Gloublar transfer mode

By Lawrence (*****)

Date 11-06-2009 04:59 Edited 11-06-2009 05:04

Globular Transfer is a mistake.. Both literally and figuratively.

Take your short circuit parameters and increase voltage until you get an inconsistantly open arc with dropletts that are larger than the electrode wire diameter and alot of spatter.. This is globular transfer.

No advantage with stainless... or carbon steels for that matter.

I'll have to check in the morning when I have my codebook nearby.. But I don't think GMAW-S is prequalified in D1.6.

GMAWP may be a spray transfer process that can weld some square grooves with full pen in all positions.. But the status of GMAWP as a prequalified process may also be questionable.

Surface Tension Transfer    "STT"   (Lincoln)
Regulated Metal Deposition    "RMD"   (Miller)
Cold Metal Transfer    "CMT"   (Fronius)

All the 3 noted above are special adaptive/synergic CC/CV short circuit modes that are designed for open roots in stainless pipe (and other things). All manipulate current with propriatary waveforms... CMT also manipulates wire feed in synchronization to the pulsation.

By no1welder (*)

Date 11-06-2009 18:08

Thanks for your input on the gloublar transfer mode. As for the GMAW-S mode it is in the AWS D1.6-3.29(8) note(4)

By Metarinka (****)

Date 11-06-2009 15:19

The reason Globular is not prequalified is because it gives very erratic inconsistent results, and is more prone to defects than other transfer modes. IIRC some codes go as far as banning it.

With 3/16" material in the square groove design. I would say your best bet would be to spray transfer as you have backing tape.

Don't quote me on this, but off the top of my head I thought short circuit was not prequalified for CJP groove welds in 1.6? I'm a little rusty now as I no longer work to that code and I was always doing GTAW, but I thought I remember that.

By 803056

Date 11-08-2009 14:27 Edited 11-08-2009 14:29

I am confused. Literature recognizes four distinct modes of metal transfer when using GMAW. They are:

a) Short circuiting transfer characterized as low heat input, low voltage, low amperage typically using a CO2 Argon mixed shielding gas. Capable of welding in all positions, but fusion type defects are common. There are variants of the process as mentioned by Lawrence.
b) Globular transfer characterized as high heat input, higher voltage, and higher amperage than S.C. transfer and utilizes 100% CO2 shielding gas. Limited to flat grooves and flat and horizontal fillets. Good penetration and fusion, but with more spatter compared to the other transfer modes if inductance is controlled.
c) Spray mode transfer characterized as high heat input using higher voltage and higher amperage using a shielding gas containing at least 80% Argon. Limited to flat grooves and flat and horizontal fillets.
d) Pulsed spray mode transfer which is a combination of short circuiting and spray mode transfer where the metal transfer is preferably during the spray portion of the current cycle. Characterized as lower total heat than spray mode transfer, but with the ability to weld in all positions.

Of the four modes of transfer, only short circuiting mode is a concern with most welding standards. Limitations on thickness ranges qualified are used to "discourage" its use, but few welding standards prohibit its use outright if it is qualified by testing.

AWS D1.1 has placed some limitations on the type of power supplies used for prequalified welding procedures, but that does not prohibit a company from using any type of power supply if they qualify their welding procedure. It has been the recent editions of D1.1 (2004 or 2006 if I remember correctly) that limits the type of power supply used for semi-automatic welding processes. That being the case, states that reference a different edition of D1.1 in their building statues may not restrict the type of power supplies used unless the EOR specifies a more recent edition of D1.1 in the project specification. For example, Connecticut has adopted the 1989 edition of AWS D1.1 for designs based on allowable stress and the 2000 edition for designs using Load Reduction Factored Designs. Neither edition has limitations or restrictions on the type of power supply used. Inspectors are well advised to know what edition of D1.1 is applicable in the jurisdiction they work. They could be imposing requirements that do not apply and the fabricator can seek redress (money) for lost production, late delivery, etc.

Best regards – Al

By Metarinka (****)

Date 11-09-2009 22:03

Al did anyone make mention of restricted type of power supply? Because I certainly didn't.

My point was that from my memory in using D1.6; GMAW globular transfer was banned from prequalified weld joints because of it's erratic nature. Leaving the only prequalified transfer modes as Spray and SC (pulse is not banned, but I think it's an essential variable that doesn't fall under prequalified joints?)

This is all off the top of my head.

but anyways if my memory serves me, globular transfer is severely limited or banned in some codes due to it's inherent erratic nature. Or the procedure has to be qualified. Either way, I cannot think of a specific situation where it is desired over another transfer mode.

By 803056

Date 11-09-2009 23:38

You're right with regards to D1.6.

My comments were with regards to D1.1. Where that came from is anyone's guess. Another case of "Hey Stupid, read the darn question!"

Best regards - Al

By 803056

Date 11-10-2009 13:02

OK, here we go.

I took off on a tangent with regards to D1.1, but you forced me to take another look at D1.6-2007. Actually, I was wadding through the debris on my desk and stumbled across a copy of the code.

Back on subject, D1.6 does not limit prequalification to any particular transfer mode of GMAW. As a matter of fact, clause 3.4.1 states: "Shielded metal arc welding (SMAW), gas metal arc welding (GMAW), .............. may be used for prequalified WPSs, and therefore approved for use without WPS qualification tests". Clause 3.29(8) states the following: "The progression for all passes in vertical position welding shall be upward, except that GTAW, GMAW-S, and FCAW-G are prequalified vertical down for base metal of 3/16 inch maxium thickness." And finally, Table 3.5 footnoot d states: "Pulsed GMAW is prequalified in all positions except vertical down. Prequalifiaction of short circuiting transfer of GMAW is limited to helium based shielding gas mixes, .............."

The use of globular transfer is not prohibited. It is included in Tables 4.1 and 4.1S as one of the transfer modes when a WPS is qualified by testing (see item 3.2 in both tables). It is not excluded or limited in any way by any clause that I could find.

Let me retract my previous response and say, "Hey Stupid, read the code before you answer the question!" Had I read the code I would have had the right response the first time. Dummy me.

Best regards - Al

By js55

Date 11-10-2009 13:38

Al,
Whats wadding? :)

By welderbrent (*****)

Date 11-10-2009 14:38

That's when you take all the papers on your desk, 'wad' them up in little balls, and practice your file 13 hoop shots!!! That's how I clean my desk when I'm looking for something IMPORTANT!!

Have a Great Day, Brent

By 803056

Date 11-10-2009 14:59

Swimming?

Al

By Metarinka (****)

Date 11-10-2009 14:48

My memory is getting fuzzier than my logic.

I guess I should have read the code before answering. I was very certain D1.6 limited transfer modes in prequalified welds. On that same grain, is transfer mode a essential variable? If you specified a voltage/ WFS range right on the border a part could go from SC to spray or globular within the parameter range.

By Lawrence (*****)

Date 11-10-2009 16:36

Why in blazes can't the D1.1 committee put a simple statement in about GMAWP just like you mention here for D1.6. ????????????

Prequalified ... Yes or No.

Thanks for that Al.. I don't have the 2007 edition of D1.6

::::::Putting that on the order list.

By ssbn727 (*****)

Date 11-10-2009 18:37

BECAUSE.....

Respectfully,
Henry

By HgTX

Date 11-10-2009 20:09

D1.1 didn't put in that statement because they haven't made that restriction. The only transfer mode D1.1 restricts is short circuit. If it's not short circuit, then wherever you see "GMAW", your choice of mode other than GMAW-S applies.

Hg

By Lawrence (*****)

Date 11-10-2009 22:57 Edited 11-10-2009 23:01

Hg

There is however a restriction on CC power supplies in Clause 3.

And every GMAWP power supply on the market today has both CC and CV electrical characteristics. Furthermore, there are thousands of older 1990's style power supplies like the Miller Maxtron and ArkPac that produce GMAWP using strictly CC power.

"3.2.4 FCAW and GMAW Power sources. FCAW
and GMAW that is done with prequalified WPSs shall
be performed using constant voltage (CV) power supplies"

I think this restriction merits the specific addressing of GMAWP that I'm talking about....

I've been a broken record on this issue for years... Sorry for hijacking the thread.

By 803056

Date 11-11-2009 04:11

I recognize that some inverter power supplies with pulsing capability utilize both CC and CV, but I didn't realize that was the case with all pulsing power supplies.

I was under the impression that it was only certain "canned" programs that utilized wave forms that changed slope during the cycle to include both CV and CC characteristics. Am I mistaken?

Best regards - Al

By Lawrence (*****)

Date 11-11-2009 06:53

Al,

Any/All of the GMAWP power supplies out there provide a welding arc that is "adaptive" as well as synergic.

The adaptive arc has both CC and CV tendencies.. Meaning:

A. That the spray transfer Arc Length remains constant regardless of contact tube distance from the work. This is a CV attribute.

B. That the current remains constant regardless of the contact tube to work distance. This is a CC attribute.

Every GMAWP power supply on the market provides an arc with both of these attributes so that the "current" and "trim" remain consistant during changes by the operator in "stickout"..... Unlike traditional CV GMAW which an extension in the length between the end of the contact tube and the work would reduce current.

They are identifyable as CC/CV by what they do.

Miller explains *adaptive* GMAWP this way in one example:
"“hybrid” CC/CV (constant current/constant voltage) process that overcomes virtually all of the limitations of older and competitive pulsed MIG technology. Accu-Pulse solves DTR’s welding problems in several ways. First, it adjusts the current to a predetermined level at the beginning of each peak and background phase (see Fig. 9). Once the target current is reached at the beginning of each phase, the CC control of the current turns off and the CV control loop turns on. The current floats within a limited range based on the actual arc condition present and the voltage is kept constant allowing Accu-Pulse to maintain a much shorter actual arc length" http://www.millerwelds.com/resources/articles/Auto-Axcess-multi-MIG-gmaw-welding/

Miller, Lincoln, ESAB, Fronius.... It doesn't matter.. If arc length (a function of voltage) and current, both adapt to operator changes by keeping arc length and amperage constant... The power supply MUST be delivering CC and CV..

The various manufacturers certainly have different wave forms to achieve similar ends. ... But to wrap it.. All GMAWP power supplies are CC/CV this is not even a question. They are what they are.. And.. All GMAWP arcs out there in the market produce both CC and CV attributes.. Case closed :)

By ssbn727 (*****)

Date 11-11-2009 07:46

Hi Larry!

You mean all of the newer GMAWP power sources do, but not necessarily the older versions of GMAWP power sources because not all of them had the capability to do what you explained back then and you would be surprised how many folks still have the older model (pre-adaptive/synergic) power sources still hanging out in their shops. And you will also find some places using both types of power sources which can really complicates things with respect to maintaining parameters and calibration... Throw in some unstable primary input power being fed into the facility and it can drive you to start pulling your hair out of your head because in certain locations, the power service can fluctuate sometimes to more than 10 VAC either way which would then go beyond the limits of power factor correction and as a result, cause the parameters on these newer power sources to act really goofy from such changes.

The only way to prevent that from happening is to install some expensive electrical equipment that many shops balk at because of their own ignorance, and their main excuse will be something like this: "Well, with my older machines I don't have these problems... Why should I have to buy all of this additional equipment just to run these newer power sources which are so darn sensitive to input voltage fluctuations when the older machines I have don't give me such grief???" too many fab shops think with this sort of mentality and end up either closing up shop because they chose not to adapt, or they do adapt and their only regret is that they didn't do it sooner, but because there are still too many shops out there that operate this way, it will take some time before all of the code committees welcome the newer and better power sources into their world even though some are already starting to do just that.

"God grant me the serenity to accept the things I cannot change... The courage to the change the things I can... And the wisdom to know the difference. ;)"

Respectfully,
Henry

By Lawrence (*****)

Date 11-11-2009 12:54

Correct Henry.

I mentioned in an earlier post that 90's style power supplies like the Maxtron and ArkPac were strict CC GMAWP power supplies.

One way to tell the difference is that the newer *adaptive* units have only two control knobs.. Wire feed speed and a second for trim..

Non adaptive Non-synergic units would require all parameters.. (peak current, background current, pulse width, frequency, voltage, etc) to be adjusted each time the wire feed speed was adjusted or the contact tube to work distance changed. (a real pain if you remember) MMP pulser pendants attached by 17 pin connecter to the feeder afforded the operator control of all parameters individually... Which would be fine if the operator was also a rocket scientist with the phyisical reflexes of Anderson Silva.

I can tell you that if anybody is trying to run one of those machines today... for manual welding.. They are wasting their time. I'll bet you Henry that 99.5 % of those old CC only GMAWP units are either on the scrap pile or the pulsation option is switched to the off position.

By ssbn727 (*****)

Date 11-11-2009 19:01 Edited 11-11-2009 21:27

Hi Larry!

I bet the pulsation option is turned off on 99.999% of them! ;) I mean, this is what I used to see on almost all of them back in the early eighties when I used to service equipment in the Greater NY metro region which could easily be looked at as a microcosm of what goes on all over the US, and I used to shake my head & chuckle every time I used to see that!!! :) ;) ;) I still see the same these days too!!! :) :) :) LOL!

Btw, they were CV power sources with the pulsing option built right into the power source and I'm not talking about the older inverter type power sources like the Powcon's with the remote pulser units you're talking about which were out in the market way before the Miller, Linde/L-Tec(Present day ESAB), or the Lincoln units... I'm talking about the older transformer-Rectifier CV power sources, and the reason why most folks turned the option off was because the pulsing option back in those days really were limited to maybe having the capability of 240 hertz maximum and this was only useful in very limited applications which were far and few in between.

I was working repairing these power sources back then when the whole paradigm shift of offering inverters as opposed to the old tried and true transformer-rectifier power sources started to become the trend... I can remember all the complaints about how the high pitched sounds were a pain in their ears, but they liked the way the darn thing would weld, yet would always think that they were being cheated on the price because they could get three times the amount of a machine if they stuck to a traditional power source instead!!! LOL :) :) :)

Of course I would just ask them if they noticed if their electric bills were lower after using the inverters over the older transformer-rectifier units, and their response was always: "Yeah! I didn't know they were so good on AC!!! ;) :) :) LOL!!!;) Yes Siree!!! Back in the days when things started to change was when I saw it occur first hand, and yet it seems just like yesterday! ;)

Respectfully,
Henry

By HgTX

Date 11-11-2009 14:36

Here's my take.

Right now, the code as written doesn't have restrictions on GMAW-P. Maybe it should. Maybe it's broken. That means that if a user of the code feels like GMAW-P *ought* to be qualified rather than prequalified, they're up to their own sense of right and wrong to do that, rather than relying on the code to force them to. It's hard for me to have a sense of what ought or ought not to be prequalified, since I live in D1.5 where almost nothing is prequal.

I'm not a member of the D1.1 qualification task group, but I've brought this up with them. Maybe something will change, maybe it won't.

Hg

By Lawrence (*****)

Date 11-11-2009 15:24 Edited 11-11-2009 15:27

I think thats a reasonable way to look at it too. (with the code such as it is now)

But I can envision an outside auditor taking a non-compliance view to GMAWP as far a pre-qualified status and having some pretty good ground to stand on.

Still think an interpretation should be made so that compliance is not driven by a "feeling" one way or the other.

Code should be black or white... GMAWP either is pre-qualified or is not pre-qualified. If you are using it with a pre-qualified WPS you are in compliance or you are not in compliance. It would be nice to know for sure eh?

By bozaktwo1 (***)

Date 11-11-2009 17:48

I would hope that the next revision of D1.1 clarifies this a bit, because I am looking forward to upgrading some of my technology to GMAWP here over the next few years. If not, I'll still upgrade but will have to qualify my procedures. Not a back-breaking chore exactly, but the stuff we do is steel, nothing gets much simpler than that.

By HgTX

Date 11-12-2009 15:55

The clarification may be less prequalification for GMAW-P than is available to you now.

Hg

By HgTX

Date 11-11-2009 21:34

What provision would the auditor say you were in noncompliance with? The code makes no distinction between spray, globular, and pulsed spray. The designation "GMAW-P" doesn't appear, nor do designations for spray or globular transfer modes.

Hg

By Lawrence (*****)

Date 11-11-2009 21:44

Thought I 'splained already.

If the power supply produces anything other than CV current for GMAW the WPS cannot be prequalified.

By 803056

Date 11-12-2009 04:36

Time to pull out the handy dandy oscilloscopes.

Best regards - Al