aluminium extrusion snap design

[brynnchoquette]

I am looking for any guidance and information on designing an aluminum extrusion with a snap fit cantilever beam. I am aware of this thread created in 2004 (thread404-100527) however there is no useful information. I have spent a couple of days scrounging through google search results however all that I can find are design guidelines for plastic snap fits. What I am lacking from these guidelines are variables specific to aluminum rather than plastics. As the design I am working on is one that will be used through multiple open/close cycles, I want to ensure that elasticity is maintained.

 

[KENAT]

Perhaps you could research aluminum springs and get some ideas from that.

After all, that's a big part of what a snap fit is.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[MikeHalloran]

If you can find a spreadsheet for plastic snap fits, you should be able to hack it enough to change the important material properties so you can design aluminum snap fits.

I second KENAT's suggestion; learn to design aluminum springs first.

You will run into another problem, if you get that far.
You will want to anodize the aluminum for corrosion resistance; that increases its friction coefficient, especially against itself.
You will need to lubricate the hinge at the root of the snap fit, and the pivots and rubbing surfaces of whatever you use for a latch.





Mike Halloran
Pembroke Pines, FL, USA

 

[hendersdc]

This design guide was provided years ago on this forum, I have found it very helpful. It is geared for plastic snaps but as Mike said you can ignore their material properties and swap out some for aluminum and be in good shape. You will have to determine what the max permissible strain is for your material that won't cause permanent deformation.

 

[drawoh]

brynnchoquette,

I have designed a number of springy things, using various materials. A good spring material has high allowable stress in relation to its elastic modulus. Beryllium copper and titanium are very good for this, as are many plastics. Aluminium is not good. Your design is more likely to work if you don't need a lot of force and you can use thin walls. Those walls will likely be too thin for extrusion.

Most of my designs have been optical fixtures which get set on alignment and then not touched again. If your application will be operated repeatedly, you need to worry about metal fatigue. Think high, repeated stresses, and non-ferrous materials.

--
JHG

 

[drawoh]

MikeHalloran,

Anodizing reduces the friction coefficient between pieces of aluminium, at least until the anodize finish scrapes off. We make all sorts of threaded housings here out of aluminium and they work fine, as long as they are anodized. Bare aluminium and chemical filmed faces gall. This was a very expensive lesson for us.

--
JHG

 

[tbuelna]

Aluminum alloy mechanical properties are well documented. The "snap fit" of your mating parts should ensure that neither component is stressed beyond the minimum yield point of its material at the worst case combination of tolerance stack-up between the parts. It is easy to hold tight cross section dimensional tolerances with the aluminum extrusion itself. But it is very easy to over-stress small aluminum parts using a snap-fit if there is even a small variation in the machined fit tolerances.

 

[brynnchoquette]

Thank you very much everyone for your input.