FCAW vs. GMAW

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Soooo I have been wanting to ask some experts as I'm not at that point yet in my life lol. I work with some thick material at work 3'' sometimes. I was brought on to lead up welding sense the company lost all 3 welders they had in a short period of time. Some of the guys know how to weld. But in my opinion shouldn't(arguing that 3'' plate doesnt need to be preheated) The guys were saying that the "good" welder they had would do a root pass of FC and do multiple passes of Solid wire until it matched print. Sometimes the print calls for an inch wide weld. Now I was always taught to do a root pass with GMAW and follow with FC until it meets print. I was kinda hoping someone could explain either one to be better than the other. Or even if FC is worth using at all. I get that it can do better outside, and on dirty surfaces. But its in a shop, so why the hassle of using 2 different welders?
Reply:I can see why flux core would work as a root pass as it welds hotter and can get better penetration. Then follow up with solid. Are these butt welds?Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Are you talking gasless fluxcore or dual shield? IMO dualshield root and fill would be best but they may be using hard wire for economic reasons.
Reply:I know it burns hotter but it never seemed like I was able to get the penetration that I can with gmaw, but I'm far more experienced with gmaw. And to clearify its dual shield, sorry. I don't think economics has anything to do with it. But I could be wrong. It's welder preference really. One welder used it a lot. One didn't at all.Sent from my HTC One V using Tapatalk
Reply:Are you doing in position fillet welds? What do you have available for machines? Spray transfer MIG may be a good option for in position. Dualshield would be better for out of position.
Reply:Did I read this right that you were brought on to lead up welding?
Reply:Originally Posted by Josh429erSoooo I have been wanting to ask some experts as I'm not at that point yet in my life lol. I work with some thick material at work 3'' sometimes. I was brought on to lead up welding sense the company lost all 3 welders they had in a short period of time. Some of the guys know how to weld. But in my opinion shouldn't(arguing that 3'' plate doesnt need to be preheated) The guys were saying that the "good" welder they had would do a root pass of FC and do multiple passes of Solid wire until it matched print. Sometimes the print calls for an inch wide weld. Now I was always taught to do a root pass with GMAW and follow with FC until it meets print. I was kinda hoping someone could explain either one to be better than the other. Or even if FC is worth using at all. I get that it can do better outside, and on dirty surfaces. But its in a shop, so why the hassle of using 2 different welders?
Reply:Josh429er,Can you post a picture or drawing of the weld on 3" material that you're asking about?  If it's permitted, please also post the type of steel being used and the general purpose of the weldment.Lots of details influence the choice of welding process and filler metal.  Some examples:Is the weld made in the flat/horizontal position, vertical position or overhead?Is the joint a groove weld, a fillet(T or Lap joint), or some other type of joint?Is this an open root groove weld or is there a backing strip or bar used in the joint?Are you having any specific problems with quality or productivity with the way it's being done now?Do you have a welding procedure in place now that would need to be changed and re-qualified?I and others here can offer some help with figuring this out, but we  need some more details in order to give the best advice.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Okay, Sorry for the wait. Been really busy. 1. I can position the piece wherever I need it. So most the time its in the flat unless its small and I get lazy ill do a vertical down.2. Its all butt or t joints with huge bevels.3. Open root grove. No backing bar.4. The only problem is that one of the solid wire machines welds like garbage. I think it gets to hot for the wire they run. But as far as weld qaulity none. productivity none5. No welding procedures.....EVERMachines are old. 60's and older. All are Lincoln Idealarcs for stick,tig, and mig. flux core are hobarts same vintage or older I think. They do not display voltage but I max I run the machine very hot and around 700ipm iirc.
Reply:wire is .35 for solid and 3/32 for fc.
Reply:Unless it's specified in a written procedure, it's welder preference. Personally, I would throw a preheat of 250 degrees minimum and weld all the way with flux core if urea a filler weld or a backed groove weld. If it's an open groove joint, I would hard wire it for the root and hot pass the flux core all the way out.-Hillbilly
Reply:Seems strange you asking because any shop doing large thicknesses on a regular basis follows some kind of code.  Most code shops have a book of approved procedures that are backed up by a consulting engineer.  Guidelines for preheat/postheat and approximate settings will be listed.  Too often that little book sits in the bottom of the foreman's desk until a sharp inspector asks to see it.  Open root butt joints are limited simply because only certain processes will make a sound weld when the back side is not shielded.  Flux core generally will not shield on the back side of a root properly so normally open roots are done with hard wire.   If you have a backing bar or tape  then that is a different matter.   If you can operate in flat and horizontal you will put down more pounds per hour doing spray transfer with hard wire or metal core.  Time is lost removing flux if you use flux core.   You will find that different geographic area will approach the same problem differently favouring one process over another.  It is no different that some people preferring Lincoln equipment and others preferring Miller.  In the end the engineer takes responsibility so he gets to choose.
Reply:Originally Posted by Josh429erwire is .35 for solid and 3/32 for fc.
Reply:Well there are no engineers left at the company. And there has never been a weld procedure ever. And I know for a fact that .35 for gmaw, but flux could be 1/16 not sure I swore I put a 3/32 tip on it.Sent from my HTC One V using Tapatalk
Reply:Originally Posted by Josh429erWell there are no engineers left at the company. And there has never been a weld procedure ever. And I know for a fact that .35 for gmaw, but flux could be 1/16 not sure I swore I put a 3/32 tip on it.Sent from my HTC One V using Tapatalk
Reply:Surely he means .035 not .35. But that would be mighty small to be welding 3 inch plate.Ranger 250 GXTSmith Gas Axe
Reply:Yeah sorry forgetting my 0s, do they even make a .35 wire? Yes its to small I agree. The small stuff I turn the welder down to about 75% mark on its capabilities. Sent from my HTC One V using Tapatalk
Reply:Thanks for filling in the missing details.  Since there is no established welding procedure to follow, you're "living in the wild wild west" of welding.  I will second the recommendation that you pre-heat 3" material to at least 250°.  This drives off all the water and helps reduce the chances of hydrogen induced cracking.  Preheat to 350°F probably wouldn't hurt, but 250 minimum.  Pause in welding if the interpass temperature rises above 600°F.  This may or may not happen depending on how large the plates are and how much amperage is used in welding.If you're working in flat/horizontal then you can put the root in with your MIG machine and 0.035" solid wire.  Open root will mean using short circuit, making pre-heat doubly important to help avoid cold lap or lack of fusion defects.  You could use your flux cored wire for the root pass, but you must back gouge or grind out the first pass and re-weld the back side to ensure a sound weld deposit.  You'll likely want to put in a second pass with short circuit MIG to help avoid burning through with the later fill passes.If this is structural work that falls under the guidelines of the AWS D1.1 code, there are no pre-qualified welding procedures for GMAW short circuit.  They all require use of a backing bar or gouging out the root and re-welding it from the back side of the joint.  You've not said what this weldment is for.  If it's critical, and it's hard for me to imagine something welded from 3" thick material that's not critical, you'd be best off gouging the root and re-welding it once the groove is filled and capped on the front side of the joint.  Gouging and re-welding may help with any alignment issues as well; helping to pull the joint back to it's original position.Once the root  and hot passes are in, you could set up the GMAW machine for spray transfer.  You'll need a gas mix with 15% or less CO2, the balance being argon.  Spray transfer with 0.035" wire will get you about 7 lbs per hour of deposition.  Good, but not great.If your flux-cored wire is large diameter, as you stated, you'll be much better off using that to fill and cap these welds.  There are 3/32" gas shielded flux cored wires for flat and horizontal only welding.  Here's an example:http://www.hobartbrothers.com/upload...abCO_70XHP.pdfThat Hobart wire comes in 1/16", 5/64", and 3/32" diameter.  The largest diameter has a deposition rate of 11 to 25 lbs per hour.  If you have a large enough power supply, you can put down over 3 times the metal with a large diameter flux cored wire as you can with your 0.035" solid wire.  You'll almost certainly have to position the joint in the flat position to take advantage of that highest deposition rate.  You might need serious gear to shield yourself from the heat and UV from an arc that hot as well.  But if you're already running a wire this diameter, you already know what I'm talking about.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector