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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
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.
Was there any reason you needed the strength of steel in your drive pods?
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.
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.
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.
Excellent, thank you!
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
Important note: 5052 isn’t heat treatable, but it is annealable at 345°C (“holding at temperature not required”). It will lose considerable yield strength in the heat-affected zones of the plasma cuts. 5052-H34 (half-strain-hardened and stabilized) has 31 000 lb/in2 yield strength; 5052-H32 (quarter-strain-hardened and stabilized) has 28 000 lb/in2 yield strength; 5052-O (annealed) has 13 000 lb/in2 yield strength.
(See ASM Handbook, Volume 2: Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, particularly Table 58: Typical mechanical properties of alloy 5052.)
Thanks everyone, for the replies! I think I have enough information to go on now. Much obliged!
1/6" seems an odd size. Is that correct?
I believe he meant 1/16th.
Yes, 1/16". Brain got ahead of my fingers.
Use voice recognition software. My brain rarely outruns my mouth!
Oh, wait, that might be the problem… 