EDITOR ’ S CHOICE DESIGNING WAVE SPRINGS
TFC
Your questions answered
The Juno space probe uses over 60 different springs to perform three major functions ; to open the doors to the solar panels , to guarantee the doors remain latched during flight and to position the arms it uses to measure Jupiter ’ s structure . Of course , it ’ s not just in space probes where projects require springs with very specific requirements .
Here Simon Ward , technical manager at leading supplier TFC , the leading supplier of Smalley wave springs , answers some questions about designing wave springs .
WHAT IS A WAVE SPRING ?
An alternative to the traditional coil spring , wave springs are produced from prehardened flat wire and formed to a precise diameter with a sinusoidal wave form . When loaded , this means that they can act like a spring by deflecting and providing a pre-load between two surfaces . Therefore , wave springs can be used to pre-load seals or bearings , absorb shock and compensate for dimensional variations and thermal tolerances .
HOW ARE WAVE SPRINGS MANUFACTURED ?
Wave springs are manufactured by coiling flat wire on edge , known as edgewinding . This process increases design flexibility and reduces the lead-time for bespoke designs . It also ensures that prototype batches are manufactured in the same way
Comparator Angle Yellow as production parts , so any prototype or pre-production testing can be considered valuable production data .
With edgewinding , only the required flat wire material is coiled , eliminating material waste . The circular-grain metallurgy also improves strength , and the cold rolling process causes metal grains to elongate and lock together , which provides good mechanical properties .
TFC ’ s engineers also use a No Tooling- Cost™ process , which reduces production times and allows any modifications at the prototype stage to be made quickly and easily . Therefore , this process can help provide an economical custom option in weeks , not months .
WHAT TYPES OF WAVE SPRINGS ARE THERE ?
There are five main types of wave springs , each with distinct features that determine spring performance under load . These include Crest-to-CrestTM wave springs , which have a multi-turn flat wire design and are suitable for low-medium forces . For low deflections , you can use overlap and gaptype wave springs , whereas Nested and Wavo ® springs are typically used for higher forces . Finally , linear springs are formed in a straight line and are another in the wave spring family .
CAN I CHANGE THE SPRING RATE ?
You can change the thickness of your wire and the wave form to achieve the required spring rate for any given application . Most wave springs are manufactured using carbon spring steel or 17-7 PH as a standard material , but the choice is up to you .
You can also alter the number of waves per turn and the number of turns . For instance , if you need a light duty spring for a smaller application , you can use thin wire or remove waves from your design . Single turns are best suited for applications with low to medium forces . For high force and precision , manufacturers can consider a nested wave spring with multiple turns .
WHAT SIZES ARE AVAILABLE ?
Wave springs are available in a vast number of diameters . The smallest off-the-shelf wave spring is typically around 5 mm and , at the other end , bespoke sizes can be manufactured up to about 3 m .
If a designer can ’ t find an off-the-shelf size that suits their application , they can order a custom solution that meets their exact requirements .
WHAT MATERIALS CAN I USE ?
There are several options and your choice is often determined by the required temperature and corrosion resistance . Common materials include 302 and 316 stainless steel , which can withstand temperatures of up to 200 degrees Celsius . For applications with elevated temperatures , 17-7 Ph / C stainless steel has a maximum recommended temperature of 343 degrees Celsius . For extreme low temperatures , like those found in cryogenic systems , 300 series stainless steels or Nickel alloys are generally preferred .
Corrosion can also cause springs to fail , so designers will consider whether the environment is corrosive before specifying a material . 316 stainless steel offers high corrosion resistance because of its molybdenum content and is often used in sea water applications . If the environment is highly corrosive , high performance alloys like Inconel and Elgiloy are specifically designed for such a surrounding .
When designing a wave spring , TFC accounts for dimensional constraints , the desired load / deflection characteristics , cycle life demand and operating environments and temperatures . Each of these factors will determine your choice of materials and , therefore , the final design of the spring .
TFC ’ s engineers are on hand to design custom wave springs for all applications . Visit https :// www . tfc . eu . com / or call 01435 866011 to speak to a member of our design team , who will gladly work with you .
For further information , please visit www . tfc . eu . com
16 PECM Issue 54