pic: Weld Testing :D

[Dr.Gusta]

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[donkehote]

What size tubing and what wall thickness is that? Just curious, as I would like to use this test as proof that welded joints are strong enough for FRC. A mentor I know is firmly in the "welds are weaker than bolts" camp.

Very nice piece, and a good test.

[MrBasse]

Originally Posted by donkehote

What size tubing and what wall thickness is that? Just curious, as I would like to use this test as proof that welded joints are strong enough for FRC. A mentor I know is firmly in the "welds are weaker than bolts" camp.

Very nice piece, and a good test.

If welded properly, the weld should be stronger than the base material.

That's impressive strength on aluminum, I'm kind of surprised it held up with that angled piece doing the bulk of the work.

[Dr.Gusta]

1x2x.125 wall. If done correctly the weld should be stronger than the material you are welding.

[JamesCH95]

Originally Posted by MrBasse

If welded properly, the weld should be stronger than the base material.

That's impressive strength on aluminum, I'm kind of surprised it held up with that angled piece doing the bulk of the work.

Originally Posted by Dr.Gusta

1x2x.125 wall. If done correctly the weld should be stronger than the material you are welding.

This is not always true.

While the weld should be designed to be stronger than the base material, this isn't always the case. Frequently teams will make parts out of 6061-T6, but when welded 6061-T6 turns into 6061-T0, and the welding rod alloy (generally 4043) won't ever be as strong as the parent material, even if it's re-heat-treated. The weldment must be designed to take this into account.

The trick here is that the HAZ (heat affected zone) near the weld is still parent material thickness, but has been annealed by the welding process, and is thus weaker than it used to be. This is where most failures will occur. While the HAZ is not precisely the 'weld bead' itself, it is part of the weld in a holistic sense.

To address the 'bolts are always stronger than welding' stance some people have... It depends, on a lot of factors. They each have their place. To point out one specific example in FRC: welding the old C-Channel kit frames saved about 3lbs in brackets and fasteners and resulted in a stiffer, stronger chassis. The C-Channel was 5052 alloy, no heat-treatment and thus no strength loss when being welded.

[MrBasse]

Originally Posted by JamesCH95

This is not always true.

While the weld should be designed to be stronger than the base material, this isn't always the case. Frequently teams will make parts out of 6061-T6, but when welded 6061-T6 turns into 6061-T0, and the welding rod alloy (generally 4043) won't ever be as strong as the parent material, even if it's re-heat-treated. The weldment must be designed to take this into account.

The trick here is that the HAZ (heat affected zone) near the weld is still parent material thickness, but has been annealed by the welding process, and is thus weaker than it used to be. This is where most failures will occur. While the HAZ is not precisely the 'weld bead' itself, it is part of the weld in a holistic sense.

To address the 'bolts are always stronger than welding' stance some people have... It depends, on a lot of factors. They each have their place. To point out one specific example in FRC: welding the old C-Channel kit frames saved about 3lbs in brackets and fasteners and resulted in a stiffer, stronger chassis. The C-Channel was 5052 alloy, no heat-treatment and thus no strength loss when being welded.

I think that is where the "properly" and "correctly" come in to play. If you are welding an item for heavy use, you had better be sure that you are using the proper materials. In the 6061 case that you mentioned, the wrong materials are employed if they aren't up to the task that is placed upon them. All these alloys and issues raise all kinds of things that I don't even like to think about...

Personally, I love steel.

[JamesCH95]

Originally Posted by MrBasse

I think that is where the "properly" and "correctly" come in to play. If you are welding an item for heavy use, you had better be sure that you are using the proper materials. In the 6061 case that you mentioned, the wrong materials are employed if they aren't up to the task that is placed upon them. All these alloys and issues raise all kinds of things that I don't even like to think about...

Personally, I love steel.

Indeed, not understanding and using the proper WPS for a given structure leads to many a sad weld.

I think the 6061 case is a good one to talk about because I think many people get the 'welding is terrible' from experiences with 6061 and not understanding the implications of removing the heat treatment.

And it is awfully hard to beat the weld-ability of steel. Difficulty working on it in the pits with hand tools, and relatively awful machining properties, are the reasons we don't use it often though.

[MrBasse]

Originally Posted by JamesCH95

I think the 6061 case is a good one to talk about because I think many people get the 'welding is terrible' from experiences with 6061 and not understanding the implications of removing the heat treatment.

And it is awfully hard to beat the weld-ability of steel. Difficulty working on it in the pits with hand tools, and relatively awful machining properties, are the reasons we don't use it often though.

I completely agree with everything you say about aluminum. Materials should be chosen based on their workablilty (welding, machining, bending, etc.) as well as the strength in their intended purpose.

We use steel simply because we can use less of it that aluminum (as far as taking up space) and if something bends we just bend it back. A lot of our robots have been primarily made from steel 1/2" square tube. Almost every kid on our team can weld it, drilling is easy, and with the right cutters machining is no problem at all.

[Seth Mallory]

The students learning to weld on out team on the first day are introduced to the hammer and vice test. Almost every weld they do in training before build are clamped in a large vice and broken with a hammer. This way they see inside their welds and can improve. Having them see the welds that look great on the outside but have no penetration at the joint is a learning experience. The students do their own testing and just ask us when they feel the need. I have not seen a broken weld on our robot in years. One benefit of this simple testing is our welders have improved their skills enough the we weld mostly 1/16 wall instead 1/8 wall. This is a large savings in weight.

[fox46]

That is either the smallest RTI ramp or the biggest Jeep I have ever seen....

[twgeary]

The Jeep is sitting on 37's and the alum is about 6" tall.

Tim
Mentor Team 5107

[fox46]

http://en.wikipedia.org/wiki/Ramp_travel_index