GMAW vs FCAW on Large Steel Frames

Date 09-13-2007 15:06

Hello 1fastguy, you have a few limitations with the current set-up that you have described, IMHO. You may also have some other issues with regards to meeting specific code requirements. Using GMAW with the 75/25 gas limits you somewhat on the wire transfer mode that you will be able to achieve. 75/25 typically limits you to either a short-arc or possibly a globular mode of transfer thus limiting the speed with which welding can take place and in the case of globular transfer will produce somewhat erratic and not so great looking weld(I also do not believe this combination will qualify for D1.1 type work). If you were to possibly switch to an .045 or even an .052 E71T-1 type of gas-shielded wire you might be able to better maximize the voltage and wirespeed capabilities of the equipment that you are using. You can also end up burning up or shortening the life of your power sources as well though. If you do a considerable amount of this type of heavier steel you might want to look into a more powerful power source.
If you are truly stuck on using the GMAW process I would suggest a gas change to enable you to reach a true spray-transfer, here though, the 250 amp power source is still possibly borderline on being able to provide enough voltage/amperage to achieve the spray mode. In either scenario, it is likely that if the work is code oriented you will need to qualify the process and your welders. My $.02 and some things to consider. Regard, aevald

By jwright650 (*****)

Date 09-13-2007 15:06

I'm partial to FCAW for heavy weldments. The deposition rate is there to really put down the filler, but it comes at a cost of high amperage and heat with large diameter wires. We use 3/32" E70T-1 with 100% CO2 in the 1G and 2G positions, but we run it at about 450a/30v, so it gets pretty hot on your hands with really long welds. Also look into a hand held SAW setup to see if that would work for your application, this is another process that can produce high deposition rates.

By swnorris (****)

Date 09-13-2007 15:42

If you're chosen process is GMAW, I agree with Allan's suggestion of changing the gas mixture because the 75/25 mixture you're using is for the short circuit transfer mode, which is really not good for penetration. I would suggest an argon with 3 to 5% oxygen gas, however you will be in the spray transfer mode with a 98/2 mixture at a minumum of 220 amps.

I also agree with John, as I am partial to FCAW as well, and I think the handheld SAW is a good idea if your setup allows it.

By 1fastguy (**)

Date 09-13-2007 19:41

Thanks guys, I realize that we are right at the limits of our welding process for our shop. This is our first attempt at doing this large of a frame. We are use to building frames in the 2-3inch tube size with a .187 or .250 inch wall useing the method I discussed. We have 6 250 amp mig machines on the floor, I am looking at getting a 350amp machine for this job and going to .062 diameter wire for faster deposition. I am curious about the gas for this operation I was going to switch to straight carbon dioxide. I have never used the argon mix you were talking about. Can you elaberate or give some other suggestions of gases to try?

By aevald

Date 09-13-2007 20:55

Hello again 1fastguy, if you decide to go with the FCAW gas-shielded method you will be able to find different wires that will specify different shielding gases. There are some that are designed to operate on 100% C02 only, there are others that can be run either with the 100% CO2 or a 75% Argon/ 25% CO2 mixture, and there are others still that are designed to be run on a 90% Argon/ 10% CO2 mixture only. If you decide to go the FCAW gas-shielded route you may want to do some inquiring with your welding supplier and see if they would be willing to give you some sample rolls to help you to make a decision on the route you would like to go.
The mix that was referred to in the other post was an example of a mixture that would allow for the GMAW process to be done in the spray transfer mode. There are quite a number of these types of gases comprised of slightly different "recipes" for lack of a better description. I will probably be corrected on these numbers but I believe you will get the idea, A minimum of 90% Argon along with various other mixtures of Helium, CO2, and O2 can be mixed to make up shielding gases for the spray transfer mode. Some examples might be 90% Argon/ 10% CO2,* 95% Argon/ 5% CO2, *98% Argon/ 2% 02, a tri-mix gas might be something like this 95% O2/ 3% He(helium)/ 2% O2, all of these various mixtures have been deemed to aid with specific arc characteristics, penetration, wetting of the puddle, spatter, and other things. I hope this gives you a little bit better understanding. Regards, aevald

By Lawrence (*****)

Date 09-13-2007 21:47 Edited 09-14-2007 08:48

Fastguy

I don't know if you are so much *at the limits* of your equipment. I just think you need some process control training.

For any structural steel that is thicker than 1/8 inch you should forget about Solid wire and C02 100% and 75/25. They are not cost effective or dependable for anything above sheet metal.

FCAW
Your regular Constant Voltage (CV) Mig power supplies that are rated at 250 amps are suited very well to run 0.045 Gas shielded E71T-1 All position FCAW electrode. At 400 inches per minute you will be close to 220 amps and 27-30 volts with a very high deposition rate of about 8 lbs per hour. Your machines could put out three 8 hour shifts seven days a week with this stuff and not be overworked. The big advantage of FCAW is that it has better side wall fusion properties and will weld in all positions (Lincoln OuterShield 71M E71T-1 for example)

GMAW
This topic is pretty deep to go into in the forum but,......... If *ALL* your structural steel work can be fixtured in the flat or horizontal fillet positions than GMAW with spray transfer and 0.045 filler will be a reasonable choice (second to FCAW in my opinion)
0.045 ER70S-X solid filler wire at 240 inches per minute and will draw about 220 amps at 27 volts with a deep penetrating spray transfer depositon rate of a little more than 6 pounds per hour. Shield Gas selection is dependent of a number of factors... But all are argon rich (over 80%) with a balence of active gas. Common mixtures are 98/2 Argon/Oxygen and 90/10 Argon/C02. (Hobart HB 28 ER70S-6 for example)

I don't think large diameter wire or new equipment is the answer for you... The proper process, parameters and transfer mode is.

By Sean

Date 09-14-2007 00:09

I think that everyone's made some really good suggestions and I agree with all but I'm wondering why no one has mentioned MCAW (I believe in the US it falls under GMAW-C)? Please correct me if I'm wrong. MCAW can really only be done in flat and horizontal positions and most won't work so well out of position. If they do there deposition rates are not effective. It also may not create as much of "learning curve" as switching to FCAW and it would give a good balance between the GMAW and FCAW. Also an 0.045" MCAW will provide a slightly better deposition rate than 0.045" FCAW and better than an 0.035" GMAW.

Personnally, I'm not a big fan of 250 amp machines for FCAW or even GMAW (spray). IMHO you can't maximize your FCAW productivity on any large fabrications with a 250 amp machine (if most welds are in the flat and horizontal positions). Voltage seems to get maxed out at 28 to 29 volts. With the 250 amp machine with an 0.035 GMAW, with a 85/25 Ar/CO2 shielding gas at 220 to 240 amps, 28± volts will provide good deposition rates too. The bad news is that at those parameters welder technique problems may be highlighted. Lawrence makes a great point about proper process selection and parameters. Take a look at the deposition rate tables for the same size wire. Spray transfer with a small wire may deposit more metal than a slightly larger wire in short circuit...

Has operating factor, joint design (ie overdesign) and welding position been looked at to improve productivity? All of this will impact deposition rates and productivity too.

As for shielding gases. Here's a decent article about them http://www.thefabricator.com/Consumables/Consumables_Article.cfm?ID=1024
What you will notice in your welds is that as the argon content increases you will get deeper, finger like penetration (argon has a narrower arc characteristic). If you increase the CO2 content you will get wider penetration. Also you will note that as CO2 content increases so does spatter and fumes (there is more CO2 to break down and react with slag or glass formers as applicable). With higher concentrations of argon you can also decrease your voltage slightly for the same amperage because of its higher ionization and lower thermal conductivity.

By TimGary (****)

Date 09-14-2007 12:37

After using a lot of GMAW hard wire and FCAW for heavy structural welding, I am completely sold on MCAW. I use it with 250 amp machines and 92% Arg + 8% CO2 sheilding gas and .045" wire. This combination gives maximum penetration, maximum deposition, no slag to clean and practically no spatter. We don't even have to use anti spatter solution anymore. The wire flows like butter and is easy to use.
Just my $.02 worth...
I almost forgot to mention that the cost of MCAW wire has come down to the point that is is the same price or cheaper than the other types.
Tim

By ssbn727 (*****)

Date 09-14-2007 02:46

Hi Larry!
Question: Is that a typo when you mentioned; " Your regular Constant Current Mig power supplies" or, did you mean to write: " Your regular (keyword here)Constant Voltage/Potential MIG power sources instead?
No offense, just out of curiosity. ;)

I personally suggest to anyone basically the same what Allen mentioned with respect to 3 phase power sources being more suited for a more demanding heavy industrial environment, and I would also encourage someone looking for more durable power sources to look towards "overkill" in selecting maximum amperage ratings... In other words, if one is going to be welding at the high end of an amperage setting of about 275 to 300 amps maximum, then consider purchasing a 400 amp power source... even at 250 amps max, a 400 amp machine will more than likely - especially if it's the best brands, will enable one to produce 250 amps @ 100% duty cycle with relatively no undue stress on the power source... One can also achieve higher voltages with high amperage output power sources. ;)

If one is working the power sources with very little downtime 24/7, then I suggest a more robust power source like a Miller Deltaweld 652 or lincoln's equivalent 600amp power sources... Yup! overkill is the way to go especially if welding for prolonged periods @ higher than average amperages... Not a good idea to push one's power sources so close to their limits for too long especially when one starts to realize that their duty cycles have significantly decreased @ those high amperages!!! :)

Respectfully,
Henry

By Lawrence (*****)

Date 09-14-2007 12:42

Good catch Henry
Thanks

L

By aevald

Date 09-14-2007 02:12

Hello again 1fastguy, I believe that Lawrence hit it on the head when he gave you the advice to consider looking at your method of process. You can very likely make your equipment work just fine providing you make a few changes in the wire and gas combinations. That could mean using the GMAW Spray process, the gas-shielded FCAW process, or the GMAW Metal Core process(in a sense this is comparable to the GMAW Spray, yet it provides for higher deposition rates). Quite a few years ago I had one of the Lincoln technical reps. visiting our shop to participate in a seminar on wires and shielding gases, I believe the metal core wires were fairly new then, one of the things that he told me about this type of wire was that it worked really well on structural tube steel shapes if you didn't have time to clean the inhibitors from the tube surface. Instead of having the inhibitors cause pinholes and other flaws in the weld, the wire itself aided with a sort of cleaning action(don't believe this was a planned thing, but it was something that he noted). He also told me that they suggested this wire for a lot of robotic applications as well as hand welding.
The FCAW gas-shielded process will give you the most versatility regarding the positioning of your welding, as it will allow welding to take place in all positions, the other processes tend to limit you to flat and horizontal applications. I still tend to suggest trying to test drive these other types of wires and make some gas mixture comparisons, maybe not necessarily for this particular job, but possibly in anticipation of other jobs that you may have coming down the road.
I have made an assumption based upon your initial information saying that you are using 250 amp CV machines. My assumption was that these machines are likely the more home-shop oriented combination roll-around units. I have been in a large number of shops in my area that use a lot of these machines. I chuckle when I hear the owners or the shop foremen complaining about all the machine breakdowns or saying how disappointed they are in how they hold up. Using a machine of this type in an industrial environment is a stretch of their engineered intent. I am not saying that they cannot provide you with plenty of service life, however they are much better suited to a one-owner type of operator who is more likely to take proper care of them and not abuse them. Shop power can certainly be another consideration for a choice of this type of machine. If you don't have access to 3-phase power in your shop these machines are definitely the way to go. If your business is evolving into something that is more industrially oriented and you do have 3-phase capability I would suggest looking into the more powerful, commercially suited welding power sources and feeders. They will give you more consistent performance and service life. Just a few more thoughts for consideration. Best regards, aevald

By DaveBoyer (*****)

Date 09-14-2007 03:35

Duty Cycle: I am making some genralizations here, but bear with Me. It seems that the single phase 250 machines are in actuality 200 amp @ 60% duty cycle, and some are below 40% duty cycle at 250 amps, while the 3 phase machines are often rated at 100% duty cycle and can provide quite a bit more amperage at 40%-60% duty cycle. The above comments about how hard You drive a given machine should definatly take into account what % duty cycle the 250 rating is taken at. There is a point where increased wire diameter doesn't give increased productivity due to the machines inability to provide optimum amperage, this is described as the current density, and I hope the others can elaborate on it some. When selecting a wire diameter for My 300 amp @ 60% machine it seemed that I had nothing to gain by going larger than .052 dual shield, altho there is enough power to run .062, the machine should, at least in theory, run the .052 better.

By aevald

Date 09-14-2007 06:16

Hello Dave, great point to include when considering various choices and set-ups.
Have you ever noticed, for lack of a better term, "the sweet spot" when it comes to operating specific wire diameters on machines with plenty of top-end left in their power range? I'm mainly referring to GMAW spray when using say an .045 diameter wire. In some instances you might try to push the settings to put out a bit more weld metal than the wire was really designed to run at and then it seems to me that the weld puddle characteristics tend to go to hell in a handbasket. I'm just wondering if I'm the only one that feels that way. Regards, Allan

By darren

Date 09-14-2007 17:43 Edited 09-14-2007 17:53

great thread guys . the truth about machines instead of the hype in a pamphlet. the 652 is an awesome machine for bigger currents, lincolns products are great too just havent used there bigger machines on a constant level. machines are not accuratley labeled most of the time nowadays. you start pushing the upper limits of inverters "100%' limits and they start smelling hot.
we have plenty of literature in our shop that states that .045 has the highest deposition rate and penetration and least response to welder input variables(larger sweet spot).

as far as gmaw spray dave ive tried every current/volt combo possible to get the fastest deposition and good looks. i found that if it is not back weaved then around 28.5v is as high as you can go without undercut and bead distortion. with a back step weave and enough wire that it is going from a pure spry to a harsh crackle within every stroke or back step weave you can go up to 30.8, maybe 31v. after that the weld looks like crap. the most worry some part is the 'puckers' on the weld from cooling to fast. it pulls the parent metal all around. depending on the level of skill i will set the welder for guys around the 27 to 27.5v range to ensure that less experienced hands can produce welds without too much pick ups and they gradually move up a little. for tacking i like around 25.5v right around the globular/spray transition, but its hard to get the less experienced to change their machine. spray tacks plainly put suck, they just lay on top and are cumbersome. small moving tacks at the 25.5v range make dug in not to big tacks that you can run right over. in short patience is definitely a virtue with hard wire, hell in a hand basket is a way nicer term that i would use to describe beads welded too hot with gmaw.

oh yah the sae 800 torpedoes in our shop are way under rated we burn 5/8 gouging rod for hours at a time and there is still lots of throttle left. youd think with all the technology today they would be able make the old red face and torpedo arcs very easily, go figure
darren
ps metal core really is the way to go for production with the less experienced gmaw-mc= gas metal arc welding -monkey certified

By DaveBoyer (*****)

Date 09-15-2007 02:40

Allan, I don't have enough experience with spray transfer to comment on this. I use .035 and short circut on the 200 amp machine, and have the 300 set up with dual shield, but havn't yet built the projects I got it to build. I think the 300 will spray .045 OK, but that would be pushing the 200 pretty hard.

By 1fastguy (**)

Date 09-14-2007 19:13

Thanks for the info, even if it was a little off topic. Lawerance I think you hit it on the head. Your comments were exactly what I was looking for. As I stated before we are not a heavy industrial Co. 90% of our work is in the 1,2,3 Inch tube with a .125, .187 or.250 max wall. On any given day we are building SST, Mild Steel, and Alm Frames at the same time all different sizes and configuerations flowing through a diverse production lines. So for that application the 250amp millermatics work awesome and are extremly flexable! I am going to try the 98%, 2% Argon, O2 mix using our .045 wire. My comment on the limits of the power source was meant to be that if we recieve any contracts for frames thicker than .500 we would have to have a stronger power source with a larger wire size.
Thanks again have a good weekend.