The core of the ring is cast from precious metals. Currently silver, or gold. This metal core adds rigidity to the design to protect the internal electronics against flexing. The lustre of the silver or gold adds a classic design element that helps the world see this as a jewellery project rather than an electronic curiosity.
The process is as follows:
- Design the items to be cast using CAD (Computer Aided Design) software, I am using AutoDesk Fusion 360.
- Arrange the items onto a casting tree in the CAD software. Care is taken to minimise the sharp corners and hard to reach areas (when the metal is cast into the final shape).
- Print the casting tree using a resin 3D printer. It is important to use casting specific resin, as it will perform better in the later steps.
- Place the 3D print into the casting flask and surround with investment casting material. Usually this is a gypsum based powder that is mixed with water, degassed, poured into the flask, then degassed/bubbled again.
- Place the casting flux in the burnout oven. This is an oven that follows a set heating program, around 14 hours of slowly ramping between the temperatures recommended by the investment material manufacturer.
- The metal to be cast is placed in the melt furnace and brought to its particular pouring temperature. (I use ~970c for silver)
- The flask is placed onto a vacuum table, which sucks air through the porous investment material. This will help the metal flow into all the details, and stop the expanding hot air from pushing out the metal.
- When the vacuum in the table is ready, the metal is pored into the flask.
- 15 minutes is allowed for the metal to solidify.
- The whole flask is dumped into cold water to break up the investment material.
- Finally! we have a metal version of the casting tree we designed in the CAD software. This process will usually take ~ 2 working days. ~10h for the 3D printing, ~14h for burnout. Total manual labour is about 2h, not including the item design time.