Page 83 - MetalForming July 2017

Custom Spring Design from A to Z
When designing a custom spring, consider several key factors including the spring’s service environment and desired cycle life, and its installation location. The three primary design parameters: wire size, relaxed free length and solid height.
BY RITCH FROEHLICH
Some factors to consider when sizing a spring: direction of wind, particularly when engineering a torsion spring (shown here), and assembly requirements. Wind direction dictates how energy is directed through the spring—right-hand (clockwise) or left-hand (counterclockwise).
The custom-spring designer’s first consideration is the environ- ment in which a spring will be required to perform—temperature, for example. For instance, if the spring will experience heat in excess of 650 F, it will require a high-temperature metal alloy such as Inconel. Or, if the spring will work in lower-temperature envi-
Ritch Froehlich is owner of Ace Wire Spring & Form Co., Inc., Mckees Rocks, PA; www.acewirespring.com.
ronment, perhaps a less costly material will suffice, such as oil-tempered spring wire.
Keeping with the theme of environ- ment and material selection, the design- er must establish early in the design process if the spring will come into con- tact with any form of moisture or chem- icals, such as chlorine or bleach, or if will operate outdoors and be exposed to salt water. In this environment, pro- fessional spring designers likely would opt for Type 316 stainless steel. Though
there are other costlier materials on the market, 316 stainless often is used in these applications. And, for springs sub- jected only to a high-moisture source (such as tap water), Type 302 stainless steel may suffice.
Cycle Life
The next requirement in material selection to address is cycle life—the number of times the spring will cycle during its lifetime. For instance, if designers are engineering a spring that
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