Mig vs tig and HAZ

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The company I work for manufactures some Stainless Steel cylinders with attachment arms welded on. Also the cylinders are seamed by welding. The welders take great pride in their work and prefer to use Tig over pulsed or regular mig. The cylinders are typically rolled from 1/2 inch 316L Stainless Steel.  The arms are 3/4  X 4 inch bar stock. The weld is accomplished by doing at least 3 passes with the tig at a high amperage. The problem is although the welds look super the distortion on the cylinder is bad and they take a long time to do.. It has been suggested by management that the welds should be done with MIG both to reduce time and to reduce distortion. It is managements position that three 200 amp tig passes at 10 minutes each will distort much more than one 250 amp five minute mig pass. The welders still want to tig. Forget the time cost what do you all think or the distortion? It would seem that the tigs HAZ would be much greater just due to the high heat for the much longer time. I really don't know how to try to prove the point to the welders or management. Can anyone point me to any literature regarding this?Thanks
Reply:In my opinion the TIG doing 3 passes and letting it cool down between would have about the same HAZ as one pass. If you dont let it cool down The HAZ will grow. I think the best option for you guys would be pulsed MIG something like a Miller Matic 350P. When done right pulsed MIG will have an awsom bead with little to no spatter. In pulse mode the HAZ is minimized greatly. The HAZ is relative to inches per minute of travel and avarage amps put into the piece. Your avarage amps going into the part on pulse will be 30% to 80% less depending on pulse cycle settings. I love to TIG also and put much pride in it the pulsed MIG is just plain fun to weld with. It is easy to weld out of position I can even run verticle down stringers on aluminum and steel and in most cases it welds just like it is a flat weld. I do not know the penetration on the down hill stringer so I dont do it on critical welds, but it looks great. Have your boss call your LWS and ask for a demo. I used one in Atlanta at a Miller trade show and as soon as I got home I orderd one. Steel Thunder Welding LLC. St. Thomas VI USAMM350PBOBCAT 3MAXSTAR 150 STH375 EXTREME PLASMA6.5 HP COMPRESORDEWALT 18, 24, AND 36 VOLTO/A TORCH SETAND SO MUCH MORE I DONT REMEMBERALL IN MY 2005 2500HD EXTENDED CAB L/B
Reply:Sounds like you have an approximation of both the GTAW and GMAW (tig & mig) parameters for these welds, so you could figure the heat input and see if there is a big difference, since higher total heat input should give a bigger HAZ and possibly more distortion.If heat input and final weld size were equal, I would guess that three small GTAW stringer beads would produce less distortion than one single GMAW bead.Below is just an example, it all depends on the actual amps, volts, and travel speed!  If these were machine welds, they could probablly be done 3-6 inches per minute (ipm) for GTAW or 25-30 ipm for GMAW.  For manual welding I was guessing around 3 ipm for GTAW and 12 ipm for GMAW.Joules = watt x secWatts = amps x voltsJ/in of weld = # of passes x ((amps x volts x 60 sec/min) / travel speed)GTAW = 3 passes x ((200 amps x 10 volts x 60 sec/min) / 3 ipm) = 120 kJ/inGMAW = 1 pass x (250 amps x 25 volts x 60 sec/min) / 12 ipm = 31 kJ/inI'm guessing the results will show pulsed GMAW to be less heat input and distortion.How about doing a controlled experiment on some test plates?Last edited by pulser; 01-30-2008 at 05:12 PM.
Reply:If I was the manager there I would ask the welding supplier to provide a Millermatic 350P as a demo machine to keep in the shop for a week for the welders to  experiment with and find out if pulse-mig is a viable option for that application.  That is what we did at our company when we decided we needed to replace our aging welding machines with new technology.  We had the demo machine for a few weeks to test out and ended up ordering 3 of them for production.   If you give your welding supplier the idea that you may end up buying a few new machines from them, they will probly jump at the chance to provide a demo unit to your company.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Originally Posted by pulserSounds like you have an approximation of both the GTAW and GMAW (tig & mig) parameters for these welds, so you could figure the heat input and see if there is a big difference, since higher total heat input should give a bigger HAZ and possibly more distortion.If heat input and final weld size were equal, I would guess that three small GTAW stringer beads would produce less distortion than one single GMAW bead.Below is just an example, it all depends on the actual amps, volts, and travel speed!  If these were machine welds, they could probablly be done 3-6 inches per minute (ipm) for GTAW or 25-30 ipm for GMAW.  For manual welding I was guessing around 3 ipm for GTAW and 12 ipm for GMAW.Joules = watt x secWatts = amps x voltsJ/in of weld = # of passes x ((amps x volts x 60 sec/min) / travel speed)GTAW = 3 passes x ((200 amps x 10 volts x 60 sec/min) / 3 ipm) = 120 kJ/inGMAW = 1 pass x (250 amps x 25 volts x 60 sec/min) / 12 ipm = 31 kJ/inI'm guessing the results will show pulsed GMAW to be less heat input and distortion.How about doing a controlled experiment on some test plates?
Reply:Originally Posted by CWWelderThe company I work for manufactures some Stainless Steel cylinders with attachment arms welded on. Also the cylinders are seamed by welding. The welders take great pride in their work and prefer to use Tig over pulsed or regular mig. The cylinders are typically rolled from 1/2 inch 316L Stainless Steel.  The arms are 3/4  X 4 inch bar stock. The weld is accomplished by doing at least 3 passes with the tig at a high amperage. The problem is although the welds look super the distortion on the cylinder is bad and they take a long time to do.. It has been suggested by management that the welds should be done with MIG both to reduce time and to reduce distortion. It is managements position that three 200 amp tig passes at 10 minutes each will distort much more than one 250 amp five minute mig pass. The welders still want to tig. Forget the time cost what do you all think or the distortion? It would seem that the tigs HAZ would be much greater just due to the high heat for the much longer time. I really don't know how to try to prove the point to the welders or management. Can anyone point me to any literature regarding this?Thanks
Reply:Thanks to everyone for there replies. This is exactly the type of info I was looking for. I will look into the Miller 350P unit. Our experience with pulsed mig in the past indicated it was very hard on the tips. I notice some recommendations for a spoolgun with the 350P. Does this help with tip life or is that even an issue with the 350P? As far as the joint design, imagine a round 36 inch diameter x 36 inch tall 1/2 thick cylinder. The attachment bars are 3/4 inch x 4 inch bars that have been milled to fit perfectly to the perimeter of the cylinder. The 4 inch dimension has the radius of the cylinder cut into it. The fit up is full contact with the body of the cylinder.Thanks
Reply:I would fit this up with a gap to allow for shrinkage witch is the culprit of the distortion.SA200,Ranger8,Trailblazer251NT,MM250,Dayton225AC,T  D-XL75,SpoolMate3545SGA100C,HF-15-1  RFCS-14 When I stick it, it stays stuck!
Reply:Originally Posted by CWWelderThanks to everyone for there replies. This is exactly the type of info I was looking for. I will look into the Miller 350P unit. Our experience with pulsed mig in the past indicated it was very hard on the tips. I notice some recommendations for a spoolgun with the 350P. Does this help with tip life or is that even an issue with the 350P? As far as the joint design, imagine a round 36 inch diameter x 36 inch tall 1/2 thick cylinder. The attachment bars are 3/4 inch x 4 inch bars that have been milled to fit perfectly to the perimeter of the cylinder. The 4 inch dimension has the radius of the cylinder cut into it. The fit up is full contact with the body of the cylinder.Thanks
Reply:Ok I will be the first to admit I know nothing about joint design to minimize distortion. And no I are not blaming the welders, we have some great welders who take tremendous pride in their work. Most have learned to weld using stick or mig and have been mostly self taught tig. My only reason for starting this thread was to try to learn how to minimize the distortion. My thought was the 3 passes of tig may be the culprit.  Any suggestions on how to redesign the joint to accomplish that will be greatly appreciated. And yes it is just a fillet weld around the arms currently. Here is a shot of it without the welds.Last edited by CWWelder; 02-01-2008 at 02:04 PM.
Reply:[QUOTE=CWWelder;160702]Ok I will be the first to admit I know nothing about joint design to minimize distortion. And no I are not blaming the welders, we have some great welders who take tremendous pride in their work. Most have learned to weld using stick or mig and have been mostly self taught tig. My only reason for starting this thread was to try to learn how to minimize the distortion. My thought was the 3 passes of tig may be the culprit.  Any suggestions on how to redesign the joint to accomplish that will be greatly appreciated. And yes it is just a fillet weld around the arms currently. Here is a shot of it without the welds.*****In any case, you need to determine the minimum fillet size required for assembly strength.  I'd try pulsing with the 350P, for starters, as others have said. You should be able to arrange with your LWS, for a demo of the 350P.You have not described the type of distortion, distortion measurements, etc. that is the problem.A description of the end use/function and requirements of this assembly, wouldn't hurt, either.-Is it distortion of the entire I.D. of the cylinder? -Is it weld HAZ distortion sucking the ID walls along each 4" leg of the bars?-Or a combination of the above?-How much measured distortion?-What is the current method of dealing with this distortion?-If plug welding from the inside, as I suggested above, is not satisfactory, then installing a rolled doubler plate of 1/2" thickness. Depending on the type or types of distortion that is occurring, then consider using only longitudinal or circumferential, small fillets--possibly stitching, not full length, not wrapping the corners.    http://www.weldingweb.com/attachment...1&d=1201898304     There's a bunch of ways to deal with this, some you'll deem cost & time effective, some you will not.      The more complete the information you provide, the more usable the answers you can receive. Attached ImagesBlackbird
Reply:Something you might try is skip welding. That is what we call it in the oilfield, not sure on the true technical term. You weld X distance and then skip Y distance and weld X distance again. Once you have reached where you started begin at the end of the first bead and weld X distance and skip to the end of the next bead and begin there repeating the process until complete. It does help to minimize distortion and the difference can clearly be seen. I have seen a 6 inch mig weld done at about 300 amps pull 1 1/4 inch plate out of line, but when cut to 3 inches and skipping the deflection is not visible. If you are looking at new processes contact Lincoln and discuss their new STT process (a process which is neither mig nor tig but is designed to replace tig welding in manufacturing). It was designed specifically to replace Tig welding on pipelines, but I am sure it is adaptable to other uses. Mig will always beat out Tig in a manufacturing environment from an economic standpoint. Plain and simple Tig is slow, Mig is fast. I love Tig welding as a welder, but I also own the company and use Mig everywhere I can. It's the fastest process (which my customers love because it lowers their cost) and it's the most economical for me aside from the initial expense of setting up to do it. The learning curve for mig is not as high as Tig and stick as well and this is also a consideration.The difference between art and craft is the quality of the workmanship. I am an artist.