We use molded cable assemblies everyday. Even in this wireless age cables and wires are everywhere and are a key item connecting medical, military, industrial controls and communication devices to other equipment. Most cable assemblies have some type of over molding and this article will cover some critical points about over molding.
Over molding is used to cover a component on a cable assembly and several important functions – bonding, strain relieving, environmental protection and ergonomics. The components that can be covered include medical connectors, industrial filters, military circuit boards and retail security devices to name but a few.
The process to over mold a component to a wire harness is fairly simple to describe but requires extensive knowledge of the materials and process used. The item to be over molded is placed inside a mold, typically by hand, and then plastic is injected into the mold. Inside the mold is a cavity shaped to the desired features of the over mold. Think of filling a water bottle with jello through a little hole in the side of the bottle. Once the jello firms the bottle can be removed and the jello will retain the shape of the inside of the bottle. Now imagine putting something in the center of the bottle before the jello is added. Sounds simple, but care must be taken to make sure the right material and process is used or the material won’t keep the right shape or the bottle could open and the material leak out.
Bonding components to a cable assembly is critical for many applications. Over molding is used to make sure any force applied to the cable is transferred directly to the component. Often this is used when connectors are attached to a cable or wire. The connection point is often not as strong as the connector or cable, and if too much force is transmitted to the connector a failure could occur. By using the right materials the over mold can make sure and force goes from the cable directly to the connector and bypasses the point where the wire or cable is attached to the connector.
Strain relieving allows cables to bend in a larger radius. If a wire or cable is bent too often in a small radius the conductors inside can break. Think of bending a coat hanger back and forth. Over molds are used to make sure the bend radius is large enough to avoid the coat hanger effect. These are can be seen on most molded cable assemblies with connectors on the end. The strain relief is the part of the over mold that has rings and slots. These rings and slots allow the wire or cable to bend but not in a small radius. The design of the strain relief must be done correctly to match the over mold material and the design of the cable.
Environmental protection by over molding keeps items attached to the cable safe from the elements. Typically this is for protection from liquids, chemicals, dust or blunt forces. Industrial cables, military cable and medical cables are often used in harsh environments subject to many conditions that would harm the components inside the over mold. The over mold acts as a seal or cover that protects items such as connectors, ferrites and circuit boards. By covering these items the over mold material make sure the components are safe. The material used in these applications is critical since molded cable assemblies can be exposed to very harsh materials.
Most molded cable assemblies are handled at some point, some quite often. Having an ergonomically correct over mold in these cases is important. For example if a connector is attached to a cable or wire and it must be griped by someone it is important that the shape of the over mold makes it easy to grab. This is accomplished by making sure the shape fits well into a person’s grasp and has features that allow retention.
Meridian Cable, http://www.meridiancable.com, has designed custom molded cable assemblies, http://www.meridiancable.com/
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Meridian Cable, http://www.meridiancable.com, is a custom cable assembly designer and manufacturer with over 30 years of experience supplying the medical, industrial controls, military and communications industries.