Questions on welding required on ætab & slotÆ weldment
Questions on welding required on ætab & slotÆ weldment
(OP)
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,
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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RE: Questions on welding required on ætab & slotÆ weldment
RE: Questions on welding required on ætab & slotÆ weldment
The fact the no filler rod is used should get documented in the weld process specification.
RE: Questions on welding required on ætab & slotÆ weldment
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: question on standard US weld notes and it's not as simple as my previous employer in the UK.
KENAT,
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RE: Questions on welding required on ætab & slotÆ weldment
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
RE: Questions on welding required on ætab & slotÆ weldment
ht
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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RE: Questions on welding required on ætab & slotÆ weldment
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.
RE: Questions on welding required on ætab & slotÆ weldment
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.
RE: Questions on welding required on ætab & slotÆ weldment
RE: Questions on welding required on ætab & slotÆ weldment
KENAT,
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RE: Questions on welding required on ætab & slotÆ weldment
RE: Questions on welding required on ætab & slotÆ weldment
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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RE: Questions on welding required on ætab & slotÆ weldment
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.
KENAT,
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RE: Questions on welding required on ætab & slotÆ weldment
RE: Questions on welding required on ætab & slotÆ weldment
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.
RE: Questions on welding required on ætab & slotÆ weldment
KENAT,
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RE: Questions on welding required on ætab & slotÆ weldment
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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RE: Questions on welding required on ætab & slotÆ weldment
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
RE: Questions on welding required on ætab & slotÆ weldment
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.
RE: Questions on welding required on ætab & slotÆ weldment
I'm wondering about removing the note about integral filler though.
Mike Thanks also.
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RE: Questions on welding required on ætab & slotÆ weldment
RE: Questions on welding required on ætab & slotÆ weldment
For GTAW I would think that the tab has to be the same length as the mating part thickness if you require a flush or close to flush contour.
If the tab is only half the thickness, then it will definitely wash away and leave a concave contour, maybe that's OK? Strength wise, you're not sacrificing much at these thicknesses if the weld is not completely filled in.
A word of caution however, depending on the code of construction, if applicable, the use of GTAW with or without filler metal typically requires two different WPSs. I don't know how picky your customers or end users are, but you should be aware of that.
RE: Questions on welding required on ætab & slotÆ weldment
For instance, if the part is aluminum, welding without filler and slightly hot will in all odds cause a longitudinal crack, where as welding without filler at the proper heat can create what visually appears to be a good weld but a dye pen. test will show minute surface cracking.
On steel, it's more readily done without filler but, depending on the joint setup, you can end up with problematic underfill amongst other issues.
RE: Questions on welding required on ætab & slotÆ weldment
In the one conversation I had with the current vendor about 9 months ago I recall them talking about 'melting' the tab. My concern was making it clear for any new vendor what is going on.
However, based on the above, I think I'll remove the comment about integral filler.
We don't have anyone qualified to prepare a WPS, and don't see us getting it from the vendor. The best we came up with was a not about "WELD PROCESS GTAW IN ACCORDANCE WITH INDUSTRY BEST PRACTICES" which is virtually meaningless but makes me feel a little better than saying nothing.
Thanks to everyone, you're really helping me out here.
KENAT,
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RE: Questions on welding required on ætab & slotÆ weldment
On the existing drawings the few that might be considered 'primary strucural' have the size specified.
However, a bunch of others which are 'secondary strutural' don't have a size specified.
From what I can find online and in the 2 DRM I have it seems that sizes should always be given for fillet welds. My boss says he remembers not specifying fillet size on non critical welds at a previous employer but can't find any examples in his data.
So, if I leave the size unspecified is that OK, if not explicitly to AWS A2.4 than at least to common industry practices?
KENAT,
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RE: Questions on welding required on ætab & slotÆ weldment
RE: Questions on welding required on ætab & slotÆ weldment
Most commercial weld shops can't reliably make a GMAW weld smaller than 1/8" or so. So, dim. the bead at 1/16" to 3/16" and cover the bases.
Back to the tab+slot welds, if you want the tab to be melted down, call out integral filler and add a note that allows additional filler if required. We have somewhat similar geometry on parts here, wherein a flange ring is machined with a 1/8" hole, intending that a piece of weld filler rod be inserted into the hole and engaging in a slot in a mating part behind it, thus indexing the assembly properly prior to welding. The whole mess then gets buried under fillet welds. One vendor suggested the idea, and uses the hole, the other vendor ignores the hole and verifies clocking by other methods. Either way, the use of the hole is spelled out in a drawing note that states the hole is to be filled with filler metal and plug-welded prior to starting the fillet welds, the note called out from the tail of the weld callout. Would strongly urge you to specify such non-standard geometry similary, something like "Note 314: Engage tabs and slots as shown in detail X. Slot weld to flush (or concave, or whatever you want) condition using tab and additional filler as required, machine, grind or sand smooth to surface finish requirement xyz".
RE: Questions on welding required on ætab & slotÆ weldment
I've tried to incorporate your suggestions and I've now passed it over to our contract checker to see what he thinks.
KENAT,
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