Hi Bill,
I have seen what you are experiencing, but I have no advice as I'm not at all familiar with the short arc GMAW, but I am interested in any advice that you may receive. Keep me posted on any info you receive on this.
Thanks,
John Wright

Increasing CO2 percentage will increase penetration but will also increase amount of spatter you will see. If procedure was qualified using 100 CO2 why did you change and did you requalify? You will not be able to get into a spray transfer with any gas that contains 25% or greater CO2. More than likely you are in a globular type of transfer which is good for penetration but alittle on the messy side. Amps and volts sound alittle low. Could try bumping it up a couple of volts as well as increasing wfs up maybe another 50 to 75 ipm. I would also favor the thicker walled material just a bit.

Hope this helps

kam

In my opinion. welding .625 thick material with short circuit GMAW is definitely pushing things. I think you would be better off with spray transfer or Flux core, or metal core.

Since you are doing a fillet weld, there doesn't seem to be any reason to stay in short circuit mode. Why not try spray, as it would result in a quicker weld anyway? If you need to carry a smaller puddle so that you don't get sagging from rotation, try the metal cored wire that H.Dibben suggested as you could get into spray at lower amps than solid wire. However, if you do stick with short-circuit GMAW, then preheating the thicker side should help significantly. It essentially makes the thicker part act thinner. How much you need would have to be determined by experimentation.

Hi Bill,

While FCAW would work as well, I suggest that you consider staying with the GMAW for the following reasons:

No need to change electrode inventory
Operator familiararity with GMAW
No need to clean slag
Reduced spatter clean up
Root Pass installation

In explanation, proper technique combined with the GMAW spray arc transfer mode should cure your LOF problem.
You can qualify a new WPS using the following example as a guideline:

Change shielding gas to 90% Argon / 10% CO2
(You can achieve spray transfer readily with at least 85% argon in the shielding gas, but the higher the Argon percentage used = the lower voltage required to achieve spray transfer. The less voltage required to achieve spray = the less strain on the duty cycle of your welding machine. 90/10 works best for my applications. You might try both 90/10 and 95/5)

Continue to use the short-circuiting mode for installation of the root pass.
(While the whole idea of changing over to Spray transfer is to help you increase penetration, this is not helpful when trying to put in the root. This is assuming of course that your joint prep is a butt weld with no backing. If backing is used, then drop the Short Circuiting transfer all together. Using 90/10 gas, short circuiting transfer is achieved with a voltage setting below 24V. You'll need to try a couple of test pieces to find the best setting your Operators are comfortable with. I suggest you start around 19V and go up from there.)

Ensure proper root pass exterior profile prior to application of 2nd pass.
(You need a flat or slightly concave surface at the base of the bevel before filling. If the top of the root pass is humped up in the middle, or very convex, you wind up with sharp valleys on either side, close to the bevel walls. Often, if these "sharp valleys" are welded over, LOF or voids will be left in the weld. This also applies to subsequent passes. If a pass is placed in the bevel that only fuses with one bevel wall, and a sharp valley is left between that pass and the other bevel wall, then LOF will likely result. These "sharp valleys" may be avoided by proper technique and/or ground out when necessary. Additionally, you'll find that excessive weaving inside the bevel will also cause LOF voids at the root of the bead. If the arc is allowed to wander up the bevel wall during a weave, the puddle has a tendency to "bridge over" and a small void is created the root of the bead. This void has an aggravating tendency will continue along with the puddle, sometimes all the way to the end of the bead, leaving a long narrow void that is not visible from the surface. For this reason, it is not advisable to try to weld in the bottom of a deep narrow bevel. It is best to widen the bevel enough to prevent accidentally allowing the arc to climb the bevel wall.)

Fill and cap with Spray Transfer mode.
(Using 90/10 gas, you can achieve spay transfer at a voltage setting above 24V. Again, try a couple of test pieces to find the setting that works best for your Operators. You'll find that the exact setting that matches with the electrical characteristics of your welding machine will result in no or very little spatter. This setting will also result in a very flat bead profile with excellent fusion along the toes. After filling the bevel, you'll want to turn the voltage down before capping, but still stay in the spray mode. This will help the Operator place a slightly convex cap bead while reducing the chance of undercutting the base metal.)

Good Luck and please let us know how it works out for you.
Tim Gary

Hi Bill!
There's no doubt that you'll get some good advice here with respect to the GMAW process...
However, if you want to get some answers to your specific situation then go visit this site: http://www.weldreality.com
When you enter the site, click on the link "weld product questions" and describe your situation to Ed Craig himself.
Ed will definitely set you straight but he may push his training materials on you which btw is'nt a bad idea to purchase anyway (prices are reasonable considering the wealth of knowledge inside)...
Post your query verbatim in Ed's site and you'll get an answer usually the next day.
I personally have to agree with H. Dibben on his advice to switch to spray or flux cored. As far as globular transfer is concerned; you might as well "stick" weld because that is the type of metal transfer in SMAW!
100% CO2 short arc is definitely going to give you more penetration because it's a reactive gas (hotter arc plasma) as opposed to a 75/25 argon/ CO2 mix which is mostly inert and that's why you have to set your welding parameters out of the true short arc range into globular transfer but will it be sufficient to eliminate LOF especially on the thicker part - is questionable. Preheating the thicker part will help also...
GRoberts and Tim Gary's advice is also excellent even though Tim's advice relates to a groove instead of a fillet weld.
Bottom line is to visit Ed's site because in my opinion he knows more about GMAW/FCAW processes and weld process training than anyone else in the business as you'll find out for yourself!

Respectfully,

SSBN727 Run Silent... Run Deep!!!