10/15/1998 | 3 MINUTE READ


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Quality assurance issues and uninspired fastener design may have caused engineers to shy away from specifying fasteners over other joining options in the past, but fasteners have been quietly growing in sophistication and reliability. Perhaps they're worth another look. By Colleen Dejong, Senior Associate Editor


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Can a fastener help you become ISO 14001 compliant? Maybe. One of the qualifiers of ISO 14001 is the assurance of a clean, safe work environment. And through the use of fasteners in place of, say welding, this may be more readily realized.

According to Brian Slater, an application engineer at fastener manufacturer Penn Engineering & Manufacturing Corp. (PEM, Danboro, PA), self-clinching-type fasteners such as PEM's Autospec studs nuts and standoff fasteners also can provide faster assembly operations, since inserting the fastener and securing the two pieces together can be done in one step.

Essentially, a self-clinching fastener is one that cold-flows into a pre-designated recess in the pilot of the fastener. A ring with ribs or serrations prevents the fastener from moving around in the part being assembled.

Other than quicker assembly, the self-clinching fastener offers the average engineer a couple of other options. First of all, they take up less space than your average screw and bolt, so they can be specified into some pretty tight spaces.

Secondly, they're a good match for thinner sheet metal—you know, like the ones OEMs are specifying now to reduce vehicle weight. They have greater holding power than traditional sheet metal screws, and cause less stress to the sheets than tapping or welding.

Right now, these type of fasteners are being used all over the place—air bags, water pump covers, sun roofs, engine mounts, door strips, and ignition coils, just to name a few.

The Large and Small of It

There are a couple of other trends that may be driving an increased use in fasteners that are worth noting. The first is the growing use of electronic systems in vehicle systems. Soldering circuitry and other digital components may work on calculators, but it's not really a technique that can be reliably used in a circuit board that will be careening down a pot hole-filled highway at 80 mph along with the rest of the car.

For that reason, makers of automotive electronic systems are turning to mechanical fasteners such as PEM's Connect'r Ware and miniature fastener products to join circuit boards and other digital parts together. The tough little fasteners are also easier to accurately position on such a small level.

On a larger scale, the popularity of pick-up trucks and SUVs is driving engineers to take a look at much, much larger fasteners. At Huck Fastening Systems (Waco, TX)—a company that makes fasteners for semis, off-highway vehicles, and trains—they've seen a big increase in inquiries from automotive OEMs and suppliers. According to representative Jim Hutchinson, oil pan attachment, door panel bolts, and pick-up bed applications are all in development, with more applications anticipated.

Upon Closer Inspection...

Mectron's QuAlifier
Mectron's QuAlifier inspection device is capable of inspecting small parts quickly, making it easily adaptable to fastener testing.

Okay, there's a certain flurry of interest around fasteners right now, but how do you really know they'll hold up when they're supposed to and fail when they're supposed to (like in airbags and break-away steering wheels)? And is it really possible to inspect millions of pretty small parts? All of them. And, of course, you've got to be able to document that you've done it.

It's a challenge, certainly, but it's not impossible. Mectron Engineering, Co. (Ann Arbor, MI), for example, has configured its QuAlifier inspection system for inspecting small parts to inspect, verify, and sort fasteners. The system uses both lasers and magnetic imagery technology to detect defects in SEMS, patched, and flanged hex shaped fasteners.

The lasers (six in all) in the tester are coordinated to provide 12 inspection points through 360°. Each inspects two points that are 180° apart, looking at as many as 84 different part features, depending on the type of fastener being inspected.

Testing the metallurgical soundness of the fasteners is a magnetic imagery system that uses an eddy current to perform inspections on the fly. A magnetic image is developed as it passes through the QuAlifier, and a part signature is developed using Mectron's Shadow Gate software. The part signature lets inspectors look at critical defects like cracks or bad material mixes, and verify properties such as hardness and plating thickness.

An independent part outline is displayed on the system's touchscreen for visual inspection. Those deemed non-functional are separated into a reject bin, while parts that pass are relegated to a packing system that sends them on their way.

A Comment from the Peanut Gallery

In the midst of getting educated about fasteners, one engineer indicated that one reason it's become so much easier to engineer fasteners into a part design is because several manufacturers have put CAD drawings on the Internet. Now he doesn't even have to leave his computer to find the right fastener, and he can spec it right into the drawing.


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