Q. Best sheet metal design?

[TheModMaster8]

I will preface this by stating that I am reposting this on behalf of my brother. as he hasn't used CD that much...

Hello everyone. I am trying to learn more about what: thickness, type and alloy other teams have made their sheet metal drive base frames from. My team tried .125" 5052 aluminum, but it was a little heaver and more malleable than i liked. i would love to hear what your team used or any knowledge you may have on this topic. i don't quite have a specific design in mind yet, i want to see all the options i don't know of first

[Chris is me]

Thinner 5052, used in better shapes and bent such that the geometry of the part provides the structural support you need. .090 5052 is pretty commonly used and works well. My team used .125" this year because of the rough game (and the lack of other things to take that weight up), but generally .090 is preferred.

If you're having problems with strength, deflection under load, etc. it's most likely a design problem and not inherent to the material. Sheet metal is harder to get right than tubing based designs.

If you / your brother have some specific examples / photos of where this material has let you down in the past, I can try and provide half-decent design advice for working out the bugs in the future.

[InFlight]

Both 5052 and 6061 are commonly available in sheet form. The Yield strength of 5052 is only 28KSI, where 6061 is 40KSI. The 6061 is easier to machine, you can weld with either.

Unless your worried about corrosion resistance, stick with 6061 sheet.

We typically use 1/16" plate (0.063) unless there is a need for something heavier. If your bending 0.125" sheet you will definitely need to have a larger bend radius on your sheet metal brake to not induce stress cracking.

http://www.americanmachinetools.com/bend_radius.htm

[Cothron Theiss]

Originally Posted by InFlight

If your bending 0.125" sheet you will definitely need to have a larger bend radius on your sheet metal brake to not induce stress cracking.

From my experience, teaching students to bend and/or weld .125" and especially .25" 6061 is pretty difficult. If your design requires tighter bends and welding at some point, I would stick to 5052. 5052 is a great alloy to teach students to weld on, and if you outsource your welding, some shops will charge less for the easier allows to weld due to the different costs of filler materials. (This is probably a case-by-case thing, so it's just better to ask.)
If your frames won't include many complex bends or require minute and difficult welds, 6061 is an amazing alloy.


EDIT: A complete aside, but teams 2024, 5052, and 6061 are missing out on some of the coolest potential team names ever. Whoever becomes team 7075 has a great opportunity.

[InFlight]

Originally Posted by Cothron Theiss

From my experience, teaching students to bend and/or weld .125" and especially .25" 6061 is pretty difficult. If your design requires tighter bends and welding at some point, I would stick to 5052. 5052 is a great alloy to teach students to weld on, and if you outsource your welding, some shops will charge less for the easier allows to weld due to the different costs of filler materials. (This is probably a case-by-case thing, so it's just better to ask.)
If your frames won't include many complex bends or require minute and difficult welds, 6061 is an amazing alloy.

.

Bending .125 or .250 sheet with a tight bend radius is a bad fabrication detail; the effects of which will be more apparent with higher strength 6061.

There really isn't any appreciably difference in the cost of ER4043 or ER5356 filler for 5052 and 6061 respectfully. Good welding takes considerable practice however; and does not appear to be a common skill with most high school students. The over focus on performing well on standardized tests has eliminated most shop class options in the middle and high schools.

We avoid welding aluminum if possible. We fully CAD, water-jet the aluminum sheet, bend, and rivet. You can replace a riveted assembly; you can't take apart a welded assembly. Pneumatic riveting through a series of water-jetted holes is also significantly faster than setting up for a single weld.

[Cothron Theiss]

Originally Posted by InFlight

There really isn't any appreciably difference in the cost of ER4043 or ER5356 filler for 5052 and 6061 respectfully.

I'll have to ask one of the machine shops I've sent parts to about why they quote 5052 welding services as cheaper than that for 6061. I'm honestly not too sure about it.

Good welding takes considerable practice however; and does not appear to be a common skill with most high school students. The over focus on performing well on standardized tests has eliminated most shop class options in the middle and high schools.

Isn't that why we're here? Quality shop classes are becoming a rarity in high schools and FRC is able to, in the right situations, fill the void and educate students.

We avoid welding aluminum if possible. We fully CAD, water-jet the aluminum sheet, bend, and rivet. You can replace a riveted assembly; you can't take apart a welded assembly. Pneumatic riveting through a series of water-jetted holes is also significantly faster than setting up for a single weld.

I think this is a matter of resources. My team does not have access to a water-jet. My team does have a mentor that's been welding aluminum for 30 years and loves nothing more than to pass on his craft. I don't know if the OP intends to weld some of the joints in his drivetrain, but I thought I'd include the information anyhow.

[AllenGregoryIV]

Originally Posted by InFlight

Both 5052 and 6061 are commonly available in sheet form. The Yield strength of 5052 is only 28KSI, where 6061 is 40KSI. The 6061 is easier to machine, you can weld with either.

Unless your worried about corrosion resistance, stick with 6061 sheet.

We typically use 1/16" plate (0.063) unless there is a need for something heavier. If your bending 0.125" sheet you will definitely need to have a larger bend radius on your sheet metal brake to not induce stress cracking.

http://www.americanmachinetools.com/bend_radius.htm

The vast majority of sheet metal designed robots use 5052 .09 or .125. I assume he is suggesting make robots similar to 148 or 971 that use sheet metal extensively for almost all their parts. They also limit the amount of welding and use rivets for most of their fastening. Teams have had success using 1/16" 6061 but from what I gather you have to be a bit smarter at your design then with .09 5052.

[Csherm]

Do teams use steel sheet metal on their robots? If so what alloys and thicknesses are most common?

[Basel A]

Originally Posted by Csherm

Do teams use steel sheet metal on their robots? If so what alloys and thicknesses are most common?

This question is interesting to me because my team randomly got a large amount of 24 gauge galvanized steel, and I'm not sure how much use we can get out of it. Thoughts?

[MrBasse]

Originally Posted by Basel A

This question is interesting to me because my team randomly got a large amount of 24 gauge galvanized steel, and I'm not sure how much use we can get out of it. Thoughts?

We've used galvanized in the past but only sparingly. You need fantastic ventilation if you plan to weld it, the edges tend to be incredibly sharp, it doesn't paint well without scrubbing with vinegar or something similar, if you paint it you stink like vinegar for a day or two, but it is strong and when thin it is also pretty light.

We use it mostly for mock ups, prototypes, and guards. Traditionally we plasma cut it with the vent fans turned to 11. We also use a shearing press when simple shapes are needed.

The beauty of steel over aluminum is that we can bend it, flatten it, then bend it again and again and all is well. We have often made structure and manipulators out of galvanized conduit as well. After a rough match, you can hit steel with a hammer or pull on it really hard to force it into place and you're ready to go with enough time left over to help your aluminum neighbors replace an entire assembly that got bent too far. The entire superstructure on our 2014 bot was a mix of 1/2" and 3/4" conduit reinforced with 24 gauge galvanized sheet metal.

[Cothron Theiss]

Originally Posted by Csherm

Do teams use steel sheet metal on their robots? If so what alloys and thicknesses are most common?

I remember there being at least one team on here that talked about their use of steel sheet metal. I'll look for the thread in the meantime.

[AustinSchuh]

Originally Posted by AllenGregoryIV

The vast majority of sheet metal designed robots use 5052 .09 or .125. I assume he is suggesting make robots similar to 148 or 971 that use sheet metal extensively for almost all their parts. They also limit the amount of welding and use rivets for most of their fastening. Teams have had success using 1/16" 6061 but from what I gather you have to be a bit smarter at your design then with .09 5052.

We were almost exclusively 090 5052 for our sheet metal this year. It held up fine to the torture that was this game. There was some 060 somewhere, I'm sure. None of the sheet metal was welded. We did weld the sheet metal -> tubestock joints, and tubestock -> tubestock joints.

Since we got access to a mill, we added 1/4" plate to our repertoire. Sheet is good for certain problems, and milled constructions are good for others.