Thread: 12mm plate with small MIG?

Hello,
Ive got some 12mm plate that need some welding, it will be fillets and outside corner welds. Im a TIG and MMA person myself but i though this job would be a good one for my MIG (lots of tacking and stuffing around) welds will be aprox 100mm long each. I do have a mig but i just want to know how it will do and if it would be powerful enough. its a unimig 172 which the only specs i can find is 150amp max. i was thinking of maybe running it on c02 as well to get some heat into it or even the argoshield heavy mix. Just after some opinions.
other option was to stick weld it, maybe get some 3.2 iron power rods to get some metal down.

thanks

Multiple pass?

Michael

Originally Posted by Michael G

Multiple pass?

Michael

I thought multi pass was going to be the way to do it, more worried about the peno in the first run. I mentioned iron power rods in hope to maybe get it done in 1 run?

Originally Posted by brendanh

I thought multi pass was going to be the way to do it, more worried about the peno in the first run. I mentioned iron power rods in hope to maybe get it done in 1 run?

Provided your technique is good, penetration on the first pass shouldn't be a problem. With a fillet you can add passes to get the total bead size up, but you could consider starting with a bevel and root gap if you really want full penetration.

7024 or similar will certainly put the metal down faster, but I don't think it'll guarantee good penetration any more than a correct procedure with MIG.

Supose multi pass mig it is then, allow to cool between runs? Need to minimize distortion as much as posible. Think running on co2 would be of any benifit?

I seem to remember a good comparison of mig penetration with straight CO2 vs Argon/CO2 mixes but couldn't find it. My memory of it was that the CO2 bead was narrower and deeper in terms of penetration into the joint, which mirrored the external appearance (more crowned bead, less spread out). Argoshield heavy is still mainly argon, I thought it was 75/25 argon/CO2, but apparently its less CO2). I've used this (not by choice - left over cylinder) and 'light' (93/5/2) on the same job and to be honest I couldn't tell them apart, but this was on 8mm plate.

[edit: http://www.mig-welding.co.uk/welding-gas.htm
http://www.youtube.com/watch?v=NEHlfh6DO8o
Not what I was remembering but might be of interest]

I think confusion comes about because every publication you seem to read is all about doing the job in the shortest time possible and thus everything is done if possible in one bead, and the welding machine is matched to the job..

You will find it hard to find where multiple passes and MIG welders are mentioned in the one sentence.. But set up properly doing a big job with a small MIG is easily possible through multiple passes...

Multiple passes are seemingly done all the time... I sometimes get up and close with medium sized container ships up to about 200m long... You look at the welding on the outside of the hull and it is made up of pass after pass after pass, and there are some pretty crooked passes that weave all over the place as well..

Just make sure the MIG is set up right so you get good fusion with what you are welding... it is so easy with MIG to get a good looking weld that is just sitting on top of the base material...

i remember watching that video from Jody.

You would much rather a weld that's spread out on a fillet and outside corners wouldn't you? Think i might just get the argoshield as it seems it gives a better appearance as well. As well as doing a couple run on it.

Iron powder electrodes aren't one of the better choices if you want penetration as they typically have a softer arc and while giving superb bead appearance and greater deposition rate, you do lose out on penetration. Top of the tree for penetration would be cellulose electrodes, (fire sticks), with low hydrogen, rutile and finally iron powder.
As far as penetration profiles go, CO2 has a broader, more stick weld like profile with Argoshield mixes having the narrower wine glass type profile. Unless you want to spray transfer with a mig or are welding car panel type thicknesses, than I really can't see any real advantage to Argoshield and several negatives, namely cost and a propensity toward root run gas pores.
No welder, other than submerged arc or possibly 1.6mm flux core will lay a quality 12mm fillet in one pass, regardless of what the manufacturers propaganda may say and outside corners will need to be multi pass unless they are set up flat otherwise you would not control the large volume of molten metal involved, so multi run is the name of the game. A 150A mig will happily run 10-12mm three run fillets, although you will have to be aware of your duty cycle if large amounts of continuous welding is planned.
For a quality multi pass mig weld, a good wire brushing or preferably a light grind back to clean metal is required between runs as the silicon left behind on the weld is a major cause of lack of fusion between runs, not to mention the need to remove scale from the plates before welding begins. Tune your welder for a good crisp arc - despite what some believe, excess voltage does not increase penetration and actually harms the weld, have good clean plate and keep your wire at the leading edge of the puddle.
If you want to mig this job, then CO2 and .9 wire would be my first choice.

Originally Posted by Karl Robbers

Iron powder electrodes aren't one of the better choices if you want penetration as they typically have a softer arc and while giving superb bead appearance and greater deposition rate, you do lose out on penetration. Top of the tree for penetration would be cellulose electrodes, (fire sticks), with low hydrogen, rutile and finally iron powder.
As far as penetration profiles go, CO2 has a broader, more stick weld like profile with Argoshield mixes having the narrower wine glass type profile. Unless you want to spray transfer with a mig or are welding car panel type thicknesses, than I really can't see any real advantage to Argoshield and several negatives, namely cost and a propensity toward root run gas pores.
No welder, other than submerged arc or possibly 1.6mm flux core will lay a quality 12mm fillet in one pass, regardless of what the manufacturers propaganda may say and outside corners will need to be multi pass unless they are set up flat otherwise you would not control the large volume of molten metal involved, so multi run is the name of the game. A 150A mig will happily run 10-12mm three run fillets, although you will have to be aware of your duty cycle if large amounts of continuous welding is planned.
For a quality multi pass mig weld, a good wire brushing or preferably a light grind back to clean metal is required between runs as the silicon left behind on the weld is a major cause of lack of fusion between runs, not to mention the need to remove scale from the plates before welding begins. Tune your welder for a good crisp arc - despite what some believe, excess voltage does not increase penetration and actually harms the weld, have good clean plate and keep your wire at the leading edge of the puddle.
If you want to mig this job, then CO2 and .9 wire would be my first choice.

Thanks Karl, very informative, much like your help in my cast iron welding. Ive look and the price different with co2 and argosheild is 20bucks, not much but if you think c02 would be better then thats what i would go to. Could you tell me the disadvantages to argosheild in a job like this?
Question on duty cycle, ive been taught, even at tafe, that's its based on 10mins. for example lets say it has a 50% duty cycle, does that mean it will weld continuous, without stopping, for 5mins then cut out? or is it 5mins of total arc time per 10mins? i can never seem to find an answer to this.

Duty cycle is normally calculated on a 10 minute cycle as you say, but some cheap machines use a 5 minute cycle and other top line Japanese machines used a 60 minute time period. I doubt there would be much difference between 5 minutes continuous and 5 minutes total arc time in a ten minute period for all practical purposes.
In my opinion, Argoshield is largely wasted unless you are welding car panel thicknesses or are utilising spray transfer, (which is a downhand process and your welder is too small to spray anyway) and the penetration profile being of the wine glass shape already mentioned is at a bit of a disadvantage if you wander off line or off angle. I find that CO2 is a very reliable gas in that it produces a sound weld and handles contamination such as rust paint and galvanising far better than Argoshield while being less prone to porosity. Even on new, non Duragal RHS and hot rolled steel, I have seen Argon mix produce random porosity that could not be blamed on external factors.
The retailers of Argon mixes will use the sales features of less spatter and the ability to spray transfer as reasons to choose Argon mix over CO2. These are both valid points but deserve some qualification. Firstly a well tuned welder using CO2 is not that spattery and the spatter produced by CO2 is far more easily removed compared to Argon mix spatter that sticks like the proverbial. Secondly, spray transfer, while a very efficient process producing aesthetically pleasing welds is somewhat limited in its application to downhand positions, so for the average user presents little real advantage. There is also less Argon mix in a given cylinder than for the equivalent size of CO2, so the cost differential increases further. I found, as did others when undertaking WTIA certification, that Argon mix had the tendency to produce the odd few gas pores in the root run of fillet welds, certainly sufficient to cause a failure of that weld when examined.
Do not believe everything a retailer tells you about MIG gas, they also recommend a flow rate starting at 15LPM - roughly twice what will work.
In short, Argon mix provides a better advantage for the retailer than the welder in most cases although in automated or robot applications I can see potential advantages.
Having said that, if your heart is set on Argon mix, then go with it as it will do the job quite nicely for you and your cylinder rental will probably be a larger cost than your gas usage.

Thanks for that. looks like i will go with the co2.