Polychromatic sets theory is used for boxes parts CAPP expert system so as to store knowledge rules of selecting machining method in form of contour matrix. Through the logic operation of coloring in the knowledge based, the machining schemes relating to the features can be obtained. Genetic algorithm is used to sequence machining step in the machining center to make the process of sequencing machining step more flexible and convenient, and the result of sequencing machining step more reasonable.

Based on the polychromatic sets theory, a relational model of cutting-tool choice was established, which was shown with a contour Boolean matrix. Through the coloring logical operation, the cutting-tools candidate set was calculated to meet machining conditions. With the candidate cutting-tools set, the fuzzy optimization was made for every part feature. And with considering the effects of the time of cutting-tool exchange, processing sequence and other relevant information for the selection of cutting-tool, the choice of cutting-tools is optimized as a whole during machining.