Within the complexities of modern manufacturing, the creation of custom cable assemblies stands out as a testament to both engineering precision and the nuanced understanding of materials science. These engineered products are tailored to meet the specific needs of various applications and are pivotal in powering, connecting, and ensuring the reliability of a wide range of electronic devices and systems from dozens of industries.
To better understand the variables that drive these complex processes, let's unravel the overall steps within manufacturing custom cable assemblies.
What is a Custom Cable Assembly?
At its core, a custom cable assembly is a grouping of wires or cables, designed and configured to deliver electrical signals or power from one point to another. These passive devices can be simple- consisting of a single wire and a couple of ring terminals, to wildly sophisticated mil-spec harnesses that are tailored to specific requirements for the application.
Whether it's in aerospace, automotive, medical, or consumer electronics, custom cable assemblies power devices and transmit data using a jacketed electrical conductor and some form of terminated connection on each end. The customization aspect covers everything from cable length, color, and connector types to the electrical specifications and environmental conditions faced in service.
Manufacturing Bulk Cable: A Deep Dive into Materials & Processing
The Role of Copper
Copper serves as the arteries and veins of cables due to its excellent electrical conductivity and flexibility when drawn into wire form. This element is key to ensuring efficient power and signal transmission across cables, reducing loss, and improving signal integrity./p>
The journey from raw copper ore to refined electrical wire involves several stages, including mining, smelting, refining, and finally, drawing the copper into extruded thin strands of wire. The transformation of copper into wire is achieved through a drawing process, where the metal is stretched and thinned into long, flexible strands. The raw copper is meticulously drawn through a series of dies, steadily reducing its diameter and increasing its overall length. This process not only determines the wire's gauge but also its current carrying capacity and strength.
Unjacketed stranded copper wire.
The bare copper strands are then spooled onto enormous reels and subsequently spun into the 7 strand, 26 strand, or higher strand counts of wire creating the center conductor we know and use every day. Now the stranded wire bundle just needs an electrical insulating jacket to function as a cable.
The Need for Thermoplastics
Thermoplastics serve as the protective and insulating sheath around copper wires. These materials, derived from petroleum, undergo polymerization to form long chains of polymers. The versatility, durability, and low cost of thermoplastics make them ideal for cable insulation and wire jackets.
Extruded wire jackets and insulation are the most common type of jacketing for electrical cables. While some cable types are wrapped with tape-like insulating films, wrapped cables are less common and primarily use exotic materials like PTFE and FEP tape, rather than extruded thermoplastics such as PVC, TPE, and XLPE. Both manufacturing processes create a wire that can pass electrical power and signals while electrically insulating the center conductor, thus preventing short circuits and protecting the wire from environmental damage. It should be noted that the majority of the world’s hook-up wires and data cables use extruded thermoplastics as the outer sheath material.
Bundling Wires into Multiconductor Cables
Once single conductor wires are extruded and jacketed, they can be bundled in groups of like single conductor jacketed wires forming a multiconductor cable. For example, to create a three-conductor multiconductor cable that complies with UL2517 specifications, wire manufacturers will extrude thousands of feet of three different 18AWG single conductor wires- one red jacket, one black, and one white. Then these individual wires are bundled and fed through machinery that adds a metalized foil shield, a drain wire, and then an overall braided shield of tinned copper braid.
Once this three-wire shielded bundle is complete, it’s ready for the final extrusion process. This jacketless cable is then fed through an extrusion machine where molten thermoplastic envelops the cable and cools. As it cools, the extrusion is fed through a die that produces the outer jacket to precise dimensions and is then spooled onto large reels. In this example, the final outer diameter of the finished jacket is 6.30mm+/-0.25mm. The result of this process is a finished bulk cable that is ready to terminate with connectors.
UL2517 wire cross-section with three 20AWG wires and shielding.
Termination and Cable Assembly
Wire Preparation
Preparing a wire end for a connector first involves stripping the insulation to expose the copper. Some wires are pre-tinned during the extrusion process, and others require a secondary tinning step to comply with the end-application requirements.
This process helps the wire's conductivity, makes it easier to solder, and helps inhibit corrosion and oxidation. The wire insulation is stripped per the connector manufacturer’s guidelines using various types of automated equipment. Simply program the machine with the desired strip length, feed the spooled wire into the machine, and then wait for the job to finish. The result is a wire that is prepped, stripped, and cut to the required lengths ready for termination.
Crimped & Soldered Terminals
The majority of electrical connectors use crimped terminals where metallic tabs are bent and formed into a position gripping the bare wire. In addition to the metal-to-metal contact created, some terminals are required to clamp down onto the plastic wire jacket itself to properly secure the connection. This step must be performed per industry standard specification IPC-620 to ensure a high-reliability circuit.
While automated crimping machines offer a fast, low-cost, and ultra-high volume method to manufacture these types of custom wire harnesses, some applications demand a higher reliability connection than a traditional crimped terminal. Terminals equipped with solder cups require that the stripped and tinned wire be attached to the terminal using a soldered connection. These soldering processes are largely done by hand and are labor-intensive, requiring skilled technicians to complete the job. However, when performed in accordance with industry-standard IPC-620, a soldered joint serves as the highest reliable means to attach a wire to a terminal in the industry. For this reason, soldered connections are common in medical, military, and aerospace applications.
Connector types that require a housing to position and hold the terminals include the typical single-row, dual-row, and circular connectors. These are commonly white, beige, or black plastic connectors with metallic terminals stuffed inside after the crimping is complete. Other simple types of crimped terminals do not require a connector housing include- these include ring, fork, and spade terminals. Always follow the connector manufacturer’s assembly instructions for crimping and insertion/extraction steps.
Single-row thermoplastic connector assembled with fork terminals.
Overmolding the Assembly
Overmolding is the process of adding a thermoplastic layer over a terminated cable assembly end, connector, or other component. This step provides enhanced protection, strain relief, and an attractive aesthetic finish to the custom cable assembly. Not all cables require overmolding, but for those that do, the overmold helps reduce damage to the portions of the cable that are subjected to stress, flexing and environmental abuse.
The process of overmolding first requires the design of a special tool, similar to that for an injection molded part. The terminated cable is placed within the tool, and molten plastic is shot into the tool using automated equipment. Once the overmold has cooled, it can be removed from the tool and flashing can be trimmed off the part.
Final Inspection
The final inspection of custom cable assemblies involves rigorous electrical tests, such as continuity checks, hi-pot tests, and other customer-specified functional tests. Dimensional measurements like overall length, and critical dimensions on the overmold are measured at an agreed AQL (agreed quality level). These steps ensure that each assembly meets the requirements for the end application and that the highest standards of quality and workmanship are met.
Packaging and Warehousing: The Final Steps
Once deemed compliant with all customer requirements, the finished cable assemblies are packaged according to standard protocols and can be stored in warehousing facilities under stocking agreements, ensuring they are ready for immediate deployment. Cables that are longer than 10 feet may require special coiling and package requirements to ensure the terminals and delicate electrical connectors are not damaged in shipping. Other cable products can be packaged within a Gaylord and palletized for shipment, again driven by customer requirements.
Summary
The manufacturing of custom cable assemblies is a complex yet fascinating journey from raw materials to finished products. These products are vital to so many devices across the globe, powering them and enabling them to transmit data. Sourcing custom cable assemblies is simple as long as there is thought put into the design, the requirements for the application are clear, and an effective manufacturing partner is utilized. With this, it’s possible to produce high-quality, custom cable assemblies that meet the precise needs of clients and industries worldwide.
