When terminating wire there is a specific process that will ensure the quality and long service life of your wire harness. This includes compliance with customer requirements and engineering standards, and are often limited by the crimping tools, dies, and presses at your disposal. The crimp height, pressure, and pull testing metrics might indicate a need for further inspection, however the ultimate word in whether the harness passes or fails is the tensile strength of the crimped harness. Here are several common tests for your wire assemblies.
The height of your wire’s crimping is a frequently used data point used in manufacturing quality control processes, although use of this metric exclusively is not recommended. Typically the height of the crimped or welded terminal is measured to verify that it has been crimped to the optimal die cavity and with minimal pressure. However, this may fail to reveal hidden defects, such as broken wire strands, improperly removed insulation, cracked or oxidized metal, or any number of other problems. Fortunately, crimp height is an easy and non-destructive type of quality control test, making it a common tool used by the majority of harness quality control systems.
The pressure of your crimped connection is also an important indication of both the operator and the equipment’s performance in producing a quality harness. The trouble with crimp pressure as a performance metric is that there are relatively few wire presses that feature a crimp pressure or quality monitor. Virtually no hand tools used in the North American industry have a monitor available. For a small or medium harness manufacturer, pressure monitors may not be a cost-effective investment. However, in countries that have adopted use of these specialized monitors, they are utilized as a telling data point for the quality of the harness.
Pull testing is the process used to investigate the tensile value of the wire to get an indication of the sample wire termination’s breaking strength. Knowing the tensile strength of your harnesses is hugely important for resolving any concerns about mechanical properties of the wire. It also indicates with incredible accuracy the electrical integrity of your crimped connection.
Now that you know some of the common quality assurance methods for testing your wire harnesses, you may be wondering how often you need to pull and test a sample to maintain the quality of your production line. Naturally this differs from company to company, and will depend on a wide variety of factors including how critical the wire harness is to its end use mechanism, the manufacturer’s recommendations and industry specifications.
Ultimately, the best plan is to start with a high frequency sampling plan, and then slowly reduce your testing frequency until you achieve the optimal level of production and interference for quality control. In other words, if you pull two samples from the press every 4 hours for 6 months without failure, you might reduce the test to a single sample per day for another 6-month test.