Resin casting is used to encapsulate the electronics, to keep them safe as well as providing a tactile, smooth outer surface. The resin is clear to allow light to charge the internal super capacitors, and to allow the time display to be visible.
The process I usually use is the following:
- The model to be cast is designed using CAD (Computer Aided Design) software. Care is taken to avoid features that are hard to cast, like very thin walls or points etc.
- The model is rigged with a cone and sprue, that will become the way that the resin is poured into the part. Extra sprues can be added to assist flow to hard to reach areas of the model.
- The model and sprues is attached to the bottom of an appropriately sized container.
- A 2 part silicone is mixed, then degassed in a vacuum chamber.
- The silicone is poured into the container.
- The whole container is placed in a vacuum chamber again, to help remove trapped bubbles.
- Optionally the whole container can be placed inside a pressure chamber to cure. (this means any remaining bubbles will be the same size when casting the resin).
- When the silicone is cured, it is cut open to remove the master model.
- The mould is then placed back inside its container to hold it closed.
- The resin is mixed, and degassed in a vacuum chamber.
- The resin is poured into the mould.
- The mould is again placed in the vacuum chamber to free all the air trapped in the bottom of the mould. When releasing the vacuum, lots of resin will be drawn deeply into the mould.
- The mould is placed in a pressure chamber to finally reduce the size of any remaining bubbles.
- The mould is removed from the pressure chamber and opened after curing (48hours or more)
- We now have a copy of the master!
- Remove the cone and sprues leaving the final part. Finishing and polishing is needed here to remove sprue connections etc.