GMAW and GMAW-P for qualification

By Lawrence (*****)

Date 02-11-2008 21:48 Edited 02-11-2008 22:02

Welcome to the forum Wiggles

Depends on the code.

ASME Section IX doesn't seem to differentiate between GMAW and GMAW-P or FCAW for that matter.

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.

By fbrieden (***)

Date 02-12-2008 05:55

Isn't that considered an essential variable?

By Lawrence (*****)

Date 02-12-2008 12:42

I don't have my D1 handy this moment... but I think polarity is the essencial variable. I don't think pulsation in GMAW is mentioned as an essencial variable.

By Kix

Date 02-12-2008 13:19 Edited 02-12-2008 13:24

In D1.6 (structural stainless) the essential variable is a change in the mode of metal transfer from globular,spray, and pulsed spray to short circuit. So does that mean if you qualify it in short circuit that you can switch to pulse if you want? In D1.1 a change in the just the mde of metal transfer for GMAW is considered an essential variable as well as polarity. Pulse is considered one of the 4 modes of metal transfer so I'd say that D1.1 is considering a change from GMAW to GMAW-P an essential variable. What about vice versa?

By wiggles8879 (*)

Date 02-12-2008 14:52

Thanks for everyones responses. I should have mentioned before (remember im a noob) that we qualified all of our WPS's to a DCEP setup. I think that means (correct me if im wrong) that if you switch to GMAW it would be a change to CC/CV? I was a welder for 10 years before getting my CWI so not real familiar with the whole WPS/PQR thing yet and just want to make wure im not doing stuff wrong for my employer. The welder in me says that GMAW-P and GMAW are basically the same thing other than that there is more spatter from GMAW than GMAW-P and that GMAW-P runs hotter than GMAW so i wouldnt be able to use the same WPS because theie would be too much variation in the settings between the two. Thanks in advance for any help anyone can give me its a confusing topic for me right now.

By Kix

Date 02-12-2008 15:56

DCEP and DCEN are not categorized with cc/cv. You qualified you WPS's with DCEP (direct current elctrode positive) because that what you run the GMAW process on. The machine you were using was a constant voltage power source. CC=constant curent / CV=constant voltage. If you switch from GMAW-P to just plain GMAW you are changing a mode of metal transfer. What Lawrence was saying is that in the pulse transfer your using CC and CV which miller talks about and Lincoln trys to shy away from apparently I think. I did not know this either about pulse. The codes are using the different modes of transfer as essential variables. D1.1(2006) requires requalification of a WPS if you change the mode of transfer and that all it says. Other codes are more specific. The way I read it is that per sec 4 Table 4.5 PQR essential variables requiring WPS requalification on page 138 # 14 says a change in the mode of transfer. I don't think Pulse is considered prequalified in D1.1 (2006) , but you never told us what code you're working to. So if you are using D1.1 and your WPS's are for GMAW then you will have to qualify new procedures for GMAW-pulse.

By wiggles8879 (*)

Date 02-12-2008 18:12

thanks everyone for their input it has been very helpful. Yes i am qualifying them to D1.1 sorry for the mixup i forget their is so many different codes. I think i have it right now i have to requalify them because the code is pretty vague on the subject of pulse so i am running a test where i work to see if its feasable to switch to GMAW. The welders (understandably) dont like it but i think its best to just requalify to GMAW.

By motgar

Date 02-12-2008 15:15

I would have to agree with you wiggles. Looking at;

ASME Section IX;

QW 350 Welding Variables for Welders

QW-355 Semi-Auto GMAW including FCAW Essential variables

Ref. Paragraph QW-409.2 Electrical: A change from spray arc, globular arc, or pulsating arc to short circuiting arc, or vice versa

AWS D1.1:2006

Table 4.12 Welding Personnel Perfomance Essential Variable Changes Requiring Requalification

(1) To a process not qualified (GMAW-S is considered a seperate process)

AWS B2.1:2005

3.6.1.1 Welders

(9) for GMAW, a change from spray transfer, globular transfer, or pulsed spray welding to short-circuiting transfer; or vice versa

By motgar

Date 02-12-2008 19:19

I am wondering this now. Are you asking about welder performance qualification or procedure qualification? You stated above that the previous CWI qualified the welders in GMAW. All other variables aside for now. Are you asking if a welder, who is qualified for short-circuit GMAW, qualified to use pulse GMAW?

By wiggles8879 (*)

Date 02-13-2008 17:33

motgar ill try to clarify i am looking at whether i need to requalify my welders to GMAW globular. They are welding GMAW-P spray right now. If i have to requalify them i think i also have to requalify all of my WPS to reflect that before i requalify the welders to make sure the perameters will work. Changing the mode of transfer I believe means you have to redo the WPS. Please correct me if im wrong.

By welder5354 (**)

Date 02-14-2008 05:24

There are only about 5 references to GMAW in the ASME section ix code.
So, if GMAW was qualified, except for short-circuiting mode, then why would it not be qualified for GMAW-p.?

QW-304 Welders
Except for the special requirements of QW-380, each welder who welds under the rules of
the Code shall have passed the mechanical and visual examination prescribed in QW-302.1 and
QW-302.4 respectively. Alternatively, welders making a groove weld using SMAW, SAW,
GTAW, PAW, and GMAW (except short-circuiting mode) or a combination of these processes,
may be qualified by radiographic examination, except for P-No. 21 through P-No. 25, P-No. 51
through P-No. 53, and P-No. 61 through P-No. 62 metals. Welders making groove welds in P-
No. 21 through P-No. 25 and P-No. 51 through P-Np. 53 metals with the GTAW process may
also be qualified by radiographic examination. The radiographic examination shall be in
accordance with QW-302.2.
A welder qualified to weld in accordance with one qualified WPS is also qualified to weld in
accordance with other qualified WPSs, using the same welding process, within the limits of the
essential variables of QW-350.
dh

By Goose-em (**)

Date 02-14-2008 20:07

So let's say your WPS uses 28 volts, an essential variable, no? If you move outside the range listed on the WPS then the procedure will need to be requalified, correct?

So without all the pulse mumbo jumbo let's look at it from a different perspective.

Pulse typically does not give you a voltage parameter to adjust but instead gives a trim control which is not voltage.

If you are measuring the voltage during GMAW and it says 28 and then measuring it with GMAW-P and getting 28 the variable has not changed but if you set the trim to 28 it would change as trim isn't voltage.

Therefore in order to utilize the same procedure without testing you would need to measure the voltage using a meter and determine if the voltage range falls within the range given on the procedure if not rewrite the procedure.

Of course pulse behaves much differently than traditional GMAW so if it were me I would retest just to ensure a sound weld was being made. I would also change my WPS to read trim instead of voltage as that is a parameter that the welder can control and recieve feedback from. How would the welder know if he were welding at a certain voltage?

I would also suggest providing training to my welders on the new process, yes it looks like GMAW but it doesn't act like GMAW.

By js55

Date 02-14-2008 21:10

Voltage is not an essential variable for any of the 5 main fusion welding process (GTAW, SMAW, SAW, FCAW, and GMAW) under ASME Section IX.
You gotta get to ESW, LBW, etc., before it becomes essential.