Aluminum Strengths?

[fox46]

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/T...ner-Spray.html

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

[JamesCH95]

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

[dtengineering]

Originally Posted by farmersvilleRob

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?

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

[BJT]

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

[Gary Dillard]

Originally Posted by BJT

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 (c) = .5 in
Length of span (L) = 13 in
Force (at 1g) = 280#
Moment (simply supported beam) = F*L/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.

[AlexH]

For material properties check out http://matweb.com/

[pfreivald]

Please forgive the thread-o-mancy, but this was the most relevant one I could find for my question...

We found a company with a CNC plasma cutter willing to do some sheet metal work for/with us (yay!), but they're primarily a steel place. We used 1/8" steel on our octocanum wheel pods last year, and they held up *great*.

This year we'd like to go lighter, so I requested 7075 T-6... They proffered 5052 as an alternative that's easy for them.

Is this a good substitute? Would those with experience on FRC drive trains consider 5052 a reasonable alternative to steel? (I know it's lighter... The question is, how does the strength and the stiffness compare?)

We have no metals experts on our team, so looking up the numbers doesn't do a lot of good at this point in time. Any expertise people are willing to share would be most appreciated.

Thanks!

Patrick

[JamesCH95]

Well, 5052 (~30-35ksi yield strength) will be half or less of the strength of 7075-T6 (68-73ksi yield strength). 5052 in similar in strength to lower grades of steel (A36, 36ksi YS for example) whereas 7075-T6 is similar in strength to alloy steels like 4130 (70-75ksi YS). I would be suspicious that plasma cutting would wreck the T6 temper in 7075 thus making it weaker, but 5052 in not heat-treatable so it would not lose any strength. That, along with it's superior formability, low cost, and wide availability, is probably why the shop suggested 5052 over 7075.

If you want to drop weight I would suggest using thinner steel with a higher strength, or more accurately evaluating your actual strength requirements and sizing material accordingly. I suggest this because I have learned that steel cuts *much* better with plasma than aluminum does. I think it's because steel is much less thermally conductive than aluminum is, so there's a smaller kerf angle and less slag. But that's beside the point...

Using a thinner alloy steel would be particularly effective if you heat-treated, say, 4130 or 4140 to ~Rockwell C22-27ish, to pick a hardness range that's very strong (something like 130ksi-145ksi YS) and still somewhat ductile and tough. Your plasma cutting sponsor might have heat-treating furnaces and could just throw your parts in (mounted on fixtures) with their parts. This may be huge overkill though...

Just my $0.02 on your predicament.

Edit: FWIW most AM kit frame elements (c-rails, the axle mounts from 2010, etc) are folded 1/8in 5052 aluminum and all hold up very well to FRC abuse, so making drive pods with the same material and thickness seems reasonable to me.

[Akash Rastogi]

Originally Posted by pfreivald

Please forgive the thread-o-mancy, but this was the most relevant one I could find for my question...

We found a company with a CNC plasma cutter willing to do some sheet metal work for/with us (yay!), but they're primarily a steel place. We used 1/8" steel on our octocanum wheel pods last year, and they held up *great*.

This year we'd like to go lighter, so I requested 7075 T-6... They proffered 5052 as an alternative that's easy for them.

Is this a good substitute? Would those with experience on FRC drive trains consider 5052 a reasonable alternative to steel? (I know it's lighter... The question is, how does the strength and the stiffness compare?)

We have no metals experts on our team, so looking up the numbers doesn't do a lot of good at this point in time. Any expertise people are willing to share would be most appreciated.

Thanks!

Patrick

Was there any reason you needed the strength of steel in your drive pods?

[Joe G.]

Originally Posted by pfreivald

Please forgive the thread-o-mancy, but this was the most relevant one I could find for my question...

We found a company with a CNC plasma cutter willing to do some sheet metal work for/with us (yay!), but they're primarily a steel place. We used 1/8" steel on our octocanum wheel pods last year, and they held up *great*.

This year we'd like to go lighter, so I requested 7075 T-6... They proffered 5052 as an alternative that's easy for them.

Is this a good substitute? Would those with experience on FRC drive trains consider 5052 a reasonable alternative to steel? (I know it's lighter... The question is, how does the strength and the stiffness compare?)

We have no metals experts on our team, so looking up the numbers doesn't do a lot of good at this point in time. Any expertise people are willing to share would be most appreciated.

Thanks!

Patrick

Without having seen your drive mods, my inclination is that 1/8" steel was overkill for your application. I've seen 6061 and 5052 hold up perfectly fine in a number of similar applications, often with pocketing or thinner stock.

Second, think about how smart design can add strength to your modules, to make up for the loss in raw strength. Did your original design incorporate flanges? This is one of the reasons that 5052 is preferred by a lot of sheet metal places -- 5052 aluminum has very good properties for bending. Consider the failure modes you might expect your modules to encounter, and reinforce them by beefing up your design, rather than your material. You should be fine.

[pfreivald]

Originally Posted by Akash Rastogi

Was there any reason you needed the strength of steel in your drive pods?

Yes: paranoia.

Last year was our first year ever trying a truly different drive train, and we wanted to make sure that, whatever else happened, we could still drive around.

We created a weighted table of priorities for an upgraded drive train for this year, and "as robust" topped the list. To be honest I'm not sure whether or not we're at "overkill" on this, as none of my mentors are metals experts. Thus, I consult the gestalt crowd-source resource of Chief Delphi.

[pfreivald]

It's been brought to my attention that I screwed up! (It happens...)

We were using 3/32 steel last year, NOT 1/8, and want to replace it with aluminum... Either 3/32th or 1/8th, depending on the alloy, etc.

[Cory]

Originally Posted by pfreivald

It's been brought to my attention that I screwed up! (It happens...)

We were using 3/32 steel last year, NOT 1/8, and want to replace it with aluminum... Either 3/32th or 1/8th, depending on the alloy, etc.

I have yet to see a scenario in FRC where a stronger alloy than 6061 was needed for frame members.

The only application where it makes sense is shafts, gears, and sprockets.

5052-H32 or 34 is the default material for anything that gets bent. Look at any successful sheet metal drive from recent years and it's not going to use anything fancier. It's all about how you design and load the members, not the alloy type.

[pfreivald]

Excellent, thank you!

[Paul Copioli]

Patrick,

148, 1114, and 217 all use 5052-H34 aluminum for any item that is bent metal. We use 6061-T6 sheet metal for flats, depending on thickness. Our shop has 1/6", 0.090", and 1/8" 5052-H34 for the bent items.

The three teams have different philosophies on metal thickness so we use 1/6" up through 1/8" on the drive base.

217 uses more 1/16" and 0.90", except for the bumper mount, where we use 1/8" to try to get as close to the max bumper weight limit.

Anything fully hardened (T6, T651, etc.) is not appropriate for bent sheet metal. The half hard 5052 material is specifically used for sheet metal as it is a good balance between strength and ductility.

Paul