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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What is Engineering anyway: faq1088-1484

 

[ornerynorsk]

Regarding integral filler, I've heard of people trying this with GTAW or Oxy Fuel, but I think it is generally not a good practice to omit filler. I'm no certified welder, mind you, just my opinion.

 

[DVWE]

Kenat,

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.

 

[Adalius]

Depending on what your material is, and admittedly I haven't re-read all these posts to find if you mentioned it, omitting integral filler can be a very bad idea.

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.

 

[KENAT]

I believe they are using GTAW and the structure is steel AISI 1010 or 1018. It's essentially a welded frame for a workstation that houses a few electronics boxes and has a desk on top.

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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[KENAT]

Not quite the same issue but same weldment so I'll tag it on. As well as the slot welds there are some fillet welds.

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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[kslee1000]

I think you shall provide guidelines in how to determine weld size for connecting secondary members, and the minimum weld size for the project.

 

[btrueblood]

Kenat,

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".

 

[KENAT]

Thanks, all.

I've tried to incorporate your suggestions and I've now passed it over to our contract checker to see what he thinks.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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What is Engineering anyway: faq1088-1484