AC or DC for TIG on steel?

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Pure argon shield, Red band 3/32 tungsten, on about 1/4 material in the 150amp range using a pedal. I've been using AC but I've read on here and elsewhere I should be doing DC....I switched it over to DC and it makes a whole different sound. The arc is way more contstant and steady too, except that it seems to take alot more amperage to melt anything. The hand torch seems to get WAY hotter too. If I keep going like that, a few minutes is all I can handle before my hand is getting burn through the gloves. The machine is a fairly old Miller dialarc 200...Any advice?
Reply:dc, with hf start. if ya got 1/8" tungsten set up I would switch to that.thinking you dont have a water cooled torch since it is getting so hot?
Reply:ok, HF start only on DC then and not constant? The torch is a watercooled one and it does seem to be circulating because I just had a hose come off in the shop the other day and flood the floor near instantly. What is the dis-advtange to using AC?
Reply:a/c is pretty much for aluminum only, than it would be a/c with continuous hf. for all your steels, stainless steels  and such  you should be set at d/c with a hf start  ( if you have that option on your machine)Last edited by elderthewelder; 11-08-2005 at 10:52 PM.
Reply:Yes, it has the HF start/continous/off options on it. I'll try it some with how you suggested and see how it turns out. Perhaps switching the HF from continous to start will make a difference in the heat? Dont know.
Reply:you should be fine, get the mill scale off your steel ( by grinding or sanding) and it will weld up a little cleaner
Reply:Billy, I hope you all don't mind, but based on your story of welding steel on AC, then switching to DC but not getting much melting and the torch getting hot, and finally the question of continuous HF, I'd like to try and define a few terms and explain my understanding of some aspects of TIG welding.1. Gas Tungsten Arc Welding (GTAW), accepted term of American Welding Society (AWS).2.  Tungsten Inert Gas (TIG), common term for GTAW.3.  Heli-Arc:  early trade name by Linde Corp. for GTAW with helium gas.4.  Direct Current Electrode Negative (DCEN), also called straight polarity, the torch (and thus tungsten electrode) is connected to negative terminal (-) of power supply, workpiece is connected to positive terminal (+) of power supply.  Electrons flow from tungsten electrode to the workpiece.  Impact of electrons is primary source of heat and melting at the workpiece.  Produces deepest penetration into the workpiece.  Tungsten can tolerate high current and maintain a sharply ground point without melting into a ball.  Used in GTAW of steel, stainless steel, copper, and most metals/alloys.5.  Direct Current Electrode Positive (DCEP), also called reverse polarity, the torch is connected to positive (+) terminal of power supply (used for shielded metal arc welding (SMAW), commonly called stick welding, not normally used for GTAW.  Electrons flow from the workpiece to the tungsten electrode.  Impact of electrons melts the tungsten, with the very least penetration into the workpiece.  Tungsten can only tolerate very low current before the tip is melted back to form a ball.  Only application I've heard of was for repair of cast sculpture where the "arc cleaning action" was required to remove surface oxides (see cleaning action below).On the older transformer type power supply, reverse polarity may be used to intentionally "ball" the tungsten prior to AC welding of aluminum, see AC below.Reverse polarity provides a "cleaning action" that removes oxides from the surface of the workpiece and this is why alternating current (AC) is used for welding relatively thin aluminum.  6.  Alternating Current (AC), 1/2 cycle of DCEN + 1/2 cycle of DCEP, 60 cycles per second (Hz).  Intermediate between DCEN and DCEP, tungsten can tolerate moderate current without melting.  Normal AC welding with the older transformer type power supplies will tend to produce a ball on the end of the tungsten (see below newer inverter).  Used for GTAW of aluminum for cleaning action.Some power supplies provide a "Balance Control" that allows adjustment of the AC to supply more or less DCEP and cleaning action, and more or less DCEN and penetration.Newer inverter type power supplies allow adjustment of arc constriction via changing the AC frequency from the standard 60 Hz, the tungsten does not tend to ball-up, and a AC welding of aluminum may be done with a sharped tungsten.7.  Continuous HF is required with AC GTAW to keep the arc "ignited" as the current goes to zero in the AC cycle.8.  HF start is a convenient way to initiate the DC GTAW arc without actually touching the tungsten electrode to the workpiece, i.e. scratch starting, where tungsten contamination of the weld can be a problem.Newer technology "lift arc" or "touch start" allow starting the arc without HF, by simply touching the tungsten to workpiece, pausing, then lifting.9.  Final comment on tungsten types.  You do not need any special type tungsten electrode for different base metals or for AC welding.  Now-a-days, if you or your company is concerned with the radioactive thorium in the "red stripe" electrode, simply choose the ceriated or lanthanated and forget it.  The type of tungsten will have no appreciable effect on your weld penetration, surface finish, porosity, or whatever.You do not need pure tungsten for AC welding of aluminum.  I think that pure tungsten was promoted for AC welding with a balled end because of problems encountered with the ball on 2% thoriated tungstens.  The issue with the balled thoriated electrode is that it sometimes forms a hole in the ball which causes arc instability and wander.  The pure tungsten melts at a lower temperature and does not form this hole in the ball.  This issue with the balled thoriated tungsten in not a big deal, if it becomes a real hindrance, switch to reverse polarity and remelt the hole out of the ball.If you use a new inverter AC power supply, you can weld with a sharpened electrode, it does not tend to ball-up like the old transformers.
Reply:Thanks for the post pulser. I'm addmitedly a little bit "newbish" to welding and have self taught myself most everything I know so far (Which isn't a whole lot). No books or manuals, just mostly trial and error. After reading elderwelder's advice I swapped the machine over to DC straight polarity with HF start, and had much much better results then when I was previously on DC with HF continous.  The machine makes a whole new sound and the arc is not near as erratic as before. Its very smooth, and constant now.  It does not get near as hot as it previously did either. My question is, just out of curiousity, what are the downfalls to welding on AC like I previously was other then the tungsten melting and difficulty of keeping a steady arc? I'm only asking because, even though it didn't seem to work near as good as DC with HF start, it did work.
Reply:I think you just about summed it up, it will work, but DCEP is better.  Also your neighbors' TV may be screwed up by your continuous HF.Guess if all you had was an AC buzz box, converted to TIG with continuous HF, you could get by and weld both aluminum and steels.Best of luck to you.
Reply:Thanks Pulser. To give you an idea of what I had been accomplishing on AC, heres a picture attached. This is of a bottom steel tripple clamp I made and welded together to hold some larger diameter front forks for one of my three-wheelers. This was really the first project where I've done alot of steel welding. I've done a fair amount of aluminum in the past before though. The welds did come out pretty good looking even though I was using AC and thats why I was curious to what dis-advantages it had vs DC on the previous posts. Thanks for clearing that up and helping me out.  Attached Images
Reply:It looks like you get along just fine with AC.
Reply:on tig, you need not run dcep,  thats reverse polarity and in the early days of stick welding you had to run electrode neg, tehrefore its called straight polarity.  ON tig, you also must run electrode neg, except on ultra thin alum you would run dcep.  You ought to run it with DCEN  and have HF only for start and you also want to run your panel amperage at 1 amp per .001" of thickness.  Therefore for 1/8" .125 you want 125 amps.  For 1/4 .25 you use 250 for 1/16 you use 63 amps.  Hope this helpsCHRIS
Reply:hi everyonecan i know why i should have both AC and DC TIG for my industry. I would like to weld Aluminum, Stainless Steel, Brass mainly. Can I be happy with a DC TIG for the purposes? What lead weld-experts to buy AC TIGs as well? Which factors I would consider at the time of purchasing a TIG for 8 hrs per day utilization? thanks in advance.
Reply:well if i rember right ac has a cleaning efect to it that dc dont so in some aplactions like alum welding it helps alot chuck
Reply:WIth alum yes you neeed ac for tig, unless its alum foil. but yes for mild and stainless steels you need dc.  AC needs a high frequency to jump across the the pos to neu balanceCHRIS
Reply:You CAN weld alluminum with DC in TIG, but you will have either a dirty highly penetrated weld, or a shallow, but very clean weld.  the deep is DCEN, and the shallow is DCEP.  DCEN takes a smaller electrode, and DCEP takes a huge electrode for the same amount of amperage.  but I would not suggest a DC tig weld, if you have other alluminum options. Brian Lee  Sparkeee24
Reply:Where did you attend training for welding to learn from an expert?
Reply:metal who are you asking this question of?CHRIS
Reply:You can also TIG the 1/4" Aluminum with DCEN with Helium Gas, 2% pointed Tungsten with HF on Start only.Helium gives you an instant puddle and very deep penetration on any thick piece of Aluminum.Just another Aerospace trick to weld thick Aluminum.  I can get an instant puddle going on a 12"x12"x12" block of Aluminum with this set up.Try it.
Reply:metal what size tungsten do you recommend with this setup?IF it Catches...Let it Burn
Reply:Originally Posted by MetalSculptorJust another Aerospace trick to weld thick Aluminum.  I can get an instant puddle going on a 12"x12"x12" block of Aluminum with this set up.Try it.
Reply:lmao  good job elder... i believe you before this troll.  well hell I belive you before a lot of trusted experienced hands..but thats just because you can back up what you say, or I can prove it anyway by tryin it out.  DONT FEED THE TROLLIF it Catches...Let it Burn
Reply:Originally Posted by elderthewelderI have been welding aerospace for 20 years ( I dont claim to know it all) It is common knowledge that you can weld Alum with DCEN, but it is not the recommended methodBut I will call instant B.S if you say you are welding a 12" thick piece of aluminum.
Reply:I never have welded 12 inch thick aluminum but on 2 inch thick at room  temp. you can get an instant puddle using dcen and helium.  I have done this many times over the years.  That is using about 250 amps.  Sharp tungsten.  You can get a really nice weld and quick.
Reply:Because we weld for the semiconductor industry, we weld aluminum exclusively with DCSP.  Just like any other welding process, once you've done some  practice, it's no problem. And Pulser, just for clarification, not to be argumentative, the impact of the electrons in GTAW is not what causes the heat, it's the resistance of the material to the electric current that causes it to get hot and melt.  (Think about a  fuse).  In order to have the impact of the electrons cause a kinetic energy transfer sufficient to cause heat for welding, you would have to be accelerating the electrons to approximately 1/2 the speed of light, and then concentrate them into a spot approximately .010/.020".  That particular process is known as electron beam welding.I r 2 a perfessionalI read that if you run DCEP more heat is generated in the electrode .. And less on the base metal .. which fits your pattern to a "T" ?? I'm still learning too .. but did read that ..
Reply:DCEN when used for aluminum is sucessful for thick section when used with Helium. You will not have the same sucess if you attepmt the process with Argon. Yes the weld area will have the appearance of being dirty, sooty the price you pay for Helium use. I believe anyone can get a "puddle" on a 12x12x12 block of aluminum but the puddle doesn't mean you are going to get the penetration required to perform a sucesful job.Ric
Reply:Originally Posted by elderthewelderI have been welding aerospace for 20 years ( I dont claim to know it all) It is common knowledge that you can weld Alum with DCEN, but it is not the recommended methodBut I will call instant B.S if you say you are welding a 12" thick piece of aluminum.