Pulse MIG, essential variable?

[Supe]

Is using pulse with MIG considered a change in essential variables under AWS code? I'm unsure as it is still a spray transfer.

[MoonRise]

My opinion, Yes.

And the variables of the pulse time and waveform(s) are variables as well, not just that fact that it is pulsed.

[Supe]

Anyone else have an opinion on the matter? AWS terminology tends to lean towards SS, globular, and spray. I don't necessarily believe that pulse shouldn't be classified separately with a MIG process, but I need some cold hard facts here. Trying to help a friend out who in theory would need to requalify ALL of his procedures.

[A_DAB_will_do]

I will second Moonrise's opinion. Yes, pulsing is an essential variable in the WPS.

I can't quote you chapter and verse from the code. But in my opinion pulsed MIG is a fundementally difference welding process because it enables a weldor to create welds out of position; welds that can't be accomplished(generalization) by short circuit transfer or standard spray transfer.

[lewray]

I third that. The pulse is definatley a varible on the WPS.

You could always create your own WPS to include pulse. Im sure you would hate to go to that trouble though.

[qaqc]

Supe,
From what I understand pulsed GMAW is not prequalified due to the fact that it is not a true CV power supply. It will run CC at start up. Hope that helps as a code answer

[Go1lum]

Originally Posted by qaqc

Supe,
From what I understand pulsed GMAW is not prequalified due to the fact that it is not a true CV power supply. It will run CC at start up. Hope that helps as a code answer

The only GMAW wire transfer mode that is not prequalified under D1.1 is short circuit.
Supe i don't know about that it's tricky. i'm goin to say yes. you need to requalify since changing to pulse would probably change the current. The codebook only allows 10% increase or decrease in current and 7% change in voltage and since you may need to change the shielding gas.

[Supe]

When you look into it, this one definitely isn't as cut and dry as one with "common sense" would think. Various different AWS codes interpret it differently. Some appear to distinctly separate it, others would tend to sneak it in with spray assuming the background current meets those output parameters of +- 10%/7%.

Under D14.4 which I was particularly interested in for helping out a friend, it would appear that it is considered an essential variable requiring requalification of the joint.

[Fat Bastard]

I looked through my D1.1 I don't find anything saying one way or the other.

My opinion if not directly prohibited it is allowable.

[Go1lum]

I just consulted with my teacher on the question (He is a CWI) and we referenced the D1.1 code book. Pulse MIG is an essential variable. Table 4.5 says a change in wire transfer is an essential variable. Since pulse is its own wire transfer then yes your friend needs to requalify his procedures.

[qaqc]

Originally Posted by Go1lum

The only GMAW wire transfer mode that is not prequalified under D1.1 is short circuit.
Supe i don't know about that it's tricky. i'm goin to say yes. you need to requalify since changing to pulse would probably change the current. The codebook only allows 10% increase or decrease in current and 7% change in voltage and since you may need to change the shielding gas.

Go1lum,
Look at AWS D1.1 3.2.4 (06) it is talking about the power supply, not the transfer mode. To be prequalified the supply needs to run CV only. Pulsed runs in CC and CV.

[gaustin]

Pulsed arc is shown on the WPS form for D1.1 and is addressed as a variable so If his procedures were qualified by testing, then requalification would be needed.

If the procedures are prequalified, the only transfer mode that is NOT prequalified is short circuit. However new prequalified WPS's would need to be prepared .

There is my opinion.

Have a good day

[Supe]

Originally Posted by Go1lum

I just consulted with my teacher on the question (He is a CWI) and we referenced the D1.1 code book. Pulse MIG is an essential variable. Table 4.5 says a change in wire transfer is an essential variable. Since pulse is its own wire transfer then yes your friend needs to requalify his procedures.

But the question at hand is whether D1.1 or other AWS codes draw a definitive distinction between pulsed MIG and spray transfer. Even the sample D1.1 WPS in the Annexes show only Globular, Short Arc, and Spray as the three transfer types, with "Pulsed" being listed as a current type.

Also, while the pulse process has distinctive CC characteristics, companies like Lincoln (Miller is more forthright and honest about it) say that their arc characteristics are "proprietary information," and as such can't be labeled as a CC machine.

If being qualified to B2.1 standards, the answer is clear-cut. Other AWS publications be it D1.1 or otherwise are much more open to interpretation.

[gaustin]

Though "Pulsed" may be considered a current type, D1.1 says

13) A change in type of current (ac or dc) or
polarity (electrode positive or negative for dc
current)

So that does not apply to Pulsed Transfer as I read it. Because of the confusion and lack of clarity in the code I have always just qualified Spray-Pulsed as a process.

Of course then you get into addressing frequency, background current, peak current, pulse duration, percent peak etc..

Good Luck !

[Go1lum]

Originally Posted by gaustin

Though "Pulsed" may be considered a current type, D1.1 says

13) A change in type of current (ac or dc) or
polarity (electrode positive or negative for dc
current)

So that does not apply to Pulsed Transfer as I read it. Because of the confusion and lack of clarity in the code I have always just qualified Spray-Pulsed as a process.

Of course then you get into addressing frequency, background current, peak current, pulse duration, percent peak etc..

Good Luck !

Table 4.5
14) A change in type of current (ac or dc) or polarity and mode of transfer. (GMAW only)

Pulsed is not a current type, it's a mode of transfer. "pulsed spray transfer" is the correct name and yes it's still a spray transfer but in pulse metal is only deposited at amperage peak. True spray transfer has metal being deposited all the time. So pulsed is a different mode of wire transfer and is an essential variable. As for it using CC and CV that is false as far as i'm concerned. According to the lincoln book " plused GMA welding is a modification of short arc and spray transfer welding." both of those transfer modes are strictly CV and is pulse is a modification of both were does CC come into play.

[gaustin]

I don't think pulsed is a current type. Its just that in D1.1 annex it appears that way. GMAW Pulsed is a transfer mode and should be addressed on the form as such. As to why it is next to current , beats me .

I think power supply type as CC or CV is just that. A constant current machine maintains (or tries to maintain) a given amperage regardless of voltage. A GMAW power source though the current may vary, is a CV power supply from what I understand.

The "constant current" means the current is constant regardless of voltage.

I am accepting any corrections for this as I haven't looked into this in awhile. I will read up some more and correct myself if necessary. My point is that just because a machine pulses voltage does not mean it is NOT a CV power source.

[Go1lum]

Originally Posted by gaustin

I don't think pulsed is a current type. Its just that in D1.1 annex it appears that way. GMAW Pulsed is a transfer mode and should be addressed on the form as such. As to why it is next to current , beats me .

I think power supply type as CC or CV is just that. A constant current machine maintains (or tries to maintain) a given amperage regardless of voltage. A GMAW power source though the current may vary, is a CV power supply from what I understand.

The "constant current" means the current is constant regardless of voltage.

I am accepting any corrections for this as I haven't looked into this in awhile. I will read up some more and correct myself if necessary. My point is that just because a machine pulses voltage does not mean it is NOT a CV power source.

you are not pulsing voltages. you are pulsing amperage. as far as the CC and CV pulse is strictly constant voltage. yes you are pulsing the amperage but if you CC to pulse then how are machines like the MM350P capable of pulsing when they are CV not CC power supplies.

[Engloid]

Originally Posted by gaustin

Pulsed arc is shown on the WPS form for D1.1 and is addressed as a variable so If his procedures were qualified by testing, then requalification would be needed.

There are many things shown on the AWS's sample WPS that are not considered essential variables. That said, you can conceivably produce more than one WPS from the same WPQ. For example: Think of how you can qualify the procedure for a carbon steel plate test with stainless filler, and then the welder is qualified to weld both materials. Likewise, you can to the PQR for this, and then write WPS's for carbon to carbon and for stainless to stainless. Correct?

Where's JTMc? He seems to know quite a bit about this stuff without having to look it up....or maybe he's not as lazy as the rest of us and he looks it up.

[David R]

You guys figure it out. I can't see how you could pulse spray with out a CV power supply.

I think its gotta be a CV, but look at the wave forms in the link.

Lincoln and Miller website say it changes the current.

http://weldingweb.com/showthread.php...ght=pulsed+MIG

After looking for a while, the amps do the work. The amps change when I change the settings.

Look at min and max amps for different settings and look at pulse width ( the space between the amp pulses)

Also the volts are in uS or Micro seconds, not milliseconds like the amps. I may be looking too close.

I can do this again if you all want on volts but slowing down the time to MS.

Maybe I should do an amp trace of MIG.

To answer the original question, different gas and surly different amp settings. My machine reads out in average amps and average volts for 5 seconds after I stop welding.

I have NO IDEA of the answer to the original question, just some observations.

David

[gaustin]

Originally Posted by Engloid

There are many things shown on the AWS's sample WPS that are not considered essential variables. That said, you can conceivably produce more than one WPS from the same WPQ. For example: Think of how you can qualify the procedure for a carbon steel plate test with stainless filler, and then the welder is qualified to weld both materials. Likewise, you can to the PQR for this, and then write WPS's for carbon to carbon and for stainless to stainless. Correct?

Where's JTMc? He seems to know quite a bit about this stuff without having to look it up....or maybe he's not as lazy as the rest of us and he looks it up.

Incorrect. AWS D1.1 does not allow a procedure to be qualified on carbon steel with stainless filler metal and then that same PQR support stainless to stailess. Stainless steel is not within the scope of D1.1. I am pretty confident no other codes do either. You can produce more than one wps from a single PQR as you indicated. I am just not aware of material types allowing that change for procedure qualification.

For performance qualification the same goes for D1.1 since stainless is an unlisted material. You may very well be thinking of the allowances by ASME . In the case of ASME a welder who tests on carbon steel GTAW is qualified to GTAW on SS with Carbon or SS filler metals. This allowance is based upon the fact that the filler metal F Numbers are the same for carbon and stainless filler metals (F6) this is not the case for SMAW. (F4 and F5).

I agree that many things on the AWS forms are "extra". I think "pulsed" on the sample form is in reference to transfer mode and not current. Transfer mode is addressed by the code and would require requalification of the procedure should the transfer mode change.

Pulsed transfer mode is also prequalified by D1.1 . All modes other than GMAW Short Circuit are prequalified.

So the answer to the orginal question is YES if another transfer mode was used. However also consider that he may be able to write a prequalified WPS for some siituations if he is working with the allowances of chapter 3.

I think pulse welding can lend itself to some of the non fusion discontinuities that are produced by short circuit transfer. Just an opinion based on a few inspections performed and welders tested. The synergenic machines now in use can minimize this because of filler metal specific programs that control t he various parameters.

Currently the variables for pulsed transfer are not addressed by D1.1 as far as what I have read but I do not have the 08 code so my info may be out of date.

[Engloid]

The concept behind pulse MIG is that it puts out pulses that create small droplets from the end of the electrode. These droplets are already melted prior to meeting the puddle. With short circuit transfer, they are not. That's the significant difference in the two.

[qaqc]

plagiarized:

AWS D1.1 has a note on
"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"

Now.... I believe the committee intended this directive specifically to address suitcase welders run off engine driven power supplies that deliver constant current power, which is inconsistant at best for GMAW or FCAW.

Nonetheless, EVERY GMAW-P power welder on todays U.S. Market is powered by CC/CV power source... Miller admits to using both CC and CV power on their synergic GMAW-P pulsation programs... Lincoln is another matter.. .They are holding their data very close to the chest, saying this information is "propriatary"...... >shrug<

I think if you look at the most basic physics of a synergic GMAWP welding arc, it is very clear that it exhibits attributes of both constant current and constant voltage.. Miller actually explains it very nicely in some of their product literature. The newer GMAWP machines are anything but basic but this is all the more reason to suspect that they are CC/CV

I wrote D1 committee and was given several polite unofficial notes in return suggesting that there are many GMAW-P machines out there running on CV power alone... I just disagree with this view and suggest that the facts are that there are no strictly CV pulsed mig power supplies out there on today's marked (there are some older 80s and early 90s CV pulsers). I asked them to address this question officially to the proper subcommittee but that takes time and I think they are still working on it.

I know lots of folks who are using prequalified WPS's with GMAW-P, by virtue of the reasoning that GMAW-P is a spray transfer mode and spray transfer is a pre-qualifed process.....and lots of others who think that all GMAW-P procedures must be qualified by testing for the reasons already mentioned....

I wrote Ed Craig about this thinking he would know the truth if anybody did... And was surprised that he did not give a fig about CC or CV... all he cared about was mode of transfer and weld quality... I see his point.. but it does not answer the question of compliance in the face of an audit.

I'm pretty sure that future editions of D1.1 will half to address this more directly.

[gaustin]

A CC machine will produce only a VERY small change in amperage with a major change in voltage. That is a characteristic of CC.

A CV machine will show a significant change in amperage with an increase in voltage.

For a Semi Auto process to have an increase in amperage as is with pulsing, one of two things have to happen. Either the resistance goes down (increase in wire feed speed) OR the voltage goes up.

It is possible that something has changed regarding the definition of CC and CV.

Being "Constant" if it it be current or voltage has NOTHING to do with the current going up or down as far as the definition of a power source type.

So for a pulsed arc power supply to truly pulse either the WFS or the voltage must vary . If the voltage is to vary, it must be of a significant amount to increase the amperage.

Its my opinion that a CV machine is used for pulsed arc because of the volt/amp curve generated by a CV machine vs a CC machine.

The "pulsing" has NOTHING to do with the classification of the power source.

[ojcool]

What would be the difference in pulsing vs say, the frequency adjustment? To me the frequency is a kind of pulsing .

Does anyone know where I can find some information that discusses all the different settings and what they do on a AC/DC HF SW machine? Just so I can get a better grasp on what you guys are talking about.

[Country Boy]

Pulse MIG, essential variable? No it's not a recognized variable of any sort.

Pulse(ing) is more accurately considered an "Electrical Characteristic" that influences the "Transfer Mode" than a "Transfer Mode". This is absolutely the case in the ASME world where a client of ours was recently forced to rewrite and requalify a procedure in the middle of a NB audit.

There are GMAW Pulse Software Programs and entire systems (Lincoln's SST for instance) where the Mode of Transfer is Short Circuiting and others where the mode of transfer is Spray. In both ASME Section IX and AWS D1.1 there are penalties/restrictions if the mode is Short Circuiting.

AWS D1.1 is vague on this, so be careful in how you approach Pulse GMAW procedure qualification/review. Get on the phone and ask the programmer what the Mode of Transfer is, get it in writing and go with that. Work safe, don't modify forms and insert variables that aren't clearly defined and expect other folks to understand what's meant, that's Code Committee work.