Weld Settings for Thick Sections (GMAW)

I have a project I am working on that I will be welding some thick sections of steel using my Millermatic 252. I don't do a lot of welding, mostly TIG work and I only have the MIG for welding up stuff around the shop. The 252 is supposed to be able to weld 1/2" in a single pass, and the settings guide indicate what voltage/feed to run in this case. The sections I need to weld are 1"~1-1/4" thick welded to blocks in a butt weld fashion. I am prepping the sections with a full bevel at 45deg to allow for full penetration. My question is how do I know how to setup my MIG for this. It seems the suggested settings are for single pass welds so how does one know how to setup the welder for multi pass welds.

P.S. I am also already going to preheat in an oven before welding and the material is I would consider super clean.

It's very doable, but I would do a double bevel. It also depends on what materials are being welded. Is it 2 pieces of 1" plate welded together? Picture would help.

Cranking both dials to Max will not do it. You have to set it up properly. Your first pass will be cold so if you do a double bevel or grind out the back side and towels would be a good idea.

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Dual shield flux core or solid wire? Wire diameter? How hot is the preheat? material designation?

I think your welder will get into spray.

You need to check your gas ratio.

I wouldnt try to run it at max temps if dont run a mig much. You will have a mess of weld that is just melted wire no penetration, find a temp and wire feed speed that you are comfortable running at on a thick practice piece and multi pass it. I run .045 dual shield and that would be probably 3 or 4 passes if its beveled all the way out I dont know what settings I run at I just keep adjusting until im burning in without melting the tip and getting wagon tracks

Here is an article that discusses the transfer modes in GMAW. The section on spray transfer shows the shielding gas mixes and amperages required for various wire sizes.

Understanding transfer modes for GMAW - The Fabricator

Thanks for the input guys. I have attached a pic of one of the sub-assemblies Im trying to weld to show better what Im trying to achieve. Based on the above and other research I have been doing I grabbed a bottle of 98/2 ArO2 mix. Im hoping to get my welder into spray transfer which seems to be the go to for thicker sections.

One of the questions I was hoping to get answered was, is it fair to say generally speaking in a situation of very thick sections gouged out you could weld with the welder in settings for 1/2" thick plate and weld in fewer passes or say weld in 1/4" thick plate and weld in more passes. What Im trying to ensure is that if I normally weld 1/4" plate at 22 volts and around 190ipm feed, Can I also weld this at those settings and just take more passes to fill it up.

P.S. I know some of you may point out my prep doesn't show an open root, this is correct I have opted to leave the material thicker and the root closed to ease the fit up and after welding I am going to machine off enough from each side which should remove any lack of penetration at the root. It will in effect be an open root after machining

Thanks

Hi Matthew,

If you end up using spray transfer, I would suggest you consider and check maximum interpass temperature. I'm saying it for not so much the effect on grain structure, but more so a pleasing welding process without fighting extreme undercut, etc. can be had by you. Those edges will soon show you what I'm talking about if it gets too hot and you don't wait until temp goes down south of 500 F.

Let us know how it goes and the parameters you used. Some pre and post machining of the final project would be nice to see.
Good luck, you'll make it work!
Gus

Yup, spray is nice, but it's very fluid.

The weld prep could have been a narrower angle as well.

You might want to add some run off tabs to make the welding easier.

@digger doug, I ended up using 45deg only because it was convenient with tooling I had setup, I dont mind working a little more to fill it in

When trying to weld thick parts with a underpowered machine, stick and tig are best and mig isn't that great. I always say a 110v stick machine can weld up an aircraft carrier, something a 110v mig never could do.

Your pieces are pretty small for trying to do spray welding. You will have cold starts and hot ends. I don't think the joint is designed properly for avoiding cold spots in the corner.

How well does this have to hold? Is this just over designed or is it critical? Your pass temps will be hard to control properly with that design, hence another reason for TIG.

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Here is part of the data sheet for Hobart's Quantum Arc 6 ER70S-6 wire, that shows the voltages and wire feed speeds you need to achieve spray transfer.

.035 wire in spray at 205 amps looks like about right for your machine.

The corner comment is spot on.

How about a "Rat hole" ?

I’m not a fan of 98/2 for thick sections (3/8”+) or multipass welding. It transitions to spray at lower power settings so you can keep the 252 around the 100% duty cycle (should be around 175-185 amps). However, the 98/2 spray tends to have less penetration at the toes and a pronounced nipple shaped penetration in the center.

C25 will actually carry more energy and have a better penetration profile running your machine at a 40% duty cycle load (about 220-230amps) if your hell bent to go north of 6 lbs/hr deposition rate with .035 wire.

Good luck,
Matt

It's worth repeating some of the concerns raised in the above posts, that corner is going to be a serious defect in the weld with your chosen process in all but the most skilled hands, welding heavy section with a low powered mig in a internal corner is a virtual guaranteed defect trap thats hard to clean every pass. Right were you don't want any flaws at one of the highest stress points. Going for a full width 45 degree prep is really not ideal, its making the top of the weld a lot lot wider than it needs to be, a J prep would really reduce the weld width and reduced width always means less passes, faster but crucially far less shrinkage issues. The run off and especially run on bits are really important with mig, if you can avoid any stop - starts in the part its always good practice especially if your battling power limitations.

Based on your pic i would have just machined that part from solid, the end result would be stronger and with anything mill wise of Bridgeport or better it would be faster and easier.

You would do well to look at your machines duty cycle too, not something that matters on short welds, but on bits like this, its far better to make full use of your inter-pass temp range to allow for plant duty cycle if you need too. Torch duty cycle also needs considering, these are the kinda welds were you get enough heat reflected back - weld long enough to burn up underspec torches and most torches are rated running CO2 not hotter mixed gases. Equally you want to get the weld clean after each pass - remove any residue you can.

Good technique, proper inter-pass temps and good cleanliness can make up a lot for lack of outright power - penetration through power alone.

digger doug said:

The corner comment is spot on.

How about a "Rat hole" ?

Click to expand...

Can you explain that for us in the cheap seats?

Basically leave the corner as a hole - don't weld it, structurally out right strengths a nats lower, but fatigue life strength goes through the roof. You avoid all the weld in a corner defects - impurities and crack formation area. its std practice on anything that sees fatigue type loadings and lots of flexing, from construction to marine - ships etc.

@adama What is not shown in the picture I posted(because the idea was to show the size of material and the prep) was that there are features the would be prohibitively difficult to machine out of one block. Whats posted is actually a small part of a 15"x20"x5" weldment that to machine afterwards would need 16" long 1" end mills etc.

As for concerns about the corner, I had already decided to TIG the root pass with my SyncroWave 250Dx. As stated before the inner 1/8" of the corner of the weld will be machined out afterwards. I think @adama mentioned shrinkage but I have a solid plan for fixturing. Im also as is standard practice with all the work I do like this going to send it out to get normalized.

@Matt_Maguire, I have a bottle of 75/25, but based on everything Ive read, Multipass in short circuit is more difficult then spray because the toes can end up cold alot easier then in spray. I also under the impression that getting into spray with less then 80% Ar is not an easy feat. I played around running some test passes and I was able to get what I felt was a good weld at the higher voltages but alot of splatter which I assume is indicative of globular transfer. I did run a test coupon of a faux joint prepped as above same material etc. Looked pretty good when I cut it, no visible gaps at root or between passes. Im trying to track down some stuff to do an etch then maybe I will post it for feedback.

Thanks

Spray is an odd thing.

Increasing voltage and wire feed, short circuit turns to globular,
the same basic sound just louder.

Spray, all becomes quiet (can you chant Ohm.....) looking at the end of the wire,
you'll see the "penciling down" rather than the full diameter wire with a glob
on the end.

Matthew Kinsman said:

As for concerns about the corner, I had already decided to TIG the root pass with my SyncroWave 250Dx. As stated before the inner 1/8" of the corner of the weld will be machined out afterwards. I think @adama mentioned shrinkage but I have a solid plan for fixturing. Im also as is standard practice with all the work I do like this going to send it out to get normalized.

Click to expand...

No do not fixture heavy sections that hard, use preheat to control shrinkage, but if you manage to fixture 1" thick materials dead solid and take no other measures the welds will just crack as it cools. Molten metal shrinks as it solidifies, it continues to shrink as it then cools to ambient, its a basic fact of the physics of welding, as a welder its all about managing that, not fighting it! Post weld normalization is great practice, but it won't remove any cracks you have that are there from a over constrained weldment thats been carried out badly. IE it fixes and improves things, but it won't reverse any errors or defects. On heavier stuff like this it also pays to use the lowest grade filler tensile wise you can get away with, again it just reduces cracking risks through shrinkage as it yeilds and stretches as it cools. Also eliminates issues like hydrogen cracking too. IMHO a really common NOOB engineer-welder mistake is over specifying welding materials to try and gain strength when in reality there just increasing the likely hood of joint failure.

For etch, if you warm a section std vinger or any of the acid based toilet cleaners will work in a push, not ideal, but will make it really clear as to what is going on.

Globular is splatter heaven, gotta go up above there or stay bellow.

In practice how ever you do that root that corner may well still have a lot longer life if its not there, very few parts fail do to outright lack of strength, most fail in fatigue do to stress rises like that kinda corner weld. Structures have a nasty habit of focusing stresses into corners, by not haveing any material in that focal point the part ends up far far stronger, its counter intuative till you run it through FEA type software and see how by removeing that focal point of material, even 1/2" away the sresses are then down so much lower and into numbers that won't cause a material failure. Its kinda all down to the reasons cracks proper-gate, its not so much the way the crack weakens the material, its all down to how the crack focuses the stress at the very end of it till it proper-gates.