By electrode 
Date 11-22-2014 15:13
Edited 11-22-2014 17:35
Sir,
EDIT: As measured by your questions' cogency here's my personal answer:
"Yes..., no..., or yet... maybe?".
I hope you may understand what I mean, i.e. what do you expect?
My personal recommendation:
"To receive appropriate answer(s) or to avoid kerfuffle; please ask more specifically.".
Nadeem,
WELCOME TO THE AWS WELDING FORUM!!
Short and to the point, your question: Why is GMAW used?
Because of it's versatility, range of use, and multiple applications; the range of material thickness applications being very extreme. Because of no slag for clean up. And more.
But, more specifically to your follow up question: more spatter, porosity, and low quality compared to FCAW: not really. It's all in the material preparation and the exact combination of shielding gas, electrode classification, electrode manufacturer, and welding parameters employed.
GMAW in many situations will require more attention to pre-weld cleaning than FCAW. But, it will require less time to clean between passes and after final pass as there is no slag.
Spatter- not with the correct shielding gas and a good grade of electrode. Buy cheap and reap the results. Cheap gas: CO2, more spatter. More expensive gas: Ar/CO2 75/25, little spatter especially with welder set correctly and running a good quality electrode. More spatter, more clean up time.
More than once I have sent electrode/wire back because I or my son forgot to specify and they sent me the cheapest stuff on the supply floor. Won't use it; you get what you pay for.
If your question is because you are or have experienced a problem, try changing some of the items I listed and take Al's post into consideration with the multitude of process variants: Spray, Short Arc, Globular, and Pulsed. I recommend Spray for heavier materials and structural where a possible code involvement will not allow some of the others or Short Arc for thin light weight steels in non code applications.
Both have a nice looking finished weld profile appearance if all is set right. If you could give us more info or have more questions please continue.
He Is In Control, Have a Great Day, Brent
Hi Nadeem,
As both Al and Brent have already mentioned, there are pro's and con's for both processes... For instance, GMAW is a process that may not work so well out in the elements without any protection from the wind, and with FCAW-S there's no need to concern so much regarding the wind factor because there's no shielding gas required for FCAW-S... Although with GMAW, the quality of the welds will be equal or even superior to FCAW and visa versa if all of the factors and variables mentioned by again both Al and Brent are optimized... And the welders are proficient enough in their own operating skills to maintain optimal parameters because if they're not properly trained in both processes or they have been welding exclusively with only one of the processes instead of both, the resulting weld quality from the process in which they have had less arc time with may turn out to be disappointing, insufficient and unacceptable...
The bottom line is that both processes have their pro's and con',s and it is just as important to consider how and in what environments either of these processes have an advantage, or a disadvantage when one considers application, and environmental factors and the limits of both in each process... Then we must also consider operator proficiency as well, along with proper technique which is in the same category as operator proficiency... Finally, add all of the factors and parameters mentioned by both Al and Brent, and then sprinkle in what I described as the other factors and parameters together in order to make a checklist if you will... Use it to help you decide ultimately which process to select from the two for the application for optimal results.
Respectfully,
Henry
GMAW has four widely recognized transfer modes; short circuiting transfer, globular transfer, spray transfer, and pulsed spray transfer.
Each transfer mode has its own characteristics and both positive and negative characteristics. Let's consider each transfer mode when carbon and high strength low alloy steels are being joined.
Short circuiting transfer: low voltage, low wire feed speed (low current), low travel speed, low heat input, with the advantage of welding in all positions. Excellent for thinner materials where high heat input is not necessary. The disadvantage is the low heat input is prone to fusion type defects/discontinuities such as incomplete fusion, incomplete joint penetration, overlap, etc. Careful selection of welding parameters, close monitoring of the welding parameters, and limiting the process to thinner materials optimizes the opportunities for successful welding. Insufficient inductance, excessive wire feed speed, insufficient electrode extension can result in excessive spatter.
Globular transfer: higher voltage, higher wire feed speed, higher travel speed, higher heat input using straight CO2 or CO2 rich mixes provide deep penetration, wide weld beads, higher travel speeds, but the transfer mode can produce some very ugly welds with objectionable spatter. Close control of the welding parameters and proper inductance adjustments with the correct electrode extension will produce welds with acceptable weld profiles. Welds are limited to flat grooves and flat and horizontal fillet welds.
Spray transfer: higher voltage, higher wire feed speeds, (similar to globular transfer) with argon rich shielding gas (80% argon minimum) will produce a weld bead with deep penetration, narrower profile (compared to globular), high heat input, smooth uniform weld bead, but it is limited to flat grooves and flat and horizontal fillet welds.
Pulsed spray transfer: Requires a power supply with pulsing capability, thus the power supplies can be two to three times more expensive than a conventional power supply. This transfer mode uses pulses of high current to facilitate axial droplet transfer after which the current drops to a back ground level (low current) during which time no metal transfer takes place. The number of pulses can vary for 20 to 2000 pulses per second. There are several variables that must be properly set and monitored. The electronics are complex and the parameters used for one machine model will most likely not produce satisfactory results with a machine produced by a different manufacturer. Most machines are too complex for the average welder to set without specific training. To circumvent this problem, many manufacturers preprogram the welders for the specific base metal, electrode diameter, and shielding gas to be used. The advantage is that the transfer mode provides the benefits of spray transfer, but permits the welding to be in all positions.
Best regards - Al
