The findings reported in this paper provide a model for consistently achieving optimal cutting conditions when shaping foam plastic, such as polystyrene, with an electrically heated wire-based cutting tool. General relationships between wire temperature, power input, feed-rate, kerf width and work piece material composition were developed and an optimal machining algorithm was proposed and tested. The findings provide a significant advancement toward a fully automated machining facility and the associated development of a novel, large scale rapid manufacturing (RM) system.