Welding terms and technique

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aero_dan
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Welding terms and technique

Postby aero_dan » Thu Dec 04, 2014 6:42 pm

I had a question about the term in my plans, "stepback welds". I have done a fair share of welding and even took a class in it as part of my AA in Autobody back in the day. I understand about puddles, distortion, duration on site, etc.

Gayle was very helpful, but there are still a couple questions. The plans call it "stepback welding", but I wonder if the corect term for the shrink-wrap method should be "Backstep welding"? I am sure those like Kevin or MCM will know the difference. I have, in my limited experience, not been that successful in making the "elongated bubble" of the stepback style while building MS tanks. I use a small Lincoln/century/Sears 110 MIG. Albeit somewhat "roadwarriors" in its guts from mods over the years, the machine is pretty-much beefed up stock ( :roll: ). I have done the "Backstepping type welding process with the great result.

So, If I try to boil down my concern, Am I suppose to do the elongated bubble AND the stepping-stitch welding or just the stitching like I thought in the first place? :shock: ? I know I am over thinking this, I need to just build it and not get caught up in terms.

FYI, I really like reading the post here. The knowledge is fantastic.
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So many boats, ...so little time.

gdcarpenter
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Re: Welding terms and technique

Postby gdcarpenter » Thu Dec 04, 2014 8:12 pm

In construction I tell the client:

Good, fast, or cheap. - pick any two!
This is my first, last and only boat build.

http://www.gdzipbuild.blogspot.com

Kevin Morin
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Re: Welding terms and technique

Postby Kevin Morin » Sat Dec 06, 2014 10:12 am

Aero_dan,
I'm not used to the term stepback welding, but have heard the term backstep welding. I'd tend to think they were the same idea given they're just a rearrangement of the two syllables? Not that I can confirm this from any sources.

In my understanding of the shrink wrap method, if you're right handed, AND starting at the stern (boat upright and on starboard side for this example), you'd begin welding the outside chine, for example, 4 to 6" along the chine toward the bow, then; the welding is done toward the stern (direction of travel). Next weld is another 4-6" forward (direction of progression) and it ties into the first weld's origin as the direction of travel is opposite the direction of progression, and the third weld ties to the 2nd weld's first puddle and so to the bow.

It is my understanding that this is back stepping the welds to form a continuous seam, and similarly if you were welding a chain pattern weld, they to can be backstepped in the same pattern but with different, not continuous results.

I'd have the entire seam well tacked with tacks spaced measured distances along the seam and about 1-3 puddles off the beginning and end of the weld stitches you're going to "back step" in my terms. The weld's direction of travel is opposite the direction of the next weld's location. IF I planned to use 4" or 6" stitches I'd have marked the tacks to be at 1/2 those distances apart, and located 1/2" to 1" off the weld pattern's beginning and ends. This "burns out" the (ground and dressed) tacks when welding a stitch whether in continuous or chain weld.

I'd suggest finding a good quality carbide burr and die grinder to neatly pocket the beginning of each weld where they tie into the just weld put down just before, in continuous welds.

After the hull panel perimeter welds are in then, as I understand shrink wrap, you'd push the hull longs out to the plate and tack- then stitch those with a chain not continuous weld?

In all hull welding of my experience lack of control of spacing or planning and placing welds has been a big contribution to wrinkles, and uniform spacing, weld size, uniform weld wattage and net heat applied all seem to result in smoother hulls. Weld proportion seems to me a huge variable as I've seen well formed boats tacked fair and wrinkled by over-welding; too hot, to slow, too large a bead especially in the framing welds seems to be a large factor in smooth hulls.

Not sure if I've helped or hindered, hoping to give some reference to term backstep welds as I use that term.

I don't use this method as I add welds in a different pattern on the aluminum hulls I've built. So, as I opened, I'll close; this is my understanding not my practice and others' may be a better reference?

Cheers,
Kevin Morin
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aero_dan
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Re: Welding terms and technique

Postby aero_dan » Sat Dec 06, 2014 2:21 pm

Hey, Thanks so much Kevin.

I have researched the terms, and if I understand what was printed, and if the writer knew what he was talking about, ... the opposite term was discribed as a technique to elongate the molten bubble while in the weld, as stated in that report, to improve the penetration as well as the granular layout of the platelets of steel. In a word, to reduce platlet casting (poricity) and give a grain and denser, more polar consistancy of the molten metal before it cools. It seems there are a number of theories on this stuff. And even more since I was in skool back in the day. I understand clearly what you discribed and this was the way I was taught to make tanks and do sheetmetal bodywork on cars, ...back when they were made of metal. :lol:

Thanks again, the quest continues.
Better, faster, cheaper. Only ever found 2 of the 3! (But still lookin.)
So many boats, ...so little time.

Kevin Morin
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Re: Welding terms and technique

Postby Kevin Morin » Sat Dec 06, 2014 2:51 pm

Aero_Dan,
So you were asking about a weld technique NOT the sequence of putting down the welds!!!!? :lol:

Just shows how old guys don't read as well as they might!

IF, and in this case that is a huge question given my other post?, IF... I follow what you're discussing the actual wire tip movement of the arc in the molten puddle of the weld is claimed to be improved in metalugy, decreased in porosity and improved overall by a series of movements within the puddle while that portion is 'wet'?

One thing to consider here is that if a welder is using an inverter power supply there could be entire weld modes at work that improve all those characteristics? I know the Lincoln 350MP Power MIG that I use has more modes and controls than I'm fully conversant employing in welds, and other power supplies will have more digital controls to attempt improvements over this 10-12 year old power supply.

In the 'old days' when stick electrode welding was more prevalent than MIG, it was common place for a welder to 'whip' the puddle in certain rods, and drag the puddle in others. It sounds like the terms "elongate the bubble" is more or less derivative of this technique?

With MIG, whipping a puddle with some alloys of wire is helpful but in other wires just won't work.

Thanks for clearing up what was being discussed, sorry not to see it from the beginning!

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

mcmbuilder
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Re: Welding terms and technique

Postby mcmbuilder » Sat Jan 31, 2015 7:37 pm

Unless a person is a very seasoned professional welder then they should avoid "whipping" with MIG wire. If you do it in a manner that changes the stick out enough to change the amperage input or interrupts the shielding gas coverage it will trap gases and form porosity. If you are doing so to get a "hotter" puddle then the better alternative would be to use 85%ar/15% CO2 or 90%/10% and move into a spray mode. I do a lot of welding inspection work dealing mainly with weld failures, most of the aluminum MIG weld failures I have dealt with failed because of trapped porosity caused by "whipping" the mig wire. 99% of my aluminum work is with 5000 marine alloys and 6063 and 6061 alloys with 5356 or 4043 filler metals, so I can't speak about all alloys but for those you should always avoid whipping the wire.


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