Welding

Mon Sep 29, 2014 5:59 pm

Looking for a bit of advice. I'll be welding in a rear inner arch panel this week. I plan on plug welding the arch lips together using a mig welder as I don't have a spot welder, but I'm concerned about rust coming back due to unpainted metal on the arch lips where they meet. I'd like to paint them before I weld them together but I've had bad results in the past - the weld doesn't look good and never penetrates the metal I'm welding onto. I've tried zinc and copper weld through primers. I've even sctratched the primer away through the hole in the top panel. The weld through primer seems to prevent a good weld. Any tips? Would a bigger hole in the upper panel help? Wrong brand of weld through primer? Wrong setup? What am I doing wrong?

Mon Sep 29, 2014 6:17 pm

What weld through primer are you using? Ive used the upol 8 for spot welds and have found that although the weld is not as good as on bare metal it does bond - on the tin is said light coats only ?

I have repaired one side of my rear arches and instead of spot welding i made the inner arch finish slightly short of the outer arch (wheel arch lip) and then just welded the edge lightly

for rust prevention i used weld through, then zinc primer and topcoat both from inside the car and inside the arch - i then polyurethaned it and waxed the sh!t out of it

heres a good guide i bookmarked , initial g is a professional so maybe follow his advice before mine

- http://www.e30zone.net/modules.php?name ... c&t=238588

Mon Sep 29, 2014 6:48 pm

Thanks for the link. I'll have a look in a bit. I've been using upol #2. It creates soot when I weld near it and makes the wire explode rather than build up a pool of metal. I tried adjusting my mig settings and I've tried argon/co2 and straight co2 but there is no improvement. The primer is also remarkably soft - I can scratch it off with a thumbnail. No good for overpainting I should think. I might try tacking like you did on your arch. Both lips will be trimmed back and rolled flat for tyre clearance though.

Mon Sep 29, 2014 6:59 pm

yeah its the No2, green can- the 8 is is acid etch

i agree its soft but its only meant for use sandwiched between two bits of metal, if you have overspray on accessible parts you can wipe it of with cellulose thinners or acetone even when dry or rub it back

i haven't really noticed any soot, but its is a pain to start the pool, you have to weld quite hot for a plug weld but after the difficulty in starting the pool it does flow- yes its not brilliant but its better than nothing

Mon Sep 29, 2014 7:04 pm

Just had a quick read. Think I'll give panel bond a try.

Mon Sep 29, 2014 7:35 pm

+1 For the upol weld thru £11 from halfords, cheaper than eBay, also body shop recommend the worth stuff the other day to me.

Mon Sep 29, 2014 7:58 pm

Never had a problem with the upol stuff, granted it does need a touch more power and its best to let it fume off fully for about 20 mins before welding but no issues in years.

1 car I did 8 years ago still looks fresh as the day I did it.

Tue Sep 30, 2014 1:16 pm

Billet Hamber weld through is good.