Effects of position on gmaw

Date 10-12-2007 15:09

Hello LHall, I'm going to take a shot at this although I believe your question is a bit vague and maybe this will help to refine it somewhat. GMAW can basically be sectioned out into 3(4 if you include GMAW-P) categories. Short circuit transfer, globular transfer, spray transfer, and possibly pulsed spray transfer if you like to differentiate that one. Each of these transfer modes is generally achieved through a combination of shielding gas type, arc voltage level and the control or setting of these. All of the GMAW transfer modes are dependent upon the arc voltage values and gas types to determine how the weld beads will end up on the plate, so to speak. Out of position welding with GMAW will be dependent upon the transfer mode to a great degree. Short circuiting transfer and pulsed spray transfer can be used for a fair amount of out of position work, yet they too will have their limitations. Short circuiting transfer will not have the penetration characteristics necessary for thick section plate welding in most cases, even the pulsed spray transfer mode will have limitations when making vertical-up welds, horizontal welds, and overhead welds.
GMAW has conditions that are present that impose limitations for it's application in out-of-position welding, it has a shielding gas to protect the weld from contamination and it has the physics of surface tension to aid in shaping the weld deposit, it also has wire make-up to control the strength, and certain deoxidizers to help with surface cleaning action. Other than that it doesn't have the weld formers that are present in the other processes to shape and support the weld pool while it is in it's molten state and to allow it to maintain it's shape while it is being operated in an out-of-position scenario. Just a shot here, hopefully you will provide a more detailed question and hopefully others will chime in. Best regards, aevald

By L.Hall Date 10-12-2007 16:08

sorry that was vague. I am using spray tranfer. Welding in the up hill direction as well as the down hill direction. This was done at a twenty degree anlge for both.

By Lawrence (*****)

Date 10-12-2007 16:48

For uphill progression on carbon steels greater than 3/16 FCAW is really a better choice.

GMAW-P will run uphill but not anything close to the deposition rate of FCAW.

Traditional Spray Transfer GMAW is not suited for vertical up or downhill progression regardless of gas mixtures. The puddle it simply too fluid.

By aevald

Date 10-12-2007 18:30

Hello Lawrence, I certainly agree with your post here. Sorry, I am going to take this thread off track slightly. Now I have a question for you as well as some information. In our school's service area we have an OEM that manufactures some sizeable types of equipment. They use both FCAW-G and GMAW-short circuit and spray. A number of years ago one of the co-owners decided to streamline their operation, the first thing they did was clean out all of their welding machines and replace them all with one manufacturer's brand. Then they did the same with all of their welding guns and peripheral parts. Finally, and this is the one that I have some issues with, they had a special tri-mix shielding gas concocted. They use this gas mix on both their GMAW applications and their FCAW-G applications. I have done some work over in their facility and haven't noticed any outright issues with the tri-mix as it applies to use on the FCAW wire. It doesn't lead to any cracking issues or other obvious weld issues that I have noticed, but it does run way different than this same wire type runs when you use 75/25 shielding gas. They also run a considerable amount of downhill weld progression with both the GMAW spray and FCAW(yes I cringe when I see this) on heavier plate(3/8 to 5/8"). Since they are an OEM they are not really bound by any specific codes relating to the manufacture of their particular type of equipment.
Having described this scenario, I come to where our program fits in here. We have a considerable number of welders, and those who are trying to work into becoming welders for this company, they are urged to come over to the school and take classes that pertain to their duties on their jobs and the company pays for this training and schooling. My dilemna becomes this, I try to train individuals based upon correct procedures, uses, parameters and all of the other things that apply to our trade. When I run into this, I feel as though I have to point out the pitfalls that could result from some of the incorrect things that go on out in industry at times, obviously this causes confusion for a large number of these individuals. One of the ways that I have to try to justify this particular manufacturer's methods, as opposed to possibly more correct ones, is to state that the engineering may be over-engineered enough to allow these practices not to cause failures. This particular manufacturer sticks to the old addage "if it's worked ok up to now, we don't see any reason to change anything". I'm just wondering if you see much of this sort of thing and possibly what sorts of approaches you see for dealing with this issue. Best regards, Allan

By Lawrence (*****)

Date 10-12-2007 19:10

Allan,

I'm in the same boat.

Some of the local employers that hire our grads, even hire our students part time while they go to school and often pay them to do it, operate day to day process controls that are not likely to be found in a code compliant environment.

Other local fabricators have called me in to train or certify their welders and just as quickly asked me to leave after I inform them that the welders are not the cause of the problems they are experiencing, it's thier inferior process. That I can't certify them if they don't use a process or procedure that is certifiable. I guess you can't win em all. Although I'm learning to be more "diplomatic" after I make a first facility tour.

I don't teach it they way they do it. If a student insists on using techniques that are... shall we say "unorthodox" I will not argue with succsess... But they never succseed when the old wrap around bender starts to play a part in the testing of welds.

We do have discussions about best practices in process control, what is code quality and what may be good enough for the job at hand.

I expect our grads to be agents of change when these local companys are forced to work to qualified procedures in order to compete... The companys that aren't able to adapt will die, it happens all the time, and nobody wants to see that. If I can't convince the management up front, well, I just have to be patient and wait for my students to move up into the ranks of influencial craftsperson or decision maker.

By aevald

Date 10-12-2007 22:15

Hello again Lawrence, thanks for the response. It is difficult to bring people to understand that there is the point where you can get by and then there is the point where things have indeed been done correctly and the results will prove themselves out. Best regards, Allan

By aevald

Date 10-12-2007 17:00

Hello again LHall, if you are referring to raising a plate 20 degrees up from the flat position and welding from the low end to the high end(uphill) or welding from the high end to the low end(downhill), that is probably within the possibilities that spray transfer would allow you to accomplish. Both weld progressions can possibly give you different types of issues, the downhill travel can work, with the correct gun manipulation, wire diameter, wire speed relative to arc voltage, and travel speed. You can't allow the molten pool to outrun the point of melt provided by the arc or this will cause cold-lap to occur. The uphill travel progression will possibly cause excessive weld build-up towards the center of the bead or deformation of the weld pool due to the puddle being so fluid that it won't freeze while the weld pool is rounded out, instead it will pull towards the middle of the bead before freezing and possibly cause undercut along the bead edges in the process. To a certain degree this can also be addressed with proper gun manipulation and some of the same additional items mentioned concerning the downhill progression. Just my $.02. Best regards, aevald

By 803056

Date 10-12-2007 21:49 Edited 10-12-2007 21:52

Hello Lawrence and aevald;

You hit the nail on the head, all is good until they have to qualify the procedure or the welders. I would be a rich man if I collected money every time I heard, "We never had a problem until you showed up!"

Wait a minute, I do collect some money every time I hear that refrain! I always say, "Their ignorance is profit in the bank!"

I don't argue or point out the errors in their ways until they get to the point or exasperation and ask me what I recommend. Then I put them on the right path and usually have good results in short order.

As instructors, your responsibility is to teach the youngsters the proper way to weld. The employer will teach them the shortcuts and how to save time and money, but it usually bites them in the a$$ sooner or later.

I had a client that used downward progression on stainless with GMAW in the short circuiting mode of transfer. When I started teaching a welding class for them the supervisor was quick to show me the errors of my ways and told the students that they have been doing it that way for years without any problems. A few practice pieces later, neither the supervisor or the "ace" welder could pass a simple fillet break test in the vertical position on 1/8 inch thick material. As they left the training area they both mumbled something about going broke if they had to meet "code" and couldn't weld vertical down with GMAW.

All the welders passed the required tests by the end of the class, but the supervisor was still mumbling that he couldn't see why they shouldn't be welding using downward progression. I said it was perfectly acceptable if he or they could pass the fillet break test using their technique. They never did get anyone to pass using downward progression.

I'm confident they are using downward progression as I write this post and I'm sure they pile on enough weld to make it "stick", but it will be interesting when there is a failure and they have to explain why they continued to use a technique that was shown to be questionable. I'm just as sure the supervisor will blame it on the welder's "lack of skill."

Best regards - Al

By aevald

Date 10-12-2007 22:27

Hello Al, thank you for putting another face on this issue. I believe this sort of thing is industry wide and not just restricted to any one geographical area or industry. Unfortunately this issue is not likely to go away anytime soon, or if ever. I believe the bottom line here revolves around just the sort of thing that both you and Lawrence alluded to: until someone gets hurt or litigation steps in or some other sort of monetary based issue crops up, much of this sort of thing will continue to go on. I believe we always hope that our efforts are based on doing it faster, better, more predictably, and less expensively, sometimes folks just use portions of this equation and don't consider them as a package. Best regards, Allan