Check out sonic welding.
There is also some pretty good glue in the plumbing aisle.
I have a project and I have been trying to figure out a way to join PVC parts together. I took a couple of pictures of product that did this but I am not sure of the exact mechanism or part. I wasn't sure if this was some sort of rivet, plastic welding, or insert. I am looking at the rings in the pictures. The rings do not go all the way through to the other side of the two pieces of plastic. IMG_6644.jpgIMG_6642.jpg
Check out sonic welding.
There is also some pretty good glue in the plumbing aisle.
Looks like they Heat swaging or Heat Staking the plastic. Probably an automated machine.