Reliability and quality are extremely important for consumers. However, inevitably there comes a time in a product’s lifecycle when the item will require service. Whether the product is a home appliance, commercial foodservice appliance, vending machine, ATM machine, or computer server, the less time it takes to repair the item the better.

Downtime for maintenance is costly in terms of both service labor cost and temporary loss of equipment use. Frequently, the labor portion of the service call exceeds the costs of the replacement parts. And, depending on the application, downtime translates into lost revenue, as in the case of a vending machine or foodservice appliance. In some cases, lost revenue can be enormous. An out of service computer for a financial institution or airline reservation system, for example, could result in millions of dollars worth of lost revenue for a relatively short period of downtime.

For such products, it is imperative that product designers consider ways to improve serviceability and make maintenance procedures faster and easier. One way to accomplish that goal is to use a fastening method that permits quick removal of metal panels to speed access to a product’s internal components.

Fig. 2. Internal view of a D-SNAP element.

DIRAK has developed a snap-based technology called D-SNAP™ that offers tool-free assembly and eliminates the need for threaded fasteners when joining metal panels, or when fastening hardware to metal panels. In addition to simplifying and speeding both assembly and disassembly, the technology also eliminates instances of small fasteners falling into the equipment, where they can cause subsequent damage during operation of the product.

On average, it can take several minutes to install a normal hinge or handle on a door panel. First you have to make sure you align the part correctly on the cutout and then you have to fasten the part to the sheet metal with several screws. The entire process is time consuming.

Compared to costly, labor-intensive traditional installation methods, the new fastening technology can save time and effort, allowing panels to be removed and reinstalled in just a fraction of the time it takes for other methods. The technology, therefore, has the potential to shorten the duration of general service calls.

Fig. 3. D-SNAP element can be easily disengaged for removal.

Currently used in the assembly process of industrial enclosures, this technology is also well-suited for residential and commercial appliances, heating and air conditioning equipment, vending machines and kiosks, medical equipment, and electronic cabinets. The technology has been integrated into a wide assortment of fastening products including panel fasteners, hinges, handles, locks, and latches.

Advantages of this technology include:

• Quicker and easier installation.
  
• Tool-free assembly.
  
• Blind assembly from one side.
  
• Quick disassembly and reinstallation.
  
• Suited for automated assembly.
  
• Reduced downtime for service.
  
• Reduced inventory requirements.
  
• Vibration resistance.
  
• More secure installation.

The technology hastens the servicing of an appliance by making it easier to remove access panels. The lack of threaded fasteners also eliminates the possibility of small parts falling into sensitive equipment during servicing. Once service is completed, the panels can be securely reinstalled just as quickly with the same clamping force that was achieved in the factory.

Fig. 4. The D-SNAP fastener adapts to different panel thicknesses by varying the distance between the head and clamping pitch.

The basis for the technology is like the spring lock commonly used for doors in homes.  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 that the door can be opened.

In similar fashion, a D-SNAP element consists of only two parts — the guide and the spring which seats in a cutout within the guide. (See Fig. 2.) The guide includes single or multiple triangular wings at the ends that are defined by the wing pitch and clamping pitch.

For installation, the D-SNAP fastener is simply pushed through the rectangular cutout.  Once the wing pitches have cleared the cutout, the D-SNAP elements snap automatically into position due to the pressure force from the compressed spring. (See Fig. 1.) Installation is complete once the “click” sound is heard. This tool-free assembly method is quick and secure. Removing the fastener is trouble-free and can be achieved by using a socket, screwdriver or key. (See Fig. 3.) The D-SNAP elements are pulled back into the channel against the spring force, and the D-SNAP fastener can be easily pulled out.   The only part design change required to employ the new technology is to use a rectangular cutout instead of a round hole. Since most cutouts are punched by a turret press or cut by lasers, changing the cutout shape simply involves reprogramming the equipment. Even though punched-hole sizes vary by application, commonly used standards have evolved over time. The same applies to the rectangular cutouts. D-SNAP fasteners are made in the length and width dimensions most frequently used.

Fig. 5. Proper clamping pitch ensures that the element engages securely.

Given that space is often tight in most applications, the fasteners need to have as little depth as possible. Generally, these fasteners can be installed in edge areas and other dead spaces. Minimum installation depth of a D-SNAP fastener is only 0.276 in. (7 mm). As long as the minimum specification is maintained, D-SNAP fasteners can generally be made in all desired user-specific installation depths.

The D-SNAP fastener needs to adapt 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 D-SNAP fastener’s clamping range. (See Fig. 4.)

In any D-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 of this triangle. The clamping angle amounts to 14 Deg to 15 Deg. Based on the tangent function, a ratio of the legs of the right-angled triangle of approximately 4:1 results, so that with the height of the wing at 0.157 in. (4 mm), the height of the pitch amounts to 0.039 in. (1 mm). (See Fig. 5.) The height of the pitch of 0.039 in. (1 mm) is, however, not fully utilized for clamping, which allows it to compensate for the various panel thicknesses.

Fig. 6. In a pull-out test with a D-SNAP fastener in a 0.059-in. metal panel, the fastener came free only when the metal buckled and the cutout hole enlarged (right) at about 4,500 N.

At the beginning and at the end of the clamping pitch, approximately 0.008 in. (0.2 mm) of the height of the pitch is intended as a safety clearance in order for the D-SNAP element to engage securely behind the edge of the panel within the area of the clamping pitch.

The clamping range of the D-SNAP elements thus lies in the center of the clamping pitch and occupies approximately 0.024 in. (0.6 mm) of the height of the pitch, resulting in an application clearance of ± 0.012 in. (0.3 mm) and a clamping range of 0.024 in. (0.6 mm), within which the D-SNAP element guarantees secure bracing. Due to this clamping range, it takes only a few different versions of D-SNAP fasteners to accommodate the variety of panel thicknesses available.

The clamping range of the D-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 as well as plating thicknesses used.

Fig. 7. Element height and wing length are not critical so long as appropriate clamping range has been chosen and clamping pitch lies between 14 Deg and 20 Deg.

Holding and pull forces 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 D-SNAP fasteners can be designed in various ways to satisfy these diverse requirements.

Holding and pull forces need to be absorbed by the fastener with a clamping mechanism. In order to function properly once the D-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 D-SNAP fastener’s defined pitch addresses this issue. A clamping pitch with an angle of 14 Deg or 15 Deg is most effective, as it provides the necessary clamping and exhibits a self-locking effect. This was confirmed during a test where it proved impossible to pull out a D-SNAP fastener installed on a 0.059 in. (1.5 mm) thick panel until the pull force reached approximately 4,500 N. The panel first buckles and the cutout hole enlarges before the D-SNAP fastener comes free. (See Fig. 6.)

The height of the D-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 Deg and 20 Deg. The width of the wings is unimportant, but extra width can increase stability. Wider wings are recommended for thicker panels. The length and the width of the channel play important roles for the forces acting on the panel plane and for the force that could distort the D-SNAP fastener within the panel cutout, but only in an indirect way. Larger D-SNAP fasteners are recommended for heavy doors.

In addition to the existing lineup of D-SNAP fastener components, more such components using the technology are on the way. There are currently many concepts still under development, including D-SNAP fasteners for round profiles and T-Channels.

It will be possible to develop many more such application concepts in the future due to the adaptability of the fastening technology.

For more information, email: options@dirak.com