Questions on welding required on ætab & slotÆ weldment 3

[KENAT]

I’ve been asked to properly document a welded assembly that was designed/developed by other staff no longer here with the help of a vendor who now isn’t being very responsive to questions.

They use a system of tabs and slots to minimize/eliminate fixturing at the assembly level.

One thing I haven’t been able to work out is the proper term for their welding technique/procedure and how to indicate this on the assy. From the notes I have they basically melt the tabs into the slot with little or no filler added and as they end up being under flush no routine grinding. I found a little information on the internet but not much detail.

Just to make it harder someone has lost our copy of AWS 2.4 so I'm using

http://www.unified-eng.com/scitech/weld/weld.html

until we can find it.

If someone could point me in the right direct on how these welds should be specified I’d really appreciate it, at the moment they’re indicated as groove welds but I’m not sure that’s correct.

I'm in the US working to ASME drawing standards.

Thanks,

KENAT,

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[btrueblood]

Sounds more like a plug or slot weld, "with integral filler", Kenat.

 

[MintJulep]

The drawing needs to call out the desired weld configuration. I agree with btrueblood that it sounds sort of like a plug or slot weld. A sketch would help.

The fact the no filler rod is used should get documented in the weld process specification.

 

[KENAT]

Attatched a view on one of the joints with one part exploded out, hope it helps give some idea what I'm talking about.

I had a quick look at the link I gave above and I was wondering if it was more like a plug or slot weld but they seemed to emphasize adding filler while as btrue notes, it's more like I have integral filler.

As to the weld process specification, that may be more than I or anyone else here can really do. I've raised the question of how to spec welding on US drawings before thread725-175723 and it's not as simple as my previous employer in the UK.

KENAT,

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[desertfox]

Hi Kenat

Not the most definitive site for the correct answer to your question but this site using similar joint confgurations to yours calls for plug welds.

http://www.diyden.net/Buzzard_part2_rev1.pdf

desertfox

 

[KENAT]

How does the linked look, about right?

http://files.engineering.com/getfil...4aea-8c3b-f2e03fbd1b2a&file=tab-slot-weld.tif

For my purposes flat (flush) or concave will work. I can only find examples of plug or slot with flat or nothing.

As I vaguely recall the vendor said the process of using the tab as the filler usually ends up with slight concave/under flush but sometimes a little grinding is necessary.

Also on the finishing method, my boss says that 'M' is generic and will allow any of the other processes, is this correct? I believe our current vendor Grinds, so I was going to put 'G' but I want to leave it as generic as possible.

Thanks for everyones help so far.



KENAT,

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[DVWE]

Also on the finishing method, my boss says that 'M' is generic and will allow any of the other processes, is this correct? I believe our current vendor Grinds, so I was going to put 'G' but I want to leave it as generic as possible.

No. "M" specifically means machining per AWS 2.4. "U" means "unspecified" and leaves the fabricator with the option of how to contour the weld.

 

[racookpe1978]

Vender not being helpful, eh?

Hmmmn.

A simple, but first order, question becomes just this: "Is their weld failing?"

Are their techniques under suspicion, or just "undocumented" - in the apparent hope of they (the vender) thereby becoming irreplaceable as a supplier to you (the purchaser).

Very, very few welds can be made without filler material (most resemble a stud gun in practice using a combination of pressure, sudden electric current, and an almost "comsumable" small contact surface.) so I suspect they are simply using a tab and hole combination to locate the parts, and a MIG or TIG rig to fill up the gap between the tab and the hole.

If the weld is not failing, you could use a shop inspection to look at their techniques, then "re-invent the wheel" to document the results. Or - if they continue to fight - demand their process instructions and welder cert's as a QA requirement to renew the contract. They are, after all, a seller to you.

 

[DVWE]

Kenat, I have a copy of 2.4 in the office and as I recall there is a good page of examples of slot welds in there. I will try to remember to post tomorrow. I'm assuming they're probably using GTAW (Tig) to make this weld?

 

[KENAT]

Thanks DVWE, I hadn't seen that in the Global DRM but just found it in the Genium one.

KENAT,

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[DVWE]

Do you mean you found a copy of AWS 2.4?

 

[KENAT]

Oops, posts while I was typing.

racookpe, it's a long convoluted story of ineptitude, vanity, laziness... that I've been fighting for about 18 months now. Essentially we have, to say the least, incomplete documentation of the welded assy such that we couldn't easily go to another vendor in the event of their being a problem with the current vendor.

I share your concern over if they are really 'melting the tabs' as the little research I did on this suggested this would be difficult/unlikely in practice.

If this was more safety critical I'd probably put more effort into it, however I spent most of my alloted time on the project trying to sort out other aspects of the drawing pack and now am up against the wall.

A contract guy we have in did a partial mark up of the drawings we have as best he could in very limited time based on visual inspections of a finished article but they're already painted when we get them which makes it more tricky. Once I've incorporated his changes and a bunch more things I found in the process he'll go over it again.

Thanks DVWE, they are using GTAW, at least that's what the limited drawings I have says.

KENAT,

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[KENAT]

And again, I'm typing too slow...

No, our AWS 2.4 is long gone, haven't seen it since before Christmas however, we have copies of the Genium "Modern Drafting Practices & Standards Manual" & the Global DRM which after some digging both have sections on weld symbols. I just seem to recall AWS 2.4 being a bit clearer/more concise than what I'm seeing here but I could be wrong.

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[ornerynorsk]

We use a lot of tab and slot in our weldments. Technically, they are plug or slot welds, as one of the earlier posters had responded.

 

[DVWE]

Kenat,

See attached from AWS A2.4.

I think your drawing which shows a slot weld is adequate, but you can look through this to make sure.

 

[KENAT]

Thanks ornerynorsk and especially DVWE, really appreciate the help.

KENAT,

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[KENAT]

ornerynorsk, as you actually use this process can I maybe try and pick your brains a little more.

Are the tabs nominally the same length as the mating part is thick. For example, if the part with the slot is .09" thick, are your mating tabs .09" long? Half the joints in the pack I inherited are like that, however some of the tabs are going into slots in .120" thick material but are only .09" long, we were thinking this was just another error in the pack but maybe not.

Also, can you give any input on the issue of if the tabs are melted or material added etc.

Any help much appreciated.

KENAT,

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[MikeHalloran]

I made a part like that once, a rope seal holder for a gas turbine. Like a big o-ring groove made of sheet metal.

I drew it as a couple of rings, made in quarters, and a tabbed spacer, narrow enough to be bent to the correct curvature by hand, with the tabs projecting halfway through arcuate slots in the rings.

I dry- assembled the first one easily. It was a beautiful thing, thanks to laser cutting.

I put a plug weld symbol with a concave surface symbol on the drawing. I shouldn't have bothered; our welders couldn't read drawings anyway.

My intent was to have the tabs melted just enough to hold the thing together, without projecting into the space allotted to components on either side.

The welder laid down a big-ass turd of a bead on each slot, so when he was done, they all had to be ground down to get flush. Of course that shop didn't have abrasives finer than 60 grit, so the finished parts looked like crap.



Mike Halloran
Pembroke Pines, FL, USA

 

[ornerynorsk]

Hi Kenat,

For most joints we run the tab flush with the mating surface, IE material thickness, like you mentioned. We have done some joints 1/2 to 1 full thickness proud of flush in order to maximize the weld area, in effect turning it into a fillet weld. Most rarely, we have left the tab below flush to achieve a completely flush finished appearance. We've not used this where strength is an issue, but for purely cosmetic reasons. Our process is exclusively GMAW with 030 wire, so we are adding filler in any of the above-mentioned methods. Our weldments are all Gr50HSLA A1011 and similar ranging between 14 gauge and 1/4 inch. Hope that helps.

 

[KENAT]

Thanks ornerynorsk, that does give me more confidence in how I've done this.

I'm wondering about removing the note about integral filler though.

Mike Thanks also.

KENAT,

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