Butt welding panels you can't get behind

Can you butt weld long panels that you can't get behind using TIG? I notice many people flange panels they can't get behind. Is flanging ever okay for outer body panels?

http://www.youtube.com/watch?v=mSJUAT0H_Y0

 

why would you have to get behind it? you can tack weld something to the patch panel to pull it into position if needed. I would only flange a perfectly straight panel, anything with a crown can be ruined as the flanger will try to flatten out the panel.

 

The only issue with a flanged seam is water retention in the gap. If you can keep the water out you will be fine. If its for everyday use, i.e. rain, snow, salt I would advise against flanging exterior panels

 

"why would you have to get behind it?"

To planish the weld so you don't need as much plastic filler.

 

If the vehicle sits in the sun and gets hot do you see the flanged area?

 

Yes you will.

 

Once you weld a flanged panel it becomes extremly stiff and almost impossible to straighten by any means.

 

Joe ,
Referring to the video you linked, the weld that's flanged is the top seam & a bit around the taillight. The rest are plug welds and butt welds. the lapped weld is so close to that rigid corner that there would be very little distortion from welding or sun movements. However at that point, wouldn't it have just been easier to do the entire 1/4 panel up to the windows and trunk


Lets say his seam was mid panel on that quarter, not a good place for flanged lap.

 

"the lapped weld is so close to that rigid corner that there would be very little distortion from welding or sun movements."

Good point. I missed that. Thanks for pointing it out.

"However at that point, wouldn't it have just been easier to do the entire 1/4 panel up to the windows and trunk"

That's what I thought when I watched it.