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Waffle iron silicone parts

Updated: Jul 6, 2021

I design a lot of silicone/rubber parts:

Keypads, diaphragm valves, ingress protection (waterproof seals), grips, overmolds, etc.

How do I decide what type of silicone/rubber molding process to use?

Injection molded silicone is generally called LSR (Liquid Silicone Rubber) The material is typically a catalyzed (A+B) mixture that flows into a mold cavity like a standard injection mold. The mold is heated and the silicone cures under high pressure.

When designing a part for LSR, consider the rationale. LSR molds are usually much more expensive.

LSR mold tolerances are very tight. Liquid silicone flows in the mold like water, so flash is a very real problem. Some manufacturing companies use low-cost labor to trim parts. Others use Cryogenic Deflashing to deflash parts. Freeze the parts quickly, and tumble the parts to remove the thin, brittle flash.

If the part can be designed as a compression-mold, the overhead/tooling/capital investment will be lower. The process involves hand-loading small sheets or chunks of silicone putty into the mold. The mold closes, squishing the putty into all the mold crevices like a Waffle Iron. Here’s a great video on compression molding from RSP.

Compression molding silicone is generally lower cost tooling than injection molding. It also allows creative design options:

  1. Keypads with different colored numbers on the numpad

  2. Floating (unsupported) electronics or magnets within the silicone

  3. Thick walls/blocks

  4. Mixed/blended/swirled color options

  5. High-volume- some compression molding tools have 100-200 cavities!

We can create high-quality parts using either compression or injection molding processes. Last year, I wrote about prototyping with silicone, and the printing technology keeps improving.

Right now we’re printing 85A silicone mouthguards to test fit and assembly methods. Next week, we’ll print molds and place boil-n-bite pellets into the cavity to create a functional mouthguard!

If you’re interested in designing a silicone/rubber part, but don’t know where to start….give me a call. I’m always available to chat.

Make it an excellent week!


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