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Thread: TIG welding SS

  1. #1
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    Default TIG welding SS

    My TIG welding skills are admittedly rather basic. I have a job in progress where I will need to weld some 0.6mm Stainless. I have the gear, so no problem there but would be interested in any hints or tips on welding SS - is there a rule of thumb for Amps for example.
    A welder looked at a photo of my SS welding recently and said I was running too hot - how do you find the sweetspot (if there is one)? Typically I have trouble getting things to melt - could be fit up or cleanlyness or????

    Michael

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    Hi Michael,
    On thin material like that I would start with trying to use a heat sink backing behind it, like a bar of 10mm aluminium which will help to trap the argon as well as take the heat away. Copper is even better if you have the luxury.
    As always, the sweet spot amperage will be the one that gives sufficient penetration without burning through or overheating so that carbide deposits (in the case of SS) start to form. Use a fine tungsten tip (1.6mm) with a sharp point which will allow you to get a cleaner start on low amps. I'd try 40 amps and see where that takes you. If you have a foot pedal then you'll have an easier time.
    Travel speed is important too. If you go to cold/too slow you will end up pumping more heat into the part. Best to go a little hotter, but go quicker. If you go to fast then you will find that the stainless will go a grey oxidised colour, which means it didn't have time to cool sufficiently before you moved alway with the shielding. Perfect shielding will have your SS weld not having any colour tint at all, golden means that the weld was still a bit warm as it was re,exposed to air, blue is hotter, etc. So the colours give you some idea of shielding and how hot the part is away from the weld.
    Fit up on thin stuff is critical, otherwise you have to be pretty handy with your filler to stop the edges peeling back as you're trying to weld. Cleanliness is godliness as they say - clean metal helps the weld 'flow' and merge with the base metal.
    Cheers
    - Mick

  3. #3
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    Thanks Mick
    It's obvious if you think about it but I had someone point out that the protective film on SS will leave adhesive behind when you pull it off, so they said that even that surface should be cleaned before welding.
    I do have some copper bars 'obtained' for this sort of thing so I'll be using them when I can; access in some places could be tricky.

    Michael

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    A gas lens will also help with the weld shielding if you have one available.
    With material that thin you will need plenty of tacks to stop warping.
    If you need thin filler rods I have some 0.9mm 316 rods in stock and you are welcome to try some of them.

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    G'day Michael,
    If your machine does pulse, I've found that works well on thin material, especially if you don't have a pedal. Trial and error with some scrap to get the best ratio.

    If you're working with pipe or any enclosed shape, purge the inside with argon (from the top as argon is heavier than air) plug the ends with a rag if necessary. I've found this results in much cleaner welds.
    Cheers,
    Greg.

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    24 gauge(?) and basic skills sounds more than a little challenging! If your machine has the facility, I'd typically use an upslope/zap/downslope setting initially to "spot weld" something that thin to avoid the oopsies. Then if your machine has the facility, starting amps way, way down and using a 1mm electrode for the continuous weld, distortion, with what sounds like flat sheet, even with the heat sink should be fun - or not.

  7. #7
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    Hmm. Not sure what is happening here - electrode is 1mm, amps from the quick look I had are around the 24A mark GAs is argon, flow according to the ball in tube meter on the regulator is 7 lpm through a number 4 cup. Material is a ferritic SS, filler is 1.6mm diameter 316L rod. The first photo is a plug weld (filling a hole in the wrong spot) onto a copper strip. Both SS and block were wiped down with acetone. This weld is on the plastic protected side of the material (peeled back before wipe down)
    P1030812.JPG
    I don't know what that brown crackle is. It will wire wheel off but still leaves a mark. Almost like a thin plastic film
    These are some runs on an offcut of the same material. First weld is on the non-plastic side of the SS, not cleaned at all. Second photo is clean up after wire brushing
    P1030815.JPG P1030816.JPG
    Same thing but on a spot that had been flap wheel'd (new wheel, only used on this job) then wiped with acetone. Second photo is after wire wheeling.
    P1030813.JPG P1030817.JPG

    As you can see it cleans up but at the same time I'm having trouble getting good wetting - the tacks I've done so far are sitting up like... well, something that sits up. The darker material around that weld is like a baked on film.
    I had thought it might be gas but with post flow set at 12 seconds and held directly on top of the weld until it stopped the appearance was no different.
    I'm reluctant to start doing real welds if I can't get the SS clean as more amps to burn through what ever it is is more amps to blow holes.

    Michael

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    Hi Michael,
    1st photo looks like it's still got plastic or glue or something. Scrub it down with a clean scotchbrite or stainless steel scouring pad. Acetone isn't a universal solvent, experiment with metho, turps etc. wash it off and then final wipedown with acetone.
    I know the metal is thin, but as a test I would also flap disk the metal just to be absolutely sure it is just metal on the surface.
    Also what does your tungsten look like after you do a weld. Is it bright metal?, Grey? blue? Dull, Burnt up?
    Also, go and find a different bit of stainless - pick up a SS bolt or something from bunnies to weld on and at least work out if the problem is the base metal or something to do with your torch/gas/technique.
    [edit] 12 seconds is way to long for thin stuff, just give it a few seconds past when its not glowing hot anymore (try say 4 secs). You're just wasting gas. See my post earlier about oxide colours (and google it). You can use the oxide colours to fine tune your post flow time if you want to get scientific about it. Set your flow rate on about 7 litres per minute (depends on size of cup you are using).
    Cheers
    - Mick

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    Certainly appears to be glue residue.

    Using a lens? Looks too hot to me.

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    No lens - I think I have one somewhere but haven't found it yet.
    The heat is the thing. I suspect to burn through the glue I'm running hotter than I should and so when I do get through, I'm putting more heat into the metal than I should.
    I'll try experimenting with some different solvents and mechanical cleaning today if I get the chance.

    Michael

  11. #11
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    Quote Originally Posted by Michael G View Post
    I suspect to burn through the glue I'm running hotter than I should and so when I do get through...
    You cannot burn through anything with TIG, it must be removed back to clean metal.

  12. #12
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    I've been having problems with thinking recently and I wasn't sure if I should offer opinion in case its all nonsense, but maybe I've got to get on with life. Take everything I say with a grain of salt!

    With removing the film, I found that orange oily stuff the supermarkets sell is the opposite of acetone ie the two don't dissolve the same type of thing at all, so if one doesn't work, the other might. It is oily though so the orange power needs removing absolutely with acetone before welding. I also think its worth trying petrol because its cheap, but again use acetone to remove the traces before welding.
    20170205_121249.jpg
    I have loads of stock I built up from the scrapyard and some of the offcut sheets still have film on them that must be decades old. it seems to stick to the steel after years, even though some of it appears to peel off. I think it delaminates or something and leaves a sheet of plastic on the steel. I'm sure I've got stuff that would need mechanical removal, which is a shame because it will take away the very polished finish its supposed to preserve.

    I'm not a great welder but I've done a fair bit of very small welding and noticed a few things that might help. To show you the scale, the petals and leaves on the rose are 0.5mm so similar to what you are using, and the stalk of the leaf is 1.6mm. The thicker stalk was probably 3.2. Its definitely a different thing to weld really thin stuff, from normal gauge for building things. For me, I still like to just use 2.4mm tungsten for everything, but with a fairly long needle point (really sharp 10~15mm long) for fine stuff. I do have a 0.8mm tungsten I think it was, but I only used it once and its a pain to keep sharpening and you lose the point so easily if you use too much current (like over 15 amps!). I think it was really meant for robotic stuff, not manual welding but if its tiny stuff it did work at 10amps and had good access to small areas.
    20140921_123555.jpg
    All the forums say about stainless to keep the heat down which I'm sure is good advice generally, but it's debatable if the more important thing is to keep it covered in gas until its cooled, which ends up the same thing I suppose. I use a 6 gas lens at 5lpm for most things which I felt was a good compromise for coverage/cost. A gas lens lets you lower the lpm I found. I've seen arguments where people say too much heat causes the stainless alloys to separate and the iron comes to the surface at the edge of the weld and causes rust. Someone said well, no matter what you do you have to melt the stainless in the actual weld, so how come the iron doesn't come to the surface in there and rust. no-one ever answered him, but the argument rages on.

    That sugaring or corrosion where the weld has become exposed too soon which looks like dark/grey crystalised metal is if the stainless gets exposed to the atmosphere way too soon (although the other argument is, its due to too much heat). It also happens on the back of the weld if its thin of course (much more of a problem than mild steel which doesn't seem to care), but the copper bar us supposed to stop that. People use all sorts of arrangements to cover the back with argon, even just someone holding a tube on the back at the same rate you are welding. You also get a paste called solar flux which I've only seen for sale in America which you can coat on the back of your weld and I keep meaning to order some.

    Something I've never read anywhere else but was a problem for me, is using the foot pedal at low current. If you set it to 10 or 20 amps and then try to ramp up with the pedal, on my welder at least, you get a plasma gas sort of thing which arcs everywhere like a plasma ball, then snaps into a spark once the current builds up. That plasma arcing ruins a polished surface (because the plasma tracks wander out about 1cm or so. I'm definitely not talking about the hf spark, there is a definite plasma) so depending on what you are welding, that can ruin it. As a personal preference, I like to control the torch with the button to just switch on the arc, no pedal for thin stuff. Its one less thing to worry about, and you can control heat by varying speed. I'd start on 20 amps too and adjust from there. I just feel it gives you more precision, you know exactly what heat you're going to get when you start and its there instantaneously.

    It's quite different welding thin sheet as a butt joint to welding it in the middle of a sheet. The edges will try to pull apart, so give that some practice as well before going onto your real job. As someone said, no gap fitup is essential. For fine stuff I just got a 1kg roll of 0.8mm mig wire and I cut off lengths of that. 1.6mm rods are a bit heroic for 0.6mm sheet but the technique I've seen people recommend (and it does work for me too) is to put the heat directly onto the rod when starting. For fine stuff, gap between the tungsten and the work becomes much more critical. For some reason, if you lift up, you seem to get more heat and it will just burn through immediately. I try for 1mm and less and find I need to support your hand, no chance of freehand stuff.

    I'm not sure how good you are at controlling warping but it could be a problem depending on what you are doing. You can actually do a series of spot welds that you can touch almost immediately but its slow because you can't let heat build up at all and need to wait between spots. If its a small thing that's usually not a problem. I've no idea if that's good advice, but I do that in some situations and it seems to reduce warping for me.

    For preflow, I personally just touch the torch button away from the work to get the gas flowing, and bring it to the work and use the ongoing post flow as preflow. That way I know exactly when the arc is going to start when I press the button on the work. I didn't like the pre-flow switching on the arc after a delay. For that precision type welding, the more direct control you have the better I reckon. For tiny welds, you definitely need gas flowing before you start. On bigger welds at higher current you get away without it but not so much when the welds are small. Of course you should use preflow on all welds.

    A final thing is to use gloves. Even though its tempting not to because the arc is tiny and all the bits small and often need placing/holding - the big problem is the HF decides to go through your hand quite often when you start. For me at least, I rest my arm or hand on the welding table or usually a bit of scrap metal lying on the table and very often the hf comes out the button and in between my thumb and fore finger is where I feel it. Its not deadly but uncomfortable and puts you off if you are waiting for the pain every time you start! it happens to me much more when doing fine welding because you need to be braced off rigid things so much. Its definitely worth getting some insulation between you and the table.

  13. #13
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    Just back from trying a few things out. After a few experiments I can confirm it is a paint-like film and tough as, on both sides of the sheet too - even the side covered with plastic film. I tried several of the things suggested by members.
    Firstly a weld on some known stainless, and a second photo after wire brushing. I'm probably still putting in too much heat but that's something I need to work on and a known problem.
    (First photo is the top right in the second photo)
    P1030818.JPG P1030827.JPG
    I'm still not sure what finish I should be getting 'off torch'. Even holding the torch on the end of the weld until post flow stops (5 seconds I think) still gets the result on the left.
    I was asked about the tungsten - It is not discoloured or anything. (Sorry - auto focus)
    P1030825.JPG
    I've tried various solvents. Left to right are Turps, Kero and Metho. As you can see it is not being removed by any of it.
    P1030826.JPG
    I have some offcuts sitting in paint stripper at the moment but that does not seem to be attacking it at all.
    About the only thing that does work is mechanical abrasion. This is after sanding, acetone, welding then wire brush. Bottom left you can still see some varnish hanging on where I did not sand it.
    P1030828.JPG
    I'm guessing this stuff was for splash backs or cladding and I've picked up a few sheets thinking it can be welded but it is not really meant for that.
    I think until I use this material up I'll have to sand the sheet - a pain as it's extra work. I'll also have to sand the bits that I've already folded up. The most annoying part about that of course is that it will look patchy so I even though I'm just welding a couple of seams, it's all got to come off. I'll have to try some of that orange power stuff too - see if that shifts it, even if only not to clog sanding belts.

    Michael

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    Quote Originally Posted by Gavin Newman View Post
    You cannot burn through anything with TIG, it must be removed back to clean metal.
    I know, but while trying to remove it my test welds are basically doing that - burning through the varnish. I would love to know how to remove it to get clean metal so all I need concentrate on is weld. It is interesting watching the arc getting established as it blips around all over the place trying to find a place to get through before it starts.

    Michael

  15. #15
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    Hi Michael,
    the photos are good.
    I guess you've already watched a few TIG welding videos - so you'd be aware that a TIG weld shouldn't typically need any wire brushing to bring out the shine - it should be be shiny when welding and remain that way as it cools.
    I would now get that piece that you've cleaned up in your 2nd photo and weld it again, right next to one of your cleaned up welds. Any coating should have burned off, and your wire brushing will have got rid of most of the oxides, etc. So in theory you should have some pretty good base metal to try and weld on.
    If you look at your tungsten you can see that it is not shiny and you are obviously getting crud building up on the cup. It should look like a bright silver pin, not a dull grey knitting needle. The cup should remain clean if all is working well.
    I'd use a bigger cup also, at least during this trouble shooting phase.
    If you still have an issue, then it's either a) materials, b) settings or c) setup or d) environment or e) technique or all the combined.
    So to address each:
    for (a) - try as I've described above and also for piece of known stainless such as a 304 bolt or washers from bunnies. Also check that your filler wire is 304, 309 or 316 and that you are using 100% argon (not MIG mix)
    (b) list out all the settings you are using on your machine: amperage, argon flow rate, etc. Also
    (c) go for a #6 or larger cup.
    (d) check you are out of the wind, away from fans (including your welder fan)
    (e) hold the torch close to vertical above the material and then lean the top back about 10 or 15 degrees away from the direction of travel. Make sure the tungsten is only a few mm above the work piece.
    Cheers
    - Mick

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