Probably yes. I do not know exactly what part of the saw you want to weld, or if it is made out of plastic, but yes you may try to weld plastic. If you want to weld plastic, first of all, clean thoroughly all your parts with hot water and detergent and after that with some solvent, then weld the parts in place with a soldering iron. After that, you need to reinforce your "welded" part with a "sandwich" of metal net of some kind. Cut a patch of net that covers the plastic component you just welded and with the soldering iron warm up the net and embed it in the plastic. Repeat the same operation on the other side of your plastic component. It should work out. The metal net I usually use is used as window screen against insects.
Don't forget to post pictures!