Lap welding new thicker metal to old thinner pitted metal

[Dantheweld]

Hi All,

I am planning to do some Mig welding on the car on the wknd (weather permitting) and i was wondering what technique i should use to weld 1.2mm new steel to possibly 1.0mm parent steel as a lap joint. Should i start on the new metal and flick towards the old metal? I really am not sure. If it was new metal as the bottom layer it would be a lot easier. The general rule of thumb is to keep the pool on the new or thicker metal and flick it across to the old or thinner metal right?

 

[Pete_88]

For the sake of a 0.2mm difference I wouldn't worry mate just buzz it up.

 

[Pete_88]

Why a lap joint though? What you repairing?

 

[Dantheweld]

Pictures as attached. I am plating over some metal that i have sandblasted.

Along this edge the plate will sit, bending over the edge.

 

[Rob85]

Make sure to use some weld thru primer on the back side of the repair section and the parent metal as I'm sure you know lap welds on cars can become moisture traps. I would use half to 1inch stitch welds all the way round until it's fully welded out all the way. A longer seam could be possible but you don't want to end up hitting a bit of the material that is a bit thinner than the rest and then blow a hole.

 

[optima21]

I'd cut that out, make a repair section and then seam weld it in place. It doesn't look like there is much metal (or strength) left after the grit blasting

 

[Kent]

0.2 mm is not worthy of great concern but pits can be holes with foil thin bases

 

[Pete_88]

As above, I'd personally cut it out then weld in the repair section.

 

[Dantheweld]

Issue is that the bit that would be cut out is made of multiple layers that are a part of other panels. If I get most of the rust out, treat it, prime with good zinc primer, weld in the new peice, seal with epoxy primer and paint with good sealing paint then inject with cavity wax surely this will last a good few years?

 

[trewjohn2001]

You can cut back and weld the other panels together and then make a complete patch panel. You might need to make a jig if those holes are critical.