OK, neighbors here I go...

[performance]

Kevin,
Good to see you here.
I'll preface this by saying, from my years growing up in heavy equipment, you don't find Caterpillar using much short arc welding on things like backhoe booms, loader bucket pin bosses or undercarriage cross bars. Every thing like this is spray that I know of. They have some of the top metallurgist in the country and some very particular metal types. If spray was an issue, they would not be using it almost exclusively. This is in steels mostly of course...but the action/mechanism is basically the same in steel, stainless, and aluminum, though the current and voltage values at which it occurs may vary.

Much of my "schooling" would contradict many of your statements, though I guess a lot of it is opinion interjected too by various instructors. I've heard the same concerns said about short arc with porosity and weakness. When you think of true short circuit, the wire is actually breaking and melting after it contacts the metal and the arc is extinguishing at that moment of wire contact and that would seem to increase porosity and weakness. This is happening many times a second. This effect can be observed or "magnified" by turning the wire speed up too high while keeping the voltage low, in the short circuit range. While this may exaggerate the action, it does give you a slowed down look at what is happening at a smaller scale within the weld.

With spray transfer, the arc cone is doing the melting and the pinched off droplet is delivered to the puddle via the force of the arc itself. It arrives already at a fully melted metal puddle and blends right in.

The arc cone with short circuit is minimal and irregular which reduces penetration and thereby increasing the chances for defective fusing as the wire literally stubs in and out of the puddle, which is typically quite cool by comparison.

As far as wetting in, spray mode itself wets in far better, in fact so well that it is not good for out of position use without a few tricks up your sleeve like pulsed spray or STT.
But the biggest concerns I have ever heard of was that of over penetration and HAZ creation. Perhaps the bend tests you saw failed because slow travel speeds and a large HAZ in heat sensitive material. I am not aware of those tests and have seen nothing in my research to point to those tests you refer to.

Globular transfer is really a no man's land and not desirable in the least as it is more unstable and spatter-y than either short circuit or spray...sort of like an aircraft being buffeted just under the sound barrier before it breaks through. You get good penetration, but the violence of the arc can introduce defects even though it is going plenty deep.

Now, in spray mode, the droplets are definitely visible and though they are rapid motion, the eyes can still detect it. If you cannot see the droplets, then the metal is beginning to vaporize. The droplets are roughly the diameter of the wire.

Here is a detailed "treatise" that deals with many of the issues you raise. Lincoln has far brighter minds than I that write this stuff. Some of the math is over my tired head tonight. If I had a doctorate in metallurgical engineering, I'd not be sitting here tonight. I know, a lot of people that will bristle and stand against the common and studied science of the matter, just as people believe in inventing a machine that creates its own energy to run with power left over. But I am not one of those guys. Push science to the limits, yes, but stay out of it's way because it will always come back to trip you up. Maybe we are speaking a little different welding language here, but talking about the same thing and that is not uncommon in our industry. There are as many dialects of welding lingo as there are of any language. But referring back to the source documents keep us speaking the "king's" English.

As far as the comparison to TIG and globular transfer, I'd have to say that if your filler wire is melting with a large molten drop before you get it to the puddle in TIG, something is wrong.
http://www.spagweb.com/v8mini/tech_files/welding.pdf

[Kevin Morin]

Mark, thanks I figured this was being discussed without a clear common language. I see by your clarification we're not all using the collection of letters on this page (words) to represent identical 'things' in the welding process. Your spray transfer includes what we call, incorrectly I suspect, short arc. Us old Alaskan transformer trained welders have associated the larger droplets and the arc's sort of popping or crackling sounds, in aluminum MIG, as short arc. If I can see the droplets (?) I'd have said it was short arc as they form and deposit into the puddle and when the wire re-initiates the arc.... I thought that was short arc?

When I use the term 'spray mode' I'm describing a very long arc with droplets that are not visible, or perhaps better said not distinguishable to the eye, and the bend break tests I'm discussing are the tests I've done every few days for decades to make sure I'm not putting down beads that have some root face gas entrainment problems. When we open up the long arc, tiny droplet, hissing sounding, sandy surfaced welds we all call 'spray mode' they have little gas bubbles very well dispersed in the break. So what yofish must have been referring to was (too) 'long arcing' which does put down a 'foamy' weld and breaks too easily. I wasn't discussing any set of bend break tests done by a given welding testing lab, just the ones I do on my own welds as a matter of course. In those instances, the long arc weld with the very tiny droplets, is what I call spray, where the droplets we can see we call short arc, and they're much less porous welds.

In my lexicon and word choice; if I can see the droplets in almost slow motion that's globular transfer (droplets/globules same same...) OR if the droplets deposit faster into the puddle we'd call it short arc. But that does appear to be in error regarding the correct use of terms?

Next, globular transfer can be done to approximate TIG in this regard. The tungsten in a TIG torch is fixed, has the arc and is kept at a close but removed proximity to the molten puddle surface. In MIG globular transfer, at least when I do it with a transformer power supply, the wire feeds slowly, an the bulbous droplet of melting aluminum does act and appear as though it were TIG tungsten. I'm not saying they're equal,I'm not saying they are identical; merely remarking the wire's molten droplet tip is bulbous, is the focus of the arc and is controllable exactly like a TIG electrode. But this is limited to thin aluminum and not for easily done by low hour welders.

Back to the short arc, I see that short arc is when the wire touches the parent metal and is essentially melted and snapped off in a single action. But where we use the term is when the droplets (which I'm convinced you're identifying as spray mode) are larger, and the hiss sound of the what we call spray turns to the 'crackle' of what we call short arc: is really just minor variations in spray mode transfer?

I think it very possible we've (many older transformer trained Alaskan aluminum welders) been using the term short arc to describe a subtle shift in the spray mode's droplet size, with an accompanying sound shift and arc length change? This shift is the subject of extensive practice and adjustment of the wire, voltage, and gap/stickout/arc length as the shift only happens reliably when the related rates of wire and power are right. Otherwise the arc is too long even if you whip the puddle, and cold lapped if you have too much wire speed OR too little welding wattage to melt the parent metal and obtain toe and top fusion lines.

I'm still not all that clear on globular transfer because I can assure you that it has no spatter at all, it is fully and totally controllable and gives a nice uniform row or dimes weld, but the dime edge is not as clean a half moon as I'd like so I use a cold wire feed TIG gun myself. (OTC Daihen TIG Boy 300 water cooled.) The description you give does not match my experience so I'm not sure, again, the I'm using the same terms for the same physical event.

But I'm pretty sure what yofish and I have been calling short arc is what you're (probably correctly) calling spray. I think we're focused on the very edge of the rates where the droplet sizes are changed by moving the wire in relation to the puddle influencing the CV circuit after spending 4 decades paying close attention to that subtle related rate, but in doing that we're using the terms incorrectly- or at the very least differently than you're using them.

thanks for the reply

Cheers,
Kevin Morin

[performance]

Kevin,

Spray arc is more easily distinguished by the sound. I would add that you don't need to manipulate much in true spray arc, though it's possible, it rather more for vanity's sake and it can cause some popping as you swing back. Spray arc is high deposition, so constant swift forward travel is your friend...creating ripples, not so much.
Globular it seems you are referring to a setup where your wire feed is simply too low. Rather it is a point that the wire feed is actually fairly high but vol
tage is just at or below the threshold for true spray. The arc transfer is not melting back so much as it is melting in or below the puddle, pinching off violently, then burning a few drops at varying arc lengths and then shorting again violently. Here is a slo mo video of that:http://www.youtube.com/watch?v=Hl6AfuKGdP4

Here's a good video representing what spray looks like slowed down. I can see this happening, although admittedly it is a blur, I can see the drops as the enter the puddle if my lens is dark enough, at least on steel. http://www.youtube.com/watch?v=IHkbh0oKv_g

Here's a good one from a normal speed perspective. http://www.youtube.com/watch?v=xb1gvHf0H6w

Here's one of short circuit:
http://www.youtube.com/watch?v=xb1gvHf0H6w

[zoama]

Here's a link to the clearest slowest videos you'll ever see on GMAW transfer modes > http://www.ualberta.ca/~ccwj/videos/...ndex.html#fund

[DaveO]

Those videos are very well done.