Joining stainless steel and aluminum - thermal expansion 3

[dfsc]

I would like to fix an aluminum piezo stage onto a stainless steel plate. However, I am worried about the build up of stress under temperature changes due to the different thermal expansion coefficients of aluminum and stainless steel. That's why I was wondering if there is a neat way to join these elements together such that no stress builds up, i.e. such that both elements can slightly move with respect to each other? Any help is very appreciated .

Thanks,
Lucas

 

[unclesyd]

You need to post a little more information as to your requirements, like what degree of bonding do your require, temperature, environment, etc.

 

[racookpe1978]

Think about your problem statement: You want a non-corrosive (Al-Fe will corrode electrically!) joint. (Pressure-tight?) This means that the physical joint won't move ... then you want that same joint to move as the two metals expand at different rates.

 

[dfsc]

Thanks for the quick replies .

The stainless steel plate and the aluminum piezo stage have both an aperture and I would like to position the piezo stage centrally over the aperture of the steel plate (see enclosed image). The whole configuration will be mounted horizontally, so the only purpose of the joint is to keep the piezo stage in its position. The expected temperature variations are around 5 K and the piezo stage is around 0.1 m long, so the difference in thermal expansion is on the order of only 10 microns. However, I am planning to use the piezo stage to position objects with a precision of 10 nm, and I am worried that if mounted pressure tight there might me abrupt strain reliefs.

Thanks,
Lucas

 

[btrueblood]

Well, you can:

1. mount the stage on elastomeric or similar very soft mounts, allowing for relative thermal expansion of the two metals to not affect the position of the stage....but then what holds the stage in alignment, if there is any jolting or vibration? And the elastomer will expand more than either of the two metals...

2. you can tightly mount the stage using fasteners to the stainless plate. Then calculate what kind of stresses and deflections might occur due to differential expansion across 5 degrees C.

3. Make both pieces from similar material and forget the problem.

4. Devise an elaborate mechanism using flexures and thermal compensation links...you may want to look up some patents for precision chronometers.

 

[Compositepro]

The usual approach to this kind of issue is to connect the two pieces together very rigidly at one point and less rigidly at other points. No clamp screw is infinitely rigid, so I think an adequate solution to your problem is to have four clamp screws (one at each corner) and two dowel pins, one in a slotted hole, to allow for distance change between pins.

 

[unclesyd]

There is no problem with Al clad SS of vice verse all you have to do is get in the kitchen and rattle those pots and pans. EMS has a wide selection of clad material including Al clad SS. If you get your backing plate as a clad you will be able to join Al to Al with S-Bond Low Temperature Solder. Another approach might be to get in touch with the Indium Corp. to discuss using their materials, especially the Nanofilm to get the heat input needed.

http://www.emsclad.com/examples/cookware.html

http://www.s-bond.com/how_sbond_works.htm

http://www.indium.com/nanofoil/

 

[dfsc]

Many thanks for all the useful tips .

Lucas

 

[KENAT]

OK, what's your application? What kind of environment are you in?

Making some guesses about your situation:

Can you use magnets, vacuum...

What level of thermal drift are you trying to attain?

Thermally matching using similar materials may be an idea. However, even there depending what the heat source is (ambient air?) and where it is applied you may still see significant thermal drift at the scale you're talking about because of the thermal gradient between components.

For instance, you could swap the sst plate for AL. However, if it's SST currently because of corrosion concerns that may mean you anodize the AL plate or similar. This could reduce the thermal conductivity between the 2 parts so depending on the heat source the 2 parts may tend to be at different temperatures so instead of solving your problem you might make it worse!

Could you come at this from the other direction of minimizing changes in temperature? This doesn't necessarily mean a big thermally stabilized enclosure, after all it's temperature of the structure you care about, not the environment as such. Sorry if that's a bit cryptic but this type of question overlaps an area my employer has IP in so I have to be a bit careful.

If you're looking for very low thermal drift with that thermal gradient then I wouldn't be looking at SST or Aluminum without some kind of active temperature management.

There are materials that have low coefficients of thermal expansion that are often used for these types of applications. Invar 36, Super Invar and Zerodur spring to mind. However, you still want to closely match the cte of the 2 components to really minimize the specific effect you're talking about.

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