Task 2: Individual Assignment
Let’s break down this week’s assignment:
- Design a mold around the process you’ll be using
- produce it with a smooth surface finish
- use it to cast part
Design
I designed my model with Fusion360. As there is a requirement that the end result should have a curved surface - I designed the following model.
Sketch -> Extrude -> Fillet the Edges
Unfortunately as I was about to take screenshots of the next couple of steps… my Fusion360 crashed and I lost my model and couldnt recover it (weirdly) despite using a cloud-based server. So the next steps were the following (I hope my doodles are easy enough to understand).
With the Loft feature, we can basically create convex shape
The model ended up looking like this. I also made a thinner version as a thinner model is easier to create a mold of since it takes lesser time to dry.
Mold
In our group assignment - we decided to create our mold process using FDM Printing. There is a requirement to create mold with a smooth surface finish. However 3D printers print with layer lines. To do that we would have to coat the printed master model (positive part) with UV resin mixed with baby powder and cure it. Once cured, we need to sand the master model.
Slice Setting & 3D Printing
As we want a smooth surface finish - we should go slice the master model with the ultradetail setting as we want to make sure that the layer height doesn’t show up as much as possible. I was glad that I decided to go with the thinner model - since the printout itself took almost an hour.
We printed a mold container that allows us to mold any positive model as long as it fits within the container. Before we start the process - make sure you remove any build-ups or stringings from your master model with pliers or an exacto knife.
Smooth Surface
To get a smooth surface from the FDM print out we would need to follow this tedious, long ass and inefficient process. (Yes I despise this method to the ends of the earth). Make sure that you are doing this in a well ventialted room, with a mask and glove.
Step 0. Safety Data Sheet
eSun - Water Washable Resin SDS
Make sure that you prepare the following PPE: Plastic Gloves, Face Mask/Shield. Do all of this in a well -ventilated room
Step 1. Mix UV resin with a baby powder until the colour gets somewhat paler
Step 2. Use a brush and coat your master model with the UV resin mixture
Step 3. After we coat it - cure the master model with a UV light. If you have gotten a gel nail before.... this is literally a similar process. Usually nail artists will cure for about a minute - so I did the same.
Step 4. Once we finished curing - it’s time to sand till we get a smooth surface. To do that we need to start sanding with 240 grit sand paper and gradually work up to 1000. I use 240, 400, 600, 800 and lastly 1000.
Step 5 If there are still bumps and uneven surface after sanding… repeat Step 2-4 all over again till we get your smooth surface finish.
I personally hated the aforementioned process to the very core. I spent around 5 hours in total just constantly repeating Step 2 to Step 4. Why did it take so long? I have very dry fingers. Everytime I go through the passport counters, there is 80% chance that the machine won’t be able to read my fingerprints - unless I moisturise with lotion or water. My fingers really can’t recognise any bumps and all - I had to ask my other friends to feel the surface for me. I couldn’t really tell if I was sanding correctly or not. Honestly it felt like a waste of my time.
Silicon Mold
We use silicon mold to cast hard materials. The silicon type that we are using is the RTV-48 (Part A). It comes with the catalyst (Part B) that hardens the silicon to the master pattern. For RTV-48, the recommended catalyst ratio to silicon was 5%. I did couple of the silicon mold trials and found that the measurement between 3.5% to 4% is ideal.
Step 0 Unfortunately I couldn’t find the specific data sheet for the RTS-48 Silicon Rubber. After comparing other silicon rubber molds SDS - I find that in general the precaution you want to take is make sure that you are doing your job in a well ventilated room. Some rubber molds maybe harmful to the skin, some not. If you want extra precaution - wear gloves and face mask.
Step 1 Prepare the master model on the container. Stick a masking tape underneath the master model and the surface area of the container - this is done do that it will be easy for us to remove the silicon mold. Stick the master model on top of the masking tape with a super glue.
Step 2 Sprinkle baby powder onto the master model and the container. This will ensure for easier removal of the silicon mold from the master model.
Step 3 Its time for us to start preparing our silicon mold. Before that we need to figure out how much should we use. A good trick is to pur water on the master model container till it reaches the brim, pour it onto an empty cup - and measure the weight. The weight will tell you how much silicon should you pour onto the master model container.
Step 4 Time to measure the catalyst amount. As I mentioned, 3.5% to 4% is ideal.
Step 5 After you finish measuring - you want to be quick like a ninja. As soon as you pour - gently mix the catalyst directly onto the mold. Do not mix rigorously as there will be too many air bubbles forming. You do not want to mix it for too long as the mixture will set quickly
Step 6 Once everything is nicely mixed - pour it onto your master model container and let the silicon set. To avoid air bubbles forming on your silicon mold, tap the edges or underneath the container so that air will get released.
Step 7 Wait it to set. Once set - remove the mold and you’re done. I think I got a decent smooth finish on the silicon mold.
Cast
Paraffin Wax
Melt the paraffin, pour it into the mold. I tried putting an oil-based food colouring, but it didn’t work. Over all there surface feels smooth to touch although you can see some visible lines.
Cotton & Ice
Color the cotton with food colouring, pour water - and let it set in the freezer. It came out like a normal iceblock. You can’t really see the fine details on the ice sadly.
Biocomposite - Eggshells & Seashells
I used Tafia’s recipe to cast eggshell and seashell composite on my mold!
Prepare the recipe, mix everything in a pot on stovetop and once the mixture boils - set it in the silicon mold. To expedite the drying time - put it in the freezer, then let it airdry. The cast came out cleanly - and you can see the details onto the biocomposite. Is it smooth? It looks like it has a smooth surface finish - with no layer height lines visible....although when you touch there would be texture because it’s a composite.
Final Result
