Seems like improvements would be to maintain an exact temperature so that the plastic sheet wouldn’t burn, and the vacuum table could be more of a fine grid. There is a plastic heater thing that has a heating element under a hollow bar of metal. So a double sided metal plate like a panini press would be the best for heating evenly. I label my solder with what temperature it melts at, determining the right temperature for a type of plastic would be ideal, I’m thinking halfway between melting and browning/burning. A better vacuum plate would be next.