The edges are just folded over. No welds of glue were used in the factory. If you have split the fender (I think you have based on your pics), then it must be possible to slide them off from the panel over which they are folded. If you don't need to save your fender, then chopping it up in little pieces makes it easier.
Attached a pic of the same joint, but then on the rear quarter panel, left side of car. I split the skin with an angle grinder, and the little inside corner just breaks after folding it 10 times.
There may be other ways to do it, but this at least worked for me, and it retains the original shape in the panels you want to keep.
Regards,