Welding technique for bodywork

[Buzby58]

I seem to have acquired a rather splendid 2 door Moggie the kids have christened Billy, a membership to the MMOC and the wife has given up all hope of the house being painted

This is my first restoration so please be gentle!

Although the underneath looks pretty good, there's a bit of immediate welding needed to the offside flitch panel extension and the rear quarter panels.

Having invested in a Carke Mig 90 pro I've been practising and can get some decent butt/lap welds in now, but even doing it a bit at a time I always seem to get some distortion on thin mild steel plate. However, using a series of plug welds I can get a nice straight and secure finish - however, is this method appropriate/acceptable on bodywork for the MOT or does everything have to be seam welded?

And whilst I'm on the subject - is there a preferred seal sealer amongst you more experienced metal bashers?

Thanks in advance

Grant

[Alec]

Hello Grant,

I believe the general rule is that if you are replacing a panel, you can plug weld or spot weld where the original was welded. Any patches let into a panel should be seam welded. Doing the latter, there is likely to be some distortion, some of it can be dressed OK.

Alec

[mogbob]

Grant
Are you trying to seam weld in a long continuous straight line ?
If yes, then you are bound to get distortion.
On the other hand if you " move about " the line to be welded , left , right and centre no one part gets overheated.Joining the dots style.It's the contraction of the metal that pulls it in a different direction.Try say 25 millmetres at a time before moving the weld.

Another way to cut down distortion is to buy some flat copper metal bar.Clamping this behind the two sheets of metal to be welded.It won't weld to the back and acts as a heatshink, cutting down distortion.Small pieces for different welding and file down a curve on another ,to match the various profiles you need to weld.
Unfortunately copper bar is not cheap these days ,if you have to buy it, but it will transform your success rate and doesn't wear out.I've been using mine for more years than I care to remember !!

Bob

[polo2k]

the copper is also useful to fill gaps if you have cut a panel short. Take the time to polish it to a bright shine to avoid any sticking.

For a cheeper option you can use flattened copper pipe but its not as good