Molding and casting

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The weekly assignment focuses on the design and utilization of a 3D mold!

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My final project is supposed to be a robotic fish ! So I’d like to design a small object that will be a kind of commercial gadget for “Piske”.

MODELLING AND MOLDING PROCEDURE. I’m very fast with Rhinoceros but at the same time I’d like a very simple design. I take note of the approx. 15° slopes in order to better extract the silicon resin. One thing that really block me is the long times required to mill the wax. I decided not to mill the two symmetrical side of the fish.

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Once the STL file was ready, the following two software packages have been used in order to mill he wax: Modela Player 4 and Roland VPanel for SRM-20. I set X,Y and Z coordinates for rough (1/64) and fine (1/32) procedure, and then I went away. The milling takes more or less 4 hours. Then I send the model to a Roland SRM-20. The following tasks have been performed. Task 1: ROUGHING tool (end mill) diameter: 3 mm Task 2: FINISHING tool (end mill) diameter: 1,5mm. Task 1 settings: X,Y speed 24 mm/s, Z speed 10 mm/s, spindle 7000 rpm, cutting-in amount 0.6 mm, path interval 1.8 mm and finish margin 0.2 mm. Task 2 settings: X,Y and Z speed 16.8 mm/s, spindle 7000 rpm, cutting-in amount 0.2 mm, path interval 0.2 mm and finish margin 0 mm.

The machine at work !

Something went wrong, probably for a misalignment of the Z-axis. It looks like that the final (fine) pass did not work correctly. The last layer of wax is not well smoothed. I will try to adjust it using a solder to smooth the irregularities.

The worst zone.

CASTING PROCEDURE. Despite the problem we start our casting procedure, using the Smooth-Sil 940 silicon rubber. The solderer, used to try to adjust the bad part of wax is visible in the image.

I mix the two components very slowly using the correct 1A to 1B proportion (namely ratio of 100:10 in weight), probably it will be useful the help of a blender. To avoid bubbles a used a method well known in Civil Engineering for concrete: localized vibration. In this specific case I use a crayon.

The result is not so beautiful. The silicon rubber copies everything of the mould…including the adjustment made with the solder…I’m not satisfied at all even if I've decided to complete the procedure anyway.

So the polyurethane resin have been tested anyway (ratio A:B of 1:1). I’ve experienced the following problems: 1) Not correct calculation of the casting volume.Not having time to use Rhinoceros I made simple empirical calculation in order to evaluate the volume of the needed resin. The result is: too much resin. It's poured outside of the fish. 2) Lots of small air bubbles. I’m supposing they have been trapped in the small lined derived from the uncorrect 1/32 refining.

This is the final result!

Download area

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The following files are downloadable:

Type of file	Description	Link (Type of file)
Fabrication files: vectors(s) / 3D model(s)	Rhinoceros file	(3DM)