Producing End Use Automotive Connector Seals With Silicone 3D Printing

HGM Automotive Electronics is a specialty manufacturer that designs and supplies leading-edge electronic systems for automotive aftermarket use.

Guy Cardwell, director of research and development at HGM Automotive Electronics, highlighted that one of the challenges they face at HGM Automotive is that it is quite difficult to find the parts to service or restore their engines since many of the vehicles they work with are vintage cars. Connectors and other electrical components become more challenging to find, particularly as the original production of these items phases out.

They turned to 3D printing for prototyping and low-volume production because it is the best option to fabricate parts on demand, in house. However, it’s a regulated industry that needs to follow specific requirements such as ingress protection (IP) rating and chemical resistance, therefore the choice of material is very important. The most common material used in automotive connector seals is usually soft silicone, but there are really few options to produce it. While injection molding is cost-prohibitive for low-volume production, traditional silicone casting is a time-consuming method. 

With the introduction of Silicone 40A Resin, the first accessible 100% silicone 3D printing material for soft, pliable, and durable parts, Cardwell says they found “exactly the right stuff.” Through rigorous chemical and mechanical testing, they demonstrated that the new material has excellent mechanical properties and chemical resistance for end-use automotive parts. The company was part of the beta program for the new materials and used it for prototyping, but their main goal now is to start producing end-use parts in low volume production.

With the success of the electrical connectors they produced, HGM Automotive started experimenting with custom seals. These are difficult-to-source components barely found on the open market, and if they are, then it’s usually of very poor quality. The challenge of developing custom seals for the connectors arose due to the lack of a suitably pliable elastomeric material. They could make an injection mold and use a very soft urethane to produce the parts. The downside is that this mold would cost between $6,000 and $10,000 just to get started. The cost would be justified if they needed 10,000 of these parts, but the reality is a volume between 100 and 1,000 pieces a year. Additionally, once the mold is made, it is almost impossible to change the design. Specifically for connector seals that tend to be geometrically complicated, this represents a real obstacle. “It just comes down to a question of cost and flexibility,” says Cardwell.

For a production volume of 100 units of connector seals, HGM Automotive reduced their costs by 98% and their lead time by 90%.

Originally they were printing the connector seals in the Formlabs soft and flexible Elastic 50A Resin, but even that material was not flexible enough. He adds that since the connectors are being assembled manually, it probably takes the harness builders two to three times longer to assemble a connector using a harder material such as urethane rather than having a silicone seal, “simply because they are working against the material.”

Another option was turning to a regular pourable silicone casting, which they’ve done in the past for other parts. However this specific connector is designed to have nine wires penetrating the seal, so the design is highly intricate. It has holes and geometry that would make mold release difficult, and overall just a level of detail that requires the precision of 3D printing.

Silicone 40A Resin allows HGM to keep the manufacturing processes for low volume production in-house and the fact that it can be used in many different ways is very compelling. The team already anticipates other uses for it besides connector seals. The main advantage of the new material lies in its close resemblance to the production material, offering the ideal properties for HGM Automotive Electronics’ applications, especially in terms of elasticity, tear strength, and flexibility.

In automotive applications, you typically deal with situations that require watertight seals that withstand a meter to two or three meters of depth rating, depending upon the application. In addition, there are chemical resistance requirements against all standard automotive fluids, with the main ones being water, oil, and transmission fluid. To test the parts, Cardwell printed several samples and functionally tested them in the engine bay of his car. The printed silicone samples were left in the engine bay under normal operating conditions to test for their temperature chemical resistance for more than six weeks. 

“We’ve left them in different fluids in the engine bay doing the thermal cycling. We’ve tested with water, we’ve tested statically with transmission fluid, and with antifreeze,” says Cardwell. He adds that “the big one that these seals are actually preventing intrusion on, is typically water.” After six weeks of thermal cycling and various fluid exposures, Cardwell highlighted the watertightness and the temperature resistance of the Silicone 40A Resin. Automotive electronics range between -40°C to 105°C. With its glass transition temperature (Tg) at -107°C and temperature resistance between -25°C and 125°C, Silicone 40A Resin perfectly matched their needs for temperature resistance. “I proceeded with the testing that we’ve done on the material under the assumption that this would behave similarly to a comparable injection molded silicone of its style,” which it did. The material properties of Silicone 40A Resin aligned perfectly with his expectations of an end use material, making this the perfect addition to their arsenal.

After having gone through extensive in-field testing, the team at HGM is highly satisfied with the new 100% silicone resin and how it fits their requirements. They intend to use it for end-use part production of the connector seals and estimate it at 500 to 1,000 units per year. Cardwell is looking into developing their use of the resin even more and adds that “there are at least four products that are immediately attractive, just in connectors alone.”

Silicone 40A Resin gave HGM Automotive the flexibility to develop designs that could only be done with expensive and time consuming processes, allowing them to explore new markets. 

Going forward, Cardwell is looking forward to being able to tell his clients that he can just produce a custom piece, made of soft rubber. He is thinking about developing different kinds of custom seals, gaskets, and new high-voltage silicone insulator boots, as seen below.