Custom-Molded Cable Assembly: The ultimate guide on custom overmold solutions

You will often need cables that can bend repeatedly and plug or unplug for industrial and automotive applications. To achieve your goal of reducing mechanical stress and providing strain relief, you will require custom-molded cable assembly.

What are Molded Cable Assemblies?

A molded cable assembly is an assembly with molded ends creating a sealed plug or connector. 

Overmolded assemblies increase the value of your design by providing 360⁰ strain relief, flexible support at cable exits, and increased pull strength. Additionally, molded cable assemblies offer abrasion resistance, increased electromagnetic interference, and protection against harsh environments.

You can use several methods to accomplish overmolding or molding using different components depending on the end product’s electrical, physical, and mechanical requirements.

A crucial factor in the molding or overmolding process is your choice of a compound. It must properly adhere to the surface you intend to apply it on. Whether injection molded or overmolded cable is silicone, PVC, thermoplastic material, or Teflon, ensure you choose the right compound to guarantee a structurally sound end product.

Custom cables are of different types designed for specific requirements. They cost more than standard cable types. And the price might increase significantly, depending on the complexity of your custom-molded cable assembly.

Different types of molded cable assemblies

Benefits of Overmolded Cable Assemblies

Overmolded cable assemblies increase durability and performance. The point at which cables exit connectors exposes them to additional stress. Overmolded components increase strain relief and flexibility, creating a more durable cable that is less prone to premature failure. Also, they have the following characteristics.

• Customization

Thanks to the wide array of materials available, you can design a custom-molded cable assembly tailored to the precise environmental concerns of the equipment.

• Fewer Installation Errors

Custom-molded cable assemblies don’t require additional assembly. Therefore, installation is quick and easy, leaving little room for human error.

Cable Assembly Overmolding Process

To achieve the cable assembly overmolding process, you must push the material into the mold cavity, exposing it to excess pressure. The most common material used in overmolds is thermoplastic. There’s some storage space for resin in the injection molding machine. The material is often delivered in a screw-type plunger enclosed in a metal tube (barrel) or an injection ram after the heating elements are equipped into the barrel to heat the resin to molten form.

First, push the resin into the healing barrel of the molding machine at the hopper end. It mixes using any colorants and transits the barrel’s length to the actual mold, where the colorant mixture and resin get pushed into the mold cavities. Finally, the material cools, imitating any designed features in the mold, including part numbers, trade names, and logos. 

Injection molding machine

Overmolding Design Considerations

During the cable assembly design process, engineers use overmolding to provide bend and strain relief. For instance, they may use grommets as part of the assembly for any points that require installing through an opening and as a shield for the connector backshells protecting the contacts and termination points. Due to the increase in complexity tooling and the variety of materials you can use, any components that are to be injection molded should be carefully designed.

Cable Overmold Tooling Materials

Thanks to 3D printing, you can now use photopolymers for simple injection molds. Photopolymers enable the molding of resins at lower temperatures for a limited number of molding cycles.  

Manufacturers categorize Injection molding machines according to tonnage. Tonnage defines the amount of force the machine uses to keep the mold closed during the injection process. Therefore, the larger the injection machine, the more cargo it exerts, producing more molded parts. 

A die or mold is a tool manufacturers use to make the molded part. Molds are costly. Also, the more detailed and complex the mold, the higher the costs. Depending on the number of cycles to which you expose a mold, you can use different materials. And if you expect a mold to undergo thousands of mold cycles, then hardened steel is the ideal metal choice. 

Because they’re made of the most robust material, hardened steel molds are costly. However, it’s a fair price, considering the mold’s prolonged lifespan and ability to withstand many cycles without wearing out quickly. Manufacturers often use steel molds in mass-production environments. 

For molds likely to undergo several cycles, aluminum is a common choice. Aluminum serves a shorter period, but its malleability results in lower tool fabrication costs. Often, manufacturers produce molds using Computer Numeric Control machines or electrical discharge machining processes.

The material you intend to use on the molding itself will steer you in the right direction as to the material to use for the molds. If you plan on using thermoplastic resin, you can use aluminum or stainless/hardened steel. However, if the material is a liquid injection type, such as silicone, use molding tools made of hardened steel. When looking to accomplish a liquid injection, the tooling must produce exact measurements to avoid any gaps or secs that could allow the liquid to escape.

Before implementing various applications, designers often create 3D-printed models of the overmold to test the design’s fit and form. That helps avoid using costly hard tooling that could lead to the wrong results, which, should it happen, it’s impossible to alter the tooling. 

Single or Multiple Cavity Designs

When designing molding, you can choose between single or multiple cavities. Each cavity is identical to produce multiple molds in a single mold cycle with a multi-cavity mold. Some designs create multiple nonidentical cavities. A common issue is ensuring the resin flows into different designs without creating air gaps or voids.

Manufacturers deliver resin material into the heated barrel through the hopper during molding. After the heat and forces of the screw, the material softens, and the mixed resin gets pushed toward the mold tooling. Manufacturers refer to the resin that accumulates at the end of the barrel as a shot at the point. A shot is the amount of resin required to fill a cavity, which also includes an extra amount to compensate for the anticipated shrinking of the resin. Cavities typically take seconds to fill up.

Then the ram or injection screw applies pressure on the shot until the resin at the gate to the cavity cools and solidifies. The gates to the cavity are the smallest part of the mold tooling. Therefore, it’s the first area to solidify completely. Once the resin at the gate hardens, the injection molding machine cycles and prepares another shot while waiting for the next molding cycle. The resin in the cavity keeps cooling, and you can remove it once it solidifies. 

Oil or water gets circulated through the mold tooling in a series of channels to help the cooling process. Once the resin solidifies, the mold opens, removing the complete mold. Manufacturers use metal fingers or pans to make removing the mold in the mold tooling easier. And once they remove the mold from the cavity, the cycle begins again.

Pre-Mold and Overmold Designs

Some designs require that the mold comprise two parts; an overmold and pre mold. The pre-mold can consist of machine parts (pins or screws) or previously molded smaller parts. Normally, you will place these various parts in the cavity while the mold is empty. Then when the overmold cycles, the resin flows and then gets solidified.

Manufacturers often use this process when the overmold needs screws to fasten the connector to other installation components.

The Appearance of the Finished Product

After the molding process, the end product will always have blemishes and marks. Some of the reasons the molding process leaves marks to include:

• The ejector pins touch the resin when pushing it out of the mold cavity.
• Dimensional differences among the pieces of mold tooling.
• Marks where the resin entered through the gate.
• Mold tooling exhibiting signs of wear.

Blemishes and marks are inevitable. However, you can minimize the effects by specifying tight dimensional tolerance as you design the mold tooling and place gets in positions of the cavity that are not so noticeable. It’s important to consider the above factors when designing molding tools.

Injection Screw 

Conclusion: 

Custom-molded cable assemblies are robust and reliable, making them a common choice in various industries today. Most applications use molded cable assemblies to protect and interconnect cable assemblies. Feel free to contact Cloom Tech for the best custom-molded cable assembly solutions.