Assignment: Week12

moulding and casting

Assignment; design a 3D mould, machine it and cast parts from it...

Since I have not done moulding and casting before, I decided to start with a test mould first.

I downloaded the 'hello world' png file from the class schedule page and used that as the first test. I used fab modules to mill the wax. In the meantime I read up on the grayscale colour coding used by the fab modules to mill and how to design my own parts.

I milled the wax using a 1/8 End Mill for both the rough and finish mill... The finish was not as I expected as the mould was missing some details.

I used temporary mould making compund for the mould in a 1:1 ratio.

Result...

The second try proved better...

The next step was then to design my own 3D mould. To do this I used Rhinoceros and tapped a little into my Chess mania. This time around I worked on a bishop piece and exported an stl file.

Next up was to send the .stl file to the Modela. So, I started the fab modules which I had already installed.

I needed to load an stl file and send it to the modela and so I set the appropriate values for input format and output process...

I then clicked on the 'make_stl_rml' tab to open the workflow dialogue.

Loading the stl from file...

Generating png in order to process...

I at this point realized that based on the material size, I would need to rotate the model by 90° to maximize material use. The wax I had was approximately 150mm by 85mm and thus the model would also need to be resized.

I also realized that I had made an error in the design stage; I was making a 3D-1 Part mold and my stl was round rather than having a flat bottom

As such, 3 things were effectively clear at this point;

The model needed to be cut in half
The model had to be rotated by 90°
The model needed to be resized

Cutting the model in half was easily solved, I went back into Rhinoceros and redesigned the model...

The most straightforward option for rotating the model was to generate a png using fabmodules, save it and manipulate the image to my specifications.

So, reseting fabmodules and opening with the png generation option...

Loading stl file...

I then created the png by clicking on the 'make .png' button, opened the terminal from which I was running fabmodules and confirmed that the file had been saved, as indicated by the red circle.

Without closing fabmodules, I copied the image to the folder I was working from. If you close fabmodules, all files get deleted, including the .png file so a copy has to be made beforehand.

I opened the .png file in my favourite image manipulation program, Gimp, rotated the image and saved it.

I reset fabmodules and opened the .png file that I had saved.

To solve my third problem, the size of the mold, I resized the model from the fabmodules interface.

I set up the image for the rough mill and sent it to the machine.

Once the rough mill was done I realized that the milled mold had very little. Despite this, I went ahead and did the finish mill so as to get a rough idea of what to expect when I finally do it right.

So I prepared and sent the finish cut mill and sent it.

The result was...

At this point there was one glaring problem with the mold; the mold was too shallow. My model was circular and the mold appeared flat at the top. While searching for a solution I came across this old tutorial which had a table with Fab Modules Settings that explained that while working with a .png, I had to manually set the bottom height.

As previously done, I loaded the rotated image in fabmodules and resized it.

This time round I changed the bottom-height which by default was -10mm to -28mm. I arrived at this depth based on the maximum depth that my 1/8 end mill (approx. 31mm) could mill and the height of the wax which was 30mm.