Helical Compression Spring Design for Wire Sizes Less Than .015 Inch

i am intrigued that you need to specify tolerances on all these parameters. i have had only one requirement, the two working loads at the two working lengths usually. All these parameters decide the spring rate, which gives the working loads. i have been ok with ±10% on the loads. Perhaps your application requires very close tolerances. Once i needed an accurate spring with ±2% tolerance on the loads, so the vendor inspected 100% and sorted out what i needed. Cost me 20 times the normal cost, but then, as the spring cost less than 1% of the product cost, it was well worth it.

I am not looking for anything special regarding the spring tolerances. I only wish to define what can be expected during the standard spring manufacturing process in order to:

- Define the spring enclosure without running into interferences.

- Provide free length tolerance for an incoming inspection rough check.

- Specify the expected load tolerance for the application (Relief valve application)

Most spring manufacturers i have met say "Specify only the least number of parameters that you MUST have, and tolerances on them. Please permit us to change wire dia, coil dia, number of turns so as to achieve your acceptance window". This is what the DIN standard drawing format says also. So, i usually specify two working loads against the respective working lengths, and either ID or OD of the coil depending on the guiding, with appropriate tolerances. So far, this has been ok for my applications. The QC guys only check the two loads and the guide dimension, nothing else.

Of course, you may try with topnotch vendors in USA, and they may be able to give you their guidelines on the tolerances.

Good luck.

I could see a spring manufacturer advising this based on the number of rules for good spring design. I have tried placing these rules in an Excel spreadsheet and allowed the Solver to come up with an optimum design without violating the rules. To date, I haven't had a spring manufacturer come back to try to tweak the designs or ask to deviate from the specification. They match the Spring Manufacturers Institute criteria so the vendors don't seem to have an issue. My issue is that springs below .015 wire diameter appear to fall outside the SMI criteria.

Wow. You have a problem. i thought that Indian vendors were not up to the international standards. i have to think now. These guys here use Fed software for design, they are well versed in DIN and US standards, and are willing to go wherever in the world to meet my window of acceptance.

Your vendors seem inflexible, too bad. You might want to talk to one of my friends who happens to be a vendor to my client. He was a vendor first, became a friend by mutual respect earned.

It is not that the vendors are inflexible. I have just tried meeting their manufacturing requirements up front. In truth, I rarely hear from them. They just supply the springs per the SMI spec. Since I am not deviating from it, they don't appear to have issues.

I have not used the DIN spec to date. Does it include tables pertaining to my original question, and if so, do they include springs with less than .015 inch [0.381mm] wire diameter?

Regrettably, i no longer have access to DIN spring standards, since i retired way back. You can try the website of Fed9 software. It is German, and uses DIN standards extensively.

i will try to get some useful links tomorrow (it is 11 pm here !) ... you can try FED9 and Hexagon on google....

Here is a link to FED software, may be informative for you :http://www.hexagon.de/fed1_e.htm

An image of the DIN drawing format, you will see it on the webpage also.

Thanks!

I will check it out.