That's more or less how it is done. Thermal cycling of the molds is one of the bigger factors in determining the operational life of a mold. Moldmaking is a very advanced art, the people that do this have a formidable array of software at their disposal to model how the mold and the plastic will behave as well as a massive amount of accumulated trade knowledge. I know several, one of which is outstanding and in very high demand because he can reduce the number of trials to a minimum. Materials science is nice compared to software because you can actually learn something and build on it for a whole career instead of the next five to 10 after which you have to re-learn everything.
