aluminum spring 1

[JJJackbk612]

Hello, I am trying to find some aluminum spring material. The shape of the spring needs to be rectangular (1 ½”L x 3/8” W x 1/16” D). I don’t know the spring constant at this point but it has to be higher than what you get from typical material machined out of stock from the hardware store.

The spring will be held at one end and the other end will be moving in an arc. I don’t know the spring constant but I know what displacement I need from the high tension position to the low tension position and that’s about 5/8”.

My question is: does anyone know where I could purchase such a material even if it was not that exact profile that I need I could machine it.
Thanks,

Jacques

 

[3DDave]

There is no form of aluminum that can do that.

 

[JJJackbk612]

This is what I originally thought then I googled "aluminum spring" and there are some manufacturers that make aluminum helical springs. What are they doing that's different?

Also in my case I am not worried about a fatigue limit, the spring only needs to work once.

Cheers,

Jacques

 

[EdStainless]

Little things like modulus (AL springs exert little force) and yield strength) come into play long before fatigue, butt hat is an issue with Al also.
You start with the force and displacement, and then design the spring, not the other way around.

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P.E. Metallurgy, Plymouth Tube

 

[JJJackbk612]

Yes, I have no problem designing the spring from 1st principles. My main issue is finding the right aluminum alloy. Aluminum 7075 seems to be a good candidate, it has a 61,00 psi yield strength.

 

[3DDave]

So you meant helical spring when you said it was a rectangular bar? It's hard to get good answers from really bad questions.

 

[JJJackbk612]

Don't know where you get helical spring from. it's a rectangular cross-section bar. It's also hard to get good comments without getting side-swiped like that.

 

[3DDave]

some manufacturers that make aluminum helical springs

Want less side-swiping? Put up a picture of the item you are designing and the calculations that led you to believe that it can work.

 

[3DDave]

http://lmgtfy.com/?q=metal+in+small+quantities

 

[JJJackbk612]

Thanks. I have found a source McMaster Carr, unfortunately they don't deliver in Canada and I'll have to get around that.

 

[EdStainless]

1. The spring constant is based on geometry and material, any Al alloys of the same size and shape will have the same K. It is just that stronger alloys will flex further before taking a set.
2. Have you bothered to calculate the stress involved for flexing this piece 5/8"? Just as a guess it sounds very high.
3. 61ksi is very weak for spring material, since you need to work at about 20% of yield to get good life. Think spring steels with 200ksi strengths.
4. All Al alloys have poor fatigue resistance. If you are looking at more than a few thousand cycles you need to start looking at other alloys.
5. Why not steel (or a stainless)? You could make it a lot thinner and lighter, and get more force and longer life.

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P.E. Metallurgy, Plymouth Tube

 

[JJJackbk612]

Thanks, all very good points
2. Not yet, will do shortly. I am going to start with a much thinner plate 0.030", stress will be lower;
3. Good point I am going to look for a stronger aluminum alloy;
4. I only require 1 cycle;
5. It needs to be aluminum, the higher concentration of aluminum the better, it is part of something that needs to be 100% recyclable.

 

[EdStainless]

JJJ, so the entire thing is Al, no other materials at all?
One cycle you might get.
If the stress is too high consider stacking multiple thin leaves, they would need a film or lubricant between them but that is minor.

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P.E. Metallurgy, Plymouth Tube

 

[IRstuff]

You've made 6 posts, and not once did you say what load is applied to get your 5/8" deflection.

So, what spring constant do you need? Once you've figured that out, you can then use existing formulas to figure out what material properties are required.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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[EdStainless]

Since he didn't post a load I figured that he would take whatever he got, since he has fixed all of the other variables.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[IRstuff]

I don't have my aluminum yardstick handy, but I do have some 6061 (probably) Al name plates that are 20 about mils thick; they'll deflect about 5/8", but only over about a 3-inch span, which means that for 1 1/2" span, something on the order of 5/16" deflection is more realistically possible. Steel at roughly the same thickness can easily do the required deflection over the required span.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

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[3DDave]

IRStuff, He was looking at material over 3 times as thick and half the length of the test. The stiffness is around 30 times higher from thickness alone ((.063/.020)^3), and supporting the shorter material has to take up some of that length, so maybe 2.5 times stiffer due to shortened length; overall around 80 times the sample yield strength. Now he's shifted to .030 for some reason which is still over 3 times as stiff; pushing a required yield to 8 times that of your sample.

A first principles calculation would have calculated the strain required to get the desired deflection. Since that is geometry driven and no geometry is given, we are left in the dark as to what the OP had in mind. I would have started with the desired deflection and the allowable strain to determine the material thickness and then look at the width limit to set the required modulus of elasticity to get the desired force; possibly with the use of multiple leaves if the combinations are unsuitable.

 

[hendersdc]

What is driving you to aluminum? Is it just recyclability? Steel can be recycled too!

 

[IRstuff]

" He was looking at material over 3 times as thick"

I was trying to steer the OP a bit, and possibly inject some realism into his problem definition.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

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[JJJackbk612]

You all make very good points. The 7075 material is not expensive, and I can get a variety of thickness'. I'm working this experimentally as I have to do tests that will prove the principle, that is the desired deflection for the span of the bar. Multiple leaves may be required to get the desired deflection however not sure what bonding material I could use as contamination is a problem, the parts must be food grade compatible.