Accordion Spring design

[AsHRITH S]

I am looking out for generalized design procedure for Accordion spring.
I looked into the web a lot but couldn't find information regarding the same.
It would be of great help if experts out there could guide me through the same.

 

[MikeHalloran]

What do you mean when you say 'accordion spring'?

Please provide a drawing or a representative photograph.



Mike Halloran
Pembroke Pines, FL, USA

 

[AsHRITH S]

Here is the link for Accordion spring representative photograph.
I am ataching this link since i am unable to upload the photograph because of a technical issue.

https://www.google.co.in/search?q=a..._1M%3A%3BNIOUA3jZmCxBdM%3Bhttp%253A%252F%252F

http://www.sonnax.com%252Fparts%253...=HZ-FWMugCIXNgAbzv5aQBg#imgrc=pvcgw1JO3n4LBM:

 

[israelkk]

Same post was asked in thread 404-416836 sometimes ago. Hope you will find more. But as I said then this is basically a flat strip folded. As to my best >35 years of experience I didn't see a closed form formula for such a spring. You can always use FEA. But if it is for large deflections it may be tricky. Can you give some info on the use of this spring?

https://sites.google.com/site/israelkk/

 

[AsHRITH S]

The spring to be used in one way starter clutch.
The deflection isn't large.
I am not getting how to start with calculations for the required load.
We can achieve the required load by trial and error. But, I don't want to do that thing.
I want to standardize the design procedure for this kind of spring.

 

[israelkk]

Why are you looking for such spring which is not a common spring?
What is the force and deflection you need?
What is the space you have for the spring?
Did you consider other type of springs such as Helical Compression etc.?

 

[AsHRITH S]

We have space constraint & this spring can serve our purpose well.
It reduces assembly time in the end product.
Have higher life expectancy.
These kind of springs are available with only certain vendors worldwide and has to be imported.
I want to develop this kind of spring in our place and use it.
Forming of the spring is comparatively easier (Need your advice)
Min load required to start compression of spring is 0.17N
7.6mm is the place available for placement of spring.
I tried with helical compression spring, Rectangular spring.But, they all have space constraint in my end application.
I have only two option left
1) Find appropriate calculation for Accordion spring.
2) Re-design the product, which is a tedious task again.

So, I would like to go with option 1. If that isn't favorable only then I can move on with option 2.

Waiting for your advice.

 

[israelkk]

The load 0.17N and 7.6mm space are not enough information. Lets assume a helical compression spring.

1. What is the maximum spring diameter you can allow?
2. What is the maximum spring compressed length when compressed by 0.17N?
3. How much more compression (extra travel) is needed during work?
4. What is the force needed at the second load point (after the extra travel)?
5. Are there any requirements for the inside diameter of the spring or just the outside?
6. How many life cycles the spring has to live?
7. Environmental conditions?

And any more info you can give.

Producing a helical compression is very common and very cheap the larger the quantity the cheaper the spring.

 

[3DDave]

Advice - two parts:

1) hire someone with sufficient FEA experience to do the job.
2) have a long talk with the company who already fabricates this type of spring. They are the experts.

 

[AsHRITH S]

Hello,

Assume that I have bent a sheet metal of 0.1mm thick, 9.4mm height & 3mm width to form a "V" with an angle of say 20°.
Now, definitely, I can have a spring action when I try to compress the top ends of "V" provided the material is elastic. Let's assume that the material is AISI 304.
Now my question is how can I calculate the possible deflection because of this kind of profile?
I searched many sources for the same & also I tried to assume it as a cantilever beam and tried to find the deflection. But, I failed in it since I didn't get appropriate results.

I am sure that FEA has the answer for this. But, I am not sure from where shall I begin the quest.

 

[MikeHalloran]

You should be able to model the spring as a series of cantilevers, each of which has a concentrated load and a moment at its distal end.

Regarding the 180 degree turns at each fold:
To a first approximation, I would ignore them, just assuming they are rigid enough to transmit the axial force unmolested, and contribute little to the deflection.
To a second approximation, I think you can also model the 180 turns at each fold as a short cantilever, using the developed length of the turn as the cantilever length, i.e., unwrapping the turn for local calculation purposes, and sort of rewrapping the turn, rotating the direction of the force, for combination with the next 'leaf' in order to eventually get the overall deflection.

It's the sort of thing you can do in Excel if you beat on it long enough.

There is another complication; these springs are normally used inside of a rectangular or arcuate cage. I.e., they are not really stable like columns under axial load, but must be constrained by some surrounding structure, so you may have to model the turns as not a pure cantilever, but as a cantilever that may or may not have a support roughly midway along its (developed) length. That may make the force summations more, uh, interesting.



As noted several times already, the shortest/fastest path to getting what you want is to get in contact with someone who is already in the business of making these springs, and, er, develop a commercial relationship with them. Doing otherwise will feed your ego if you succeed, but will also probably cost you years.




Mike Halloran
Pembroke Pines, FL, USA

 

[israelkk]

If I understand you correctly the spring is "V" shape both sides 9.4 mm long, 3 mm width and 0.1 thick. The maximum deflection each side can have until the 20 degree angle is closed is 1.63mm. The force to deflect one arm 1.63 mm is 0.3N. Because you have two arms it means two springs in series, the force to bring both arm to contact will be 0.15N. According to your previous posts, 0.17N is the initial force but you didn't give deflection requirements pass the 0.17N initial force. Your current "V" spring will not do the job because at 0.15N the spring can no longer move. If you add more folds to the spring the force will decrease accordingly while the deflection will increase.

From the the above mentioned data, you at least can have a helical spring 3 mm diameter and 3.2 mm long at 0.17N load. According to my quick check this can be done with a helical spring made of round wire. I took the liberty to press the spring extra 2 mm travel beyond the 0.17N to reach 0.33N with no problem including fatigue.