Advice for plug welding with mig welder

[Smallfry]

Don't want too much pentration were it distorts the metal and causes rusting down the line. Fine line between too much and too little. Gonna fiddle around with the settings another bit till I get it perfect then get to work after that haha.

Any welding will cause "rusting down the line" unless it is properly protected afterwards.

Have used 7 to 8mm holes for years. 5mm will not work properly. I also do not hold the torch still either. Start in the centre, then do a little circuit of the hole to finish. Will always need grinding back, as then you are sure it has worked.

I have never been able to achieve a flush plug weld that actually holds properly.

 

[caprinut]

Yes it's the latter that you have described. I have used the two terms interchangeably. I understand both are different. Any how you would have known from the photos which one I was talking about from the heat disapiation.

Spot welds don't have as much heat dissapation (blue) and little surface disturbance when used correctly.

 

[Nomad]

I've just finished fitting new floors and sills in my classic rebuild so have had plenty of practice recently to find what works best for me, I do exactly as said above by @Smallfry

 

[JOEPRO]

I found a bigger hole worked better for my plug welds, think my hole punch was 5mm but ended up at 6mm or 7mm iirc.

Yes I drill approx 10mm holes for plug welding.

This is for rust repairs on Mercedes jack points like my S600 below:






Copper spray primer to protect the inner joint from rust. I use galvanised repair sections and grind it back away from where I am welding.

10mm holes, clamp tight and plug weld up fairly hot. Then buff back with flap wheel. Old toothbrush is great for applying a thin smear of seam sealer after then zinc rich paint and black waxoyl shutz over the whole lot.

 

[Pigeon_Droppings2]

I use an air punch for making the holes...drilling works but can get a bit tedious I find especially when the backs of the holes need cleaning.

As above...I also start in the middle and then do a small circuit to get it filled nicely.