I would like to know how do the insert a PTFE ring (form example) into the seat ring. I mean, I would like to know the process to do an inserted seat ring, which machines do they use,etc.
This sounds like a question for a manufacturer. If you have a particular valve in mind, you should express your interest in that valve and feature/technology to the manufacturer. If it's not a closely guarded secret, they might just share the info with you in hope of making a sale.