When the need for fastening strength and reliability are accompanied by a desire for quick assembly and convenient access, one may consider the use of time-tested quarter-turn fastening solutions, commonly referred to as DZUS fasteners manufactured by Southco.
With the wide range of product design refinements added to this technology over the past century, a broad selection of off-the-shelf systems is now available—including designs developed specifically with a high clamp load, positive stud retention, fuel-saving weight reduction, and vibration resistance for the requirements of aerospace applications.
The fixed cam designs incorporated into quarter-turn quick-access fasteners provide a good balance between performance and intuitive functionality in applications that might otherwise require a nut-and-bolt or machine screw fastener. These fasteners are often found where service access and refurbishment are required more frequently. From the avionics in the cockpit, to entertainment systems, to more structural applications such as engine cowlings and seating, quarter-turn solutions are found in numerous applications on a wide variety of aircraft.
The quick and repeatable access that quarter-turn fasteners provide can be introduced into just about any configuration an engineer might encounter. Turnkey solutions are available for a wide variety of installation environments—including blind-hole applications, near-edge installations, composite panels and frames, and aluminum—and often offer low-cost installation as well.
Quick-access fastener head styles can include winged designs for tool-free installation and removal, slotted or Phillips-head recess for use with standard screwdrivers, or specialty-tool designs for restricted access. And they are available in a variety of metallic alloys, platings, and engineered thermoplastics to match the needs of the application.
How one determines the correct quarter-turn solution depends on the parameters of the application. In addition to identifying the right material, quarter-turn fasteners are selected based on load capability, vibration resistance, cycle life, and the ability to accommodate variations in material thickness. That last factor is extremely important.
Quarter-turns operate on the principle of a fixed cam. This means that in 90° of motion, the fastener must engage a receptacle and lock the outer panel to the inner panel or frame. The more travel designed into the cam, the more variation the fastener can accommodate. However, to increase the travel, the angle of the cam must be increased, which tends to decrease the cycle life of the system. For this reason, the various quarter-turn designs available will normally include trade-offs among the different selection criteria.
Whichever system is selected, most quarter-turn fasteners deliver similar benefits:
• Time and cost savings: Snap-in, clip-on, and adhesive-mount components reduce assembly time and decrease installation costs. Quarter-turn fasteners also reduce service time for subsequent disassembly and re-assembly, decreasing the overall cost of ownership.
• Vibration resistance: To accommodate variations in material thickness, spring compliance is built in to most quarter-turn solutions. This compliance has the added benefit of providing positive locking, which offers resistance to releasing under vibration.
• Design flexibility: Standard quarter-turn systems can be adapted to multiple material specifications, including lightweight aluminum and composites, while keeping the interface consistent and intuitive for the customer. Standard options in actuation, installation styles, ejection, component retention, and trim enhance the opportunities for more application-friendly designs.
• Ergonomics/industrial design: An intuitive self-aligning interface allows for easy fastening and access with simple tools, security tool recesses, or ergonomic hand actuation. Meanwhile, the fasteners can accommodate a designer’s color scheme and industrial design concepts.
John Snyder, Product Manager, Southco DZUS Quarter-Turn Fasteners, wrote this article for Aerospace Engineering.