Aluminum Strengths?

Any idea on the strength of any of the 6061, 6063 or other high grade “airplane” aluminum when it gets down to .125 and . 06275 of an inch? And are there any special ways we could have this aluminum piece be coated with something to electrically isolate it?

For AA 6061 sheet, see page 3-264 of MMPDS-01. Be sure to verify the AMS specification to make sure you’ve got the right material for these tables.

AA 6063 is not a typical aircraft alloy—it’s quite weak. (Actually, neither is AA 6061, but at least it’s a fair bit stronger.)

AA 7075 (page 3-371) and AA 2024 (page 3-71) are more common high-strength aircraft alloys.

As for electrical isolation, maybe a paint or conformal coating? Epoxy-based, perhaps?

When it comes to Aluminum you have to mind the post processing, too. 6061 is very weak, but 6061-T6 is quite strong. The T-6 designation is a quenching procedure in hot oil which increases both the yield and ultimate strength of aluminum. There are many other aluminum grades, like 5052-H34, which we use for all of our sheet metal.

For insulating it Plasti-Dip will work with proper application at the nominal 12v level. Depending on what you want to insulate the spray version may be the better choice.

Thanks guys. How thick would you guess that both of those insulators are when applied? I would like for what I’m isolating to be less than .125" but I’ll take what I can get. Also, I meant 6061-T6 lol my bad.

edit: Would like the insulator I’m applying to be <.125"

When you ask how strong or what the strength of something is, please provide more details in the application (i.e. bending, tension, compression, fatigue, fasteners, etc)

Some have mentioned typical alloys 5052-H34, 6061-T6, 7075-T6. In addition to these 5052-H32 and 2024-T3. This list contains the alloys that are (typically) used and kept in stock at the aircraft modification shop that i work at.

Also, is it extremely important to find a sheet of aluminum that is 0.06275"? The fractional size of 1/16th (0.0625") is usually sold as 0.063". Please inquire if you have any other questions. Sheet metal design can be very useful, IF you know how and where to use it.

Here is the Plasti Dip spec sheet. http://www.plastidip.com/docs/plastidip_uv.pdf How thick the coating is depends on how you apply it and how many coats you use. It claims a diectric strength of 1400v/mil but also recommends a minimum thickness of 12-15mil “for best results”. So yes way less than 125mil

I’m sorry that I can’t be detailed on the application, but the impulse on lets say just this 1/16th of an inch thick aluminum shape is ~4.5 Kg m/s of compression. The only other force would be an optional fastener (servo screw more than likely) that doesn’t support anything. Also, this wouldn’t be flat bought, but rather manufactured so beginning size isn’t that big of an issue.

Thank you! I will definitely bring this up in our conference call.

Not to take things TOO far off track, but I was under the impression that -T6 temper was an artificial aging process that would just involve holding the material at a somewhat elevated temperature for a few hours. Specifically, 375F for about 9 hours, according to one google hit. I suppose you could do this in an oil bath, but I don’t think I’d call it a quenching process…

Kevin,

All of the -T tempers are “solution heat treated”, then quenched. Sometimes water, sometimes oil. T6 is specifically at 900 degrees then artificially aged for 8ish hours after quench.

Paul

It’s true! Paul is up 24x7 during comp season! :slight_smile:

Be careful with 6XXX series aluminum in welded applications - the strength in the heat affected zone drops by as much as 75% (9 ksi instead of 36 ksi for 6061-T6 tensile yield).

Shows how much I remember from my materials classes of almost a decade ago. Use it or lose it, as they say. So the heat treat goes Solutionizing -> Quenching -> Artificial Aging. Which makes sense now that I think about it.

Anodizing aluminum will make the surface of the metal non conductive. Painting, nylon dip, will also make the surface non conductive. Chem.-Film or alodine will coat the surface but will be electrically conductive.

Structural shapes like angles, tubes, extrusion, made from .125" 6061 material are plenty strong. Great for load bearing but a bit on the heavy side. We only use .125" thick alum for parts outside the bumper zone and we expect to be hit. We use .062" thick alum 6061 for most tubes. It is a good trade off for being lightweight and strong. Our shooter super structure for this years robot is made from .035 thick 1.25 dia round tube. We use a glued and rivet construction method and it is super strong and lightweight. We really did a good job.

We use 5052 H32 for all of our sheet metal parts. The chassis is made from .090" 5052. The brackets are mostly made from .062" 5052

To electrically isolate the part, I would have the piece Line-X’ed http://www.linex.com/ or use another brand of professionally applied truck bedliner (Rhino-liner?). These coatings are usually a two-part polyurethane and are applied in thicknesses ranging from 1/16" to 1/8". They are TOUGH and once you apply them, they will never come off. Go find a location in your area that applies these coatings, drop by and explain who you are and what you are doing- ask if they can hit it with a coat of product the next time they are spraying it for a customer (makes it convenient for them as they don’t have to go through the equipment setup and cleaning for one tiny job. Offer to put their logo on the part or on the robot if they can do it free of charge- I know they always have stickers they put on vehicles they have sprayed.

You may be able to use one of the rattle-can bedliners sold in autoparts stores but they aren’t as tough and don’t have the same kind of build/thickness that the professionally applied 2-part products do. If you go this route, I would recommend the bedliner sold at Carquest under the name Plastikoat. http://www.plastikote.com/products/Truck%20Bed%20Liner/Truck-Bed-Liner-Spray.html

I used this product on the interior of my Iltis and have been very impressed with the application.

Depending on your application, which you have been quite secretive about, I would suggest using a material that is non-conductive without any special treatments, such as fiberglass. Strength is comparable to 6061-T6 aluminum at a lower density and you won’t need to bother with coatings. Kevlar filled nylon might also work, but is a bit weaker.

Again, the more you can tell us about your application, the more CD can help you. I’ve never really seen any benefit in keeping many robot design secrets, most teams do what they want to anyway. But by sharing your concepts they can be improved by suggestions by more people. Just my $0.02

So far you’ve had answers to the “strength” question… at least as far as yield and UTS is concerned.

In most of our robot applications, however, stiffness is a far more important factor as that describes how the material will respond to bending and compressive loading. Stiffness can vary greatly depending on how you shape the material.

It is hard to tell from the information that you have given us so far whether you ought to be more concerned about stiffness than strength…

Jason

When mounting our bridge pusher downer, we were wondering if our pneumatic cylinder would bend the piece of 1 inch, .063 square tubing it was mounted to. we performed a very scientific test with a couple 2x4s 13 inches apart which we placed a piece of the tubing on. The cylinder has about 100 pounds of push so we had a 150 pound student stand on it, it passed. It also passed the 200 pound mentor test and the 280 pound mentor test. The 280 pound mentor stomp test resulted in a slight bend, that stuff is tougher than I thought:)

And then you can show the students the engineering behind it (or better yet, show them first, then test it):

1 inch, .063 inch thick square
Moment of inertial (I) = (1^4-.875^4)/12 = .0345 in^4
Distance to center axis © = .5 in
Length of span (L) = 13 in
Force (at 1g) = 280#
Moment (simply supported beam) = FL/4 = 910 in-#
Stress = M
c/I = 13,200 psi

A “stomp” is probably 2-3 g’s, so the stress could have exceed 36 ksi, which is the yield strength of the material.