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  1. #1
    Join Date
    Aug 2013

    Default problems welding after plasma cut.

    Anyone ever had problems welding material that has been cut with a plasma. I'm having problems tig welding outside corners on aluminum that has been cut with a plasma. I file off the edge and then hit it with a stainless brush. When I try to weld it its almost like trying to weld cast aluminum. When I cut it with a band saw or with a disk it welds just fine. Should I grind it smooth after I cut it with the plasma? Any ideas?

  2. #2
    Join Date
    Sep 2005
    Salem ,Ohio


    Yes aluminum, steel, stainless steel i have had problems over the last 30 years. You need to grind all of the cut edge off esp on alum. I weld pressure tanks and refuse to cut the holes with a plasma just for that reason...Bob
    Bob Wright, Grandson of Tee Nee Boat Trailer Founder
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  3. #3
    Join Date
    Dec 2007
    Los Angeles


    Plasma leaves a heavy oxide behind, as you have noticed.

    You can dress the edge for welding with an Aluminum burr.
    Ed Conley
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  4. #4
    Join Date
    Aug 2013

    Default problems welding after plasma cut.

    I tried the burr on aluminum and it worked perfect.

    I tried grinding on stainless after plasma but still welds bad.

  5. #5
    Join Date
    Oct 2009


    Use a flap wheel dedicated to stainless to clean the plasma edge, sand until its shiny and no remnants of the scale from the plasma is left. Only way to ensure its perfectly clean if it is required.
    Miller syncrowave 200 runner with coolmate 4
    and wp2025 weldcraft torch
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  6. #6
    Join Date
    Feb 2009

    Default Alternative gases

    It is my understanding that using a bottled gas instead of air helps.

    In particular, on stainless, it is my understanding that nitrogen as a plasma gas leaves a very clean edge.

    I have not tried this myself.
    Con Fuse!
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  7. #7
    Join Date
    Jun 2012


    There are a lot of different plasma options that can improve the edge quality and weldability on different materials.

    Air Plasma is the most common plasma. Air is roughly 20% oxygen and 80% nitrogen. On steel, the nitrogen content in air creates a nitride (case hardened) edge. This can affect weldability, and definitely makes the edge very hard (machining, drilling, tapping become difficult. On aluminum it is the oxygen content in air that leaves a rough, porous, slightly oxidized edge, again making it more difficult to weld. On stainless....again, the oxygen in air produces a rougher edge with oxidation. In all cases a few passes with a flap disc will remove the roughly .005" contamination, making weldability a non issue.

    Most air plasma systems can also use nitrogen. Nitogen makes the nitride hardening on steel worse, and also produces more dross on steel. Nitrogen in an air plasma will not noticeably improve aluminum and the ambient air we are breathing will still oxidize the edge. Cutting aluminum and stainless submerged under an inch or so of water will improve cut edge oxidation on both aluminum and stainless....but will increase dross.

    Do not use an other gases in an air plasma system.....unless the manufacturer approves it, same goes for under water cutting!

    On high end industrial plasma systems there are a variety of engineered solutions for dramatically improved edge quality and weldability. Oxygen is used on steel cutting.....with 100% weldability. F5 (95% nitrogen, 5% hydrogen) with a nitrogen shield gas is used by at least one plasma manufacturer (Hypertherm) to improve stainless edge quality and weldability on thicknesses under 3/8". Argon (65%) /Hydrogen is used on thicker stainless. Aluminum can be cut with other processes as well.

    If you have a supplier that cuts parts that you have to weld.....check their equipment listings. Keep in mind that air plasma systems are kind of the bottom of the capability list when cut quality, weldability and productivity (faster cutting, lower cut costs) are required.

    Jim Colt

  8. #8
    Join Date
    Nov 2003


    Thanks Jim

    are these gas options usable on an older unit like a standard Powermax 1000 in a CNC application (PlasmaCam)

    or does it take special setup, power supply and consumables ??

    The more you know, The better you know, How little you know

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