I hate to post this question because it could go in any direction... Gaps.
In mass production work, from time to time, due to part tolerances, formed parts, sturctural parts and supplier parts, there's going to be a stack up of tolerances. Usually they are less than 1/16" which in most cases i can live it all day. Other times we see gaps greater then 1/16" up wards to 3/8". The majority of the joints are fillet welds and then there's groove welds, square butt joints, and a few flares. Our shop uses GMAW Spray and with the robots running pulse. Everything is mild steel. When our guys come across a gap that they know a robot is going to burn through, most times, they switch settings to a short curcuiting range and run a cold pass to bridge the gap. Sometimes, i even walk up behind the guys and fnid that they are doing this is a downhill progresion when they have already been told not too.
I am not looking for a leature!! What I am looking for is how do other mass production shops deal with this issue. I know if i reference D1.1 or D14.1 or D14.3 or most other specs, short curcuiting is not prequalified. When i read D1.3, all modes of GMAW (including short curcuiting) are prequalified BUT all of the prequalified joints are what i would consider full blown welded (finished) joints, not what i am doing. I am doing cosmetic or non-structural, bridging gaps type of welds. In that respect, eventhough i am welding to D14.1 or 3, should i write a WPS in accordance with D1.3 or use the current WPS for spray and list a cold setting for gaps?
If i need a WPS just for short curcuiting, how would i go about with the PQR since most of the welding is not for a completed weld (finished weld) joint but for bridging gaps or non-final welds?
By Superflux 
Date 06-22-2015 23:59
Edited 06-23-2015 00:11
First off it sounds like a comprehensive inprocess OAL tolerance inspection program needs implemented. This should reduce the compounding of errors.
Question; What happens when the errors compound the other direction and fits are less than zero or have become "metal bound"?
Sounds like to me maybe the saw shop, plaz cutting or fit-up stations need the corrective action before it becomes a welding problem. Seems like (as is all) too often the blame gets passed down to the Wrong department.
"when they have already been told not too."
1) Remove piece from the station and send back through for rework... immediately.
2) Pull their certs (for non compliance) and BUST them back to grinders or pushing a broom.
Word will travel FAST. Compliance will soon follow.
I don't have my specs with me at the moment, so just going off memory, a quick response is:
The scope of D14.3 states it's for structural welds. Use this spec for ROPS/FOPS.
For misc sheetmetal portions, use D1.3.
D14.3 and D14.4 call out for max t joint fillet weld gaps to be 1/8" and 1/16" for lap joint fillets.
5/16" max gap for groove welds.
1/8" max gap recommended for robotically welded grooves.
If you have joint gaps betond these dimensions, you can repair by applying buttering or layering welds on the end of the short part to build up length to meet joint gap tolerances. Max buildup dimensin is 2.5 times part thickness?
D1.3 doesn't specifiy max joint gap conditions.
Joint conditions beyond spec tolerances are to be rejected.
Exceptions to spec requirements have to be approved by Engineering and accepted by the Customer.
Don't trust my weary memory on these specifics. The point is that you need to research your specs to find the answers to your question.
Tim
Would you need a PQR and WPS if you're just bridging gaps?
If you have a contract with a customer in which you state that you are providing prouct manufactured in accordance with a code or specification, you are legally liable to provide just that. In that case, every weld must be compliant, unless you have exceptions built into the contract. Code work means making every weld in accordance with a qualified or pre-qualified procedure, and by a qualified Welder.
If you're not doing code work, you can weld any way you want to, but there are still liability concerns if your product fails.
Tim
