Why not lay down filler wire ?

[Wyn F]

Still slowly getting me head around tig welding but something puzzles me about its process
Have been watching various tig videos and seen the operators adding filler wire bit by bit ...
Why is it done like this?
Why not just lay one solid length of filler wire along the join, then weld whilst its static in situ?
Could you not tig weld like this in the same way ?
Would it work? If not why ?
Just curious more then anything else

 

[the snooper]

I don't tig weld but I would imagine if you did it would only be a very thin bead where as if you feed it you will get the weld you need rather then the little amount that is available

 

[ben8vgte]

When you dip the rod you freeze the pool and use it to control the weld bead size as you lay it, you can just run the tig down a tight join and fuse it together. But even then I still have a rod in hand incase it starts to burn a hole or needs a little more..

 

[Wyn F]

Cheers, I need to go away and understand the process more
I took it the arc melted the metal and the filler rod just strengthened the join
Hence the idea of just laying down a solid rod to do the same

 

[BrokenBiker]

you could use the lay wire technique, i quite like it in arkward positions. Simply puddle up, add the filler but intsead of dipping the rod you leave it in and just move on through with the torch. Check out jody at welding tips and tricks on youtube. He has loads of tig vids explaining the differences between dipping and lay wire, free hand and walking the cup and so on, i find him very informative

 

[BrokenBiker]

also thought i would add, you dont lay the wire on the joint then weld, you just keep the rod pushed into yhe puddle. still have to feed it but dont have to dip and you get a slightly smoother looking weld unless you weave

 

[Wyn F]

Many thanks for the info

cheers

 

[Lawnmowerboy]

I was told it isn't a good habit to get into. Better to be concentrating and keeping in practice feeding it properly.

 

[wheresmejumper]

To do it right takes a lot of skill.you have to keep the rod in the very edge of the pool
too far in and itll put a big blob of weld down, disaster.
At the same time, you have to make sure you're actually penetrating the base material with the arc, not just melting filler wire over the joint.
it has its place though, when done right it makes a visually better weld

 

[hotrodder]

As said it's a valid (and used) technique with pros and cons to it. Adding filler wire cools the weldpool so using a lay wire technique changes quite a few things subtly. Take a fillet weld for example... goal is to melt both pieces together and add wire to provide reinforcement commensurate with the thickness of the pieces being joined (the thinner of the two if they're different).

Weld size in the pic is represented as 'throat thickness' (a) but 'leg length' is also used as the weld is kinda a right angle triangle in shape. Simply measuring either of these only gives you a theoretical weld size though as the actual throat is dependant on achieving 'fusion at the root' of the weld. This thread is about arc length but demonstrates well enough... http://www.mig-welding.co.uk/forum/threads/arc-length.7862/ If you don't melt the root of the joint the weld the resulting void effects the functional size of the weld i.e. can end up with a physically bigger weld that actually has a thinner throat due to the void inside it

If the weld is made by dipping the wire you can watch the root fusing while you go as long as you don't carry too large of a weldpool/get the angles of attack wrong and end up with 'cold lap' which is where the weldpool flows over the joint before it fuses resulting in LOF (lack of fusion) at the root. Same weld made with a lay wire technique and you're relying on experience/settings to avoid LOF since the wire is layed in the joint and the arc used to melt all three together while pushing wire into the pool as needed

With a butt weld a lot depends on the thickness of the part i.e. heavy wall pipe and you want/need a prep and root gap whereas with thin wall tube you can 'sink' the root in with zero gap or prep. Laywire technique not so useful on thinwall stuff as you don't need (or want) too much filler wire and trying to use it means you need to run hotter (or slower) 'cause wire cools the weldpool.
If you've got a root gap you can see the edges breaking down (shown in the tutuorial) and you basically just keep filling the keyhole that forms as the edges melt. Laywire technique is very valid here BUT if you get it wrong you're more likely to produce a weld with LOF defects and incomplete penetration

Material being welded also plays a role as different alloys (not short for aluminium!) behave differently with some being runny others sluggish etc

 

[BrokenBiker]

very informative hotrodder, no one has explained it to me in that much depth and i fear i may have been doing it wrong before now. Just lucky it wasn't on anything that took any load.

 

[Ed.]

Also the arc will melt the wire which get drawn into the pool and leaves gaps in the laid down wire unless you push some more wire into the pool, that is, as the arc melts the bead contains more metal then was in the filler wire if it was laid flat for the given distance, hence the reason for dipping in the filler rod, secondly as the arc melts the work and as you dip in the wire it melts a bit off the end which freezes the pool and so you move forward a bit and repeat. I hope that makes sense to you.

Cheers

Ed.

 

[Wyn F]

Many thanks for all the info peeps. Appreciate your time and detail reply's
I would like to say I understand it all, but then I would be lying
Sure in time once I've given it a try it will become clear

Wyn

 

[Bristolbulldog]

I have tried the lay wire down, and the wire just burns back, and the globulises (new word!?). This may be because I'm useless at adding wire.

I've seen mig wire feed added to tig. That looks great to me. Can I add a cheap mig welder, strap the wire feed to the side, and tig like that? Or is the setup going to be too difficult, I.e too much wire etc etc.

 

[BrokenBiker]

I have tried the lay wire down, and the wire just burns back, and the globulises (new word!?). This may be because I'm useless at adding wire.

I've seen mig wire feed added to tig. That looks great to me. Can I add a cheap mig welder, strap the wire feed to the side, and tig like that? Or is the setup going to be too difficult, I.e too much wire etc etc.

search for tig cold wire feeders. I hate using them cant get the hang of it but if you want a wire feeder they are your best bet

 

[ben8vgte]

I have tried the lay wire down, and the wire just burns back, and the globulises (new word!?). This may be because I'm useless at adding wire.

I've seen mig wire feed added to tig. That looks great to me. Can I add a cheap mig welder, strap the wire feed to the side, and tig like that? Or is the setup going to be too difficult, I.e too much wire etc etc.

Sounds like too steep an angle for the rod and your adding to the arc, rather than dipping in the edge of the weld pool..