GMAW Short circuit

Date 12-24-2013 22:57

The answer to your question will depend upon many variables.

1) Is there a code involved?
2) Which code might be involved?
3) Shielding gas in use?
4) Operator experience with GMAW-S.
5) Pre-heat applied?
6) Electrode diameter?
7) Thickness effectively welded will vary depending upon which material is being welded, SS or Carbon.
And more.

After considering all of the possible combinations of this question there may be no definitive answer to your question. The problem is, at some point in your adjustments of wire feed speed, volts, gas, etc you will be using either Globular or Spray instead of short arc.

But, if maintaining a pure short arc with shielding gas, volts, and wire feed speed I would speculate between 1/2-3/4". And you will need pre-heat of a couple hundred degrees to accomplish that. On a normal basis I would suggest you are more limited to 1/4-1/2". Again, all of this depends upon all the factors already listed and especially operator experience.

Could you weld even heavier sections? Yes. But with great care and much more pre-heat and welding parameters that will be out of the range of what is normally considered to be Short Circuit Transfer.

Have a Great Day, Brent

By Jorge Giraldo (**)

Date 12-26-2013 03:19 Edited 12-26-2013 03:43

Hello Brent.
Thanks for your answer.

You are rigth: my question was too vague. I attach a diagram wich contains the metal transfer modes with ER70S-6, 0.045" diam., 92Ar/18CO2 in function of Amp. and Voltage. Encircled in purple are the GMAW-S parameters considered true short circuit.

I qualified some WPSs according AWS D1.1:2010 with ASTM A36 base metal, 5/16", no preheat, in positions 2F and 3F with average 200A and 20V. However, considering the technical recommendations found in books for GMAW-S and the real posibility to obtain lack of fusion or penetration, I have opted to limit the WPS to 1.1 the thickness of the qualification test plate (coupon 5/16"; WPS almost 3/8").

If I understand you correctly, I could weld thicker base metal if I choose preheating and parameters in the range of "high-energy" short circuit (the right purple zone of the diagram). It appears logical to me and, from my experience, I should verify these new WPSs with mechanical tests (Break test, as stablished in AWS B2.1). What do you think about the last proposal? Or is better to pass to another transfer mode as you said?

As you can see, I have no much confidence in the GMAW-S above 3/8", but I have no never worked in ranges above 220A with this tansfer mode.

Happy holidays and happy new year.

Jorge

By ssbn727 (*****)

Date 12-26-2013 12:14 Edited 12-26-2013 12:19

Feliz Navidad Jorge!

Brent gave you some very good points to consider and just about everything is considered except for joint configuration...
For example: If two plates are butted together with no space in between, the amount of penetration and fusion will not be as good as if you decide instead to use a joint configuration with a root opening and/or even joint preparation by including a bevel on one member depending on the type of joint you'll be welding/joining, or bevel both members of the joint...

However, if you want to skip joint preparation all together, then for the thickness you're using for the qualification test plate (coupon 5/16"; WPS almost 3/8"). I would either opt for spray transfer like Brent suggested with a smaller diameter wire size to limit the amount of heat input for the thickness of the plates being used...

Or you could also go with Flux Cored Arc Welding instead as there are plenty of welds being deposited with this process, and it has the added bonus of being able to weld out of position if that's a concern too... If done properly, the slag deposit and spatter concerns will not be an issue to contend with so long as the optimal parameters are chosen, and with just a small amount of practice if the welder(s) isn't familiar with FCAW because if the welder can GMAW-S, then FCAW will be very easy for them to learn and master...

One must also consider warpage and distortion and welding @ the parameters you listed will give me concern about not being able to control these two potential problems afterwards especially if you're working to tight enough tolerances for fit up to be a major concern. :eek:

If I were you, I would try both to see/determine which of the two is the more efficient, and cost effective as well as giving you the best results in mechanical testing but then again, there are so many factors that I am not aware of regarding the specifics of your project that I really am only speculating here of course. :lol:

Either way, have fun determining which of the two processes and methods of metal transfer will work out best for your application! :smile:

Dios te Bendigas Amigo!
Enrique A.K.A. Henry

By welderbrent (*****)

Date 12-26-2013 12:35

Your reluctance to use GMAW-S on materials thicker than 3/8 is well founded. It is not a good choice.

As Henry noted, there are limitations to using GMAW Spray as it will not perform to satisfaction out of position.

FCAW-G would be my choice for heavier weldments especially when considering possible out of position welding.

Now, if that is not really an option for you, GMAW-S is possible just not preferable. There will need to be testing, more than likely pre-heating costs and time, and operator training. Using .045 electrode in the short circuit mode is asking for lack of fusion especially at the root.

Again, as Henry pointed out, in some joint configurations it is more possible as the first pass(s) would be on thinner material that would reduce pre-heat time and increase fusion probability. The welding itself would be the pre-heat for continuing passes.

There are lots of things that are possible in welding that are not the choice of preference. It appears you know a fair amount about the process and have done your due diligence in researching this application. Follow your gut feelings, as they appear to me, and use another process. Unless of course that is not really an option, you have few welds to do this way, and it is not a public safety issue.

Have a Great Day, Brent

By electrode (***)

Date 01-02-2014 13:03

Sir,

first and foremost - happy new year to you and to the AWS welding forum.

Then, my apologies for my ignorance.
Interesting responses by some honourable individuals, that is to say.
I myself, however, must admit to not really understand your diagram.
Also, your further and more detailed explanation on heat input, wall thickness limitation etc. is hardly comprehendible to me.

Alphonse Allais once should have said: "La statistique a démontré que la mortalité dans l’armée augmente sensiblement en temps de guerre."
Loosely translated: Statistics reveals that during wartime the death rate among those serving the army explicitly increases.

This always in mind I do understand statistics as a valuable means to gain information from information that we already know.
For my personal taste. Quite much too often we are coming across drawings and plots nowadays proving brightly colourful but beyond that (rather) meaningless.
This, quite much too often, due to simple misunderstandings.
Diagrams, at least in my opinion, should primarily accumulate data in a way to improve their understanding.
To enable this the statistician, drawing the diagram, needs to reveal his "recipe".

Hence.

Could you kindly share your "recipe"; i.e. the exact boundary conditions (experimental setup etc.) employed for producing the diagram data and how you could tailor these conditions in a way to finally achieve "true short circuit" at ~ 340 A / ~ 26 V?
If you really could have obtained "true short circuit" (whatever "true" means) setting these parameters, well, that, at the very least, would be somewhat surprising to me.

Who knows. Since nobody else has obviously yet paid attention to this, maybe I'm simply overlooking something here.

By Lawrence (*****)

Date 01-02-2014 13:46

Hey Electrode!

Great to see you post!

You are like Sherlock Holms!

I see now, what you are saying about the graphic. Those don't at all look like short circuiting electrical characteristics do they?

By electrode (***)

Date 01-02-2014 14:11

Lawrence,

thank you very much for warmly welcoming me (back).

Afer a while I was reading a post today from 'ssbn 727' that made me think.
Regardless of all dispute and controversial debates.
At the end of the day, this place yet remains the "world's greatest welding forum"

Regarding the topic.
As you say. Some of them appear ... questionable.
Surely the OP can shed some light on this.

Happy New Year.

By Jorge Giraldo (**)

Date 01-06-2014 22:27

Hello Sir Electrode.

The best for you and yours in this new year (and for the forum’s people too).

One of my habits (a bad habit, may be, but necessary in my country where welders and welding personnel has very little chances of education) is try to show some of the tools that may guide the decision making process, especially in a forum like this, and probably the attachments are being matter of confusion rather than clarity.

We have constructed several graphics for GMAW according to Colombian needs, but the attached one was extracted from a Miranda & Quintino’s work and, leaving aside the external appearance, serves to know the mode of metal transfer in terms of the welding parameters, transition current level and the regions where you probably will have instability (Henry did a journey across the graphic in his post). This is called a “Transfer Mode Map". Briefly, to plot the particular map attached in my post were used electrode ER70S-6, Ø0.045” and travel speed of 14 ipm. The experimental input variables were: voltage between 12-38V (almost 10 levels) and Wire Feed Speed (80, 200, 240, 280, 360 & 400 ipm). Each point in the map corresponds to each pair of parameters. I take this map for these reasons: same class of electrode, same gas mixture, same diameter, otherwise, the map would not apply and you would have to look other one or construct it.

Boundary levels: (1) current covers the spectrum of the wire diameter and class; (2) voltage covers the spectrum used in GMAW: In the upper part of the map you are in the limit of the welding equipment and spatter, and in the lower part you have instability, particularly “stubbing”.

How tailor and analyze: In order to know the transfer mode (globular, spray, SC, mixed transfer: SC/S, SC/G), you may register the signals of V and I (values in the time during welding) and analyze the shape of the curves in order to determine what metal transfer mode is happening with this parameters. In that way you can tell that the ~340A/~25V for this wire and gas is short circuit transfer, because the shape of its curves looks like the illustrated in handbooks (I take off the "true" that meant that this curves are typical of SC and not of mixed modes – the qualifying is redundant-). I was surprised too when I saw this map the first time years ago, we “rechecked” the data in all the SC region and the map is OK, but I have never used this parameters in real joints or under practical conditions (Code jobs, for example).

I don’t know Mr. Electrode if this (heavy) post meets your request (I hope yes) or if I'm still very “lost in translation” because my poor English (I did my best in a short time).

I appreciate the exchange of ideas and experiences that occurs in the forum and I never wished to be offensive with anyone in any way. If I choose incorrect words or tone is for my English weakness, not on purpose as Henry kindly says (Thanks Henry for your comprehension!).

Well, have a good day.

Jorge

By electrode (***)

Date 01-18-2014 17:11

Sir,
thank you.
I tend to disagree - more or less.
But, working to capacity at present, I'm unable to spare time.
I hope to be able to return to this soon.

By electrode (***)

Date 04-15-2014 08:49 Edited 04-15-2014 08:59

Sir,

I have been asked by the system whether I really wish to reply on a 98 days old post and, if so, whether I'd have a good reason for doing so.
Well, not sure actually, however, as time allows I would like to briefly get back to this subject.

In the meantime I could read Pires', Quintino's and Miranda's paper that you did mention in your message. Luisa Quintino and Rosa Maria Miranda are actually representing surety for high-quality publications. I found this specific paper quite confusing though, due to mingling a load of different – not really trivial – theories and hypotheses to finally produce … (partially at least) confusing transfer maps.

Trying to describe GMAW droplet transfer physical behaviour applying (just) pinch instability- and static force balance theory, mainly indicated in the Pires et al. publication, is slightly missing the mark, at least in my opinion.

As for example and knowing that a picture is worth a thousand words. Let me, as an excerpt, enclose below a sketch of the theoretical droplet model from the paper (depicting the anode spot contraction and thus the reduction of the "conduction zone" at "higher" CO2 contents) upon Pires et al's considerations are mainly based upon.

Then, I will embed a single sequence image showing the 'droplet' appearance when safely exceeding the transition current using ø 1.2 mm (~ ER70S-6) wire electrode under 82 % Ar and 18 % CO2 for achieving streaming spray transfer.

One may easily see the difference between theory (used for producing these "transfer maps") and practice (as the welder uses to adjust current and voltage to increase both weld performance and e.g. deposition rate and – eliminate significant short circuit occurrence).

To summarise, as unfortunately recognisable quite often in physical models of welding phenomena. The latter has not really much in common with the former.

I thus would like to stick to what I already said and I do moreover dare to say; the existence of a transition current between short circuit- and spray transfer in GMAW should be well-accepted among the experts since proven through a row of thorough experiments and studies. Hence, it remains quite hardly understandable to me that carbon dioxide contents of 18 per cent in argon shall show droplet transfer modes similar to "short circuit transfer" after exceeding the transition current.

However, as I once used to say. Maybe I'm simply overlooking something in this special subject.

Regards

By Jorge Giraldo (**)

Date 12-31-2013 22:52 Edited 01-01-2014 01:08

Hello.

As Henry and Brent said, the GMAW globular and spray (not pulsed) are not applicable for welding out of position and GMAW-S is unsuitable for welding plates of 9/16" with the parameters used in our PQR, regardless of the AWS D1.1 allows for production up to twice the thickness of the test assembly (2T = 2 * 5/16" = 5/8"). Since it is a small structure comprised of eight I-beams (7 butt joints and several fillet on thickness 9/16" approx., out of position) and that there is no FCAW on the shop that I advise, we decided to manufacture it with SMAW process using a prequalified procedure (typical, safe and easy to make for very few joints).

I agree, in part, with Al that the lack of fusion depends mainly on the heat input (no much of preheating). I have used the following formula as a reference to avoid incomplete fusion on carbon and low alloy steel: HMIN = 30T^2 + 15T (where T is the thickness to be welded in inches and H is in kJ/in). It was proposed by Duan K. Miller in a Welding Journal’s article (July 2001). I have obtained good results with it in several process, but the short circuit GMAW is tricky: for example, if I took my PQR parameters, I got an approx. heat input H=25 kJ/in, which means that I could weld 5/8” without troubles… with other arc process, may be, but not with GMAW-S. What happens with other higher short circuit parameters in GMAW (like 280-300A and 24-26V in the diagram)? I don’t know really, I have no tried, but the relationship “Heat Input/Thickness” is not so simple and plain when you are dealing with GMAW-S.

I attach the Duan’s article, because (in my opinion) is very useful for those involved in welding.

Well, no more welding for this year. Thanks a lot for the discussion and share your knowledge, and I wish you and your family a happy new year.

Jorge

Attachment: TOOLSFORREVIEWINGWELDINGPROCEDURES.pdf (909k)

By ssbn727 (*****)

Date 01-03-2014 11:24

Yes you can weld out of position with globular transfer although it is much harder than one may think since there's a certain technique to use that will limit the amount of spatter deposited also so proper training is required beforehand... With FCAW, less training is necessary... I also noticed he chart but I chose to refer to the parameters Jorge listed in his post and not the parameters in the chart since they weren't all all what is known as short circuit transfer values and instead more in line with globular and depending on the wrie diameter size chosen ,could also be used for spray transfer as well... The values Jorge listed in his post were as mentioned:

"I qualified some WPSs according AWS D1.1:2010 with ASTM A36 base metal, 5/16", no preheat, in positions 2F and 3F with average 200A and 20V. However, considering the technical recommendations found in books for GMAW-S and the real posibility to obtain lack of fusion or penetration, I have opted to limit the WPS to 1.1 the thickness of the qualification test plate (coupon 5/16"; WPS almost 3/8")." He then goes on to say that:

"If I understand you correctly, I could weld thicker base metal if I choose preheating and parameters in the range of "high-energy" short circuit (the right purple zone of the diagram). It appears logical to me and, from my experience, I should verify these new WPSs with mechanical tests (Break test, as stablished in AWS B2.1)."

And this is where I also take issue since those values go from short circuit and then transitioning to globular then into the upper limit of the globular spray transition and then into spray transfer although @ the lower end of spray transfer parameters so I decided to refer to the values Jorge listed in the written post instead since those were more aligned to short circuit trasnfer using that specific wire size diameter.

From my perspective, the only problems I noticed were and no disrespect to Jorge but, was the choice of wording and the language barrier Jorge had to overcome did allude to creating some unintentional confusion in his post which does happen with other folks in here at times also even when both parties have command of their interpretation of the English language depending on what side of the pond they're located... Then again, that's just my observation so I would appreciate not to read too much into it, or confuse it as being offensive in any way because that is NOT my intent here. :eek:

Btw, thank you for your kind words Electrode and Happy New Year to you too!

Respectfully,
Henry

By Lawrence (*****)

Date 12-30-2013 14:53

Something I noted that has not been mentioned yet is that the shield gas mentioned by the original post said 92Ar/18CO2, which exceeds 100%..... The drawing posted said 82/18 Ar/C02

The original post also noted operations on Austinetic Stainless steel base metals...

The proposed gas combination is NOT typical for GMAW operations on stainless steel.

By Milton Gravitt (***)

Date 12-31-2013 20:20

It should be a trimix shouldn't it Lawrence.

M.G.

By Lawrence (*****)

Date 01-02-2014 12:49

Milt,

For stainless GMAW (in the short circuiting transfer mode) The trimix with helium is common.

However with the advent of GMAWP for stainless... A 2% oxygen or a 2% C02 (my preference) can produce much better sidewall fusion than the helium, and a 2 part mix without Helium is always going to be a bit cheaper and more versatile if you are doing a good bit of welding.

By Milton Gravitt (***)

Date 01-02-2014 14:50

Lawrence , I didn't think you where never to use oxygen on stainless steel. So you can use oxgen if you are using this welding process GMAW-P.

M.G.

By 803056

Date 01-02-2014 15:03

When using spray transfer, globular, or pulse transfer, oxygen in the shielding gas changes the surface tension of the weld pool to flatten the bead reinforcement and reduces the tendency for producing undercut. The oxygen in CO2 does essentially the same thing.

The amount of O2 must be limited and balanced by the amount of deoxidizers in the filler metal or porosity can result.

Al

By Milton Gravitt (***)

Date 01-02-2014 19:35

Lawrence,Al is this in the AWS A5.32 2011 for gases and gas mixtures.

M.G.

By 803056

Date 01-02-2014 19:55

Probably not. You should be able to find more information is the Welding Handbook that covers the welding processes.

Al

By Milton Gravitt (***)

Date 01-02-2014 21:36

Thanks Al & Lawrence for the info.
M.G.

By Jorge Giraldo (**)

Date 12-31-2013 23:08

Hello Lawrence.

You are wright, is a clear mistake: the gas is 82Ar/18CO2, like the diagram.

About welding in SS, I think this may be matter of another independent post: is a WPS that came into my hands related with GMAW-S on approx. 2" thickness. In order to clarity and don't mix two different applications, I'll put a different post with this issue.

Jorge.

By Lawrence (*****)

Date 01-02-2014 12:47

Jorge,

I cannot think of a single application where GMAW with a short circuiting transfer mode would be preferable on steels 2" in thickness.

By welderbrent (*****)

Date 01-03-2014 01:29

Al,

No, I goofed, didn't explain myself well enough once again. After asking several questions I continued on with a train of thought that never saw print.

We all know that often GMAW-S gets used for applications with no code requirements. Many shops use it for practically everything, including applications where it is not acceptable for code work and then try to say they didn't use it or didn't know they shouldn't.

Anyway, my rambling was based upon the possibility that the OP wanted to know how heavy of material GMAW-S would successfully weld in non-code applications such as 'Farm Code' farm equipment with no other applicable codes or public safety issues to consider. Thus, with some references to what we see so often where personnel crank the volts and wire feed up beyond normal Short Arc values removing it from that area, I also made mention that with some added pre-heat, to aid with the beginning fusion short comings of Short Arc while all the base material is normally pretty cool and there is not enough heat input to quickly allow good fusion at the root, that you can push the envelop on what would be normally accepted as a maximum thickness for Short Arc.

This all supposes that the question was based not only upon code restrictions but just a general 'How thick will this process go if I really want to?'.

Now I have probably really confused the issue but that basically was what I was trying to say. The codes will have their standard pre-heat but if you want to do heavier sections with this process it is wise to go beyond normal code tables because Short Arc does not develop the heat input to get good fusion in the root on heavier members without some assistance.

It comes down to the same idea of using 3/32" 7018 electrodes when you really should be using 5/32" to get the job done on heavy members.

For the most part, it is not the way to accomplish the job. But depending upon the reason for the question, the application, and the availability of processes it may be the OP's only option. But I clearly stated my opinion that another mode or even another process needed to be used.

So, I hope I cleared up my other response. Probably not. But thank you for challenging what you saw. It wasn't as clear as it should have been.

Have a Great Day, Brent