Base Plate material selection

[LONDONDERRY]

Greetings-
I'm designing an optical instrument and I need to select a grade of aluminum for a baseplate. The following is some information on my design:

*The instrument size is 330mm x 550mm and the baseplate thickness will either be 1/2" or 5/8" thick.

*The instrument will be light enough to pickup and move around. However, the baseplate can't flex to this will effect the optics. Optical breadboard is out of the question to use.

* the baseplate need to have a flatness tolerance of 0.005"

* There will be alot of machining to this part

I'm considering using either MIC-6 or 7075 (precision ground) I'm leaning more towards the 7075 has it has a higher yeild strength. However, the MIC-6 has a better machining and tolerance. Any suggestion?

Regards
Frank

 

[unclesyd]

Here is another cast jig plate that we used for it's stability. We used this material especially when machining was required on the back side

http://www.howardprecision.com/Brochures/PCP/Alca 5.pdf

I don't know whether it's applicable for your requirements you
might want to consider aluminum metal faced honeycomb panels.
Here are links to two of many suppliers of Aluminum panels. I would definately give Flatiron a call with you requirements.

http://flatironpanelproducts.com/Flatiron_Panel_Products/Welcome

.html

http://www.pacificpanels.com/GPpanel.html

 

[LONDONDERRY]

unclesyd-
Thanks for the tip, honeycomb panel waw looked at but can't be used in my application. The other material you mentioned I looked up and it seems similar to MIC -6

 

[sreid]

It's important to stress Unclesyd'd suggeston to use Cast Aluminum Tooling Plate. It is stress free and doesn't warp when machined.

 

[TVP]

I think a cast tooling plate will be better for your application than 7075-- this will have lots of internal stress after rolling and heat treating, which will negatively affect the final dimension stability. MIC-6 is obviously one of the more popular options and is a good starting point.

 

[LONDONDERRY]

I used MIC-^ in the past and the issues with it being a basplate material with precision optics mounted to it is the material / baseplate deflects if one of the corners of the basplate is lifed up. It has a lower yield strength that say 7075 which is what I'm leaning towrds using. However the tradeoff is I can't have any warping of the part during machining.

 

[TVP]

Maybe you could locally reinforce the MIC-6 by inserting a sleeve or some other type of reinforcement of a stronger material (7075, steel, etc.).

 

[unclesyd]

In your post you state that you are going to require a lot of machining on the base plate. If your machining requirements include a lot milling it is going to be tricky on your relatively thin plate. I talked to a friend that worked in our model shop who stated that on thin section plates if anything other than hole drilling should be done on very high speed milling machine.

 

[LONDONDERRY]

There will be alot of machining, as the baseplate will be webbed underneath to lighten the weight.

 

[racookpe1978]

NO! Design the baseplate against the flexing forces you are worried about.

Then, cast the baseplate to that design with the Al listed above. Casting it "too thin" (or purchasing a plate already "too thin" and then welding !!! additional webs on the back is going to induce the stress and movement and time and money and cost you are trying to avoid. Worse, each plate after fab will be slightly different, and need additional maching time to try to get it "back to flat"