MECHANICAL COMPONENTSSprings, Gas Springs & DampersCoiled spring pins help toreduce assembly costsIn any assembled component there are two ways to reduce theoverall cost of the assembly: reduce the cost of the individualcomponents or reduce the cost to assemble the components. Thisadvice from Spirol highlights the role of the coiled spring pinThe coiled spring pin is designed to be aversatile, integral, and cost-effective solution tomany assembly problems. It can lowerassembly costs by reducing the complexity oflarger, more expensive components, or by combiningfunctions into one pin, eliminating the need foradditional pieces. In addition to simplifying the designof an assembly, the coiled spring pin is easy to usedwithin automated processes, thereby reducing assemblytime and the labour required for completion.Coiled spring pins have several uniquecharacteristics that allow them to reduce total assemblycost. The coiled spring pin is designed to be aninterference fit part that conforms to the shape and sizeof the mating component’s hole. By coiling, or flexing,during insertion into the hole, the pin provides aretention force that will keep it in the hole for the life ofthe assembly. Unlike other types of spring pins thatbend only opposite the seam during installation, theentire coiled spring pin deflects, thus providingcomparatively low insertion forces and nearly uniformcontact stresses on the inside surface of the hole. Thisis important in protecting the mating component, sincepoor insertion and high contact stresses can lead topermanent damage to the mating component. It is notunusual to have a poorly designed pin skive either basematerial or plating from the host part during assembly,thereby causing poor joint performance or possiblyreduced corrosion protection.In comparison to solid pins, when coiled spring pinsare used there is no permanent damage to the host partduring assembly. Pins having external knurls or grooveswill always, by design, cut into the mating part. Evenhardened ground dowel pins, when driven into aprecisely reamed hole, will damage the hole whenremoved. It is no accident that a standard series ofoversize dowel pins is available. This method ofassembly results in the inability to rework a part eitherin the factory or in the field. With a coiled spring pin, itis simply a matter of driving the pin out, the host partis like new.Unmatched characteristicsDuring its use, the coiled spring pin brings a level offlexibility and shock absorption that is impossible tomatch with any other type of pin. A gear pinned to ashaft may have a near constant shear load appliedwhen running under a constant load, but upon startupand braking, significant increases in shear loads arerealised. When using a solid pin, this peak shear loadmust be accounted for, often requiring larger shafts orstronger materials which all increase costs. When usinga coiled spring pin, the pin will deflect slightly,absorbing some of the excess startup energy. Oncesteady state operation is achieved, the coiled spring pinwill return to it’s original condition without damagingeither itself or the mating parts. Compared to otherspring pins, coiled spring pins can absorb considerablymore deflection.In many applications, coiled spring pins can be usedto replace a non-pin alternative. Axles, gasket retainers,pivots, hinges, and levers are all common uses of coiledspring pins where the inherent benefits of the coiledCoiled spring pins suit a myriad of automotive under bonnetapplications, including automatic transmission shift housings,intake manifold <strong>control</strong> valves, ignition coils and gears, as well asmore general automotive tasks such as storage cases, fuelassemblies, accelerator pedals, door handles and glove boxesspring pin enable it to replace a traditionally non-pincomponent. Hole preparation is another importantfactor in reducing costs. coiled spring pins operate inholes with relatively wide flexibility under load: coiledspring pins continue to flex after insertion when a loadis applied to the pin. tolerance. In most operations,coiled spring pins can be installed in holes that havebeen drilled rather than prepared with an expensivereaming operation. The flexibility of the coiled spring pinalso means that holes do not need to be accuratelyaligned. It is no longer necessary to drill and pin atassembly – you only need to pin. In addition, stamped,fine blanked, cast, sintered, or laminate assemblies areall suitable hosts when using coiled spring pins.None of these features are beneficial if the pincannot be easily presented for installation. The coiledspring pin has square, burr free ends with concentricchamfers on both ends, and is manufactured to tightlength tolerances. These features allow for easyengagement with the hole, and problem free bowl andtube feeding. The coiled spring pin does not need to beoriented within the mating parts, thereby permittingsemi or fully automated assembly systems to operate inlieu of labour intensive pinning operations.To further enhance the ability of the coiled spring pinto reduce costs, it is available in three duties so that thepins may be tailored to the host material or applicationrequirements. A wide variety of standard materials andfinishes provide for the necessary strength, corrosionresistance, fatigue life, and appearance to suit anyneed. Finally, special configurations are possible, furtherassuring the coiled spring pin can meet nearly anypinning application need.When trying to reduce costs, it is important toremember that individual component costs are not asimportant as total cost. Sometimes the moreexpensive component pays back big dividends.MORE INFORMATION:Enter G365 on the card, or visit ‘latest issue stories’ atwww.industrialtechnology.co.uk for further details from Spirol andmore news on springs, gas springs and dampers36INDUSTRIAL TECHNOLOGY • July 2008
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