Fort Worth, Texas — The thermoforming industry needs a better understanding of the science behind the process and better development of standardized tests and properties, said Amit Dharia, who runs a contract research and development and testing company.
Part of the reason is thermoforming is a relatively small part of the plastics industry, Dharia said in a presentation at the Society of Plastics Engineers' Thermoforming Conference in Fort Worth. His company, Transmit Technology Group LLC, is in nearby Irving, Texas.
"Most thermoformers are smaller. All of the research, it goes to injection molding and extrusion. Very little of it goes to thermoforming," he said.
The lack of standardized tests specific to thermoforming has caused a communication gap between the resin suppliers and sheet producers, Dharia said. Over the years, several laboratory tests have been developed, but they have not been standardized, he said.
And thermformers also could do more.
"Surprisingly, I found most thermoforming companies don't do any QC on incoming components," he said.
Dharia reviewed the basics behind thermoforming, which he said is a very low-pressure process that impacts low stress in the parts. But thermoforming is different from other types of plastics manufacturing because it starts with one process — the extrusion of sheet of film — and then forms it. That means there are a lot of unknowns, he said, including the composition and extrusion history of the sheet and rates of heating and cooling. Sheet quality is very important, he said.
"Thermoforming looks simple, but it's not simple," Dharia said.
Thermoforming companies have a lot of variables to consider, Dharia said. What forming temperature to use? How long will it take to heat? What is the sag rate during heating? What is the effect of sag on measured temperature? How do fillers and colorants affect the heating rate?
Measuring temperature during the thermoforming process is very critical, and the subject needs more attention, he said.
There are so many variables in thermoforming that complete mathematic computer models are not very practical. Instead, for thermoforming, Dharia said that empirical modeling, based on testing and observation, is a must to use when doing computational modeling.
