Some advice for a novice

[woj]

Hi all,

New user, first post, so excuse my not keeping up with the forum standards and perhaps asking things covered already (did search, and found some information I need, just want to confirm some things and ask other). Also, up front, excuse my lengthy posts, I am usually keyboard happy

The story is short, I am fascinated with tig welding, but so far have never done it. More generally, I only played with a cheap stick welder for a day or so (not a very pleasant experience). My application target is mostly neat fabrication of a car exhaust system (in other words, I am preparing for my next car project, on the previous project I did the cutting and sizing myself, but had the welding done by professionals, and it bothers me that this is the only thing I cannot do myself). So, having a considerably sized bag of scraps from the previous project I though I'd give it a try by renting a small, yet proper tig welder for a week and see what I can do. I have a nearby shop that rents the stuff out and has very decent machines, I am thinking Rehm Tiger 170 DC would be just what I need (convenience link - http://www.rehm-online.de/index.php?id=37&L=1).

The advice I need confirming or given is this. I have a bag of 2inch exhaust piping remains, both mild steel and stainless (304L I believe, whatever Jetex makes) to practice on. (I also have thicker plates of mild steel to see if things work for me at all for starters.) The wall thickness is 1.5mm. The first thing I need to know is type and size of the electrode that would be good for this. For the size it seems to me that 1.6mm would do it nice, but I am not certain. For type, well, tell me? I am after one type that would work for both. Then the filler rod size? Should it be the same for stainless or mild, or different? Would 1.6 do it, or is it too thick? Is the 316Lsi rod good for welding 304L steel (my understanding from reading things is that it is, but what do I know...) Finally, some ball park figures on the settings. The amerage in general for this kind of application is not too mysterious too me (I should be trying things in the 40-60 range from what I have read), but for stainless I know that pulsing is the way to go, and the mentioned welder has it fully setable (t1/t2 and i1/i2). Here, I'd had no idea where to start.

I do understand that I am up for something difficult, that I will have to try things on my own, and that you cannot give me a straight recepie or answers. I just do not want to start too far off, and since I will be renting the machine, I will be a bit under time pressure, so I want to be prepared. And, it is only for a practice and learning, I will not yet be welding anything that will be later used by me or anybody else.

Cheers,

Woj

 

[cumbriasteve]

Just saying welcome to the forum and can't add anything else to help with your question, I personally have no TIG experience or knowledge about the machines other than what I have read here myself, someone with more experience may be along soon, unless they are living in one of our many flooded areas of the UK.

 

[Shox Dr]

You are trying to run, before you can even crawl. Have a read of the TIG help section. TIG Welding is not something you learn quickly, esp' if you haven't any welding knowledge and or experience

 

[woj]

Thanks for the pointer, I did read the MIG guides, but somehow I missed the TIG guides, and they have most of the information that I was looking for. And I also did find some info on puls welding in the meantime. As for the "you are being too optimistic" remark, well, this is not discouraging for me, quite the opposite. I have been given comments like this before on other matters I was engaging in, and have proven folks wrong very quickly. But thanks for the warning, very much appreciated

 

[Shox Dr]

Thanks for the pointer,
As for the "you are being too optimistic" remark, well, this is not discouraging for me, quite the opposite.

I didn't offer any optimism: It's not easy!

Partly what makes it so enjoyable.

 

[woj]

I didn't offer any optimism: It's not easy!

I know you did not, I meant I am too optimistic.

Partly what makes it so enjoyable.

I think we are slowly finding a common ground

 

[woj]

So, after thinking for a while if I am not too crazy to go straight to tig I did indeed rent the equipment today. So far I got to try things out for 2.5 hours or so only, managed to dip only one electrode with the filler rod. I do not yet have the discipline and I also think that I used too thick rod and electrode at first. The welds on the pics are done with 2.4mm tungsten and 2mm wire (that's what I was advised at the shop, but I think the guy was not listening to me saying what I actually want to do). Especially the wire seems to be too thick. Later I tried 1.6mm tungsten and that worked much better, the visibility of what I was doing became much better and the weld started to look better too. The filling with the rod goes wrong from time to time, this the bit that seems the hardest to me (also there was still rust on the material despite my best efforts to clean it up). Anyhow, I managed to completely connect two pipes together with a good penetration. Not what I dream of yet, but it is something, at least on the last pic it looks like what I am expecting a weld to be. Oh and yes, this is sooooo much easier than the stick.

 

[Shox Dr]

If those are your first results, you pick it up in no time. What's the inside look like?

 

[woj]

Not so easy to take pictures of the inside, especially with the phone, but I tried. It is not penetrated in all places, because sections were done with fusion only and at too high speed I believe.

EDIT: and the inside was not as thoroughly cleaned as the outside.

And yes, that was my first time, I fired the TIG for the first time in my life today

 

[woj]

To my total surprise stainless steel welding goes somewhat easier. On the outside I get different results depending on the settings and they follow what I would expect. On the inside though it got ugly. It sticks out and there is lots of porosity. Now, I know this is almost certainly due to lack of back purge. But I am only certain about the porosity, not about the stick out? I do have a setup for back purge (double flow meter, the necessary pipes, and plenty of argon) and I will be trying it out, but I need to know what else could I have done wrong.

 

[hotrodder]

Stainless has lower thermal conductivity than carbon steel so you typically need around 10% less amperage. While that effects the amount of weld penetration the 'coking' (aka sugaring) that occurs without a purge kinda exagerates things... the chromium in stainless is very reactive and oxidises LOTS producing that thick, tenacious scale

 

[woj]

That explains a lot, thanks. Indeed the situation did not change even when I went down from 40 to 30 amps, and 40 was already down from 45 that I used for mild. I will try back purging tonight and see what it does.

 

[woj]

Back purging worked a treat. I managed to get one very nice looking practice weld, but without joining, and then all excited welded two stainless pipes together. This did not come out as nice as the practice weld, but nevertheless not so bad in most places. Interestingly enough, the best part of the weld on the pipes is where I used no or very little rod. I am slowly starting to think that this is the way to go for this kind of joint. Pictures below.

Anyhow, the biggest issue I have at the moment is dipping the rod. I have problems getting it to melt and it often sticks on me. I either do something really wrong (keep it too far or too close to the tungsten), or the rod is too thick. For stainless I have only 1.6 at the moment, Monday I will get 1mm. But, any tips on how to practice the dipping and how to come over my issues are very welcome. I cannot keep consistent with the dipping and hence the welds look like they do...

 

[woj]

I am getting there, the biggest problem I had turned out to be helmet set for too dark. Also for some reason feeding the rod suddenly started to work for me, just like that, it still occassionaly sticks, but hardly ever. I guess I started to get used to all those things happening at the same time and became more calm.

I am yet to properly and uniformly weld two stainless steel pipes together, but first I want to get 1mm rod for this. The question for today though is: when you fuse without the rod do you normally use higher, lower, or the same amperage compared to when you do it with the rod? I will be trying out the pulse soon too, I can see that it can do nice things already, but for the low frequency one it is yet one more thing to keep in sync with.

 

[backpurge]

You appear to be be making good, steady progress, well done

 

[woj]

There is one more thing I wanted to ask (again, something I will be trying out, but need to know if I think in the good direction). I get this grey looking slag on my stainless welds. I can clean it off, but I still wonder what is the reason. When I do tack welds there is no slag and the weld is nice orange-ish color. So perhaps too little gas flow? I use gas lense and have the flow (last time I checked) set to about 5l/h. Or the opposite - when I tack weld I keep the tungsten at a bigger distance from the material (but also for longer in one spot)...

 

[woj]

For the record, it seems that increasing the gas flow reduced the slag on my welds. Also, there is enormous difference when welding with 1mm wire. I can dip any amount of it I want to into the puddle and everything feels easier and smoother. In the meantime I also gave it a rest with back purging, mostly because I am running out of gas and what I have left has to last me until Thursday and this is only practicing, I know it is a must and that it works now, so I skip it.

Anyhow, today's pipe join (I know it is slightly too high and slightly too narrow, I have not yet mastered my amperage setting and travel speed sweet spots) and practice pulse beads with the filler rod (at 0.5Hz 45/20 amps). I also made a fuse joint but came out very deep, I assume one has to tune the amps down for this.

 

[hotrodder]

The 'slag' is just light surface oxidation, search the TIG forum for 'weld colour' and you'll find a bunch of threads on the subject several of them very recent. Search again for 'pulse' and you'll find several threads that go into quite a bit of detail.

With autogenous welds you're melting less metal (not adding filler which cools the weldpool...) so you need less heat input i.e. can either move faster or turn the juice down a little

Arc length is probably one of the most important bits with TIG, keeping it consistant and, ideally, no more than the tungstens diameter*. Nailing this is a key skill, especially when talking tube/pipe as the angles of attack constantly change which effects arc length if you don't keep with 'em as the weld progresses


* bigger dia tungstens are used at higher amperage = bigger weld pool = slightly longer arc length

 

[woj]

Yeah, the constantly changing angle is something that still drives me nuts. But also my temporary workshop is not very comfortable, I cannot position myself such that I can rest my elbow on the same table where I have the work piece, the nearest resting point is my knee. That effectively means that my wrist is fully bent making my moves less flexible. It also means that the longest stretch of a continuous weld I can do is less than 2 cm, this can be seen on the first pic up there, there are two practice beads on top. The arc - I can keep it very close in general, even too close, when I dip the rod the puddle grows to the point of reaching the tungsten. I also get the impression that the welder that I rented is very forgiving for not maintaining the arc gap. Another thing I keep forgetting is that the overall temperatures change - when I start everything is colder and require lower speed, later I can speed up. So most of my welds now start with a mountain to later turn into a proper bead. And since my sections are short I get a grand canyon kind of thing... :/

 

[woj]

Today I discovered the wonders of high frequency pulse welding, this is precision welding I'd say! Though I am not certain about my settings yet, 100Hz 45/20 Amps split. It seems to do the trick when I go really slow, this gives me time to think and readjust myself. But I wonder whether a better weld would be produced with higher juice setting and faster speed? I also played with low frequency pulse again, that works too but not as nice. Finally, I found myself a good position for pipe welding on my table, tacked together two last clean pieces of pipe together, and tomorrow I will give them the final weld, the best I can. After that I'll call it a lesson and equipment goes back. Below a pic of the practice beads with high frequency pulse, did about 15 of them. I still get the slag, not always though, but I purpously keep the gas flow not too high (I think I'll be out soon anyhow) and I do not have a size 7 cup, something I figured I'd need reading the recommended topics

Edit: Actually, I need one more piece of advice - do normally weld from between a tack to between a tack, or between tacks, when you do sections?