Mar.15, 2013 | By Eelke van den Bos

Electricity and water form a dangerous combination in general. Electrical systems and connectors therefore need protection from water intrusion. Coho Designs, a company specialized in product development, consulting and rapid prototyping services – explored the possibilities of FDM (Fused Deposition Modeling) 3D printing to create permanent, waterproof, pressure capable over-molded electrical connectors.

The projects goal was to over-mold a 37 pin connector to make the connector water-proof and pressure capable. This needed to be done in only three days. Because of the rigorous time schedule, conventional prototyping would not suffice. This made rapid prototyping the only viable option.

Due to the limited supply and cost per connector, the customer requested Coho Designs to offer a solution that would demonstrate the likelihood of the potting material to penetrate the wire assembly and seal the connector from water ingress. This includes the adhering to the wire jacket and the elimination of air-bubbles.

Because the OEM drawing of the connector was not available, Coho Designs started the project by reverse engineering the connector using Solidworks. Accurate duplication in 3D was seen as an essential step in the process of over-molding the connector.

CAD design of reverse engineered connector.

After duplicating the connector, it was time to start working on the design of the mold. The mold was made out of silicone because the potting compound, encapsulating the connector, would otherwise permanently adhere to the ABS plastic FDM parts. Due to the size of the mold, manufacturing had to be done in two parts. It was split vertically down the center to enable pouring of the compound and bleeding of the trapped air.

CAD design of silicone mold.

The finished design for the silicone mold tool was rapid prototyped via FDM. To save time and reduce cost further, the tool was made in such a way that the parts could be used to create both the right- and left-hand side of the mold. This however required the internal plug to be 3D printed as an additional component.

CAD designs of silicone-mold tool and internal plug.

To increase the longevity of the 3D printed tool, brass press-fit inserts were installed into the rapid prototyped parts. The only thing left to design was the silicone insert fixture. The 3D printed fixture will hold the silicone molds stationairy relative to each other. It will also provide as a slope to assist the pouring of the encapsulate material. Pictures of the 3D printed fixture are shown below.

CAD designs of silicone mold and mold-fixture.

After completion of the design each part were exported and saved as .stl files. Using in-house 3D printers these parts were 3D printed overnight and ready for assembly the next morning.

silicone mold tool printed and assembled.

After pouring the silicone and removing it from the mold tool some trimming operations were necessary to make the edges crisp and allow for a nice parting line (place where two or more parts of the mold meet). 

silicone mold before trimming operations.


The silicone insert fixtures were assembled next with the mold in place. Prior to encapsulation of the real connectors the surrogate prototype, with wires installed, was carefully inserted into the mold and potted like as if it were a real metal connector.

Surrogate connector ready for potting in silicone mold.

After potting, the connector seal was trimmed to final shape. The connector could now be cut in half on a band saw to inspect for air-bubbles or other inconsistencies.

Surrogate connector without trapped air-bubbles.

The results were there. 3D Printing surrogate FDM connectors allowed Coho Designs to validate the silicone molds as aviable option to over-mold the electrical connectors in a quick and cost effective way. Moreover, rapid prototyping via FDM enabled Coho Designs to step up the challenge and meet the rigorous time schedule and exceed all expectations.







Posted in 3D Printing Applications

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Sam wrote at 4/25/2016 7:51:05 PM:

I really like your approach on this project. I have a school project and would like to know what type of specific silicone do you use?

Raf wrote at 3/15/2013 9:57:18 PM:

Even if the project is beautiful, the connector is not 100% waterproof, some water droplets may elapse between the cables (by experience)!

Anja wrote at 3/15/2013 8:15:08 PM:

Thank you Alan, corrected.

Alan Millar wrote at 3/15/2013 7:59:53 PM:

Um, silicone is not silicon. Every reference to silicon here should be silicone.

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