Quick bit of advice please

[lansalot]

Hi

Was welding a plate onto a mate's land rover chassis last night. He has a big gas-mig (sorry, don't know the make - but it's very heavy-duty) and I noticed it was running 0.8mm wire instead of the 0.6mm I'm used to with my Clarke.

The plate we were placing on top of the chassis was thicker than the chassis was, the chassis was also rusting and so the metal we were dabbing onto was a little thin.

The issue I had was really in getting the power-wirefeed right - I think we got there in the end - but instead of welding along the seam where they overlapped, I was more prone to either blowing through the chassis or cutting into the face of the new stuff. There didn't appear to be much penetration. (Now I'm typing this, it still sounds like I had way too much power).

Thing was though, when I tried it on a piece of the metal we were welding, off the vehicle, it looked great. Back on the vehicle, and much of the welding being vertical, it was cutting, blowing and general stalactites.

Any advice very gratefully received

Cheers
A

 

[Basil]

There is almost twice the metal in a 0.8 wire than a 0.6 wire (64:36) so it takes more heat to melt it. Use thin wire for thin metal and thick wire for thick metal!

 

[backpurge]

Personaly I have never found the need to go below 0.8mm, I find the larger cross sectional area of the wire gives better arc characteristics than 0.6mm, at the end of the day it's down to personal preferences and your welding set. If your machine doesn't have many voltage settings, particularly on thin material, you can struggle to get it tuned in just right.

Having said that I know people swear by 0.6mm wire and produce some fantastic results with it

 

[lansalot]

Thanks, this is quite a configurable machine - but it's not mine and I'm in no position to change the wire on it.

Any thoughts on what my problems were, how to avoid this face-cutting that was going on ? Was it simply too much power ? If so, how come the bead I put across the plate as a settings-test looked spot-on ?

Cheers

 

[malcolm]

You would often need to increase the wire speed a little going from flat (bench) to horizontal or vertical (underneath Landrover). Especially if the torch hasn't been serviced for a while. That would account for blobs and some undercutting - wire burning back too much.

0.8mm wire sounds ideal for chassis.

 

[backpurge]

Could be down to a number of things, was the test plate the same thickness and in the same condition (ie rusty/painted etc) as the actual job, was the welding position different, could you keep the same torch angle, stick out, travel speed etc etc.

If one plate is thicker than the other alter your torch angle slightly to play more heat onto the thicker section but if it is the top plate that is thicker avoid letting the weld cold lap, could be an idea to lay a buttering layer on the thinner section first to give it a bit more thickness prior to welding the two pieces together

 

[Endacy]

I found welding 1.2mm steel recently that welding accross the 'face' of a piece of metal would be fine on a particular setting, but then try a butt weld of two pieces and it blew it to bits. I found a lower setting better when working at the edge of the piece to stop it eating away at it and making holes.

 

[backpurge]

I found welding 1.2mm steel recently that welding accross the 'face' of a piece of metal would be fine on a particular setting, but then try a butt weld of two pieces and it blew it to bits. I found a lower setting better when working at the edge of the piece to stop it eating away at it and making holes.

You're exactly right, people fall into the trap of thinking one setting will suit all applications and as you've found it doesn't.

Joint type, welding position, slight variations in material thickness and condition all require the machine to be re tuned, particularly on thinner material

 

[eil]

Try and make sure that you have a good earth to both chassis and the patch.

 

[Chickenjohn]

If the chassis is rusty, it won't weld very well to the repair piece. So clean the chassis completely of all rust and paint in the weld area and a few inches around. Also, to avoid blowing back the overlap, don't overlap. It does not actually take too much longer to make a repair section accurately, scribe round it and cut the chassis so the repair fits neatly and butt weld the repair into the chassis. A much neater and longer lasting repair as well.

Also, get some steel of approximately the same thickness as the chassis and it will be easier to find the right setting.

 

[lansalot]

Thanks ChickenJohn, but we actually needed to plate and overlap - there were existing plates either side, and we needed to fit an altered shock absorber mount which was mounting on those two plates, and the space in between. In effect, we had to space-out to match the sections either side. A flush join wasn't an option in this case.