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  1. #1
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    Default TIG tungsten electrode tip geometry - science vs wisdom?

    Have been reading about TIG tungsten electrode tip geometry. Have read a couple of research papers done with various tip angles on flat plate mostly steel DCEN. The research mathematical modelling and physical metal experiments shows deeper penetration with wider (blunter) tip angles using the same current. This appears directly contradictory to what is written in welding guides from multiple sources which all claim pointy electrodes provide deeper penetration. The modelled and experimental results seem more consistent with electron physics that electrons need more energy to escape from flatter vs pointy shapes.

    I was watching a welding video last week Tig Welding Aluminum - How to Tig Weld Aluminum - Aluminum Tig Welding Beads - YouTube that showed the electrode after the demonstrator finished a lovely looking AC aluminium job. The electrode tip looked like a dog had chewed it off (about 36 seconds in). Apparently this is what lanthanated looks like on AC, according to Miller.

    So any comments from people who have systematically tried blunt vs sharp and compared penetration????

    PS
    So just found a Miller article on pointy vs blunter
    Miller - Tips to Improve TIG Arc Starts and Promote Arc Performance in Aerospace and other Low Amp Applications

    "Fig. 11 The Impact of Point Angles. Contrary to popular belief, a pointed tungsten does NOT provide deeper penetration (but it DOES provide better directional control)."

    The Miller TIG handbook, page 36 has more photos credited to the American Welding Society showing penetration on flat plate - deeper with blunt electrodes.


    The Australian Welding Society's "TIG welding – Method and Application" (courtesy of Google) page 12 still says "A small pointed angle gives a narrow weld pool and the larger the pointed angle the wider the weld pool."
    Last edited by blouis79; 5th Nov 2013 at 09:02 PM. Reason: added

  2. #2
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    My understanding is that a horizontal face will give deeper penetration, but the arc will wander and not be as controllable. A pointed electrode will flare the arc cone, but provide a very controllable arc. I assume the arc wandering is because the electrons are originating from the periphery of the horizontal face and the arc is meandering around the circumference. I have to confess that I've never tried it.

    [edit: I just looked at the link - the caption descriptions for Figures 11 and 12 are spot on I think.]

    Cheers

    - Mick

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    Quote Originally Posted by WelderMick View Post
    My understanding is that a horizontal face will give deeper penetration, but the arc will wander and not be as controllable.
    So here is what I found from my reading:


    Effect of Electrode Geometry on Maximum Arc Pressure in Gas Tungsten Arc Welding [in Japanese]
    HIRAOKA Kazuo , OKADA Akira , INAGAKI Michio
    1985 Japan Welding Society
    http://ci.nii.ac.jp/lognavi?name=nel...=ART0003954419


    Abid (2013) "Effect of different electrode tip angles with tilted torch in stationary gas tungsten arc welding: A 3D simulation"
    Effect of different electrode tip angles with tilted torch in stationary gas tungsten arc welding : A 3D simulation - Strathprints


    Abid tests a tilted torch 70deg in a computer model and with experimental metal results. The widest tip angle of 120deg shows the deepest penetration in both model and metal, which is consistent with what Miller and an American Welding Society found. A flat tipped electrode will be wandery and hard to control direction as the arc moves around the end with angle changes.



    According to Abid (who presently don't study electrode diameter effects) - results from model reproduced in metal that maximises penetration:
    a. wide tip angle miminises arc temperature and concentrates temperature distribution
    b. wide tip angle and short arc length minimise arc velocity
    c. wide tip angle produces lower current density at the tip and makes no difference to current density on the workpiece
    d. short arc length increases heat flux to the workpiece, angle makes no difference
    e. wide tip angle reduces gas shear
    f. short arc length increases electromagnetic force, tip angle makes no difference
    g. wide tip angle increases buoyancy force
    h. wide tip angle reduces pool convection


    The implication for the Hiraoka results is that one probably sees deeper penetration with lowest arc pressure and highest heated electrode surface area. (The opposite of what one would infer from reading the paper which implies that high arc pressure should increase penetration.) That makes the 45 deg angle the least good. Lower arc pressure with both very pointy electrodes and wider angles seems in keeping with practice, where very pointy electrodes appear favoured for thin work and very blunt electrodes for thick work. For a truncated cone, the arc pressure minimises at about 1.5mm for a 3.2mm electrode. Testing 90 deg tip angle, arc pressure minimises with electrodes between 1 and 2mm from 100-300A.


    At this stage, I'm getting the impression the optimal tip geometry could be a thin balled electrode (which makes a quiet arc), provided that the machine can get the arc started.

    So the practical problem is that the doped tungstens don't ball easily. That may be why the EWM TIG Primer suggests a sharpened electrode with a rounded end and says it makes a nice quiet arc.

  4. #4
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    Science and research is a wonderful thing. Dated at 1985 nothing obviousl seems to have come from it unfortunately.
    However science in the real world it must show viable application before the practical people will take it up. Initially a research finding like this is great step forward but it sounds like it was a beginning and more research was to follow. Given that our electrode angles have not changed, have they?

    The shakers and movers in the welding community won't change unless something significant occurs.

    Unless big increases in the rate of penetration can be shown and this is demonstrated to be cost effective there will not be change.

    As an example of this, take the change in electrode chemical composition.
    The last 15 to 20 years have shown tig electrode composition change due to improvements in welder design (inverters). To get the best out of inverters ability to electronically affect the arc behavior, the electrode compositions were changed. Apparently lanthalated compound has a good effect if catalogue talk can be believed.

    Grahame

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    Hi blouis,

    I haven't had time to read though that stuff you've posted - interesting stuff in an academic sense and I certainly am curious as to what findings they have, but from a practical standpoint, I reckon it's all pretty much sorted for the everyday tig welder.

    As much as I like to get distracted by the more detailed scientific approach, I find that in practice I actually keep it pretty simple mainly because I'm lazy:


    1. I always use lanthanated electrodes (either 1.5 or 2%). Why? well mainly because I've got a collection sitting in my cupboard and I find they work fine for everything I do.
    2. I almost exclusively use 2.4mm dia, tungsten except in the rare cases that I stray outside the 40 - 160 amp range. Why? see point 1 above.
    3. I sharpen all of my electrodes to a conical point with sides about 2x the diameter. These work fine for 90% of the welding I do.
    4. For high amps aluminium, I get one of the sharped electrodes and I light up on a scratch plate to ball the tip - and I find the previously sharpened cone balls quite nicely to the right proportions. I could probably skip this step as I can't remember the last time I actually had a tungsten melt off/inclusion - but usually it's not worth the risk. Most often I weld aluminium with a sharpened tungsten which balls ever so slightly at the tip.
    5. The only time I sharpen the tungsten to a thinner angle (or use a thinner electrode) is when doing very low amps tig as this does seem to help in starting an maintaining a low amperage arc.


    Keep posting your findings - I for one am interested, despite not putting to much theory into practice.

    - Mick

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    I was searching for a paper that Pete from tokentools posted once that gives a bit of detail on physics of arc behaviour. Havent found it yet, but this thread might be of interest to you. http://www.woodworkforums.com/f160/e...0/#post1587904.

    found it - here's the paper http://eagar.mit.edu/EagarPapers/Eagar109.pdf

  7. #7
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    Quote Originally Posted by Grahame Collins View Post
    Science and research is a wonderful thing. Dated at 1985 nothing obviousl seems to have come from it unfortunately.
    [...]
    The shakers and movers in the welding community won't change unless something significant occurs.

    Unless big increases in the rate of penetration can be shown and this is demonstrated to be cost effective there will not be change.

    [...] Apparently lanthalated compound has a good effect if catalogue talk can be believed.

    Grahame
    Grahame, history is interesting...... (The Wright Brothers have been found recently not to have been the first.)

    Turns out the research and images quoted by Miller on tip angle and penetration dates to 1980! Key JF "Anode cathode geometry and shielding gas interrelationships in GTAW" with byline "Electrode tip geometry and groove geometry must be compatible to ensure arc stability". An earlier study by Key in 1979 led the direction of research, after noting blunt tips (truncated cones) achieved better penetration than pointy tips. The 1980 paper failed to find a universally best tip geometry, because the path to ground obviously affects arc stability. A flat tip won't work in a groove or for a fillet weld.

    I guess the obvious did come from 1985. Prior to doped electrodes, tungstens were presumably sharpened to enhance arc starting and arc stabiloity. Core physics tells us that electrons need less energy to depart points. Japanese research in 1985 measures highest arc pressure with 45 deg angle sharpened point thoriated. People accept that highest arc pressure must equate with deepest penetration - an easy sell. Welders assume 45 deg tip is best and proceed to develop tables of amps vs thickness using sharpened tips. Getting enough amps will deliver the results required - ie full penetration and full strength. Trained welders can achieve what is required. Everything works and everyone is happy. Anyone playing with blunt electrodes will find that the arc wanders and they will know they need a sharp tip.

    Penetration as seemingly taught in Australia and Europe to this day. The correct grinding of electrodes - by Knautz GmbH & Co. KG
    Elektrodenschleifen_13.jpg

    All round the world, welders have their own "tricks of the trade", little discoveries they've made that work practically. Flattened tips prevent tungsten inclusions. Blunter tips save grinding time. A blunt flat tip works fine. Wide tip angles stop melting tips with high current and thick metal. Incidental partial balling doesn't stop them welding. EWM recommends a round tipped cone. Welding with a tip that looks like a dog chewed it seems to work fine. And so on. But TIG welding is "the hardest". Maybe part of that is because the shallower wider penetration profile of the pointy tip makes it a fine line between achieving fuil penetration and a big hole.

    Somewhere along the way, the 1980 research by Key is rediscovered and confirmed and becomes embedded in the American Welding Society Welding Handbook. Curiously, this is exactly opposite of what is taught worldwide. Most trained welders don't read research, so nothing changes elsewhere in the world. Welding still works.

    Penetration as seemingly taught in USA. Pro-Fusion: Electrode Tip Geometry Selection

    The Abid paper seems driven by computer modelling and curiosity. In the USA, it's not telling anybody anything new, so it won't change anything much. For me it helps make sense of the conflicting views on pointy electrode penetration.

    What happens next? Welding practice will continue producing the results it always has. Stick welding electrodes and MIG wires have always had flat tips anyway. The lack of penetration of lay-wire TIG could be just as much due to pointy electrodes as getting the filler in the way. When research can produce high speed automated welding to 12000mm/min (200mm/sec), then there is scope for process improvement in productivity over the recommended 200-300mm/min (3-5mm/sec) quoted by EWM Germany or the apparently widely practiced and taught 1mm/sec.

    From what I can see, it seems that energy efficiency and welding speed will be able to be improved not using pointy electrodes. The rise of inverter welders and fancy electronics makes arc starting easier with blunter electrodes, so maybe now there is room for welders to play around and see if they can get more productivity out of manual TIG? It may take a generation to permeate knowledge and practice......but change will probably come.


    The marketing blurb from the Germans suggests a blend of dopants is the "bees knees" for nearly all TIG applications except titanium and tungsten - see Wolfram Witstar WS2 - the TIG Welding guideline is the least glossy and informative bit. Recipe still claims to be secret, but does include Ytrium according to MSDS. There are a load of three oxide rare earth blend electrodes out there - probably mostly similar but not identical. E3 Tungsten looks to be on the marketing charge rebadged by existing players. It has a disclosed mix of 98.3 Tungsten, 1.5 Lanthanum, 0.08 Zirconium, 0.08 Yttrium. BOC sells packs of 3x150mm sticks of something like that (free shipping and lower price from boc_australia ebay shop). Unstated if the present BOC turquoise rare earth electrode is made by Wolfram, who supplies turquoise WS2 to EWM, who rebadges machines for BOC. Could come from Linde (umbrella group for BOC) who now sells E3 purple under their own name. I'm guessing the current BOC product is the German Wolfram WS2 and that BOC is running it out so they can sell BOC/Linde E3 purple from China in the near future.

    (I have ivory tip German made WS2 from Diamond Ground USA to play with. Diamond Ground also does free samples of all their tungstens - presumably to a USA shipping address. Didn't discover that until after I ordered.)

    Cheers

    Blouis79

    (PS can't figure how to remove the redundant unreadable thumbnails)
    Attached Images Attached Images
    Last edited by blouis79; 7th Nov 2013 at 10:19 AM. Reason: typos

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    Quote Originally Posted by WelderMick View Post
    Thanks for that - it was interesting written back in the 1980s when the author desrcibes arc physics being "too hard" for many.

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    Now that you've posted it, I'm pretty sure I've looked at Key's paper before. It certainly seems that if you're willing to sacrifice arc positional stability and starting ability then the blunter angles or truncated tip seem to be the go for penetration but only to a point (hah! pun not intended) - say between a 60 to 90 deg point. I wonder if if the supposed benefits also would occur with a fillet weld. I couldn't quite figure out what he was getting at with Fig 9 in that paper - I initially thought that might be alluding to something to do with fillets - but probably not.
    The image I have in my head (which might well be wrong) is that at very low amps, electrons evaporate from the very tip of the electrode, but at higher amps, the increased current means that electrons are also emerging from higher up the electrode (not just the point) - So if you have a very acute point, you are going to see much more flare of the arc as it is coming off the sides of the cone almost perpendicular to the work surface. At low amps, the electrons emerge right near the tip and are therefore directed straight down into the work.
    You've inspired me to experiment a bit at some stage anyway.
    Are you doing a thesis on this stuff or are you just curious?
    cheers
    - Mick

  10. #10
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    Quote Originally Posted by WelderMick View Post
    [...] I couldn't quite figure out what he was getting at with Fig 9 in that paper
    [...]
    Are you doing a thesis on this stuff or are you just curious?
    cheers
    - Mick
    Just curious. Learning stuff is fun. I figure if I learn new things thoroughly, then I can move on with confidence. The existence of "tricks of the trade" implies to me incomplete understanding. A good theory should last a long time.

    Key's fig 9 I think illustrates (without really illustrating the paths he means) that the shortest path to ground varies not just with tip geometry but with relationship to the geometry of the groove or base metal shape. If the shortest path is not a single spot, then it is implied the arc must wander. Though it all changes once there is a puddle in the base of the groove. With the 75deg v-groove a 60deg tip would still keep the arc at the tip. With the 40deg u-groove, the 90deg tip will work. With the 10deg narrow groove, the 90deg tip would still see the arc coming from the shoulder or the tip but at least that is closer to the tip than the 30deg tip with a large shoulder to tip distance and both being short paths.
    key-fig9.png


    Quote Originally Posted by blouis79 View Post
    Key JF "Anode cathode geometry and shielding gas interrelationships in GTAW" with byline "Electrode tip geometry and groove geometry must be compatible to ensure arc stability".
    Keys results suggest that a tip angle just smaller than welding groove angle is optimal in finding the compromise between penetration and arc stability, with truncation of 0.5mm on the 2.4mm electrodes he studied. With helium shielding, the pointy tips aren't inferior as they are with argon.


    - Blouis79

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    Quote Originally Posted by blouis79 View Post
    That's what I though it was initially, but then I thought "who is going to stick a 2.4mm tungsten down a 5mm groove and expect to get a perfect arc? "
    I think that hand shakes, visibility issues with the cup, angle of the torch etc. would all be a more significant contributor to whether the arc shorts out on the sides rather than the angle of the tungsten grind.
    I think that's a good example of the difference between theory and practice.
    Like you said - it's good to know the theory anyway.

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    Grahame, for those who don't like marketing blurb, the article by Matsuda 1986 "Study on Gas Tungsten Electrode report 1" shows research on all the rare earth oxides, with tip photos, microscopy and electron micrography. They assume that higher arc pressure provides better penetration and studied the previously determined "optimal" 45deg angle. Yttriated showed slightly higher arc pressure than the others. But I think the later research by Abid demonstrates the exact opposite for a given current, so suggest reading the results with this in mind. Shows thoriated with lower arc pressure than all the other oxides - which is perhaps consistent with thoriated known superiority in the field. Lanthanated is best arc starter. Lanthanated and Yttriated show best tip shape preservation.

    Ushio 1991 "Effect of Grain Morphology on Consumption of GTA Electrode" shows clear performance advantage of longitudinal tungsten grain compared to globular - which you don't get to know when buying tungsten electrodes. Suspect the higher quality brands will have longitudinal grain and the cheaper ones won't. Paper has nice photos of electrode tip wear.

    Matsuda 1989 "Gas-Tungsten-Electrode (Report 5) : Effect of Combined Additives of Rare Earth Metal Oxides on Arc Characteristics of Tungsten Electrode" show all sorts of mixes of 3 rare earth oxides show superior arc starting and wear to single oxides. Best performer studied was Y: Ce:La::3:1:1. A chinese paper by Zuoren 1999 "Tungsten electrodes containing three types of rare earth oxides" (link seems very slow, I might have got my original from another site) also showed the highest Yttrium doping (approx Y: Ce:La::1.6:0.6:0) causing the lowest electrode wear. Curiously, no existing product claims a high yttrium concentration, unless one of the secret 3-oxide recipes is this or similar. PERFORMANCE OF TIG ELECTRODES By P C J Anderson at The Welding Institute - Technical Paper Report No 220177/1/93 references this Matsuda paper, so perhaps the Huntingdon Fusion Multistrike has a recipe similar with high Yttrium??? Yttrium appears 3x more expensive than the others. Arafura - Pricing

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