pumped into the former to prevent the plastic sagging if needed.
A close eye needs to be kept on the material to prevent burning and overheating.
When material is ready, the heater can be pushed back and the mould can be raised with the handle to the left.
Vacuum can be applied which will pull the plastic to the surface of the mould.
This can be held for a few moments to allow for the plastic to cool.
We can then reverse the vacuum to push the plastic off the mould.
The moulds can be taken out and the protective film can be removed.
and excess material trimmed with a bandsaw - (wear ear protection, it gets loud)
Silicone Casting
Making the mould
I began by modifying the CAD to produce a mould to pour the silicone into.
After the poor attempt at registration with the vacuum casting, I decided to make some better registration locators. These could be printed and added to the two parts of the mould to allow better registration.I again printed using PETG - after printing the first part of the mould, I realised that it would be quite large.
I checked the mass of the silicone mould in the Autodesk Fusion model; each half was approximately 405g.
As we only had 900g of Sorta Clear 40, I decided to look at removing some weight from the mould.
I also wanted to improve the mould to ease removal of the parts - to do this I added a large amount of draft to the walls of the mould.
after doing this i was able to almost remove the mould mass by half it was mow caluclating at 233g each.
I also added a 0.1mm of tollerance to the touchig faces of the locator pins and the mould and mould walls.
I exported to Pursa Slicer increased the walls to x3 and added a little to the top and bottom layers. I also used veriable layer height in Prusa Slicer to minimise layer lines.
and increased the infill to 25% (this proabably could have been a bit more)
When printed to remove the layer lines to used heat in the form of a soldering torch.
this was a delicat process of balsting heat at the layers and hoping the whole thing wouldnt go up in flames or compleatlhy melt.
I would not recomend this if parts were dimesnion critical. Note I did this outside on a sutiabel surface.
Issues I've Encountered
AGHHHHH
what went wrong. I had a blow out when applying the vacuum - the sheet wasnt big ehough to be clamped properly - see images below
what went wrong.
Learning Outcomes
Code structure and how the types of flow required - I will need to explore more of this but this week has given me a good grounding.
I have a good grounding in the Arduino IDE and have a good understanding of the code structure and how the types of flow required.