Since were not sure what alloy is used is car unibodies (though I'm
pretty sure it's not maraging steel or single crystal hastalloy) can
someone with a welder and some scrap fenders do an experiment?
Take a strip of steel from a car body perhaps an inch or two across by a
yard or so long.
Bend the steel (gently) and feel how much force it takes to flex.
Now run a bead of weld across the center of the strip.
Bend the steel again and note:
does it take less force to bend?
is the bending concentrated near the weld?
My theory is that problem with welding stamped low carbon steel will not
be the loss of heat treatment (since it's not heat treated to start) or
the loss of strength (since the work hardening caused by being stamped
into a fender won't significantly increase the strength). I am concerned
that the heat will soften the metal near the weld which may (depending
on the joint design) concentrate the bending in one small area which
would increase problems with fatigue cracking.
Don't get me wrong, I'm a firm believer in welding. I'm just concerned
that the delayed failure mode for a welded modification may catch
someone by surprise.
If your structure is designed to minimize flex and avoid having the
loads fed into thin sections you will have less to worry about. An
experienced welder should be aware of these sort of things.
As a quick check on a welded joint you could check the paint over the
joint. If the paint is cracking along the seam the underlying metal is
probably stretching more than you want it to.
--
Andrew King
Ann Arbor Michigan
technology is the answer, what was the question?
