Custom cable assemblies use various types of plugs, connector housings, and gasketing to mate and properly seal within a system. These connectors provide a way to mechanically attach to the other system components by means of a latch or a polarized connector body.
Subtle design features within a connector’s shape allow for the proper alignment of mating surfaces that include o-ring grooves, overmolded gaskets, or other sealing faces. Connector orientation is especially critical for pin and socket style mates because a misaligned pin can cause an open or shorted circuit or allow moisture to enter the connector housing.
Compromised Connections from Corrosion and Exposure to Moisture
Corrosion is a constant issue with these types of mates because as the corrosion builds and more materials oxidize, the electrical connections can become increasingly compromised. Due to the insulating properties of the oxidized build-up, low voltage signals can be disrupted by higher-than-expected electrical resistances across the connection. According to Ohms law, with constant voltage and an increase in electrical resistance, a circuit’s current will be reduced. The connector may then fail to render a large part of the system powerless or without data communication. The impact is severe, and it can take only a handful of exposures to moisture to generate enough corrosion to impact electrical performance. Corrosion can be accelerated by several factors that include exposure to saltwater, humidity, and the presence of dissimilar metals within the connector mate.
To mitigate this, engineers will require critical connector mates to have an IP66 or IP67 ingress protection rating to help safeguard against the effects of moisture and corrosion. The certification process to meet an IP rating is lengthy, and not always necessary to satisfy program objectives. To meet these requirements, a product must be classified as water resilient against a powerful stream of jets – earning IP66, or able to be temporarily submerged underwater – achieving IP67.
For many projects, the levels of protection afforded by the IP66 and IP67 ratings help make certain that a device functions before and after exposure to moisture. In some projects evidence of water intrusion is a cause for failure, however, pass/fail criteria are complex subjects and compliance must be determined by whomever retains design authority.
Waterproofing Custom Cable Assemblies
Custom cables or wire harnesses assemblies can be developed to include waterproofing measures such as sealing surfaces, o-rings, and gaskets, all of which include some type of soft thermoplastic or silicone elastomer. Depending on the temperature range, the anticipated chemical exposure, and how the seal will be mounted, engineers will develop overmolded or compression molded seals to achieve the desired level of waterproofness. These seals can be fabricated in a wide variety of shapes, materials, and form factors.
Custom cable assembly connectors are frequently designed and tested to the requirements of IP66 and IP67 but may not be formally certified to them. This approach can be attractive in terms of cost and schedule for projects that demand the performance of an IP-rated connector but don’t necessarily need the third-party certification of one.
Option 1: Off-The-Shelf Connector with Gasket
Automotive off-the-shelf cable connector with gasket.
Cable connectors may be purchased as a complete off-the-shelf solution already equipped with a waterproof gasket or o-ring. These products are available from numerous name-brand connector manufacturers and are widely carried by online distributors. Normally these items are in stock, but with recent supply chain disruptions stemming from the COVID-19 pandemic, lead times have been impacted and must be verified for each order.
Off-the-shelf waterproof connectors are common for mil-aero, automotive, and industrial applications and usually feature o-rings or gaskets that are supplied loose. Easily attached in the field or the manufacturing floor, these seals are a consumable that can be replaced over time. Other connectors come with a seal that is an actual part of the connector assembly and permanently attached- either overmolded or affixed with an adhesive. These connectors are a low-risk choice for development activities but have limited options in terms of customization.
Option 2: Custom Gasket Design
Overmolded cable with separate custom gasket.
Custom gaskets are an option but come with added complexity. The easiest way to make a custom gasket is to cut one from a sheet or strip of material. Intricate die cut shapes can be stamped from large sheets of material, forming a custom-shaped flat gasket that can be used to waterproof two mating surfaces. Other projects will benefit from a flat gasket punched to a specific diameter. Spare gaskets can be stocked in inventory making replacements available in the future.
Molded gaskets are not expensive on a recurring basis, but the upfront engineering and tooling costs can be. The fees and timelines associated for custom molded gaskets can be mitigated by use of 3D printed molds and two-part molding compounds, especially for development runs. Engineers can effectively design a handful of options and down-select based on performance. This way, several options with subtle design features can be tested and optimized to arrive at the best choice. If high volumes are anticipated, hard tooling is recommended once the design is proven out.
Option 3: Overmold That Acts as the Gasket
Overmolded grommet to serve as the primary sealing surface.
The design intent of an overmold is to provide a ruggedized strain relief for a connector or cable assembly. Overmolds are usually made of thermoplastics like PVC and TPE that bond to the wire jacket, thus forming a watertight seal. Because overmolds are produced from custom tooling that resembles injection and compression molded members, sealing surfaces such as lips or ribs can be molded in to the overmold. But this only works if the overmold material is supple enough to behave like a gasket. Many overmold materials are made of high durometer PVC which can be 80 – 90 shore A, which is too stiff to form a proper seal. Customers must identify the design intent of the overmold to make certain that the right materials are selected.
For projects that require a complex overmold that also serves as a gasket, manufacturers will request that a .STP model of the overmold is provided at the time of production. Tolerances must be accounted for since many injection and compression molded items have wider manufacturing tolerances when compared to the tolerances of machined plastics and metals. If the project needs a gasket tolerance of +/- 0.003” for the design to properly seal, another manufacturing approach may be necessary.
Getting Started
It’s clear that buying an off-the-shelf waterproof connector is the best path forward in terms of overall program risk. While costs and lead times are generally favorable for waterproof connectors through distribution, few opportunities remain to customize these items should there be shortcomings in performance.
If a custom approach is warranted, early engagement with a full-service cable manufacturer like Epec can help identify high-risk items and tailor a program plan to meet delivery milestones.
Summary
High-performing cable manufacturers can include leak testing as a part of their production activities allowing for real-time adjustments to gasketing features. Optimizing gaskets is a major part of the development and a step that should be flagged as high risk early in program planning, including time and budget to make design changes is especially critical. This fact can be the difference between an all-pass and a test failure, equating to weeks of schedule savings and thousands of dollars in excess costs.
