Fix Broken Plastic! Never Throw It Away Any More! : 6 Steps (with Pictures) - Instructables
make the welding as strong as you can. make it simple. If it break then make it again, stronger. In any case, to make the welding stronger you can use more plastic, as with the plastic strips suggested before, or you can insert some metal inside the plastic. Suggested metal parts may depend on the job to be done.