Week 12 - Molding and Casting
Our FabLab has a small cnc-mill but the problem is, that the machine is out
of order at the time. For the milling work Aleksandra and I had to arrange an appointment with Daniele at FabLab Kamp Lintfort.
At this point a big thank you to Daniele, because he took the time for
helping us and explained everything very well. We also enjoyed working with
the other students of the Fabacdemy from the FabLab Kamp Lintfort.
We should do it in 3 steps: first pour out this mold with silicon.
Then use the silicone mold for casting.
For this assignment I have decided to design a heart in Fusion 360. I have
chosen this heart to give it to my mother on mothers day on May 14th ;-)
1. Design in Fusion 360
First I have drawn some construction lines around my form (in this
assignment a heart), in order it can be positioned correctly:
I created the lines and arcs for the heart-shaped design. For this I used the tool "line" in the sketch. Hold the left mouse button pressed for the arcs:
I also made the same step on the other side, and finally the sketched hearts were extruded to obtain a three-dimensional body. So that the mill can also mill the heart correctly, I have rounded the upper corner with a radius of 3mm:
On this picture you can see the designed form in which there are 2 separate chambers to create a 2-piece cast:
The most important fact is, that the positioning of the objects in the form is the same, so that the two halves can be placed correctly. For this reason I have also 3 holes lined up to snap the pieces together:
2. CAM-process in Fusion 360:
Next I had to think about a strategy, how I can mill my model. I used the CAM process in Fusion 360 and created 2 new tools in the library. A 6mm end-mill for the rough cut and a 3mm end-mill for the fine cut. Also Set coordinate system in the CAM. Step down, max 1/2 diameter of the tool. It is important that the diameters and the different lengths (cutting length, shoulder length, body length and total length) are precisely defined:
Defining the tool and simulate for the rough-cut:
In the simulation is very interesting to see the software calculates the volume (volume and initial volume), which is milled out. With this information you can estimate how much material is needed to fill the form.
Defining the tool and simulate for the fine-cut:
Post-process to Export the milling-job:
Use roland rms.cps Generic Roland RML; Properties: MDX40:
3. Milling process
Machine-setup: Roland MDX 40A:
As a material for the form I used a special wax. This is used in model building, for example, and can be purchased here.
For sculptures, model and castings with high heat resistance. Suitable to produce models with extremely smooth surface texture for silicone rubber mold.
Roland MDX40 milling videos:
Rough-cut (6mm tool-diameter):
Fine-cut (3mm tool-diameter):
4. Casting process 1
In the following picture you can see me with our Fab Lab Guru Daniele, how I make the silicon mass. The mixing ratio between component A and component B is 10:1. In my case it was 300g from comp. A and 30g from comp. B.
As silicone and a harder we used ProtoSil RTV 245:
After stirring the mass, it had to be transferred into a larger container and placed in a vacuum oven. The reason for this is that the air inclusions in the mass can be removed in this way. After the form was filled, I also put the form once more in the vacuum oven, because when filling this, new air inclusions in the silicon have emerged.
After the pressure in the vacuum oven had decreased to 1 hPa = 0.001 bar, the machine was switched off and waited for 5 minutes before the pressure was balanced again.
On the following photos you can see quite well, how the air connections are "sucked out" from the mass:
After this procedure, all the air inclusions were removed from the silicon mass and I was able to cure it.
12 hours of waiting ...
After 12 hours the silicone has hardened and I could very easily remove it from the wax mold. As a help I used a knife and a small screwdriver:
I thought it would be much harder to remove the silicon, but with a knife and a little screwdriver it was very easy:
The excess silicone from the sides was finally also to be removed:
The two silicone molds fit perfectly into each other thanks to the 3 designed holes and pins, below the lower point of the heart you can now also very well the "filling channel":
5. Casting process 2
Fill in with Polyester glass casting resin from here.
Brilliant, crystal clear polyester resin for the production of highly transparent casting resin blocks. The casting resin is suitable for the pouring of small objects, jewelery and other objects:
In order to be able to squeeze the two molds sensibly and to center the force, I still saw some pieces of wood:
Next, I applied the release agent paint with a paintbrush to my molds and let it dry for a few minutes:
Next, we have mixed 1000g of polyester casting resin with 2g of the harder.
As described in the instructions, this is the recommended quantity.
Another note from the manual was that we should not mix the mass with a round, but with a flat wooden stick.
As already mentioned, I used to center the pressing force 2 pieces of wood. To put them together, I used a vice. To fill the resin I used a syringe.
In order to vent the form, I additionally inserted a cannula laterally into the form.
The manual recommends that the filled mold has to cure for 2 days. So wait a second time, this time a bit longer ...
2 days later:
Remove the mold:
After 2 days, the resin has hardened and the two silicone molds have been very easy to remove thanks to the release agent. I am very satisfied with the result. No air pockets are visible in the heart. Now I have to polish the heart only a little bit.