TIG with TOT: AC Frequency?!

hey what's up welcome back you look good you've been working a torso I'm pretty sure I've said this before but if this is your first visit to my channel I'm not the best welder in the world I may be like number three I do this as a hobby I've been doing it a long time and I know it works for me but despite doing it only as a hobbyist unless there's something really good on TV I like to think I'm an attentive fellow on a scale from 1 to I don't know 60 61 I may be a light for so keep that in mind during this video I'd like to talk to you about something controversial well probably not controversial but maybe this video will make it that way AC frequency more specifically TIG welding and what changing the AC frequency does and how one might go about picking a frequency to use so what I'm about to share with you is all in my head in every sense of that phrase I should have probably thought this through more than I have but here we are open mic night hopefully it will stir some discussion people smarter than me might chime in and shed some light on the subject for me perhaps consider this veiled cry for help conventional knowledge holds that changing AC frequency changes the shape of the arc changes like the cone angle a low frequency is supposed to give you a big wide arc a high frequency would give you a tight or focused arc makes one think you might use high frequency for welding really small stuff doesn't like for pinpoint accuracy well from my experience that's a load of hogwash that's right I said it hogwash hey hey hey ok ok don't unsubscribe just yet granted I'm trying to be a little dramatic here but bear with me let's give it a try this is the HTP 221 and this will go from 20 Hertz to 200 we'll try it at 20 and 200 and surely we'll see a difference start with 20 okay so as I said this is 20 Hertz the gap at the electrode is not to know about an eighth of an inch I'm going to do this at 70 amps machines now set to 200 Hertz now maybe it's just me but I didn't see a heck of a lot of difference between those two frequencies at least not so far as width or focus of the arc now if you haven't been sitting down till now I recommend you pull up a chair so we're about to get into full-blown tinfoil hat territory this is the spot we just saw the tests run it this was run at 20 and 200 Hertz there's a little bit of a halo and to some black I guess carbon or something this thing is right out of my scrap bin I didn't really try to clean it this is at 200 Hertz I just move the block over gave it a shot at 200 Hertz same amperage and this is 20 Hertz now if you can make it out you can see the 20 Hertz is wider and that's really just sort of the cleaning action of the AC arc I didn't change the balance here only the frequency if you look at sort of what would have become the puddle in the centre you see there's sort of like a darker matte gray and then a shinier silver that's where the puddle was trying to form or starting to form at 70 amps for this quarter-inch thick stock it would have taken a little bit more heat than that for the short burst I was given it but you can see here the puddle is technically a little bit bigger than it is on the 200 Hertz shot here it's more speckles but I don't think that's a function of the arc focus or how tight the arc is in my experience that's the heat I mean apart from the fact that this was the third test in my experience lower frequencies for the same amperage put more heat into the work now if you go out there and do some research well and watch some videos there are people that test this now they'll set the Machine low and then try to run a wide bead or set the Machine high I'm talking about frequency here and run a thinner bead now I'm not calling anybody a liar but if you go and you watch those videos really closely I tend to find that they show contradictory results quite frankly the beads don't change but you go out there and search for AC frequency and you watch what happens when they do get thinner beads we're splitting hairs here when they do get thinner beads I think there's a psychological element going on like you hear a higher frequency so you're probably unconsciously moving and dabbing more frequently and then it came across Jodi's video at welding tips and tricks on AC frequency and again maybe these aren't the right words but that one came across to me is the most honest or the one that fit my evidence the best in fact I watched his whole video with a smile on my face because I noted just how diplomatic he was being about the effects of AC frequency on the weld his experience fits my experience and what I'd like to do here is share my theory of what's going on I have tried to design a little test piece to hopefully try to demonstrate what I think the effects of changing the AC frequency are but first I just want to share what I think is going on or at least give you the story that runs through my head when I'm setting the AC frequency I in fact I'm pretty sure that this theory is incorrect but again the evidence seems to fit well enough that it turns out to be a good rule of thumb for me or a handy way to think about it whether or not it's correct so the electric arc is a plasma it's high-energy electrons and ions and Stardust and fairy poop all stripped from the tungsten and the shielding gas by the voltage and the current now I'm no high energy particle physicists but in a way you can say I've got plasma in my blood the only way in my experience that I found to change the arc shape to get a wider or a narrower arc is to sharpen the tungsten to either a blunt or a sharp point the blunt or the points the wider that arc is going to be the sharper the points the more concentrated and tighter it will be the AC frequency is sort of a layer on top of that it's what the actual molten puddle is doing while you're welding so allow me potentially to introduce you to the skin effect I think that's what they call it the skin effects in AC when the frequency is very high the current tends to run through the surface of a conductor through its skin in low frequency it would run through the entire cross-section of the conductor now from my limited understanding the skin effect doesn't really become prevalent until much higher frequencies and what we're talking about in TIG welding but I find the skin effect useful to think about when I'm trying to pick an AC frequency to weld with so the classic example is say welding an inside corner in aluminum of course a wide arc won't really be able to get down tight into that corner I mean it can people have been welding with you know 60 Hertz AC since the beginning of time but higher frequency helps out of it too helps get the molten puddle down and get proper penetration inside an inside corner joint and if you think about it in terms of the skin effect you can almost imagine like the current wanting to run across the surfaces instead of down into the material sort of get concentrated on those sharp inside corners the same case could be made potentially for welding on the edge of a thin piece of material like if you're trying to do an edge buildup and you want the puddle to stay on the edge and not sort of blob over the sides stay very defined that higher AC frequency and the skin effect to me appears to explain that the other clue here is that lower frequency AC tends to be hotter like there's more efficient transfer of heat to the work if you set your machine to say 100 amps and you weld on the low end of your AC frequency in my case 20 Hertz I find that the base material will puddle faster than if I'm at 200 Hertz and again if we think about it in the whole skin effect tinfoil hat Theory lower frequency is kind of locally conducting through the core of the material instead of spreading out across the skin more heat to sort of stay in put underneath the point of the tungsten electrode resulting in a faster puddle technically if you think about it it's really the same amount of heat right if you think about it as just a like a 50 percent duty-cycle square waves no matter what the frequency is you still sort of got the same power under the curve over a given amount of time there's no reason 200 Hertz shouldn't puddle just as fast as 50 Hertz but in practice if you try to weld something at 150 or 200 or 250 Hertz you'll find that you're going to have to up your amperage so this little test piece does nothing more than just create a lot of corners for us for the AC frequency to sort of run into across up down etc I've never actually tried this test before but in the time that I've been welding aluminum I think this should demonstrate what I'm trying to demonstrate I think the big pitfall in other AC frequency tests is that people tend to do it on just a flat aluminum coupon so run a bead at one frequency changes the frequency run another bead and you see almost no difference in the two and that I think is because of the flat geometry there aren't any features for let's say the AC frequency to take advantage of that changes when you go up onto an edge I mean this is thick but if you're trying to do like edge buildup on some eighth inch plate you can do it at any frequency but it'll be easier at a higher frequency the current sort of doesn't want to spill over resulting in what seems to be a tighter arc or a tighter puddle anyway let's give this a try I'm going to clean it up a little bit I'm going to try one at 20 Hertz and another one at 200 Hertz I made these grooves a little bit wider than I should have these are 3/8 of an inch I should've probably made them like a quarter but we'll give it a try I expect the low frequency to wet out all the way into the corners and I expect the higher frequency to almost kind of want to avoid to those corners this between welds just so I'm doing an apples-to-apples comparison and then we'll try to get on the top we'll see what the outside corners do compared to the inside corners okay so I'm going to do this at 20 Hertz I've got the Machine up to 200 amps I'm going to try to run this a little hotter than normal maybe even go a little slower than I usually would I almost want to add a no lose control of the puddle a little bit to make up for the fact that I build such a large slot I'm going to floor the pedal 200 amps I'm going to try to keep it consistent between both of these try to run the same puddle speed all right 200 amps is really freaking hot I actually thought I had the argon bottle but it's a 50/50 mix argon and helium so that's probably like 200 40 amps you're looking at there but to keep it consistent I'm going to quench this and do the same exact mess at 200 Hertz okay so this worked out a whole lot better than I was expecting I'm not even going to do the welds on the outside corners because that would essentially be reproducing what other people are already done with building up edges or you know welding thin stuff with high frequency but again same current please disregard that rough start there I forgot to actually open up the gas bottle but you can see the high frequency at the same heat I mean it's even hotter than 200 amps again I'm running a 50/50 argon helium mix sort of stayed inside its little tunnel there the way I think about it in my twisted up brain is that skin effect is having trouble sort of I don't know think about almost that current travelling through the surface of this having trouble making those corners inducing all sorts of weird Eddie's and almost like an arc blow keeping that weld bead confined inside that geometry the 20 Hertz on the other hand is just a bulldozer getting a hotter arc because it's lower frequency and sort of a larger puddle spread because you don't have the same skin effect that you have at a higher frequency all right well I think that's it for this video I just wanted to get that off my chest to recap I don't think it's the skin effect that's doing this that's just the theory that runs through my head when I'm sort of setting up for particular weld it does seem to explain what I'm seeing so do higher frequencies focus the arc sort of I mean if there's the geometry around it to help whatever the physics of high-frequency arcs are to focus the arc then yes the puddle is more constrained but again if you try this on a flat piece of material you're not going to see this dramatic of a difference so I don't know if that helped if you found that interesting or not if it shed any light certainly if anybody knows what's actually going on I'd love to hear about it I've just never found a satisfactory reason of why it does what it does and I'm the kind of guy that I don't know if I don't know why I'll never remember it so in the famous words of my buddy Forrest I think that's all I got to say about that I can't offer you a physical reason why the AC frequency does what it does but I don't know maybe that helped a little bit thanks for watching

Channel: This Old Tony

Views: 339,203

Rating: 4.9346371 out of 5

Keywords: tig welding, ac frequency, tig welding aluminum, aluminum welding, ac frequency adjustment

Id: 0kghA97pyvI

Length: 13min 13sec (793 seconds)

Published: Tue Aug 08 2017

Reddit Comments

[u/hwillis]

The skin effect actually does appear at pretty low frequencies. Wikipedia to the rescue: the skin effect at 200 Hz is as low as 4-5 mm. With square waves there will be higher harmonics and the depth will be even lower. TOT has some good thoughts about the skin effect in the weld material, but the skin effect is probably most important inside the plasma itself.

Conventional wisdom about the arc cone probably comes from thinking the plasma will be confined more by the magnetic field from higher frequencies. That's technically a thing but there's almost no way it influences the plasma, since a field that strong will cause problems with attracting steel weldments.

Back to the skin effect in the arc: higher frequency will cause power to concentrate in the outside of the cone. That extra heat on the outside will dissipate a lot more before getting into the metal, and indirectly widen the arc very slightly. The heat on the outside will generate a little extra plasma from the surrounding cool gas. Say you're running at 2000 Hz with a square wave and your overall skin depth is 1 mm. If the arc is 4 mm wide, the power in the center is 20x lower than the power on the very edge of the arc. At that point it might as well be off. At 200 Hz the difference will probably be closer to ~20%, but that's still a huge difference and the overall heat into the weld will be reduced a lot as well.

The reason skin effect is usually neglected is that the overall power dissipation doesn't change much until higher frequencies, and wires are much thinner than a GTAW arc. Electrical engineers don't care much if a wire has 10% more resistance than expected, but when you're welding a 10% change in settings can be a big problem.