Too much penetration

[disco_monkey79]

Having read several books on Mig welding, I notice they all advise against too much penetration, without really going in why this is undesirable. Is it just a waste of material (which I can live with), or is there more to it?

 

[3Rs]

Yes there is a reason, in short it can lead to stress cracking in the Heat Affect Zone, and cause the joint to break. This is because there was too much heat used while welding the joint, making the joint brittle, on a plate, And if your welding a pipe it would also cause the above and create turbulence in side the pipe which would result in the pipe being worn away and creating a hole, a bad thing if it was oil, Gas,water,fuel oil. or compressed air.

 

[disco_monkey79]

Thanks for the reply.

How do I know when how much is too much? One of my books has a handy guide re butt joints, and I relatively happy there, but what about lap joints?

If the bead is penetrating as much below the work piece as above, is that too much or OK? I'm interested in car body repair so mostly 0.8mm or so sheet, but in some places it'll be 1.6mm or near as dammit.

What other telltale signs can I look out for?

Many thanks!