You can’t guarantee the quality of a cable assembly without sufficient testing, especially when working with custom designs. That much is simple.
So how can you best perform quality testing? How do the experts of custom wire assembly ensure the quality of the cables they manufacture? In this article, we’ve discussed the most common crimp quality control methods used by custom cable assembly experts, as well as the tooling required for each, their pros and cons and some best practices.
The north star for cable quality is the IPC/WHMA-A-620 assembly standard. Incorporating the standards into processes throughout your facility is a great starting point to achieving effective quality control systems.
IPC/WHA-A-620 assembly standards dictate acceptable quality control measures depending on the class of cable produced. An assembly’s class is determined by how critical product failure would be in its application. For instance, military and life support equipment is listed as Class III, as product failure is directly life-threatening.
In terms of crimp quality testing, two different types of tests are recommended by IPC and the Wire Harness Manufacturer’s Association (WHMA). They are the pull-force test and the crimp height test. To meet Class II standards, you must perform sufficient pull-force testing on all crimping projects. For Class I or II, you may choose between the two tests based on what makes the most sense for your operation.
The IPC/WHMA standards are a sensible signpost for manufacturers who produce their own custom cable in-house and want to know how to quality-test effectively. For manufacturers considering outsourcing custom cable production it makes a worthwhile standard to hold any potential suppliers to. Oftentimes, it will make sense to go beyond assembly standards to meet your needs or those of your customer. Come quitting time, ensuring product quality is the most important goal.
So what’s the difference between the pull-force test and the crimp height test?
A pull-force crimp test measures the amount of force required to pull a terminal off a wire. The strength of the connection, then, is determined by the amount of longitudinal pressure it can withstand before separating. Machines pull at the cable with gradually increasing force and record the moment that the termination is severed.
There are various fully and semi-automated tooling options available at an incredible range of prices, but finding economy in a pull-test process is difficult, as the test itself is destructive. We have outfitted one of our CST machines with a motorized monitor to automate pull-force testing, but there isn’t a pull-test machine that gives you that wire back in intended condition.
Because we’re able to automate our testing processes, decisions about what crimps we test in what ways come down purely to what makes sense from a quality assurance standpoint. The primary instances in which we use pull-force testing are when:
In all these situations, our goal in choosing to pull-force test connections is to provide ourselves and our customers with additional quality assurance.
A crimp height test is simply a measurement of the termination’s height against standards determined based on the wire gauge and crimp type. Specialized micrometers are used for most accurate measurement, and if a termination falls outside the accepted height range, it is automatically discarded.
If crimp height is too small, the conductors may be damaged by an overly tight crimp. If crimp height is too large, the termination may not be secure.
Since the test is just a measurement, it isn’t destructive in any way, which makes it more economical in theory than a pull-force test. Crimp height monitors are integrated onto both of our CST machines, so most of our crimps are height-tested automatically.
There’s another incredibly useful and efficient crimp quality testing method: crimp force monitoring. Crimp force monitors can be used on any machine crimp. They work by evaluating the amount of force required to perform the crimp and check it against the sample you’ve taught the machine.
If more force was applied than normal, the crimp’s tightness could threaten the integrity of the cable. If less force than normal was required, some strands of wire may not have been properly set in the terminal, in which case they’d be floating outside the crimp.
Monitoring crimp force allows you to have another viewpoint from which to consider crimp quality and ensure device performance. In conjunction with a height test and/or pull-force test, you can check on numerous features of a crimp for issues.
Just because you can automate crimp quality control measures with advanced tooling, doesn’t mean you should be removing people from the process. These tests look only at individual factors that make up a perfect crimp. There are a number of things that could go wrong, and an experienced custom cable assembly expert can look at a crimp at arm’s length and immediately identify bad seeds that happened to pass automated inspection.
All the knowledge of crimp test tooling and assembly standards gets you nowhere without a plan for how you’re going to implement quality testing, especially in cases when you can’t automate the process. And you obviously can’t perform destructive tests on every assembly you produce. When on a run of tens of thousands of assemblies should you be testing?
We recommend testing during setup of your equipment, to prove your process to be repeatable and consistent. We also test periodically throughout production for extra quality confirmation. Anytime production stops and starts, we test some more. We’ve found it most important to test anytime your machines are beginning a project, whether they’ve just been turned on or switched from performing one crimp to another.
It comes down to building efficient and effective processes with the best tools you can get your hands on. When you scale quality control effectively, you can guarantee consistent performance to all your customers, regardless of their project.
We hope this article helps in guiding your internal crimp quality control discussions. Talking with an expert is a great next step. We’d be happy to help answer any questions about tooling, assembly standards and application for your project.
We’ll provide you with a fast quote (standard time is three days, can be as quick as same-day) and recommend manufacturability improvements.
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