|Cirris "Pin-Sight" guided pin insertion device minimizes wiring harness errors. |
Cable assemblies and wire harnesses are everywhere. From the simple coil-cord attaching your telephone and receiver, to the cable that connects your PC to your printer, to the wiring harness in the dashboard of your car, to the miles of wiring in today's aircraft — cables and harnesses touch every facet of our lives. Cables and wiring harnesses are generally out-of-sight out-of-mind; we rarely think about them until something goes wrong.
When it comes to wire harness testing, there is little difference between competing manufacturers concerning the issue of "what" to test. Surely all cable and harness testers perform similar basic functions; testing would be for opens, shorts, mis-wires, insulation problems. However there can be significant quality improvements and cost savings depending on "when" the testing occurs.
Common practice for wire harness manufacturers is to completely assemble the harness, then perform a final electrical test. While this approach is effective in finding all electrical faults, it is not the most cost-effective solution for building harness assemblies. Faults found at final test are more expensive to troubleshoot and rework than are wiring errors caught and corrected at the point of assembly. If wiring errors can be detected when and where they occur, preferably by the assembly person who makes them, then quality goes up while overall cost is driven down.
Cirris Systems Corp., has long promoted the idea of driving test as far upstream as possible. To this end Cirris provides a full range of guided harness assembly aids and testers, designed to assure quality from insertion of the first wire, through test-as-you build capability on the wiring board, to final electrical test.
Thousands of Wires
Many times a completed wiring harness that contains several thousand wires is actually comprised of several smaller sub-assemblies, which are all brought together and laced into the final state. By placing small, bench-top testers at each sub-assembly cell, operators are able to self-test their work, assuring correct wiring of the sub-assemblies. In many instances the testers are set up to utilize their "guided build" capability. When used in this fashion the tester can actually guide the harness assembler through the build process, displaying from/to information for each wire along with providing on-screen graphical representation of each cavity of the connector as wires are being inserted. If wires are inserted correctly the operator is prompted to insert the next wire, if a mis-plug occurs, the tester instantly alerts the operator to the error and won't allow him/her to continue until it has been corrected. In essence this "test as you build" approach virtually assures a correctly wired harness coming off the board; it just can't be built wrong.
When deciding how large of a tester is required (how many test points?) the determining factor is usually the largest harness to be tested. If this is a 10,000-point harness you need a 10,000-point tester. Generally, the customer has few 10,000-point harnesses, but many smaller ones. Since they have the 10,000-point harness though, they must buy a 10,000-point tester, which means that all of the smaller harnesses get tested on the big tester. Hence many harness manufacturers end up with electrical testing being the bottleneck to effective throughput.
Cirris designs its testers to be modular, generally starting at a small number of points, say 128, and they are expandable from there. A customer with a 10,000-point harness was able to replace the existing large system with ten 1,000-point testers, which were distributed around the factory testing smaller assemblies. Then, on the rare occasion when the 10,000-point harness is built, they combine all the test points from the smaller systems into a single 10,000 point system. When the big harness is done they are able to quickly switch back to the smaller systems, maximizing their test flexibility and production capability.
Guided Pin Insertion
A recent addition to the Cirris line is the "Pin-Sight" guided pin insertion device. While not an electrical tester, it is a valuable quality assurance tool for the wiring harness manufacturer. Pin-Sight utilizes a CCD camera attached to a connector holder mounted on a force sensor base. It provides real-time guided assembly instructions for placing spare pins, seal plugs and wires into connectors. It also verifies that contacts are locked in by requiring the assembly person to pull back on each wire as it is inserted. The force gauge is set to an appropriate setting so that the operator can't insert the next wire until the previous one has been verified as being locked in. Pin-Sight is especially useful for wires that have unique I.D.s. In this case it is not good enough to make sure the harness is wired correctly, it is also essential that each labeled wire is in the correct cavity. Otherwise field technicians who might troubleshoot the harness later are blind to the fact that labeled wires don't correctly match cavity location per the print.
Case 1. A customer building military helicopters implemented a guided-build system for the Collective Stick assembly. It consisted of three cylindrical connectors and about 160 wires. Previously, the operator would wire the assembly on the bench with only paper-based documentation as a build aid. Once completed, the assembly was taken to final test to be tested. Any wiring errors were printed, and the assembly was returned to the operator for rework and then re-tested. Average completion time was 3.5 hours with an average of 1.2 wiring errors per assembly as first tested. After implementation of the guided assembly "test-as-you-build" system, completion time was reduced to 1 hour ±5 minutes with zero wiring errors recorded for over three years running. The customer reported the system paid for itself in 10 months.
Case 2. A major aircraft wiring sub-contractor building harnesses for a small-jet manufacturer implemented a similar guided-build system for its harnesses. The largest, consisting of 2600 wires and dozens of branched connectors, was taking 2 assembly persons 12 hours to complete, for a total of 24 labor hours. After which it was again taken to final electrical testing, where every harness had some number of wiring errors which had to be re-worked, necessitating re-testing. After implementation of the guided-build system, it was taking one operator six hours to build the entire harness, with zero errors. This customer reported ROI time of 15 months.
Electrical wiring harnesses are a critical component of many of the products in our lives — computers, appliances, automobiles, airplanes and many more. It is essential that they are 100 percent perfect, not only electrically but mechanically. Connector pins that are in the correct cavity but not properly locked in can create electrical opens or intermittent connections during operation. Although final electrical test is an essential part of wire harness manufacturing, it is a time-consuming and costly venture that adds no value to the manufacturing process. Wire harness manufacturers who improve their quality by reducing the number of errors found in final test stand are able to be more competitive. By moving electrical test further upstream and by using guided assembly aids and test-as-you-build processes assemblers do their jobs more efficiently with less rework and scrap — most of the time totally error-free. In today's competitive global environment, manufacturers who do this will flourish.
Contact: Cirris Systems Corporation, 1991 Parkway Blvd., Salt Lake City, UT 84119 800-441-9910 or 801-973-4600 E-mail: firstname.lastname@example.org Web: http://www.cirris.com