Enclosure Design Eliminates Screws.
When enclosures must withstand extreme vibration and shock during tests in the lab and subsequently in the field, engineers typically overcompensate in their designs by adding extra fasteners, especially screws, to reinforce unit sturdiness. But in the case of a remote data acquisition box manufactured by Agilent Technologies Inc., Loveland, CO, all but one screw has been eliminated in favor of self-clinching fasteners integrated as part of the assembly.
Using fewer parts while meeting all performance demands, this redesigned unit can now be assembled in about two minutes (instead of the half-hour required with other models) and disassembled within seconds. The result is a simpler design that virtually snaps together and yields time and cost savings during production and in the field.
Comparable rack-mounted enclosure designs usually contain about 40 screws, says Agilent R&D mechanical engineer Rick Euker, while the Agilent box specifies just one for an electrical ground connection. The screwless design is made possible by two different types of PEM self-clinching standoffs from Penn Engineering, Danboro, PA. A dozen of these standoff fasteners are specified to secure the unit's internal components.
Four PEM SNAP-TOP stainless self-clinching standoffs (Type SSC) are used to attach the unit's power-supply board to the bottom cover. In the process, the board sandwiches a vibration-dampening rubber bump pad beneath it. Eight PEM KEYHOLE stainless steel self-clinching standoffs (Type SKC) secure the 17- x 9-in, motherboard to the bottom cover and hold the front panel in place. Both types of standoff fasteners (each 8mm long) allow quick assembly and disassembly of the components.
According to Euker, these permanently-installed, self-clinching fasteners further promote DFMA objectives. Unlike loose fasteners, they arrive at Agilent as an integral part of the box's 0.060-in.-thick aluminum sheet metal, reducing parts count and handling requirements during assembly. The fasteners are installed by squeezing them into a punched or drilled hole using any standard press, producing high pushout values.
Other significant elements of the simplified box design included a folded "lip" that engages a groove in the front-panel extrusion to attach the two covers to the front panel without screws, and specification of connectors that would snap into the enclosure. Compared with other models, further practical advantages were achieved. Costs for strain gauge channels was reduced by 50%, and wiring costs were reduced by 97%. The reach of the remote gauge was expanded 12-to-1, and accuracy of the product was improved.
"The success of this design underscores that manufacturing and assembly issues should be considered in the earliest stages of the design," says Euker. "Doing so can cut costs in half or better and ensure product reliability at the outset."
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|Date:||Apr 1, 2001|
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