Settings and penetration

[stevemon15]

Hi guys, another complete noob to welding here.

Today was my second go at mig welding, with very slightly better results.

On my first go, I'd been tweaking the settings on the machine until I got close to something that looked like a passable bead on 3mm sheet. On this go, I was using the exact same thickness metal, and the exact same settings on the welder as what I'd arrived at last time, and on my first run I managed to melt a big hole in the metal. The only difference between this time and last time was this time I'd cleaned the metal much cleaner. Would it really make that much difference?

Also, regarding penetration, should I be seeing a raised weld profile on the reverse side of the metal as well? On the runs I did, I can see the weld just beginning to come through, but it isn't raised.

Any advise would be truly appreciated thanks.

 

[backpurge]

Just coming through is plenty

 

[Richard.]

Are you producing a butt joint ie two pieces of metal butted together flat then welded across the seam. If so penetration should be enough so that you cannot see either of the two edges and no more. If you can still see one or both of the plate edges on the reverse side then that's lack of penetration and you need to step things up a touch.
If your just running beads on a plate then it's not really something to worry about .

 

[stevemon15]

Ah okay, thanks gents. I'm just running beads at the moment. A few more practice runs and I want to try a butt joint.

 

[WeldingDirect.co.uk]

Richard has it spot on.
When I was learning the advice given was start on ~40 amps per mm and adjust from there. Gives a good starting point if nothing else.