this is the section of roof i want to weld to...is it possible with a mig.

why?

X2

any why would you ask on here?

go to a welder, or crash repairer.

but why?

processor......to hang from roof...only real place to put it......as u can see there is a raised/lowed part which is not the roof lining

so you dont wanna weld it together

you wanna weld something to it?

You could easily weld something to it but it might make the car 'unroadworthy' according to the authorities...

Can you not just use some decent self-drilling sheet metal screws?

you wont be able to see it.

this is the plan

Green: 20mm steel tube
Blue: tabs on side to mount processor to
Brown line: roof line
Red: bolt holes

Your probably better of with industrial adhesives (same stuff they glule your firewall with). Welding means potential fire, but yeah a decent & safe welder could do that.
Do know this, that is part of your cars crash system ie, designed to bend/fold in a particular way in a crash.

1) Its a modification for the chassi.. would need engineers inspection , but id put money you will get knocked back and they woould call it a write off, thats part of the safe zone area in a car
2) Heat damage , will warp and possibly heat the paint on the outer roof
3) you will need to strip the intire interiour. no matter how much of a good welder a person is it will throw sparks everywhere
4) Will make you car illegal. cops will see it and say its a risk when you crash passengers will hit it with their heads

My experince: mechanic for 4 years and welders assistant for 6 months

Glue the mounting bracket with the appropriate Sikaflex automotive adhesive. You'd need a hotnife and a hell of a lot of gusto to remove it once set.
I'm assuming that's the hinge panel for the rear hatch. Odd place to put the processor or are you wanting to fit it forward of that hinge panel, attached to the roof skin?
If that is the case, summer will kill your unit. If you can (by some miracle) insulate the unit and mount it forward of the hinge panel, concealed within the rof lining, then a U shaped bracket glued to the roof skin would be the only option. Welding will distort the panel.

look at the photo....it would attach to the roof and hang from it.....reason i ask about welding is cause its strong......wont move.

I have decided not to put it there as theifs will see it....will be puttin in the boot above my amp......

thanks all for the help

umm screw it to it????

just weld it and they have leather blankets for putting over trim so splatter dont burn it or get it tiged and just do overlapping spots welds and cool it after each one to stop distortion and well for the paint on the other side not much you can do about that.

Just find some rivnuts for it, then you just drill a hole, pop it in (with a large washer to spread the load) and bolt your processor to it.

easy to remove then in future.

If you are hellbent on welding, look to weld a nut or two to the roof then use short bolts to go through the processor mounts and into the now captive nuts - easy again to cover up and stronger than rivnuts.

Paul