Hey Lloyd, the tricky part (at least for me) is joining the two segments. I've learned how to reverse the travel angle to fill in the crater at the end of a run, which at least helps to finish one segment.
Jon
That means you dont have any interjoint bonding. Just glued around the edges.
If its a low dynamic joint..not problem. If it is a dynamic joint...expect to reweld it again..and again...
Most of the time..you can get away with it. Usually. Kinda sorta, mostly.
Gunner...remember his spare tire that disappeared? No bevelling and not enough heat....
Isn't basic fillet welding just welding on the perpendicular faces? That's the way it looks in the Navy manual, anyway.
Oh yes I remember that story! It was before I started welding, but I have always kept it in my mind as a reason to make sure that my bead has melted into the surfaces of both materials I am joining.
Jon
Yes it is.
There is a reason that pipes and other 'dynamic" joined objects are not simply fillet welded.
They break at the welds.
It still embaresses me..but (Smile) it has been part of my learning curve. Wont happen again in my lifetime. I dun lernded!
Gunner
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If you think about it (and have HF arc starting), you can position the rod exactly as it finished, and at the same point in the air as it was when you finished (usually lower, but then raise it back to the right arc length quickly), and except for some thermal distortion at the spot, you'll continue the weld almost invisibly without 'filling a crater'.
LLoyd
Are there pictures?
Not that I "need" a third positioner, but "want" is another matter...
Ernie! Since you're here, what do you think about the issue of "cold starts" with MIG when you weld around the circumference of tubes in multiple steps?
It's not something I'd do, but I note that the people who make tube frames for kit planes go to great lengths to avoid it, to the extent of making elaborate rotisserie-type fixtures to rotate the frame while they're welding a joint. Some say that cold starts, which supposedly result in high local stresses, make MIG a questionable method for those life-critical applications.
What's your experience?
Thanks Lloyd, I'll give that a go. One of the things that the Navy manual doesn't cover is how to tie in a bead to an existing welding segment. It's a pretty important concept IMHO, and one which I wish was covered by a manual or reference work somewhere, preferably online (like the Navy manual).
Jon
I thought that using HF start for MMA wasn't recommended, not quite sure why but with my Hitachi inverter unit and others I've seen the instructions for it wasn't to use HF for MMA. I tend to leave the stick welding to my old oil cooled welder and leave it on 80V OCV and strike an arc with a new rod on a piece of scrap and I then find I can just place it on the weld site and it'll light up nicely, at least that's the case with 6013 and the anvil hard facing rods I was using a few times recently.
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That's funny, because they didn't start telling folks that until Mig and Tig machines became common.
Back in the 1960s, GMAW and TGAW were almost non-existant except in factory settings, but good stick welders could be had with HF starting and arc stabilization.
Maybe 'they' don't recommend it, but there were sure a lot of weldors using it until it became 'bad'.
All that aside... yes, you can, with the right amount of skill, do exactly as you say. I weld so infrequently that I must use the machine to help augment my skills.
LLoyd
I would never recommend MIG for air frames. MIG is a very fast process and results in welds that are lightly "quenched" by the surrounding cold metal, which can make the welds harder than the surrounding metal, which can lead to cracking under stress. Cold Starts can be caused by old or dirty contactor relays in the MIG machine that cause the wire to hit before the full welding current and shielding gas are present. One way to prevent a cold start from occurring in the weld is to start the weld bead off the joint and walk it over. Similar to how older Aluminum boat hulls were MIG welded before the pulsers took over.
Industrial machines are more tune-able and can have a pre-flow of gas and usually have more substantial relays. Another problem is Whiskering, where the wire continues to feed after the welding current has stopped, which causes the wire to fuse into the cooled weld pool. The problem with some aircraft kits is that below a certain size of plane there is very little regulation or inspection.
TIG is a slower process that uses less overall heat and results in welds that are more consistent with the surrounding metal.
I imagine if you had a high-end, digital, pulsed, MIG machine you could likely dial it in and achieve reliable welds that would rival TIG welds, but you are talking a starting price of $6000 for that machine.
I would still like to see some destructive test data, and proof that the welds were properly engineered and specified in a Weld Procedure Specification (WPS) and that the welders were certified to that Procedure.
Thanks for the insights, Ernie.
I would look at the stresses that the joint will see. In the example, the most strain is on the top part of the joint, I would try to keep the tacks and stops and starts away from the upper third of the joint. If a person lacks confidence in their welding skills, it would also be possible to drill all the way through the uprights and use a longer pin, which makes the welding into place holding rather than load holding.
Stuart
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