Casting
Early in the iterative process we found ourselves casting electrical components directly into silicone bodies. Though our strategy for this particular product has changed, casting remains an important prototyping strategy to facilitate our rapid development cycles.
Positives and negatives: the mold-making process
The fastest technique for iterating high-quality prototypes is additive manufacturing. That said, casting has the advantages of greater flexibility in material selection, and lower per-part post-processing once proper molds have been made. Casting is also able to facilitate overmolding, where a flexible material is molded directly onto a rigid body. During several cycles in our iterative process we produced and tested devices that had built-in flexibility, as demonstrated in the below photos.
A rigid body is placed into a mold
Flexible resin is cast directly onto the rigid body
Overmolding allows for mechanical, and sometimes chemical, bonds between dissimilar materials
Important to the mold-making process is the production of high-quality metamolds—which, in the case below, were modeled in Fusion 360 and printed on a Form 2 SLA printer. For more on our use of 3D-printing for our product development cycle, see my page on additive manufacturing. Metamolds act as positives of the desired end-result model, from which silicone molds can be cast. The silicone molds then have built-in parting lines and alignment features, making all subsequent molds compatible. If the resulting part works post-testing, one could conceivably make dozens of identical molds, and generate that many parts at once.
Casting can be a messy process, but the proper use of vacuum and compression chambers, along with some patience and care with mold-making, can yield clean and durable parts.
Contrast the above assembly, which was entirely hand-cast, with the assemblies on the right, which used injection-molded parts.
