In my experience SS is not a problem for the normal spot welders you
would use for car body work but aluminium is not an option. As I
understand it aluminium can be spotwelded but the equipment required
needs to have a much higher current capacity to produce the same sized
spot weld due to the conductivity of the aluminium being much higher
than steel. I believe the same holds for US aluminum also . Also the
spot welder you require can depend on the steel you are welding. For
more modern cars with HSLA (high strength low alloy) steel you require a
suitable welder which pulses IIRC to produce a suitable post weld
cooling, older cars made from mild steel don't require this. I was told
by a local welding supplier that they got a lot of ex body shop spot
welders in recently as the body shops had to uprate their spot welders
to cope with the new materials, maybe similar in the US so you could get
a good 2nd hand unit.

HotRod wrote:

This car is a 1995 PORSCHE 993, not a cheap car. BUT I want to do the work
myself, otherwise I have a big shop and hoist for nothing. I think I may
invest in a Spot welder.

Another question, can I use a spot welder on aluminum and stainless?