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  • Anyone familiar with plasma welding

    I am looking for anyone familiar with plasma welding.

    Please not that I am referring to plasma welding, not plasma cutting. I already purchased a Miller Spectrum Plasma cutter.

    What I am referring to is called plasma welding.

    I have heard that it's supposed to be more precise than tig welding (which I already h ave a Miller Dynasty).

    However, I can't seem to find much info about it.

    Has anyone out there done any plasma welding?

    Thanks

    Mark Allyn:confused

  • #2
    I did plasma welding where i work for a little while. We used a thermal arc ultima 150 with the seperat pulse box for welding .008 thick stainless steel. It used two shielding gases argon for the pilot arc and 98/2 for the swirl shield (thats what they called it). It was pretty neat we used 3/32 red tungsten sharpened to a point and could make a nice small weld that was strong and looked good. If they will let me at work i will take a few pics of the welds and post them up here. If you have any specifics questions post and i will try to answer. It is pretty much the same as tig just a little different machine, setup and gas. Oh and its dc only.
    Last edited by down19992000; 12-11-2008, 07:35 AM.
    hh 187.:
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    • #3
      From what I understand plasma welding is a rather costly process, but well worth it if you need it. There have been 2 or 3 folks on the forum over the past several years with posts regarding plasma welding. You might also try doing a search for their post.

      down19992000,

      I too am rather interested in the pictures of the .008" SS as I have made of couple of go rounds with .004" hastalloy with GTAW.

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      • #4
        Can you use the Dynasty with a plasma torch?

        Folks:

        Thanks for getting back to me.

        I wonder, if I already invested in the Dynasty rig, could I use it as the power supply and just get the plasma welding torch? If it's DC, I can't see why it would make any difference. If that were the case, then I would only need to buy the torch assembly.

        My work is primarily in jewelry; if you want to see it, I have an artists journal at www.allyn.com where I have some pictures. I take old bicycle gears and stainless steel eating utensils (from thrift stores), along with other pieces of scrap steel and weld them together. Some of the pieces are small and I am wondering if this would be a suitable application for plasma welding.

        The thinnest metal that I work with is about 1 mm thick. (I don't know gauges very well) The thickest is about 1/4 inch thick.

        Mark

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        • #5
          plasma welding

          When I was a Linde factory rep, they sent me to the plasma school. I also had responsibility to demo equipment in the development lab to potential customers.

          My take on it is that it is more expensive than TIG to get started, more difficult to set up, but better for some applications on very thin materials. If you are welding something like 1/4", plasma would be very similar to TIG, except that the part could be welded faster and with less heat input. It really shines on something like .005" sheet. A person can make butt welds like that with very little training or practice. However, the same thing can be done with TIG if the right power supply is available. In another job, I developed a TIG weld procedure for .002" titanium sheet. All you really need is a TIG power supply that is designed to operate at very low amperage. Weld logic makes some good ones that run at 1 or 2 amps. With plasma, it is easier to hold the arc at low power though. With TIG, the process is more sensitive to changes in arc length for hand held work on tiny parts. For something like .030", I would be inclined to just go with TIG. That is the thickness range welded at my current employer, and we tried plasma, and the operators did not like it as well as TIG, so we did not buy the new equipment. Also, it was a cost and set-up related decision.

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          • #6
            The pilot arc I was referring to is a continuous arc that stays lit even when no welding is being done. It helps initiate the plasma arc. I don't know how you could have it set up on a tig process. And if you could it would only be good on DC since there is no zero voltage point (i copied this off another forum because I couldnt remember specifics), but its right I believe.
            hh 187.:
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            • #7
              plasma welding

              Some pilot arcs are on continuous, and some are just used to start the plasma arc. Some plasma controls have seperate control over the pilot gas and the shielding gas, and some have timers used to start the pilot arc, before the main arc clicks on. It really depends on what kind of plasma work is being done if a TIG control could be used. If it is just micro/needle arc plasma using all argon, then perhaps a torch could be rigged to a standard TIG power supply. But, it might have to be a 100% of the time transferred arc plasma column. Some plasma torches are designed for non-transferred arc, while others start the pilot arc first, and then kick in a transferred arc with a solenoid AFTER the pilot arc has been established. Hence the need for a more complicated welding control.

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              • #8
                Plasma welding is very similar to TIG as the arc is formed between a pointed tungsten electrode and the workpiece. However, by positioning the electrode within the body of the torch, the plasma arc can be separated from the shielding gas envelope. Plasma is then forced through a fine-bore copper nozzle which constricts the arc. Three operating modes can be produced by varying bore diameter and plasma gas flow rate:
                Microplasma: 0.1 to 15A.
                The microplasma arc can be operated at very low welding currents. The columnar arc is stable even when arc length is varied up to 20mm.


                Medium current: 15 to 200A.
                At higher currents, from 15 to 200A, the process characteristics of the plasma arc are similar to the TIG arc, but because the plasma is constricted, the arc is stiffer. Although the plasma gas flow rate can be increased to improve weld pool penetration, there is a risk of air and shielding gas entrainment through excessive turbulence in the gas shield.


                Keyhole plasma: over 100A.
                By increasing welding current and plasma gas flow, a very powerful plasma beam is created which can achieve full penetration in a material, as in laser or electron beam welding. During welding, the hole progressively cuts through the metal with the molten weld pool flowing behind to form the weld bead under surface tension forces. This process can be used to weld thicker material (up to 10mm of stainless steel) in a single pass.


                Power source
                The plasma arc is normally operated with a DC, drooping characteristic power source. Because its unique operating features are derived from the special torch arrangement and separate plasma and shielding gas flows, a plasma control console can be added on to a conventional TIG power source. Purpose-built plasma systems are also available. The plasma arc is not readily stabilised with sine wave AC. Arc reignition is difficult when there is a long electrode to workpiece distance and the plasma is constricted, Moreover, excessive heating of the electrode during the positive half-cycle causes balling of the tip which can disturb arc stability.
                Special-purpose switched DC power sources are available. By imbalancing the waveform to reduce the duration of electrode positive polarity, the electrode is kept sufficiently cool to maintain a pointed tip and achieve arc stability.

                Arc starting
                Although the arc is initiated using HF, it is first formed between the electrode and plasma nozzle. This 'pilot' arc is held within the body of the torch until required for welding then it is transferred to the workpiece. The pilot arc system ensures reliable arc starting and, as the pilot arc is maintained between welds, it obviates the need for HF which may cause electrical interference.
                Electrode
                The electrode used for the plasma process is tungsten-2%thoria and the plasma nozzle is copper. The electrode tip diameter is not as critical as for TIG and should be maintained at around 30-60 degrees. The plasma nozzle bore diameter is critical and too small a bore diameter for the current level and plasma gas flow rate will lead to excessive nozzle erosion or even melting. It is prudent to use the largest bore diameter for the operating current level.
                Note: too large a bore diameter, may give problems with arc stability and maintaining a keyhole.
                Plasma and shielding gases
                The normal combination of gases is argon for the plasma gas, with argon plus 2 to 5% hydrogen for the shielding gas. Helium can be used for plasma gas but because it is hotter this reduces the current rating of the nozzle. Helium's lower mass can also make the keyhole mode more difficult.
                Applications
                Microplasma welding
                Microplasma was traditionally used for welding thin sheets (down to 0.1 mm thickness), and wire and mesh sections. The needle-like stiff arc minimises arc wander and distortion. Although the equivalent TIG arc is more diffuse, the newer transistorised (TIG) power sources can produce a very stable arc at low current levels.
                Medium current welding
                When used in the melt mode this is an alternative to conventional TIG. The advantages are deeper penetration (from higher plasma gas flow), and greater tolerance to surface contamination including coatings (the electrode is within the body of the torch). The major disadvantage lies in the bulkiness of the torch, making manual welding more difficult. In mechanised welding, greater attention must be paid to maintenance of the torch to ensure consistent performance.
                Keyhole welding
                This has several advantages which can be exploited: deep penetration and high welding speeds. Compared with the TIG arc, it can penetrate plate thicknesses up to l0mm, but when welding using a single pass technique, it is more usual to limit the thickness to 6mm. The normal methods is to use the keyhole mode with filler to ensure smooth weld bead profile (with no undercut). For thicknesses up to 15mm, a vee joint preparation is used with a 6mm root face. A two-pass technique is employed and here, the first pass is autogenous with the second pass being made in melt mode with filler wire addition.
                As the welding parameters, plasma gas flow rate and filler wire addition (into the keyhole) must be carefully balanced to maintain the keyhole and weld pool stability, this technique is only suitable for mechanised welding. Although it can be used for positional welding, usually with current pulsing, it is normally applied in high speed welding of thicker sheet material (over 3 mm) in the flat position. When pipe welding, the slope-out of current and plasma gas flow must be carefully controlled to close the keyhole without leaving a hole.
                I got this off a uk site it explains more about it and does it way better than i could
                hh 187.:
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                miller diversion :

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                • #9
                  Thanks for the replies; anyone know rough estimate on cost

                  Folks:

                  Thank you very much on the help. I now have a better feel of what plasma is about.

                  Do any of you have any rough estimate on the cost to get started? Is it comperable to the Dynasty?

                  Mark

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                  • #10
                    Here is a link to a thermal arc on ebay. http://cgi.ebay.com/Thermal-Arc-Plas...3A1%7C294%3A50


                    It is 3 phase so I dont know if that is a deal breaker or not? I have seen an ultima 150 go for $750 recently so you may want to keep an eye out on ebay.
                    hh 187.:
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                    miller diversion :

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                    • #11
                      $ and sense.

                      markallyn,

                      It depends on what want as with any welding process. down19992000 has done a fine job describing some similarities and differences between GTAW and different types of plasma welding. If I recall correctly I found options for modifying a D300 for around 5K just for a power source and a complete lower end, but very nice and well above entry level, around 15K. I have not watched EBAY in some time so there may be some good deals lurking.

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                      • #12
                        plasma cost

                        I don't know anything about hot deals on e-bay or Craigs list, but when I used to sell plasma equipment in 1982, the difference was significant. A TIG sold for $3500, and a comparable plasma was $4500-$5000. When we recently priced a plasma welder here at work, it was around $8000. It does depend on what you buy. No doubt, you might find some cheap plasma deals on ebay, but then you would also be able to find some cheapER deals there on TIG. Don't forget too, the torch alone is a higher cost even if you cobble a way to rig one to a standard TIG power supply. Unless you plan to do a lot of micro work, it might not be worth your effort, unless you could get into a set-up for a few hundred more than TIG.

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                        • #13
                          Obewan dont know if i made you mad but I was just pointing out that you can find used equipment like he needed on ebay not trying to start any trouble just responding to his questions. I have had decent luck buying stuff off ebay sorry if you haven't.
                          hh 187.:
                          powcon 300 st
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                          miller diversion :

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                          • #14
                            Guys,

                            I hope nobody is mad. I think the big thing with EBAY is you really have to know what you are looking to buy. This type information can be difficult to come by without significant research time. I think we are all on the same page-maybe just a bit scattered.

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                            • #15
                              Originally posted by down19992000 View Post
                              Obewan dont know if i made you mad but I was just pointing out that you can find used equipment like he needed on ebay not trying to start any trouble just responding to his questions. I have had decent luck buying stuff off ebay sorry if you haven't.
                              I'm not mad. I was just trying to speak from my personal experience, which may be outdated. I don't buy weld equipment on e-bay because I live in a condo and don't have a shop, and my employer buys all new OEM equipment.

                              I agree with Hawk that it helps to know what you are looking for, and that takes work. Maybe the cheapest plasma on ebay would be cheaper than the cheapest tig if the bid went right and a really good deal came up. You would have to know the options and prices well to take advantage of it though. I was using generalities when I said plasma is more expensive than tig. Then too, there are the made in China units, would might be ok or might be junk. LOL. I prefer to support the USA when I can.

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