Processing Thick Cables
Special equipment is needed to cut, strip and terminate large-diameter wire and cable
About 2 million electric vehicles were sold worldwide in 2018, a whopping 57 percent increase over 2017, according to consulting firm Research and Markets. Some 69 percent of those were battery electric vehicles (BEVs) and 31 percent were plug-in hybrid electric vehicles (PHEVs).
Sales of electric vehicles should increase this year—and for many years to come. More than 2.8 million electric vehicles are likely to be sold globally in 2019, and OEMs will introduce 45 new electric vehicle models: 37 BEVs and eight PHEVs.
Although governments are reducing tax incentives for purchasing electric vehicles, global sales of electric vehicles are nevertheless expected to grow at a cumulative annual rate of 32 percent during the next six years, reaching nearly 10.8 million vehicles in 2025. Better charging infrastructure, increasing vehicle range, and lower battery cost will spur sales growth.
The growth in electric vehicle sales has harness assemblers stocking up on equipment specifically to cut, strip and crimp the large-diameter wire and cable needed to connect motors and batteries.
Electric vehicles aren’t the only application spurring investment in heavy-duty wire processing equipment, either. Data centers, vehicle charging stations, and renewable energy storage sites are also creating a need for harness assemblies containing large-diameter wire and cable.
“Anything over 4 AWG falls into the ‘large wire and cable’ category,” says Peter Doyon, vice president of product management at Schleuniger Inc. “Many midrange cut and strip machines on the market can process 4 AWG wire, but processing 2 AWG wire and larger requires heavier duty equipment.”
Cutting and Stripping
Large-diameter wire and cable requires powerful machinery, beginning with a prefeeder. The main challenge when feeding thick wire and cable is to keep it straight. Thick wire or cable is stiff and often twisted, making it difficult to achieve straightness, which is vital for accurate measuring and cutting. Prefeeders overcome this problem by limiting tensile stress, ensuring a steady flow of wire into the processing machine, and preventing or removing kinks or bends.
Prefeeders must be capable of handling large, heavy spools—typically 24 to 42 inches in diameter—and provide a constant, low-tension supply of wire to the cutting and stripping machine, says Doyon. A 1,000-foot spool of 2 AWG wire can weigh more than 260 pounds. A thousand feet of 4/0 wire can weigh more than three times that.
The cutting and stripping machine must be capable of feeding the wire to the correct length and have enough power to cut the cable and strip the ends.
One such machine is Schleuniger’s MegaStrip 9650. This modular machine automatically cuts and strips a wide range of large cables up to 35 millimeters
in diameter. The machine comes in two models. The 9650 M features a multiposition cutter head for multistep operations. The 9650 MR model adds a rotary incision unit with an automatic centering system for stripping shielded cable. Both models come standard with Schleuniger’s SmartBlade cartridge system for fast blade changeovers.
The machine can operate with up to two ink-jet marking systems. The print head positions are located after the cutter head to minimize waste. All models feature a 10-inch color touch screen user interface with intuitive icons and simple navigation. A wide range of interfaces for peripheral devices is available.
The machine can produce lengths of wire ranging from 150 to 999,999 millimeters. Strip length can be set to any distance less than 999,999 millimeters, and pull-off length can be set to a maximum of 220 millimeters. Feeding speed is 3 meters per second.
Crimping large-diameter wire and cable also requires heavy-duty equipment. Terminals, or “lugs,” for large-diameter wire are typically supplied as loose parts, rather than daisy-chained on a reel.
“The material type and wall thickness of the lug itself, the type of crimp geometry, and the cable size and stranding determine how much force is required to achieve a gas-tight crimp,” says Doyon. “Typical forces are in the range of 5 to 15 tons, although very large cables with heavy duty lugs can require 25 tons of force for a proper crimp.”
The EPS 15000 semiautomatic electric crimping press from the Schaefer Group was designed for crimping individual terminals on wires with large cross-sections. The operator inserts the terminals into the crimping tool and inserts the wires. The crimping process starts automatically when the sensor in the tool is touched or when the foot switch is actuated.
The machine can apply a maximum pressing force of 150 kilonewtons, and it can accept wires with cross sections as large as 100 square millimeters. Maximum stroke length is 50 millimeters, and the maximum shut height is 204.8 millimeters.
The press is equipped with a handwheel for manual test operation after retooling or maintenance work. Parameters are set through an intuitive touch screen interface, and the machine can be linked to a shop-floor network.
Operator safety is ensured by a closed and locked slide cover. An integrated safety switch stops the crimping process when the safety circuit is interrupted, and built-in pinch protection reduces the risk of crushing the operator’s fingers.
Ultrasonic welding is another option for terminating large-diameter wire, says Saeed Mogadam, president of Telsonic Ultrasonics Inc. The process is fast. Depending on the size of the parts, a weld can be completed in 1 to 3 seconds.
Compared to other welding processes, the joined parts are heated up less so that they do not reach their melting point. As a result, materials directly adjacent to the weld, such as the insulation, are not damaged. Furthermore, the jointed material does not become brittle at the transition to the solid material. The strength of the weld is created by the relaxation process of the first two atomic layers of the parts to be welded.
Telsonic offers three types of ultrasonic metal welding systems: longitudinal, torsional and PowerWheel.
In a longitudinal system, the welding system is arranged horizontally. High-frequency vibrations are tangentially transferred into the upper part, which moves horizontally against the lower part. The resulting friction creates an atomic connection between the two parts.
In a torsional system, the welding system is arranged vertically. Instead of moving back and forth, the sonotrode moves with a twisting action against the parts. This process is advantageous in that only a small part of the vibrations is transferred into the area surrounding the weld seam. This is gentler on the parts while achieving greater energy density in the area of the weld.
The PowerWheel system is also a torsional welding process. It was originally developed for high-energy output of between 6.5 and 10 kilowatts, but is also becoming popular for smaller output applications. The welding action is carried out in a rocking or rolling movement directly at the weld. This means that the maximum amplitude is always at the center of the weld area, and the power output can be precisely focused.
As a result, welds can be up to 30 percent narrower than those produced by a linear system. Thicker terminal connections can be welded with great strength. And, copper or aluminum wires with cross sections of 70 to 160 millimeters can be welded.