Super wide etching on Aluminum!
This was a reply to a phone conversation with mark, about an issue I'm seeing but please feel free to comment if you have had a similar one, or new suggestion. ( Please first read my "hello" in the Introduce yourself column, just to orient yourself with my background in TIG, I'm not a newby .... 30 years or so, just want to save everyones time from having to try to cover basics. I really Love the machine but want to figure this issue out. ) Thx
Hello Mark, again thank you for your time on a saturday afternoon. Well, sunday i went to the shop and burned thru half of a 125 bottle of argon! ....... layed down some aluminum for sure. Tried all kinds of things today. Here's kind of a summary of what i was seeing or finding -
First, I tried two different brands of 2% thoriated, purchased WELL apart from each other time wise. Sharpening to a point, on my good ole dedicated belt sander, also on a dedicated fine ginding wheel ( properly ground long ways ). Tried any type point imaginable, long short, truncated etc. Arc stability was essentially the same for each, and experienced no weld impurity issues ( of course we're talking non specified, non crit welds here ..... just clean good looking shiny beads on some various coupons i made from stock on hand ). Now regarding the tungsten splitting issue - Both of the batches of thoriated tungsten began to develope "cauliflower" texturing as miller welding describes it, or splitting as you call it, either way at as low as 80 amps! Mterial thickness 3/32 - 1/8 or so. Tried different cups, in fact hooked up an entirely different brand new torch. With ac balance at 0, or full counter clockwise, up to the point at which it would burn the tunsten up, and anywhere in between. Pulsing off thru out, and started with ac freq. at about 60-80 hrtz. Nothing i could do or change would prevent the tungsten from becoming jagged cauliflower like once i hit 80 amps or so. ( I would definately not consider that overheating for a 3/32 electrode with balance at 0!! ). In fact according to miller welding's site, inverters should allow you to use a SMALLER tungsten for a given amerage, and they state that 200 amps is not a problem for a 3/32 thoriated! - I could still make very nice looking beads in spite of the ragged tungsten even tho the stability was definately effected somewhat.
The WIDE etching issue remains. In fact adjusting the balance up to say 9 to 10:00, or more, seems to have little or no effect on the width of etching along either side of the weld ( 1/4 - 3/8 in on each side of the bead! ). This does appear to convince me that it "may" not be a balance issue as you stated, UNLESS it is not going as low as the 10% as stated in the specs, with the knob full counter clockwise, just a thought ( imagine if you will the ACTUAL starting point of the range of EN is say 40-50%, even then the etching should be waay closer to the weld footprint ) Again just thinking out loud here, but the taper of that potentiometer does seem to VERY rapidly favor EP range! At 12:00 I'd bet on a scope you'd be seeing 70% EP, as from there up the tungsten overheats almost instantly at quite low amperage. Keeping in mind most fixed balance squarewave machines run in the 50 -60% range for cleaning purposes. )
The other attributes of ac balance seem to be in line with what you'd expect to see, ie wider bead, as i increase the balance knob clock wise, BUT there seems to be little or no change until reaching 9:00 - 10:00 on the knob, then it rapidly goes to tungsten melt down past noon. Once again the taper seems a little odd. This does seem to be peculiar to this machine as WELL as the last one i had with the defective freq, potentiometer (frozen thru a portion of it's range - the second 250ex to have that problem, the first having the same issue but with the balance knob, as well the first machine died within 30 minutes of use. HF stuck on and no arc initiation possible, no matter what i tried. Probably dropped during shipping? This is the THIRD machine, and came with a small dent in the side, numerous superficial scuffs and marr's about the face and a small crack in the face surround!). As far as the etching I can run a bead from my Lincoln Squarewave tig right next to it and the etching footprint barely exceeds the weld footprint (1/16 in and less if i want.) If that is not an ac balance issue, then I am truly perplexed as i have tried everything i can think of, Argon pressure changes, air leaks, back cap changes, collet body, tungsten tips, grinding, complete torch change out etc. I had no ceriated, Lan, Zirc, on hand at the time but i will try some others soon.
In the end after about 5 hours of various combinations, i could not reduce the UGLY white etching footprint, ...... even while my welds were coming out beautifully, so shiny they looked like polished silver!! Some of the prettiest looking beads ive ever seen, like liquid silver (with proper heat and travel speed! ) Just that damn wide area along each side of the weld that ruins it! NOW, the interesting find ....... apparently thoriated does not like LOWER frequency AC, on the 250EX machine ..... when i ran it up to 2:00 ( 120-140 htz? ) The tungsten just kind of found a nice little blunt point or after a time MAYBE a small ball, but resisted splitting up to at least the area of 125+ amps. I did not have the time to establish a point at which the cauliflower splitting begins, but i will in the near future. Some difficulty occassionaly starting the arc tho at the high a/c frequency setting, but worth the trade off in my opinion to eliminate the splitting. There are things that i like sometimes about the old 60 htz wave, depending on the job, nice soft arc, wide buttery bead, etc. So it would be nice to be able to utilize that. But even so, i would sacrifice that for the excellent welds the machine is capable of if it wasn't for this etching issue. I have to wire brush the area precisely along the weld but always hit some of it ruining the appearance, and then i have a nasty wire brush on my piece. ( keep in mind I'm speaking of items that require appearance grade welds like sheet metal intakes, Turbo routing etc. ) You can see it as soon as i initiate the arc, and wet in the puddle. You can see the width of it, but it would be hard to put into words the physical look of it, ..... just a kind of wild electrical scattering on the surface of the metal along the perimiter of each side of the weld. Keep in mind that the arc cone is nicely focused, IS NOT wandering, just a very steady straight travel, tungsten height, speed, etc. that years of TIG welding has allowed me to perform. I will post some pic's as soon as i can to provide some visuals, matched with material thickness, and machine settings, along with some comparisons from my Lincoln squarewave on the same material. Any additional ideas info are appreciated in advance.
Sincerely, Lou
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