— Genetic programming is the usage of the paradigm of survival of the fittest in scientific computing. It is applied to evolve solutions to problems where dependencies between multiple input factors are unknown. In this paper we propose and evaluate the application of a specifically adapted genetic programming framework to optimize the rule base of an expert system. The expert system controls a computer-aideddesign software and targets the automation of a manufacturing process. The used steady state genetic programming framework introduces some variations on the selection and evolution operators normally used in genetic programming. In particular: size enforcing mutation, dynamic fitness calculation and size constraint ranking. The genetic programming system is evaluated with real data and led to an improved expert system performance of about 22 percent.