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Intelligent fasteners
Shape memory alloys and embedded systems could forever change how we assemble, and disassemble, with mechanical fasteners
Joseph Ogando -- Design News, October 20, 2003
Put down the screwdriver. Toss the torque wrench. Scrap the rivet guns, too. In the future, fasteners won't need any of that stuff. They'll just install themselves with the help of built-in actuators, instructions from their embedded microprocessors, and a remote control unit. This vision of the future may seem far-fetched, but you won't have long to wait for fasteners like these. Textron Fastening Systems (Troy, MI) and Telezygology (Milsons Point, Australia), this month introduced an "intelligent fastening system" that can perform tasks that dumb bolts and rivets couldn't even attempt.
With their embedded systems and actuators made from shape-memory materials, intelligent fasteners allow remote assembly via wireless devices. At the end of a product's lifecycle, they can disassemble just as easily, supporting an increasingly important need to reclaim components at the end of the product's life. These fasteners feature software that allows them to communicate with a computer network via wired or wireless connections, making it easy to capture information about fastener status and maintenance history. They can also be programmed to act as security devices, controlling access to sensitive components.
Or they could allow consumers to customize products in the field. "Once fasteners have some intelligence, there are a lot of things they can do," says Chris Kelliher, Telezygology's chairman.
Adding intelligence to fasteners could also have big implications for the design and manufacture of products in a variety of industries, including automotive, aerospace, and electronics. Seshu Seshasai, Textron's executive vice president of technology, notes that the need to provide access for assembly tools imposes its own set of design constraints—fastener locations that might be less than ideal from a strength perspective or that dictate a complex assembly sequence. "Remote assembly eliminates the need to make room for assembly tools," he says.
Many Fastener Forms
Rather than a collection of catalog products, intelligent fastening represents more of a technology framework that combines three integrated components—the mechanical fastener itself, an actuator, and the embedded system. The mechanical fastener doesn't necessarily have to differ from what engineers already use. "These are still mechanical fasteners," says Dickory Rudduck, Telezygology's director of technology. "The mechanical part can be whatever the engineer is used to dealing with." And the intelligent fastening system does in fact include models that outwardly resemble conventional threaded fasteners. But the inclusion of the actuator to lock and unlock the fastener opens up a host of new design possibilities, including many kinds of clips and sliding pins. "The key to all of them is the concept of remote actuation," says Rudduck.
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Smart Bolts: One early application targeted by intelligent fastners is airbag installation. Here a Nittnol wire actuates the bolt mechanism to lock or unlock the airbag. |
To make that actuation happen, intelligent fastening can employ a variety of methods. Some smart fasteners will rely on magnetic or electromagnetic actuation. One example of this type would be a magnetically actuated pin that expands a radial arrangement of finger-like clips until they engage a lip in the mating part. Other kinds of intelligent fasteners, morphing designs, will be actuated by smart materials that change shape or state with the application of stimuli such as heat or electric current. One simple implementation of these morphing fasteners is an overhang clip attached to a Nitinol wire. When heated with a bit of current to a set temperature, the wire returns to a shape that disengages the clip. According to Rudduck, various shape-memory alloys and polymers, electrostrictive materials, magentostrictive materials, and piezoelectric materials can all work in intelligent fasteners. For now, Textron and Telezygology will base their products on commercial shape-memory materials like Nitinol and a few proprietary polymers. "These materials are well out of the laboratory," Rudduck says.
The intelligent fasteners get their smarts from an embedded system that consists of a microprocessor, an energy switch, and sensors that monitor fastener status. Guided by firmware that Kelliher describes as "an operating system for fastening," this embedded system performs two important functions: It switches energy to the fastener's actuating mechanism. And it links the intelligent fasteners to larger computer networks. "The fastener becomes just another device that lives on the network," Kelliher says. This communication capability gives intelligent fasteners much of their flexibility. Using standard programming tools, users will be able to create software applications that add functionality to their array of intelligent fasteners. They might, for example, program an assembly sequence into the embedded system. Or they could add security features. Or they might gather information about fastener status and history in central database.
Like the mechanical aspects of intelligent fastening, the embedded system can take many configurations, use electronic components from different vendors, and connect to a variety of network types through wired or wireless means. "It was important that we be hardware independent," Kelliher says.
Textron and Telezygology have also developed intelligent tools for installing the smart fasteners, but these aren't your ordinary wrenches. "Usually you have to drive a fastener to torque or clamp," says Karl Schmitt, Textron's product manager for engineered assemblies. "We take that mechanism away." And the tools reflect that fact. Some of them are lock or unlock the fastener as easily as a remote control turns on a television. The most advanced installation tools are just bits of software running on a PC or handheld computer with a Bluetooth link to a nearby intelligent fastener. Rudduck recently demonstrated a couple of these digital installation tools, one that lets authorized users remove or install airbags and another that does the same for car radios. Not only did these intelligent tools provide some access control, they also guided technicians through the repair or installation process.
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Digital Assembly: The tools used to assemble intelligent fasteners won't look much like traditional assembly tools. Instead, they'll be more like remote controls. Or they could simply be bits of software running on a handheld computer that communicates with the fastener via a Bluetooth card. |
Intelligent Engineering
In some of the ways that matter to design engineers, these new intelligent fasteners won't differ much from today's dumb fasteners. Since they are mechanical fasteners, the joint strength considerations remain the same. "All fasteners still have to transfer a force," Seshasai says, noting that the concepts of tension, shear, and clamp load don't change with the addition of an embedded system. "Any joint strength you can achieve with a traditional fastener, you can achieve with an intelligent fastener," he says.
But in other ways, the new fasteners really do change things. On the plus side, they promise to provide additional design freedom. Seshasai points out that tool access and assembly sequence often dictate the fastener locations as much as joint strength does. "Now you can put a joint anywhere you want," he says. The intelligent fasteners, because of the built-in actuation, can also eliminate some of the tolerance or orientation issues associated with assembly tools. Cross threading could be a thing of the past.
They also shouldn't present any packaging difficulties, despite their onboard electronics. These fasteners tap into a product's existing wiring and electronics. Rudduck wryly notes that "digital commands take up far less space than an a physical tool." He believes that smart fasteners can attain much smaller sizes than conventional mechanical fasteners—in part because they overcome traditional spacing constraints and in part because smart materials will allow them to be smaller. "Smart materials will ultimately be applied on a nanotechnology level," he predicts.
Goodbye Nuts and Bolts?
For all their benefits, intelligent fasteners will pose some technical barriers—at least at first. "The biggest limitation is thermal," Rudduck says, noting that current Nitinol grades have a maximum transformation temperature of roughly 150C, low enough to interfere with the fastener's actuation in high-temperature automotive applications. "That would restrict our initial activities to inside the cabin," he says. Thermal limitation, however, should ease as new high-temperature shape memory alloys become available. "We'll be able to migrate into hotter applications as the materials evolve," he says. If left unchecked, RF interference could also plague smart fasteners. But Seshasai points out that it can be avoided with well-understood shielding methods, just as it is in other products with onboard electronics.
Finally, cost could present a problem in the wrong applications. On a fastener-to-fastener basis, the intelligent fasteners will cost two to five times as much as their dumb counterparts, Seshasai estimates. But they're not really intended as a drop-in replacement for simple fasteners that already work just fine in existing products. "We won't compete in those applications," Seshasai says. He argues intelligent fasteners will mostly find a home in new products where they can add value by performing tasks that ordinary fasteners can't. What's more, intelligent fasteners may substantially lower total costs—by simplifying assembly operations. "Intelligent fastening replaces robots and other expensive assembly tools," Kelliher says. "So it removes some of the capital intensity of manufacturing."
Even if the technical and cost barriers do disappear quickly, intelligent fastening will still have one more hurdle standing in its way—the confidence of engineers. Do the built in actuators add a new electronic failure mode to fastening? Will these fasteners unlock at the wrong time? That's the first thing that crossed Ron Weddle's mind. As the director of manufacturing technology for Cessna, Weddle had an early look at the intelligent fastening system. "Because they have an induced unlock feature, we would want to make sure that they don't unlock when you don't want them to," he says.
Nothing inspires confidence, however, like the years of rigorous testing required for aerospace applications. And Weddle doesn't rule out the fasteners for important access-panel and cowling joints given enough validation work. "They have potential," he says. For now, though, he says Cessna is only considering the new fasteners for joints inside the cabin. For example, the company is looking at them as a way to attach—and control access to—flight electronics.
Textron and Telezygology plan to take a similar tack in the beginning and move into critical joint applications only after technology proves itself. For the non-critical applications, though, Textron is ready to supply intelligent fasteners right now. "We can make them today," says Seshasai.
Senior Editor Joseph Ogando can be reached atjogando@reedbusiness.com.
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