mig welding plasma cut parts
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  1. #1
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    mig welding plasma cut parts

    Hello..
    So please help the greenhorn HERE out..

    I am welding together plasma table cut parts that somebody cut me out of 10 gauge mild steel. The finished project will be in the shape of a cone. I removed the slag or dross from the top and bottom of the cuts that the cutter left. I did not grind the cut itself because well it looked clean and good. The problem I have is I am getting bubbles about every inch or so.I tried grinding,brushing the area to weld on the outside. Also changed tips and tried various gas settings.(co2 mix). I tagged it all together so I can only clean weld on outside and not where the cuts butt together against each other.

    Has anybody experienced bubbles with plasma cut parts where the slag has been removed. Should the cut area even though it looks very smooth and clean be also be grinded.

  2. #2
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    Re: mig welding plasma cut parts

    post a couple pictures
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  3. #3
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    Re: mig welding plasma cut parts

    all i can think of is you didn't get all the dross off. Dross can cause pin holes and bubbles in welds.
    also impurities in the metal can. try welding a saw cut piece and see it you have the same problems.
    check your gas flow, look for leaks in hoses, Cross wind. Too much gas flow can be as bad as not enough gas. with small nozzles.

  4. #4
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    Re: mig welding plasma cut parts

    Name:  20170317_134938.jpg
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Size:  26.2 KBName:  20170317_135002.jpg
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    Here are some photos

  5. #5
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    Re: mig welding plasma cut parts

    It is about at a 45 degree downhill weld volts at 19.5 . wirespeed 250 in. m.

    10 gauge
    miller welder
    Last edited by Jakedasnake; 03-17-2017 at 05:34 PM.

  6. #6
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    Re: mig welding plasma cut parts

    You must not have gotten all of the dross off. Sometimes you really have to grind it good.
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  7. #7
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    Re: mig welding plasma cut parts

    It's going to be twice as hard to fix than it would have been to clean it up right at the beginning. If it's causing a lot of problems you can use a cutting disc between the tacks to gouge out a 1/16" slot. That should weld up a lot cleaner. In future the dross should get ground off before fitup. I myself am still trying to graduate out of the group that tacks crap together, then stabs at it with a wire wheel.
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  8. #8
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    mig welding plasma cut parts

    Try welding together 2 clean pieces of steel

    Not plasma cut
    Does it do the same thing?

    Looks like it might be a gas problem

    Blow out your liner


    Sent from my iPhone using Tapatalk Pro
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  9. #9
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    Re: mig welding plasma cut parts

    Quote Originally Posted by Jakedasnake View Post
    Hello..
    So please help the greenhorn HERE out..

    I am welding together plasma table cut parts that somebody cut me out of 10 gauge mild steel. The finished project will be in the shape of a cone. I removed the slag or dross from the top and bottom of the cuts that the cutter left. I did not grind the cut itself because well it looked clean and good. The problem I have is I am getting bubbles about every inch or so.I tried grinding,brushing the area to weld on the outside. Also changed tips and tried various gas settings.(co2 mix). I tagged it all together so I can only clean weld on outside and not where the cuts butt together against each other.

    Has anybody experienced bubbles with plasma cut parts where the slag has been removed. Should the cut area even though it looks very smooth and clean be also be grinded.

    Plasma causes some oxides and other contaminants in the cut. It may look good but it's actually not clean steel. Grinding takes care of that.
    For short-circuit mig welding it would be best to use a wire with lots of de-oxidizers like ER70S-6. Mill scale can also be a problem
    Best practice would be to grind of any mill scale and oxides from the cut about 3/4" from the weld area.

    If you can't remove mill scale and oxides is better to use another welding process besides short-circuit mig that can handle contamination better, for instance stick welding or gas-shielded flux core.

    PS.
    Some more info on plasma cutting and also different cutting gases.
    You can plasma cut it, but can you weld it?

    .
    Last edited by Pete.S.; 03-20-2017 at 12:07 PM.

  10. #10
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    Re: mig welding plasma cut parts

    I agree with trying some saw cut pieces first. I have welded plenty of parts that were torch or plasma cut, and not dressed perfectly. Lime previously mentioned , it may be a gas issue.

  11. #11
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    Re: mig welding plasma cut parts

    Could it be that you've got into some low quality sheet steel that hasn't been fully deoxidized? I know I've gotten into some cs sheet metal before that was absolutely horrid to try and TIG weld because no matter how careful you were porosity just seemed to bubble up out of it. If you could get some similar thickness material but from a different source and try welding it up the same way to see if you would still get porosity it could kind of confirm whether or not "bad material" was the source of your problem.

    How much "melt thru" are you getting? Could be you're sucking enough air in from the back side to cause that porosity?

    If I were you I'd be getting some of the drop those parts were cut from and be running some practice welds to get this problem solved before buggering up any more of the actual parts. Do you absolutely have to run down hill? Might be that turning the machine down some and running them flat would yield better results.

    Here's a link to an article that's got a pretty comprehensive list of porosity problem causes.

    http://www.thefabricator.com/article...metal-porosity

  12. #12
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    Re: mig welding plasma cut parts

    Clean it up and give your self a little bit of a gap, no more wider than the thickness of the base metal.
    And it will weld up real nice.
    Exactly what argon mix are you using?
    Try using straight CO2. Straight CO2 cuts down on some of the the contamination problems you see with C25.
    Last edited by mad welder 4; 03-20-2017 at 09:30 PM.
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  13. #13
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    Re: mig welding plasma cut parts

    Thank you a lot guys for your awesome advice. You guys are all the best.

    So I tried welding pieces from same stuff that were not plasma cut and did not get any bubbles.
    So right now I am thinking that even though the cut area looks very clean it isn't. I cleaned the slag on top and bottom of the cut well so I don't think my problem is coming from that.That leaves the cut itself. The cut area from plasma is very hard (kinda like martinsite..I have tried drilling a cut hole larger before and couldn't).

    So if I turn my volts down to about 18( 10 gauge steel) I get a lot less bubbles. But did not get the penetration I wanted. Is that because of less penetration into the plasma cut edge.(my pieces are butted together in the shape of a cone ..at a bit of an angle so there is a small gap on the outside and no gap on the inside.) The bubbles all appeared in the center of the weld.(gap area).
    Did not get the penetration I wanted at 18 volts.
    I was able to weld it together.Redid the bubbles. I switched welding machines. From an newer machine to an older(not digital) and that helped a bunch too.Maybe I ran less volts but I don't think so.

    Mad welder 4
    Thank you
    You are very right. I tried running straight co2 and almost no bubbles. lol but the welds look a lot weaker.So I usually run 75 25 mix co2 because it seems my welds look a lot better than straight carbon dioxide.

    HT2-4956
    Thank you
    So I am not getting any melt thru at all. If I turn my volts up it gets worse. Like very bad at 22 volts (10 gauge). So it is a 12' by 12' cone and pretty much stuck at the way it is sitting.

    Pete.S
    Thank you.
    I think you nailed it. Even though the cut area looks clean it should be grinded and not just the top and bottom of the cut. Thank you for the article.

    Thank you everybody for the awesome advice. I have one more full cone to do and I will grind the cut area (not just the slag on top and bottom) and post the results.

  14. #14
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    Re: mig welding plasma cut parts

    Just to clarify:

    There are air plasma cutting systems and there are oxygen plasma cutting systems for cutting steel. Air, which is 80% nitrogen will produce a nitride layer that hardens mild steel. If you weld directly on the nitride cut face you can experience some porosity in certain welding processes....though not to the extent that appears in the pics here. I suspect there is a shield gas issue with the poster's process in this case. Generally a weld directly on an air or nitrogen plasma cut will be a structurally acceptable weld (done properly) but likely would not be acceptable for welds that would be used in critical weldments....such as pressure vessels. You can remove the nitride layer with a few grinder or flap disc passes...as it is only .006" to .010" deep in most cases.

    Oxygen plasma's are used in most high end industrial CNC cutting applications. Done per book specs an oxygen plasma cut will be 100% weldable with minimal edge hardening and no nitriding.

    If you have critical welding that must be done on a cut edge, then it often makes sense to specify the cutting process (oxygen) just as you would specify a particular welding process. Jim Colt Hypertherm

  15. #15
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    Re: mig welding plasma cut parts

    Thank you jimcolt

    Just for the record it was air plasma cutting 10 gauge steel 65 amps at 190 ipm Hypertherm 85 on a plasma table with water table underneath. Very clean cut almost similar to a laser.I did not remove nitride layer but did grind any slag on edges.

    I did not think it was a gas problem because I tried several gas settings anywhere from 15 to 45 cf or whatever you call it.
    I also changed welding guns.not better. The gas bottle had been filled less than 2 months prior.
    However the welding machine ( miller invision 354MP with 70s feeder ) has always been a bitch. I think that was part of the problem because when I used an old on it's last legs Esab machine I did a lot better.

  16. #16
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    Re: mig welding plasma cut parts

    A little something else too. Grind the edges well before putting a plasma cut sheet in a metal brake.

  17. #17
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    Re: mig welding plasma cut parts

    you need to grind the actual cut itself, not just the top and bottom dross. You will get porosity from the cut edge even if the looks good. Grind to a shiny finish.
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  18. #18
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    Re: mig welding plasma cut parts

    Weld porosity is not an issue when welding on an oxygen plasma cut edge. For most welding needs you can weld directly on an un-ground raw air plasma cut edge as well, however there likely will be some minor weld porosity. If you are concerned, clean about .006" off the raw plasma cut edge....flap disc works fine.

    And I agree.....air plasma cut edges will scar the dies in a box or pan brake, and the raw air plasma cut edges can develop cracks when formed. Again, a quick pass with a grinding wheel or flap disc will completely eliminate this issue, though this (again) is no necessary if an oxygen plasma is used.

    Jim Colt Hypertherm

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