Welded Frame Horror Stories

[Tristan Lall]

Originally Posted by Ben Piecuch

So, you can't compete at the SAME event, but could you compete at a DIFFERENT event with the 2nd robot? I guess that would effectively be two seperate teams, with two separate robots, with two separate budgets, under just one school...

(Sorry, I'm not trying to hijack this thread... should we split it off into something different?)

BEN

Two teams at one school is allowed (two entry fees are paid, two numbers are assigned, etc.). Your school could compete at two simultaneous events, but since there's only one robot per team, your team could not. According to the rules, any custom-fabricated robot part can have fabricated spares that aren't part of the robot until installed, as long as they're identical to what's on the "real" robot. And if you ship spares in the crate, there's no weight limit.

[Aren_Hill]

as far as the square tube frames go has anybody used 1x1x1/16" tube since with bumpers dent resistance wouldn't be an issue. i just know it would be interesting to weld but it would be alot lighter. i'm planning on using a tube frame for a prototype drivetrain and would like some opinions on 1/8" or 1/16"
i think wildstang used 1/16" this year not positive though.

i was also thinking hybrid such as 1/8 for the outer rail and 1/16 for all smaller assemblies and small braces just to keep it light and strong

[Madison]

Originally Posted by Gear

as far as the square tube frames go has anybody used 1x1x1/16" tube since with bumpers dent resistance wouldn't be an issue. i just know it would be interesting to weld but it would be alot lighter. i'm planning on using a tube frame for a prototype drivetrain and would like some opinions on 1/8" or 1/16"
i think wildstang used 1/16" this year not positive though.

i was also thinking hybrid such as 1/8 for the outer rail and 1/16 for all smaller assemblies and small braces just to keep it light and strong

The practice chassis we built last Fall was made from 1x1x.0625 and welded and we have had no trouble with it at all. The competition chassis was bolted together rather than welded since we outsource our welding, so I can't say with any authority how it would've withstood the rigors of an event.

Though most of the work I do uses bolts, I always use 1/16" wall tubing when I can.

[KenWittlief]

Originally Posted by ewankoff

is welding any better than bolting?

yes, definately!

If metal is welded correctly the metal will fail somewhere else before the weld will break

if you use a bolt you must drill holes in the metal, which makes it weaker at that location. A bolted frame will almost always fail at the bolt holes, or the bolts themselves will break, when the metal is stressed beyond its limit.

It will take more force to break a welded frame apart than a bolted frame.

BTW, this is how you test your welding skills. you weld two pieces of metal together, then you bend the metal or pull it apart till it breaks or shears. If the weld breaks it was not a good weld.

[Cuog]

Originally Posted by KenWittlief

BTW, this is how you test your welding skills. you weld two pieces of metal together, then you bend the metal or pull it apart till it breaks or shears. If the weld breaks it was not a good weld.

So you just yank the metal appart with your he-man-ness?

But a weld is alot stronger then the plain metal itself. If I remember correctly(which there is a 50% chance I don't) it has to do with when you weld you are melting the 2 peices together the same way metal is formed, then the extreme heat changes also heat treat it a little to help make it stronger.

[Andrew Blair]

I was under the impression that, with the exception of the fact that you're adding extra metal around that joint, a weld is actually far weaker in a heat treated alloy. For example, with 6061 T6, the weld is reduced to T0, and therefore, the weld was at a disadvatage to the rest of the material. The only way to restore the strength is to reduce everything to T0, and re-heat treat.

On a side note, what's a good way to heat sink a frame so that it warps far less when welding? I remember 67 talking about doing that when they were welding their 2005 bot. I also thought they re-heat treated it.

[Cuog]

Originally Posted by Andrew Blair

I was under the impression that, with the exception of the fact that you're adding extra metal around that joint, a weld is actually far weaker in a heat treated alloy. For example, with 6061 T6, the weld is reduced to T0, and therefore, the weld was at a disadvatage to the rest of the material. The only way to restore the strength is to reduce everything to T0, and re-heat treat.

I think(again not sure) that this is only true for heat treated metals and not standard metals

Originally Posted by Andrew Blair

On a side note, what's a good way to heat sink a frame so that it warps far less when welding? I remember 67 talking about doing that when they were welding their 2005 bot. I also thought they re-heat treated it.

The best solution would be to take your time and do it right. just use spot welds all the way around allowing it to cool some before starting the next weld. Running a bead all the way around and going too quick will likely warp thin metal.

[Tristan Lall]

Originally Posted by Cuog

I think(again not sure) that this is only true for heat treated metals and not standard metals

Andrew is mostly correct. the -T6 represents a heat treatment called "solution heat treatment and artificial aging". When you weld it, you're removing the heat treatment, but not to -T0 (that doesn't really exist); it's actually the -F "as fabricated" temper, which means that no control of the heat treatment was employed during fabrication. There's more here, and even more in MIL-HDBK-5. It's possible for a weld to be stronger or weaker than the surrounding metal—there's no universal rule. The suggestion to take everything to the -O temper (that's "annealing"), and re-harden to -T6 is good in principle, but probably bad in practice because of the difficulty finding a suitable hardening oven (to fit an entire frame), and the difficulty of dealing with deformation and uneven heating. In industry, it's (very) occasionally necessary to do this, but stiffening jigs and distributed heat sources will be employed if there's any worry about deformation and uneven application of the heat treatment. More often, though, wrought aluminum alloys and similar metals come hardened from the factory to their highest strength level.

[Cory]

Originally Posted by Gear

i was also thinking hybrid such as 1/8 for the outer rail and 1/16 for all smaller assemblies and small braces just to keep it light and strong

We do this in low stress areas of our robot.

[sanddrag]

To prevent your frame from warping during welding (and to make it stronger), I recommend a design with pieces that fit inside each other, like the first pic on my earlier post. That 1x1 tube in the lower front and rear goes clear through the 1.5x2" side rails. That frame came out flatter than flat.

[dubious elise]

Heheheh...

Since team 269 began using welded steel frames in 2004, we have not had many problems at all (save rusting - but we learned quickly from that one!). That is, of course, until this year. Within days of shipping our robot in 2006, our frame was a gigantic box - taking up as much of the allowed dimensions as possible. After a pre-ship scrimmage, we realized that we wanted to make some rather drastic modifications that involved cutting off two of the corners of the box to form a sloped front to the 'bot. Of course, after doing so, you simply cannot leave stray ends of square steel tubing because that is, frankly, not structurally sound. Nor is it safe. So alternate pieces of steel were masterfully gas-welded on by one of our mentors to finish the slanted portion (we already had our electronics firmly in place and did not have time to completely un/re-wire our robot).

Everything was honky-dory until the Championships rolled around. I was messing with the netting and noticed a fissure in one of the gas welds. After pointing it out to some of the other kids on the pit crew, we checked all of the gas welds and found another one that was snapped clean through. Luckily, we were just barely enough under weight to allow for repairs involving a very long, threaded rod and some pieces of sheet metal that were used to stabilize the junctions of steel in necessary areas.

The moral of the story is probably to do things 'right' the first time. The counterpoint is that change happens. Rather than being a horrible loss, this was a great learning experience.

[EHaskins]

This year 1103 used a welded drive. The only problems we had were because of some afterthought parts that were add using rivets. I'm not really a builder, but I think we used 20-22 gauge aluminum.

NOTE: I'm not considering the turret/tower assembly part of the frame. Because we believed the turret didn't need to be welded if it was attached to the corners corners of the drive.

[Tristan Lall]

Originally Posted by dubious elise

So alternate pieces of steel were masterfully gas-welded on by one of our mentors to finish the slanted portion (we already had our electronics firmly in place and did not have time to completely un/re-wire our robot).

This is an important point: don't use an electric arc welder on a robot with its electronics attached. That can easily become an expensive mistake. If you must weld, use a torch like they did. (And welding with a torch doesn't really work on aluminum. It oxidizes too fast without shield gas.)

[Aren_Hill]

thanks for the input on my 1/16 questions i'm now planning on creating a hybrid frame with an outer 1x1x1/8 rail and 1x1x1/16 innards to keep it light from some of the scant frames i've seen on here i think it should be pretty robust

[Stephen Kowski]

Originally Posted by Gear

i was also thinking hybrid such as 1/8 for the outer rail and 1/16 for all smaller assemblies and small braces just to keep it light and strong

we did this on our base in 2005....worked incredibly well....i would recommend to any team with a professional welder, otherwise 1/16th is very difficult to weld....