Work with wire supplier to clearly define specifications
As discussed, a formula for designing stranded wire compression springs is extremely complicated; mathematical calculations are not available in a computerized program. It is therefore extremely important that the spring designer understand the complicated mathematical relationships required to work with stranded wire. Experience with a variety of different wire sizes and varying load requirements shortens the development cycle. CSS has been manufacturing stranded wire springs for many different OEM’s since WWII.
It is also important to work with the wire supplier to clearly define specifications for stranding, especially the specific pitch the wire should be woven to. The spring designer should specify the precise wire output needed before coiling the spring.
CSS typically prototypes the spring by purchasing five to 10 pieces of each stranded wire being considered, testing perhaps three designs. Designers may make prototype variations out of both music wire and rocket wire, with different numbers of coils in the spring (say, 8, 10, and 12-coil versions), and in different wire sizes. First article load testing is conducted, and inner dimension, outer dimension, and the solid height of the fully compressed spring are measured.
These prototypes are then sent to the customer to be tested in the firearm and the preferred option is selected. Sometimes, the gun designer may even take one of these compression spring prototypes, cut out one of the coils and send it back to be duplicated for the final version. The last step in the process is adjusting the final print to meet the agreed upon spring design.
The choice of stranded versus shaped wire, and selection of music wire, high tensile rocket wire, or chrome silicon depends upon the spring design and what the engineer is hoping to achieve. Careful selection of wire base material, wire manufacturing specification to achieve accuracy, as well as knowledge of design formulae for spring rate and equivalent direct (tensile or compressive) stresses, and finally, prototyping expertise, will ensure a compression spring that works well.
About the author:
Dale Pereira, Spring Sales Engineer, CSS
Dale has been with CSS for 12 years. In addition to his role as Spring Sales Engineer, he is very involved with the company wide initiative towards Lean Manufacturing and currently a Team Leader for the Sales and Estimating Self Directed Work Team.
If you found this article to be of interest, visit Military/Aerospace Designline
where you will find the latest and greatest design, technology,
product, and news articles with regard to all aspects of military,
defense and aerospace. And, to register to our weekly newsletter, click here.