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  1. #1
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    May 2017
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    Default Advice on MIG welding 2.5mm SHS with flux-core

    Hey Guys,

    I'm new to welding and basically teaching myself how to weld via YouTube videos - I was hoping to get some advice on MIG welding 2.5mm SHS with flux-core. The machine I'm using is a Uni-Mig Razorweld 250 inverter, set up on 0.9 gasless flux-core wire, I'm power limited due to only having a 10amp residential socket I can plug the machine into.
    My wire-speed is set to 6 and the Amps/volts are set to 180 which is working ok for me (the setup guide for 2mm steel suggests wire speed 8 & volts 17 - http://www.unimig.com.au/userfiles/f...250MIG_MMA.jpg).

    Question - is my wire-speed & volts setup ok?
    The technique I'm attempted on doing is drag left to right, initially I was trying to do the small "e" technique but I found I was running out of metal too quickly so instead I just drag the puddle across. Any advice would be great.

    I've attached 3 pictures of the welds I'm doing to give you an idea of the results. I'm attempting to make a box frame.

    2.jpg1.jpg

    Cheers,
    Tom.
    Attached Images Attached Images
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  2. #2
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    Near Bendigo, Victoria, AUS
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    Default

    Looks to me like you are not grinding/flap disc the paint off first. You will not easily figure out what's going on while you have all those inclusion in there. I find 'stepping' works best for me. That is starting the puddle, holding still, then moving maybe 4mm, holding still, moving again and so on. That seems to make the 'holding' spot hot enough to let the slag run off the puddle sides and not run under the edges of the 'moving' bit. But cleaning the weld area works best for me to see what's happening.
    Stick welding seems to burn the paint off better than MIG - with my equipment - and I don't bother cleaning much at all.
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

  3. #3
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    May 2011
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    Murray Bridge S Aust.
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    Looks to me as if you have a bit to much heat going into the weld. Are you running off an extension lead or direct into the power point??
    The "recommendations" are purely that, if you have a transformer close by, you have more current available than if you are some distance away.
    On my MIG welder, I have to turn the current up about 10% in the late afternoons early evenings, as everyone is trying to cook in ovens etc. causing a power drop. I asked a friend who used to work for the power company as to why and that was the answer I was given.
    Kryn
    To grow old is mandatory, growing up is optional.

  4. #4
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    Also make sure you have a good tight earth connection onto clean bare steel.

    Dean

  5. #5
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    Jun 2010
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    Canberra
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    Those welds look pretty much OK, maybe apart from the 3rd photo where you can't quite see what's going on with the fillet weld. A quick swipe with a wire brush to clean off the burned paint and other crud would make them look better, and might reveal issues that are currently hidden, but at first glance, those are serviceable welds (depending on how critical the application is).

  6. #6
    Join Date
    May 2008
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    Perth
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    First up, I'll state that flux core can be a right of a thing to work with. A messy, angry process that in its own way is better avoided until a later day.
    I also wouldn't be surprised if you get varying results depending on the wire manufacturer.

    I'd definitely recommend cutting off a number of pieces of the shs you're working with, and doing practise run after practise run.
    I'm a bit rusty with my fcaw, but I'd be bumping the volts up a pinch, dropping the amps down a touch (Wire speed also controls the amps), and seeing how that goes.
    That should give you the heat to maintain your torch pace with a little bit less filler being thrown down, so you can take the time to manipulate the puddle to latch on to both faces. What I found was that instead of watching the arc, watching the leading edge of the puddle helped me best determine my torch speed & technique. I don't remember if pushing or pulling worked better for me sorry, that's something you'll have to play with yourself.

    One thing I will say however, is that you shouldn't fret too much over the voltage & amps/wire speed. Whilst they're great guidelines, with enough practise you'll find the sweet-spot for your personal technique.

  7. #7
    Join Date
    Jan 2004
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    Mackay North Qld
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    The FCAW wire is best suited for heavier work,ie thicker walled. Its a con job perpetuated by the makers of this wire. Its pushed at the people as an alternate mig- it is not that.

    The original concept that it was designed for was that of heavy thickness plate found in construction or earthmoving fabrication work.

    The Lincoln machine I drove used 3.5mm wire(it was in inch fractional measurement then) and I welded 200x 150 x 20mm angles together to make box section for tree pusher arms-so that what I am talking about- heavy!!

    The Fcaw wire is hollow containing its flux and with the original application worked very well as the heavier diameter wire stood up to feeding through drive rolls and and a fairly long liner pretty well.

    The much smaller diameter Fcaw wire does not feed well and was never really designed for welding thinwall materials of this small size.I would say 4mm thickeness and you should have no trouble-see comments below about thickess and rolled edge.

    Because this FCAW wire can be fitted to a welding machine similar to a mig does not make it a Mig. Migs use gas and solid wire.

    Long story made short-look at the profile of what is being welded. The closed long edge of the box is rolled with the cut 2.5mm edge butted to it.Because of the rolled edge the gap to be welded is open even when the other edges are hard up against each other.
    The wire does not like to fill an open gap like a gas shielded mig wire can easily do. You done very well to achieve what you have done. If anything can I suggest a fraction-just a fly poo more wire speed and less voltage-again just a tiny bit

    Do not expect to achieve a " nice "finish as per mig.

    Note the black area ,that's acidic flux residue, clean it thoroughly or it will come through a paint finish.

    hope it helps

    Grahame

  8. #8
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    May 2017
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    Brisbane, Queensland
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    Thanks for advice guys,
    The welder is plugged into an Ampfibian Mini 15A to 10A Converter/Adapter/RCD, then that's plugged into a 10A powerboard which trips 1st - if I bypass the powerboard the RCD trips and gets me a little bit more power.

    Grahame I've noticed that if I crank up the volts and amps on the welder -welding 20mm steel it sings but cuts out after about 10seconds, the reasoning of using the fcaw was to keep costs down, I basically had a budget to work with and it was the only way I could get welding without the expense of gas, I'm renting so I am a bit reluctant to ask the landlord to put in a 30A plug for my welder he would most likely be cool with it but it would be just another excuse to jack up the rent money - which I would rather buy gas with!

    Thanks Lordbug when you said Wire speed also controls the amps suddenly a lot of things started to make sense, I'm going to give that technique a go, I did find that slower wire speed made it a bit easier to control, but I started getting issues with more splatter.

    Thanks RustyArc, yeh I need to get into the habit of welding surface to get better current flow through the steel

    Thanks, Dean, I have the ground on the table itself

    Thanks Kryn, I'm going to get a 15amp extension cord and run it from a plug next to the circuit board and see if that gets me more of a reliable current.

    Thank jhovel, I'm going to give that technique a go too, a boiler-maker friend came around on the weekend to teach me welding, we did some stick welding as he refuses to teach me MIG on fcaw as he doesn't believe in it and I should learn all the hard stuff first to make me a better welder - good point - but I also need to MIG on this project - I'm going to give stick a go on some 1.6mm SHS and see what happens.

  9. #9
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    Since privatisation of power stations the supply of power is a joke. In the old days when the power consumption went up they would switch on another generator so the voltage and current stayed at the required level. Now they don't bother unless the supply slips to below a certain point . This means that people at the end of the line may get a weak supply .
    I once measured my socket output at 215 volts not 240 to 250 like it should be we would get constant power interruptions and brown outs that fried two fridges we would watch the lights flickering and run and switch of the fridge , this is in a built up city area . They built a new substation 1k away and now our power is much better .
    I could not even run a welder properly with the old power supply problems so I just pay the local engineering shop to do my welding and it's way better than I could ever do .
    However I might give it another go now the power supply has improved .
    I am not a good welder by any stretch of the imagination but I have been shown how to prepare the jobs for welding by professionals and I see bad prep work . The joint area needs to be all ground clean and the sharp edges bevelled slightly . The earth would be better on the bare metal of the job not the bench as the steel is painted . After grinding wash the joint areas with solvent like acetone to remove any greasiness .
    I have had about 20 small jobs welded in the past few years and it has cost about $ 200 all up for a professional job so I'm not sure I need to ever learn to be a better welder but I guess you can't rely on others for ever the shop could close down .
    The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.

  10. #10
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    Quote Originally Posted by Retromilling View Post
    However I might give it another go now the power supply has improved .
    You should try using an inverter-based welder - they are far better at dealing with varying mains power than transformer units - I've seen ones that will operate from any mains supply from 100 to 250 Volts.

  11. #11
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    Thanks I will look into an inverter type welder eventually . Should I go a mig tig combination machine or two separate machines ? I think I like the idea of two separate machines .
    Can you recommend any good brands and models for home use mig upto 10mm steel and tig upto about 3mm . I am thinking I will just bite the bullet and use gas I hate slag on welds .
    The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.

  12. #12
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    Quote Originally Posted by Retromilling View Post
    Thanks I will look into an inverter type welder eventually . Should I go a mig tig combination machine or two separate machines ? I think I like the idea of two separate machines .
    Can you recommend any good brands and models for home use mig upto 10mm steel and tig upto about 3mm . I am thinking I will just bite the bullet and use gas I hate slag on welds .
    I've got a Magnum Welder MIG - it does solid wire and flux cored plus DC stick. I've put about 20 of the 15kg rolls of wire through it including 316 and 309. Replaced the gun liner once. It's never missed a beat.

    I bought an E cylinder of Migshield and it's paid for itself already on bottle rental. Gas price per litre is considerably higher so if you use a lot of gas, renting is likely cheaper. Going through maybe an E cylinder a year, not.

    I really don't like flux cored wire either. Welding outdoors, OK, limited choice. Otherwise, no.

    FWIW I have separate MIG & TIG welders. Usually I'm using the TIG on stainless and breaking down the MIG setup to swap to argon etc would drive me nuts in short order. Bad enough swapping out the ER70 wire for 316 or 309 when you're as lazy as I am. Think I'll get another MIG and leave it set up for stainless.

    PDW

  13. #13
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    I was thinking the same about having to swap stuff about , much prefer separate machines . I don't envisage having to weld outdoors much at all but I want to be able to use flux core if necessary .
    The only thing is not liking the idea of two different gas bottles for mig and tig , why can't I just use Argon for both ?
    I will buy bottles and get them refilled . One bottle will last me a long time doing hobby work.
    The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.

  14. #14
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    Quote Originally Posted by Retromilling View Post
    The only thing is not liking the idea of two different gas bottles for mig and tig , why can't I just use Argon for both ?
    You can but it's a colder weld, less penetration. Been there done that, I bought a second cylinder of Migshield. The price only hurts once.

    PDW

  15. #15
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    Using argon vs argoshield with MIG is like chalk and cheese. If you want MIG and TIG, you need both.

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