Weld Procedure Specification GMAW ER70S-6 Globular Transfer?

Date 10-22-2009 14:54 Edited 10-22-2009 16:23

Dave,

What is the diameter of the ER70S-6 welding consumable?

In your gas mixture, is it 75/25 CO2 being the main gas? I have seen 75/25 with Ar being the main gas but, not the other way around. Maybe things are a bit transposed. Do the gas cylinders state what they are?

One should be able to achieve globular transfer with 75/25, Ar/CO2, gas mixture.

By aevald

Date 10-22-2009 17:03

Hello David, have you had a conversation with the welders on this one? Globular transfer isn't a preferred method for any types of welding from a welder's perspective. It is also likely that they won't be running in that mode anyway and you will probably see them short-circuiting whenever and wherever they can as soon as the QC walks away. Qualifying the short-circuiting might include some time and cost, yet I believe everyone will be happier if you bite the bullet and do so.
I don't know how familiar you are with the various modes of transfer for the GMAW process, yet of the 4 recognized ones, 3 are user friendly and the fourth of this group is the one that is very un-friendly, that one is globular transfer. Coverage gas types, machine types, voltages, wire diameters, amps/wire speed will determine mode of transfer for GMAW. Typically, short circuiting is the first mode that will be encountered on the lower end of the voltage spectrum and usually done with 80 percent or less of argon in the mixture or else 100% C02. Globular transfer is the next mode of transfer that will be encountered and normally occurs at medium to high voltages with gas mixtures of less than 80% argon. The spray mode of transfer can occur when gas mixtures are 80% argon or greater and at the upper end of the voltage scale. The last recognized mode of transfer is considered pulse transfer and is a combination of mainly spray and short circuiting with the possibility of some globular transfer occuring depending upon specific parameters. Another thing about globular transfer, since the metal transfer occurs across the arc in a globular fashion it is very erratic and unpredictable. The "globs" vary in size and transfer frequency and don't make for a nice even weld metal deposition, that is the main reason why I am wondering why you want to write a globular transfer procedure. There are tons of other variables that allow for overlap of all of these transfer modes based on gas types and machine parameters. Please forgive me if you are already aware of all of this as I am not trying to talk down to anyone. Just a bit for your consideration. Best regards, Allan

By Lawrence (*****)

Date 10-22-2009 18:58

There are alot of holes in the notion of Globualar for production of code quality work as you describe it.

Assuming D1.1 (prequalified)

1. Vertical welds shall be done with upward progression (3.7.1) (a tough trick with globular)
   1a. Have your welders themselves been qualified by testing using globular vert up? on plate or tube?
   A flat or horizontal spray transfer qual won't sufice.

2. You note a 22-28 volt range... Thats is a huge 20% range.. Table 4.5 limits voltage change to 7% for a given wire diameter.

So even if you could write a prequalified WPS for Globs, I don't see a slick way to get your welders out of position performance quals in line without more testing... They still aren't qualified for all positions no matter what open arc GMAW mode you use.

So if your welders current production quals are for spray transfer, it's hard to see how a non-spray (75/25) gas can apply for all positions.

Having said all that... Can Globular transfer be done in all positions?   Yes.. But it isn't easy and sidewall and spatter issues are common.

Maybe somebody else can find a loophole here. But it sounds to me like you either need to go the short circuit route, or write a wps for globs and test your welders for all position welding before you are going to be in compliance.

As Alan stated. I think the lowest spatter and highest welder happiness will come with short circuit.

By swnorris (****)

Date 10-22-2009 19:05

David,

75/25 is a very "known" shielding gas mixture….. for short circuiting transfer. I agree with Allan that you'd need at least 80% argon to be out of the short circuiting transfer mode. Factors that determine the mode of metal transfer are the welding current, wire size, arc length (voltage), power supply characteristics, and shielding gas.
To add to what Allan has said, with regard to the various modes, short circuiting metal transfer uses small wire diameters and operates at low arc lengths, low voltages and welding currents. The metal transfer occurs when an electrical short circuit is established as molten metal at the end of the wire touches the molten weld pool.
Globular transfer is a step up from short circuiting. the welding current and voltage are increased above the maximum recommended for short circuiting and the metal transfer will begin to take on a different appearance. The metal transfer occurs when the drops of metal that are typically larger than the wire diameter, move toward the weld pool under the influence of gravity. This type of transfer can be very erratic, can produce spatter, and can even short circuit at times.
Spray transfer occurs by increasing the welding current and voltage beyond than that of globular. When this is done, the metal transfer becomes a true spray arc. The minimum welding current at which this occurs is called the transition current. When the transition current is reached, small molten drops of metal are detached from the tip of the wire and projected by electromagnetic forces towards the weld pool. The transition current from globular to spray increases as wire diameter increases. For example, the minimum arc current for .030 wire is 150 amps. .035 is 165 amps, and .045, is 220 amps. Welding current, wire size, arc length (voltage), power supply characteristics, and shielding gas are all factors that determine the type of metal transfer. Short circuiting is rare with spray transfer, and there is very little spatter.
You mentioned that you didn’t want to use spray because it can’t be used out of position. That’s not entirely true. Spray is generally limited to welding in the flat position only because of the large weld puddle, but mild steel such as handrails, etc. can be welded out of position with spray when small weld puddles are used…. much like the welds used in handrails, when .035 or .045 diameter wires are used. My suggestion is to take this approach and use 98/2 shielding gas.
Pulsed spray welding is a variation of spray, with the current varying between a high and low value. The low level of current is below the transition current while the high level is well into spray. Metal is only transferred to the work during the period of high current. Usually one droplet is transferred during each high current pulse. Typically, only 60 or 120 pulses per second are used. Because the peak current is in the spray arc region, arc stability is similar to that of conventional spray arc welding. The period of low current maintains the arc and serves to reduce the average current. The pulse spray technique will produce a spray arc at lower average current levels than are required for spray arc welding. The lower average current makes it possible to weld thinner gauge materials with spray type transfer using larger sized wire electrodes than otherwise possible.
Again, my suggestion to you is to utilize the spray transfer mode using either an .035 or .045 diameter wire with 98/2 shielding gas.

By eekpod

Date 10-22-2009 19:50

I'm working from memory here, but I think I remember this coming up before, and the mode of transfer is not required to be on the WPS, and if that's the case, leave it off then there is nothing to argue about, and your inspector has no foot to stand on.
Although, that might be for FCAW, but check the table and see if it's required for GMAW. Good luck.

By david bean (**)

Date 10-23-2009 18:26

Yes
It looks like i would benefit from spray arc.

but is it cost effective??

By 803056

Date 10-24-2009 16:43

I believe the mode of transfer is an essential variable whenever GMAW is used.

Some welding standards place few restrictions of the use of globular, spray, or pulse spray transfer. However, most all welding standards do place restrictions on the use of short circuiting transfer. The mode of transfer is required to be listed on the WPS for the welding standards I work with, including AWS D1.1, D1.5, ASME Sections I, VIII, IX, and various pressure piping codes. As for AWS D1.1 (2004 because it is handy) transfer mode is listed as an essential variable in Table 4.5, item 13. Certain variable listed in Table 4.5 are applicable to the prequalified WPS even when the WPS is not qualified by testing. Annex IV and Annex H are provided for additional guidance when writting a prequalified WPS.

Best regards - Al

By Metarinka (****)

Date 10-26-2009 14:19

I can tell you right off the top of my head that globular transfer will be the default transfer mode for 75/25 gas unless the parameters are low enough to but it in short circuit. Guessing that your using a common wire size like .045 or .035 than you are most definately in globular transfer.

Is it recognized by code? I don't know

but from my own experience using the exact same wire and gas, it's not desirable to run globular transfer, although it's done at jobsites across the country every day.

more importantly spray transfer CAN be done out of position but it's not considered easy.