Chances are when you think of fastening sheets of metal, the thought of using a fastener with screws comes to mind. However, what if something simpler existed that served the same purpose?
For decades, traditional methods have worked well. However, while years of R&D automated and improved processes, little progress has been made to debottleneck the most labor intensive task … hardware assembly.
Now, an alternative approach based on snap technology can save companies as much as 90 percent of their hardware installation time. It's currently used in the assembly process of industrial enclosures, but has the potential for use in other areas including: appliances, industrial machinery, HVAC equipment, automotive and furniture.
Benefits of snap technology include:
Fasteners do not loosen in use, even over time;
Blind assembly installation
Reduces cost and inventory.
The basis for the technology is like a door's spring lock. In closing a door with a spring lock, the beveled spring bolt is pushed against the pressure of the spring, past the edge of the striking plate in the door frame and into a guide channel. As soon as the spring bolt passes the edge of the striking plate, it springs out of the guide channel. The force of the tensioned spring inserts it into the striking plate, which securely locks the door. Not until activation of the latch is the spring bolt pulled out from the striking plate and back into the guide channel so the door can be opened. The same concept was used for this technology. A snap element consists of only two parts — the guide and the spring seating in a cutout within the guide. The guide includes single or multiple triangular wings at the ends which are defined by the wing pitch and clamping pitch. A rectangular cutout is required versus a round hole. Since most cutouts are punched or done by lasers, this simply involves reprogramming the machinery. Even though punched hole sizes vary, over time non-spoken standards have evolved. The same applies to the rectangular cutouts. Snap fasteners are made in the length and width dimensions most frequently used in enclosure manufacturing. Space is tight in enclosures, so the fasteners need to have as little depth as possible. Ideally, it should be possible to install them in the edge areas and other dead spaces within the enclosure or switch cabinet. Minimum installation depth of a snap fastener is only 0.276 inches (7 mm). As long as the minimum specification is maintained snap fasteners can principally be made in all desired user-specific installation depths. The snap fastener needs to be adapted precisely to the thicknesses of the panel for a secure fit. This is true whether the fastener is used to join two panels or to install hardware on a panel. This is achieved by the layout of the snap fastener's clamping range. (See above). In any snap element, the clamping pitch, the height of the wing, and the height of the pitch together create a right-angled triangle. The clamping pitch represents the hypotenuse. The clamping angle amounts to 14 to 15 degrees (see above). Based on the tangent function, a ratio of the legs of the right-angled triangle of approximately 4:1 results, so that at the height of the wing of 0.157 inches (4 mm), the height of the pitch amounts to 0.039 inches (1 mm). The height of the pitch of 0.039 inches (1 mm) is, however, not fully utilized for clamping, i.e. compensating for the various panel thicknesses. At the beginning and at the end of the clamping pitch, approximately 0.008 inches (0.2 mm) of the height of the pitch is intended as a safety clearance in order for the snap element to engage securely behind the edge of the panel within the area of the clamping pitch. The clamping range of the snap elements thus lies in the center of the clamping pitch and occupies approximately 0.024 inches (0.6 mm) of the height of the pitch, resulting in an application clearance of ± 0.012 inches (0.3 mm) and a clamping range of 0.024 inches (0.6 mm), within which the snap element guarantees totally secure bracing. Thanks to this clamping range, it takes only a few different versions of snap fasteners to accommodate the variety of panel thicknesses available. The clamping range of the snap fastener does more than just limit the number of versions needed. It also makes it possible to compensate for deviations in the thicknesses of the panels used. How to Factor in ForceHolding and pull force vary depending upon the application. Stronger forces such as weight and lateral forces come into play when using a hinge on a door. The layout of the snap fasteners can be designed in various ways to satisfy these diverse requirements. Hold and pull forces need to be absorbed by the fastener with a clamping mechanism. In order to function properly, once the snap elements are in place it is important that they do not get pushed back into the channel by the forces acting upon them. The layout of the snap fastener's defined pitch addresses this issue. A clamping pitch with an angle of 14 or 15 degrees is most effective. It provides necessary clamping and has a self-locking effect. This was substantiated during testing when it was not possible to pull out a snap fastener installed on a 0.059 inch (1.5 mm) thick panel until the pull force reached approximately 4,500N. The panel will first buckle and enlarge the cutout before the snap fastener comes free. The height of the snap elements and the length of the wings are virtually insignificant, as long as an appropriate clamping range has been chosen and the angle of the clamping pitch lies between 14 and 20 degrees. The width of the wings is unimportant, but can provide stability. Wide wings are recommended for thicker panels. The length and the width of the channel play an important role for the forces acting on the panel plane and for the force that could distort the snap fastener within the panel cutout, but only in an indirect way. Larger snap fasteners are recommended for heavy doors. Snap fasteners meet the IP Code (International Protection Code). The IP codes address several degrees of protection including: dangerous parts, penetration of solid matter, water penetration, human protection and other special information not contained in the other categories. The most important for snap fasteners is water penetration, and the snap fasteners satisfy these stringent requirements. Installation and Removal The snap fastener is simply pushed through the rectangular cutout. Once the wing pitches have cleared the cutout, the snap elements snap automatically into position due to the pressure force from the compressed spring. Installation is complete once the “click” sound is heard. This tool-less assembly method is quick and secure. Removing the fastener can be achieved by using a simple socket, screwdriver or special key. The snap elements are pushed back into the channel against the spring force, and the snap fastener can be easily pulled out. The application ideas for this technology are endless. Here are some conceptual examples which although realistic are not yet finalized — Snap fasteners for round profiles and T-Channels, Furniture (file cabinets), Automotive (mounting cell phones, GPS and MP3 players to dashboards); and Building Construction Applications (Scaffolding and Suspended Ceilings).
George Leopold's talk at last week's Design & Manufacturing Minneapolis helped restore astronaut and engineer Gus Grissom's role in the beginnings of NASA, and outlined how Grissom played a pivotal role in winning the Space Race.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies.
You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived.
So if you can't attend live, attend at your convenience.