Lap joint advise

[scotto75]

Hi,

I'm currently trying to improve my TIG techniques by practicing on 2mm mild steel. I am pretty happy setting up the correct amps on my MIG for various thickness of mild steel, but do not have that confidence with my TIG machine yet.

I have been trying various settings and consumables out and have found a reasonabley solid and consistent setup, but I'm still not sure I'm getting the amps dialled in right for the different joints. My main technique is to get a similiar thickness piece, start with the 30A per 1mm rule, so for 2mm I'll start with 60A. I hold the torch and get an arc and hope a nice puddles forms in 2-3secs max. If it's slower or quicker I adjust the amps accordingly, and then try again. Once happy I run a test bead.

Here's a pic of a quick lap joint I did today in order to post up, on the back of an old practice piece. I have a R-Tech 160 PDC which I think is a good little machine for what I do. I was using a #7 cup with a 1.6mm tungsten, ground to a long point about x2 the tungsten thickness. Gas flow was just up to 7lpm. I tried to keep a tight arc and was using 1mm filler. It's two passes, hence the slight deifference.



I think the amps are too high causing undercut. The bead is also concave. Maybe going too fast and not enough filler. Does this sound correct.

I have some time tomorrow to practice some more, so any advise as to what to do to improve would be really appreciated, thanks!

 

[Rrobson]

For this I’d run more amps, around 80. I’d also use a 2.4mm filler which would help keep the puddle “cool”. And I’d get a move on, something that small will heat up quick so you’d need a good heat sink or pick up the pace. At that thickness it should puddle almost instantly. Your getting undercut because your moving too slowly and not feeding enough filler. It’s probably sinking right through.

To improve, my suggestion is feed more filler (or go up a size) and move a little quicker. If the puddle isn’t flowing quick enough then up the amps, I’d start at another 10 at least.
Where are you aiming the arc? Otherwise not a bad effort, it’s not going to drop off!

 

[Brad93]

Tighter arc

Less amps/colder won’t help you if you’re at 60. You just need more filler, and more amps to melt that filler.

 

[backpurge]

As said above above you need to get more filler in, from the photo it looks like you’re burning through the bottom plate as well

 

[scotto75]

Thanks for the advise. I don't have any 2.4mm filler handy, but will try another lap joint tomorrow with a 1.6mm filler and higher amps.

Where are you aiming the arc?

I have the torch aimed at the bottom piece but with a sort of 20/30 degree angle toward the top piece. I have 15/20 degree angle in the direction of travel.

As you've all mentioned that 60A is too low, would the 30A per 1mm rule be wrong? I notice that the big US companies like Lincoln and Miller recommend 1A per 0.001" as a starting point for mild steel, which would be more like 40A per 1mm. Is this a more accurate guide to begin with? (The chart on this site has 55A for a lap joint on 2mm)

 

[scotto75]

So, I've had a couple of runs this morning on some more 2mm. This is at 78A with a 1.6mm filler. I'm using a 1.6mm grey tunsten with a 3-4mm point. Gas flow was at 7lpm.



The ends of my welds always suck. Not sure if it's the change in body position affecting the torch and arc length, or just that the metals super hot by that point? I tried to keep the arc length as small as possible, but I did find it harder to avoid dipping the tungsten when adding filler.

What do you guys think? It seems to be an improvement but I know I can do better.

Thanks.

 

[Munkul]

That looks loads better

As you've guessed, the metal is super hot by the end, so the top sheet is just about falling apart at the end - the heat has nowhere else to go. You could do a couple of things:
1. use a foot pedal and cheat, like our american friends do
2. weld the last inch at the left, or even 1/2", first, while it's cold. Then run your bead right to left as normal, into that last inch, and finish there. This is what most people will tend to do.

In that case, even a good solid sized tack-stitch at the end would probably have transferred enough heat for you to get away with it.

Tungsten type/size doesn't have much bearing on that sort of weld IMHO, I'd use a 2.4mm lanthanated, but I use that for everything. Always have, probably always will.

The angle of tungsten grind will affect things - a fine point is right for an edge weld, it reduces penetration. Again, I choose one angle, usually around 30 degrees, and stick with it... it works for my stuff.

Cup size and gas flow sounds about right. You could probably turn it up a bit to get better coverage, but it's steel, so it doesn't matter too much.

1.6mm filler wire on 2mm steel is about right. Don't make the mistake of jumping up to 2.4mm filler - on plain steel, it doesn't flow very nicely, and needs a huge whack of amps compared to 1.6. It also can lead to more undercut. Unlike stainless, which flows nicer, and aluminium, where 2.4 flows like a river.

 

[AndersK]

Third to try is add less filler every dip but faster so you increase travel speed hence less heat input.

 

[scotto75]

Thanks for all the feedback. I've had a few more goes on some 2mm lap joints, experimenting slightly, but still struggling to find some consistency.

Third to try is add less filler every dip but faster so you increase travel speed hence less heat input.

I ran a bead on flat plate with the 1.6mm filler and tried to go faster and not add too much filler. It's about 5mm wide.



It was easy to maintain a tight arc length and not touch the tip when adding filler, but I'm not sure if I'm taking too long between dabs?

That looks loads better

Thanks Munkul!

The angle of tungsten grind will affect things - a fine point is right for an edge weld, it reduces penetration. Again, I choose one angle, usually around 30 degrees, and stick with it... it works for my stuff.

I tried another lap joint, this time it was at 80A. I ground the tungsten to around 30 degrees. I also did half an inch at the left of the joint as you suggested, but it looks pretty crap. This is a lot worse than the last one however.



My inexperience means that travelling slower allows me the ability to judge arc length, puddle position and where and when to add the filler. If my travel speed is too fast, I lose concentration on all of these things. The main issue is the puddle splitting in the middle and melting the top and bottom. I imagine this is either torch angle or arc length, or both, going for a wander because I'm concentrating on one thing too much. Once the puddle is in the right place, I can usually manage adding filler and maintaining arc length.

 

[scotto75]

As you've guessed, the metal is super hot by the end, so the top sheet is just about falling apart at the end - the heat has nowhere else to go. You could do a couple of things:
1. use a foot pedal and cheat, like our american friends do

The old model R-Tech 160 has a two-pin connector and pretty sure it doesn't take a pedal.... although not 100%. It does have a 4T mode, but I've just started with 2T as it's less to think about. Maybe using the 4T downslope would help with reducing heat at the end of a run?

 

[Fraserb]

Thanks for all the feedback. I've had a few more goes on some 2mm lap joints, experimenting slightly, but still struggling to find some consistency.



I ran a bead on flat plate with the 1.6mm filler and tried to go faster and not add too much filler. It's about 5mm wide.



It was easy to maintain a tight arc length and not touch the tip when adding filler, but I'm not sure if I'm taking too long between dabs?



Thanks Munkul!




I tried another lap joint, this time it was at 80A. I ground the tungsten to around 30 degrees. I also did half an inch at the left of the joint as you suggested, but it looks pretty crap. This is a lot worse than the last one however.



My inexperience means that travelling slower allows me the ability to judge arc length, puddle position and where and when to add the filler. If my travel speed is too fast, I lose concentration on all of these things. The main issue is the puddle splitting in the middle and melting the top and bottom. I imagine this is either torch angle or arc length, or both, going for a wander because I'm concentrating on one thing too much. Once the puddle is in the right place, I can usually manage adding filler and maintaining arc length.

Practise seems to be the thing with tig, got mine a few months ago having never even held a tig torch before, spent a few hours every night for a while and I was a long way from professional but got pretty consistent and acceptable beads, work got busy and for 12 weeks or so the only welding I was doing was with the mig, when I got back to the tig it was almost like starting again, I'm back to OK for an amatuer( I think) welds at the moment, a good few hours in the next few weeks might get me beyond OK

 

[scotto75]

Practise seems to be the thing with tig

Thanks for the advice Fraserb. Think I'm in a similar boat. Been practicing as much as possible over the last couple of months. Only restriction is when I can get the time to cut and prep pieces to practice on. Takes forever to prep and minutes to weld into scrap.

 

[Fraserb]

Thanks for the advice Fraserb. Think I'm in a similar boat. Been practicing as much as possible over the last couple of months. Only restriction is when I can get the time to cut and prep pieces to practice on. Takes forever to prep and minutes to weld into scrap.

I gave up on practise pieces pretty quickly, not saying its the right way to do it but I didn't want to get brilliant at welding nice easy joints flat on the bench then find out I was hopeless doing anything productive. I started welding the easier joints on some of my creations and now try to do everything at home with the tig.

 

[Rrobson]

A agree with the above actually. 95% of the time those lap joints are nothing like what you’ll actually do.
re-reading the posts about I got confused between wire sizes and tungsten sizes, as stated and as you’ve found 1.6mm wire goes in much better and I generally use a 2.4mm tungsten for everything. I’ve got a couple of 3.2’s and never used them...

thin plate is never easy at the best of times with tig

 

[Munkul]

Practice is practice, imo. Just weld positional is more or less the same with TIG, its just harder to get comfy. Dial in the motor skills to your hands first.

 

[scotto75]

Yeah, I completely understand what you guys are saying. We have the odd bracket or gusset that needs a lap joint welded, but my boss does all the TIG work. I'm trying to get up to standard so I can get him to let me have a go. I have a box of various bits of scrap of box section and tubing from work and other places, and try to do 45's and birdsmouths, etc. I totally agree that welding these small plates is a bit dull, but I want to repeat the same thing until I get it consistent.

I generally use a 2.4mm tungsten for everything.

I've heard this a few times. Haven't used a 2.4mm tungsten, but have now ordered a couple to have a go as a comparison.

 

[scotto75]

Dial in the motor skills to your hands first.

Thanks Munkul. This is exactly what I'm hoping. Just stay on it until I get it consistent, then move onto a fillet or open corner. Repeat the same until I can consistently nail it.

 

[Brad93]

Just a tighter arc required on that fillet. It’s a hell of a lot cleaner

You can add a big blob of filler or usually what is far better and neater is small, regular additions of filler to build up the pool.

 

[scotto75]

Just a tighter arc required on that fillet. It’s a hell of a lot cleaner

You can add a big blob of filler or usually what is far better and neater is small, regular additions of filler to build up the pool.

Thanks Brad. Appreciate the advice. I’ll have another run tomorrow and try what you suggest

 

[scotto75]

If you keep your filler in the edge of the arc it remains hot and melts quicker meaning many more, but smaller dabs and this tightens your weld up and keeps your pool consistent and neater.

Thanks .. I've been trying to keep the filler as close to the start of the puddle as possible, but obviously my technique needs improvement. I had another go this afternoon and tried to keep the filler close to the puddle, and using smaller dabs. Wouldn't say it's neater exactly.



I have to get the tungsten up close to the join to get the puddle even, but keep hitting the tip with the puddle when I add more filler.