9. Molding and casting¶
Goal of the week:
- Design a mold around the stock and tooling that you’ll be using, mill it (rough cut + (at least) three-axis finish cut) and use it to cast parts.
The task of the week started with the idea of creating a 3D design to be milled into a block of wax and then moving on to the object, pouring plastic into the mould.
The problem, as always in these situations, was to think of a suitable object to recreate. So I started drawing on Fusion without having a clear idea.
So I started to draw my object, placing on a parallelepiped what should be the front and back of the final object.
I then added the registration keys and some details until I reached the final model:
I then added a new component to check what the “negative” of my object would actually be. The most complicated part of this week was in fact imagining the final object in relation to the “positive” and “negative” of the model I was drawing.
After checking that the model was drawn correctly I prepared the files to be milled.
MILLING¶
To create the g-code files for the Roughing and Finishing for the Roland Milling Machine, we used the software Vectric Cut3D. Once I imported the STL file, there are different required phases to prepare the file:
ORIENTATE AND SIZE MODEL
I orientated my object on the surface, choosing the TOP area. I locked the XYZ ratio. I choose mm as a unit and “Top” in Sides to Machine.
MATERIAL SIZE AND MARGINS
I checked the material size, which I left as the same sizes of my model. Then I set my origin in the bottom-left corner (at the beginning I forgot to do this and I couldn’t understand the movement of the machine). The setting of Depth of model below surface was really important because it would create the margins around the model for casting the silicone, so I set 4mm as a margin height. The Cut Plane Position in Model set the maximum deepness that the mill is going to reach. Since I had also holes, I decided to bring that setting all the way to “Buttom”.
ROUGHING TOOLPATH
I selected the type of mill that I was going to use. I opted for 1/8 end mill. The only thing that I changed was the feed rate.
The parameters I set were:
- Pass Depth = 0,0625
- Stepover = 0,0625
- Spindle speed = 8000
- Feed rate = 15
- Plunge rate = 5
FINISHING TOOLPATH
For the finishing mill settings I choose the 1/16 inches, 2 flutes endmill.
The parameters I set were:
- Stepover = 40%
- Spindle speed = 8000
- Feed rate = 30
- Plunge rate = 2
In Toolpath Parameters, I selected the Raster Angle to 45 Degrees and I pinned the option: “Create an extra pass at 90 degrees to first”.
The software allow you to visualize the preview of both the roughing and finishing process, as well as the Estimated machine Time, that for me was 56 minutes for the roughing and 26 for the finishing (that at the end I did two times because the first I didn’t put the end mill in the right position so it couldn’t reach the surface of the wax block.)
The last step was saving the roughing and finishing in two separate files. After ensuring that the Post Processor was set to Roland MDX-40 mm(*.rol), I clicked on Roughing Toolpath Save and Finishing Toolpath Save to save the files.
This was the result:
MOLDING¶
After milling, it was time to cast the silicone, to create the silicone mold.
I mixed part A and part B (that should be the 10% of B) and I poured it into the wax mold.
After waiting some hours my silicon mold was ready and I cut it in two parts:
CASTING¶
I did my first casting attempt with plastic and then with resin.
I noticed that the hole I made in the model where too thin but I tried anyway. The result was not encouraging so I cut the holes and I made a big one.
After several attempts and with the help of a stick use to take off the air inside I manage to do a perfect casting with plastic and with resin:
You can download the 3D model file here