Optimized reaction injection molding

A method of making an article by steps comprising flowing at least one fluid into a cavity, and reacting said fluid so as to produce an at least partially polymerized material in said cavity, wherein said fluid comprises a thermosetting fluid, and the parameters of said reacting are chosen so that said fluid in said cavity does not exceed desired limits on at least one of the factors of (1) chemical conversion or (2) temperature, whereby said at least one of the factors is determined by steps comprising simulating said flowing of said fluid by steps comprising dividing said cavity into a plurality of cells, assigning a marker to each cell for carrying information comprising the temperature, chemical conversion, viscosity, and velocity of the fluid in the cell, performing computations to determine said information, moving the marker a distance determined by the computed velocity, and iterating said computations for said fluid during the simulating of said flowing until said cavity is filled with said fluid, and thereafter continuing to compute at least one of said factors, utilizing as an initial condition therefor the final value of said factor computed for the simulating of said flowing.