Weld Penetration

[mana333]

I understand having too little penetration results in a weak weld, but does having too much penetration weaken the weld as well, or is it just aesthetics? Aside from the aesthetics, what are the drawbacks to having too much penetration?

 

[malcolm]

I've a few ideas:

The obvious is if the metal isn't gas shielded on the reverse it could corrode, and the corrosion could mix in with the weld a bit affecting strength.

Next with the greater heat used to penetrate further you'll end up with a bigger heat affected zone. It's not so bad for mild steel, but a lot of metals do harden in the heat affected zone, and that's where cracks tend to start.

You could get undercutting at the sides of the welds using too much power.

You'd get a big change in section between the parent metal and the weld, again not great for fatigue.

That's all I can think of at the moment. Sounds terrible, but for mild steel car work (most of the welding I do) I'd still err on the side of too much penetration rether than too little,

 

[Tristan]

But how do you know how much penetration you have ?

 

[peterd51]

Hi,

look at the other side.

If it's inside a section and you can't see it, and you really need to know, then make a test piece and cut it up to see what happened inside.

Regards
Peter

 

[snowcat]

Cut slice and etch, We did loads of those at collage its really intresting to see, cold lap, and undercut slag inclustions etc etc in a weld.