- SPECIAL REPORTS
Many OEMs require that individual wires and cables used in their products, components or subassemblies be clearly identified with a mark or label to improve traceability throughout the product life cycle: from initial assembly and testing, to servicing many years down the road.
For some OEMs, the decision to use wire and cable identification (wire ID) is a voluntary one. For others—such as those who serve the military and aerospace markets—wire ID is mandatory. In such cases, the process is governed by stringent specifications, such as SAE AS50881 (formerly MIL5088L).
Wires and cables can be identified inline while they are being cut to length and stripped on automatic equipment. Alternatively, wire ID can be applied using a secondary semiautomatic or manual process.
TYPES OF IDENTIFICATION
The most common type of wire ID is the termination ID, which clearly identifies where a wire or cable is terminated on a terminal strip or mating connector. The main benefit of termination ID is preventing miswiring during harness assembly, product assembly, testing and servicing.
Company logos, brand names, serial numbers and date codes can be marked on each wire to aid in traceability. This is common for expensive assemblies that have undergone electrical performance or other testing. If there are any field failures or warranty claims related to a product, the unique code makes it possible to trace a particular assembly back to the original test report.
Bar codes can also be printed directly on wire or cable or on labels that are applied to wire or cable. However, as a general rule, bar codes should only be applied to wires or cables wider than 0.1 inch so the scanner can easily read the bar code.
Many wire ID application methods are available, and each has its own pros and cons. Several factors must be considered to determine which method is best for a given company and application. These include industry specifications, insulation materials, types of information to be marked, typical batch sizes, processing speed and cost per mark.
Regardless of method used, all wire ID must be legible, permanent, abrasion resistant and able to withstand the environ-ment where the product will be used. For this reason, customers should always get wire samples marked to determine if the results meet their application requirements.
Hot stamp marking is one of the oldest application methods. On the positive side, hot stamp marking is low cost and creates marks that are quite legible and permanent—even on Teflon insulation. Plus, it prints on insulation of every color. Cycle time is short, about 1 second.
On the negative side, production throughput is low because the wire must be stationary and marker text changed manually. For these reasons, hot stamp marking is not recommended for low-volume, high-mix production. In addition, improper settings (temperature, pressure and dwell time) can damage the wire insulation. Some specifications require that a spark tester be used after the hot stamp marker to verify insulation integrity.
Labeling machines with print and apply technology can be used inline. Labels are expensive, but allow manufacturers to print high-resolution logos (300 dpi or better), multiple lines of text, and bar codes. Also, applying labels inline requires much less labor than printing labels and applying them manually in a secondary operation.
On the downside, labels can only be applied to stationary wire. This restriction lowers the production rate. Also, cycle time is high at 4 to 5 seconds.
A relative newcomer to wire ID is direct thermal transfer, which applies marks directly onto the wire or cable. This type of marking can be used on stationary or rolling wire or cable. Rolling the wire or cable allows marking over a greater circumfer-ence than other methods. Thermal transfer marking prints on insulation of all colors. Cycle time is short, about 1 to 2 se-conds.
Ink-jet marking is another application method. Newer ink-jet printers are simpler, faster and more reliable than their pre-decessors. They feature automatic startup and shutdown cycles and use less carrier solvent, resulting in less odor and im-proved air quality.
Ink-jet marking takes place on the fly—that is, while the wire or cable is moving—and can be used on most wire insulation types, except Teflon. This method creates permanent and abrasion-resistant markings on most PVC-type insulation.
Most ink-jet marking systems feature hardware and software that lets the end-user match font size to wire size. Users can also change text format orientation from horizontal to vertical (or tower) as desired. Special codes can be programmed to automatically print the time, date or a different serial number on each wire.
Bold, underline and italics font attributes are also possible. Some systems offer a “mirror” feature that rotates the text string 180 degrees on one end. This is sometimes necessary to ensure that all marker text is oriented the same way on a ter-minal strip, such as on a jumper wire in a control panel.
Ink formulations developed specifically for wire harnesses allow for high line speeds. Black inks are dye-based, while white inks are pigmented. Printers that use black inks tend to be simpler to operate.
Processes such as plasma pretreating and curing UV-curable inks can expand the range of insulation types that can be marked with an ink-jet. Be aware that these additional process steps add significantly to system cost and complexity.
Finally, there is laser marking, which is another on-the-fly method that allows for high production rates. The most common lasers used are those that produce wavelengths in the UV part of the spectrum.
Laser marking is used primarily in military and aerospace applications where the wire insulation contains a high amount of titanium dioxide (TiO2). Wire used in commercial applications tends to have insulation with little or no TiO2, which interacts with the laser to create markings. On the positive side, laser marking produces high-quality permanent marks, even on Teflon insulation.
Imagine a fully integrated, PC-controlled wire processing machine has produced all of the wires necessary to build a wire harness, and the wires have been collected in a tray or wire stacker. Without wire ID, it is very difficult to identify the individual wires and where they go on the harness board. The harness assembler must first determine which wire is which (by overall length, color, strip length, or terminals) and then look at a schematic or other cross reference list to determine where each end goes.
However, by marking or labeling the termination identifications on each wire, an operator can quickly identify the “from” and “to” points when routing the wires on the board.
Having the termination IDs on each wire or cable end is like having routing instructions right at your fingertips.
Another way to improve productivity is to minimize the changeover time of identification tooling by using wire of one color or a few colors. By reducing the number of wire colors from 10 to 1, for example, changeover frequency and labor can be reduced by 90 percent.
This approach also yields exceptional cost savings. Manufacturers who purchase wire in bulk pay a lower unit cost, reduce wire inventory and can mark wires using just one color of ink or hot stamp foil. Also, bulk wire comes on large reels or wire barrels that impart less “memory” on the wire, resulting in more consistent wire processing.
If the wire harness for a given product was originally designed with wire of many different colors, an alternative is to use white wire exclusively and print the name of the color it replaces on the wire. For example, the word “RED” could be printed every 3 inches along a white wire instead of using a red wire. In addition, the circuit number could be printed on the wire as well to distinguish it from other white wires that have the RED designation.
Using wire of one color, or just a few colors, might not always be possible. Some applications are governed by specifica-tions that require different wire colors be used. For example, ground wiring used in electrical equipment must be green or green with a yellow stripe. However, many other applications and circuits allow any wire color to be used.
Also consider using continuous marking to provide more information at preset intervals along each wire or cable assembly. For example, the wire part number or circuit number can be repeated every 3 to 6 inches or more along the wire. This makes it possible to identify individual wires anywhere along their length when servicing them. If a particular mark is difficult to read, another mark is located just a few inches away.
Continuous marking is best suited for on-the-fly application methods, such as ink-jet and laser. Because the wire doesn’t have to stop during the marking process, productivity is increased.
A final way to maximize inline wire ID productivity is to use wire list management software (WLMS). This software allows manufacturers to keep track of the processing parameters for every wire, including type and size, overall length, strip lengths, marker text and marking positions.
The WLMS synchronizes the functions of the wire processing machine and wire marker, including automatic text changes (depending on application method used). As a result, all wires for a particular harness can be produced in sequence without any operator intervention. Plus, no waste wire is generated when the system changes over from one wire to the next.
WLMS can also sort the wire list by size, type and color. This ensures that the wire processing system stops only for the operator to change the wire size, type or color.