Fillet welding

[sjp001]

Hi all,

I am just starting to teach myself tig welding... I have a dc r-tech, and I am currently trying autogenous fillet welds (no filler).

Most of my work is not structural but needs to look nice, so my plans are eventually to run an autogenous pass or a few tacks to secure pieces together, and then tig braze over the top of this with a silicon bronze rod. Sadly I cannot try the silicon bronze rod yet as I was sold gas brazing rods by BOC, and everywhere is closed until january...

So my question regarding autogenous fillet welds... I am finding that all seems ok when I do the first side (sorry I wire brushed it at the time to check it over so most of the heat zone is scrubbed). Then I flip the piece around to do the other side and it seems to be a lot messier. I am deliberately trying not to get full penetration on the first side so that I can make the other side match. I've attached two images to illustrate. My arc gap got too wide by the end on the back, but I''d kind of given up by this point as I could see it wasn't going great.

Is it a bad idea to try this on both sides of a fillet?

Many thanks in advance!

 

[DecK]

How long did you leave it between running the front and back? I'm not a pro welder but if you didn't leave it long enough the material might have been heat soaked and resulted in the pool being more fluid. A more experienced set of eyes will be along shortly anyway to give you the proper answer

 

[sjp001]

Thank you, that's a very good point... I didn't leave it particularly long at all. I did also notice whilst welding the back that there seemed to be a bit more flaring up which I imagine are impurities from the front face?

 

[Richard.]

Why oh why are you doing it like that. What is the material your welding on? Mild steel doesnt like autogenous tig welding too much. The filler required has deoxidising agents which need to be added to the pool otherwise you may get porus welds. This might explain why the back side is a mess. As your penetrating into a porus weld and drawing it out????? Why not just perform the joint once with filler.

 

[sjp001]

That all makes sense Richard, many thanks. The reason I am thinking of running a matching joint on both sides is purely for aesthetics, so I will try with some filler. It's not crucial so I'm also happy to just run a single side with filler if it is the best result.

I am trying this as a learning exercise in accordance with this tutorial (I have only just started learning tig) http://www.mig-welding.co.uk/tig-fillet-weld.htm but I note they only do a single side here, probably for the reasons you mention. I wondered if I could apply the autogenous process to actual projects in mild steel but it sounds unwise.

 

[Rrunnach]

Material looks like 3mm, you really should be adding filler, especially with fillets joints. Joint integrity comes with a decent throat thickness, where your weld looks concave. There are other factors, but throat T, is an important factor.

What are you making?

 

[sjp001]

I just spotted this thread which answers my question entirely: http://www.mig-welding.co.uk/forum/threads/mild-steel.58853

Rrunnach - Well done, it is indeed 3mm. I'm not making anything, just learning to get a tight arc at the moment as I have just started. I was just curious about autogenous fillets for non load bearing objects as I am likely (once I am better skilled) to use varying material thicknesses for their appearance rather than their strength and so slight undercutting didn't concern me. However I see the answer is to use filler as I don't want porous welds in any situation!

I think this thread is wrapped up now, so many thanks to you all for your words of wisdom.

 

[Rrunnach]

One final point, place two pieces of exact same size and thickness of matl into vise. Tack each corner, then autogenous weld all round. This is good practise for learning to keep a tight arc and, with cut edges free from any possible contaminants, such as mill scale, I guarantee you will have no porosity if all welding parameters are correct. Then try this on another joint type, see how you get on and feed back.

I should add, say three mm matl, making six mm. Then fuse all round.

 

[Brad93]

The metal is 3mm thick but the whole part is so small you've put so much heat into it and no filler to chill the pool, plus as Richard says, mild steel TIG rods, A15 has silicon alloyed with it, what this does is deoxidises the weld pool when you add rod. The hotter the part gets the quicker it oxidises, you've welded one side, then battered the other side which has not cooled, has reacted with the atmosphere creating an oxide layer (see how big your HAZ is) which requires more heat to melt and adds contaminatio to the weld when you break the crystalline oxide layer, with no rod t chill the pool or carry off oxides.

A fillet with no filler is fine for 1.5mm stainless for example that isnt going to be subject to any stress, but with 3mm steel you are undercutting the material and not reinforcing an area you have subjected to metallurgical change. That joint would snap with 3 taps from 1/2lb hammer silicon bronze or not.

 

[Richard.]

I would always suggest a filler for mild steel Tig. Even a clean shiney surface while there is a good chance you won't get porus welds there is very chance that you will and it's not the mill scale that causes it. You can weld it from both sides if you wish that isn't gonna hurt as the only reason your getting issues at the moment with the back side is your penetrating into the back of a (probably) porus weld. The fillet joint is not one I would ever adopt for filler less. As Runnarch said its required to be demensional from a reinforcement PoV. So you need a throught thickness.

 

[Rrunnach]

I purely use the exercise I outlined above, to give a new learner hand eye co-ordination, coupled with arc length and, SOT experience. It is good economical practise, this is done with 150 x 50 x 3mm lcs. Effectively allowing 400 mm weld/fuse to practise with using two pieces, only.

 

[Richard.]

I know. I worded that badly (missed a comma so it read wrong). I was saying he should do it as you said regarding throught thickness.

 

[Richard.]

see how big your HAZ is)

The "haz" as you specify to be big is heat tint. You cannot see the haz from the face/back side. The only way to determine the size of the heat effected zone is from a cut and etched sample. The haz would not be as widely spread as the heat tint. It is the area where the heating process has changed the microstructure of the parent material just outside of the fusion zone.

 

[sjp001]

Thank you everybody, this is brilliant help and I really appreciate you all taking the time.

I can only get the odd hour or two in on this at a time, but I started working on feeding filler today (I have only being trying autogenous so far for arc control). I became much more comfortable on the flat and felt somewhat in control, but was very erratic when I worked on the fillet and kept touching down, but I could manage a few cms where it all went better. I'm struggling to find a good angle if the torch needs to be around 10 degrees as I can hardly see the puddle and the arc reflection. I'm trying to work without dragging the cup on the work as I imagine this will be better in the long run and you can respond a little as the puddle grows when filler is added?

Richard - Thank you for all your help again, it's really useful. Yes I feel like the heat tint is there because the piece is tiny and it seems unavoidable when running the length for it to get quite hot and tint? I imagine on a big sheet that it would be considerably less.

Brad - I took your advice and put the piece in a vice and hammered it with a lump hammer, but the sheet just bent around the join. I'm sure it is very inconsistent in general though so I will make sure I always use filler on mild steel.

Rrrunnach - Thank you that sounds like a great exercise and I will definitely try it. The only thing I am confused by is how would I know that the weld wasn't porous when fusing two sheets together? When I did the autogenous fillet weld I felt it ran really smooth on the first side. It was only when I worked on the back that I noticed the porosity present.

I've used up all my scraps for now, but will update if I manage to improve my filler control!

 

[Kent]

Just use a lay wire technique if your struggling feeding wire.

 

[Richard.]

Thank you everybody, this is brilliant help and I really appreciate you all taking the time.

I can only get the odd hour or two in on this at a time, but I started working on feeding filler today (I have only being trying autogenous so far for arc control). I became much more comfortable on the flat and felt somewhat in control, but was very erratic when I worked on the fillet and kept touching down, but I could manage a few cms where it all went better. I'm struggling to find a good angle if the torch needs to be around 10 degrees as I can hardly see the puddle and the arc reflection. I'm trying to work without dragging the cup on the work as I imagine this will be better in the long run and you can respond a little as the puddle grows when filler is added?

Richard - Thank you for all your help again, it's really useful. Yes I feel like the heat tint is there because the piece is tiny and it seems unavoidable when running the length for it to get quite hot and tint? I imagine on a big sheet that it would be considerably less.

Brad - I took your advice and put the piece in a vice and hammered it with a lump hammer, but the sheet just bent around the join. I'm sure it is very inconsistent in general though so I will make sure I always use filler on mild steel.

Rrrunnach - Thank you that sounds like a great exercise and I will definitely try it. The only thing I am confused by is how would I know that the weld wasn't porous when fusing two sheets together? When I did the autogenous fillet weld I felt it ran really smooth on the first side. It was only when I worked on the back that I noticed the porosity present.

I've used up all my scraps for now, but will update if I manage to improve my filler control!

Rrunnarch also mentioned filler should be used in the fillet joint. The exercise was suggested as a way of concentrating on keeping a short arc and consistent travel rate that's all.
If your struggling to see make adjustments to the length of tungsten exiting the cup so you can still keep a tight arc and keep the cup back from obstructing your vision. A gas lens lens will make this more possible.

 

[sjp001]

Understood. I'll give this a try next time as I think you are right that I have been overly cautious about tungsten length. If I struggle I will try the gas lens you suggested.

 

[Richard.]

Understood. I'll give this a try next time as I think you are right that I have been overly cautious about tungsten length. If I struggle I will try the gas lens you suggested.

Good luck. I look forward to seeing the results.

 

[sjp001]

I had an hour to give this a try following all of your advice. Same size of metal as before in all dimensions.... It went a lot better although I made plenty of mistakes when I accidentally pushed the piece away from me with the filler and touched down, etc.

 

[robdxr2]

I'm pretty new to tig welding and have gone for an gas lens I've found its made a world of difference as specially with stainless Steel I don't think you have To be as accurate with torch angle as you get a better gas coverage it may be the wrong way of doing things and a bit of a cheat but it does give you chance to get some runs in and make progress.