Abstract: A method and apparatus for fabricating a core within a core box 10 having passages and screens 12 through which an air-sand mixture may flow to occupy cavities within the core box 10 by which the core is shaped. The method comprises providing a plurality of pressure switch sensors 14 disposed upon a core replica 16, each sensor being located in communication with a screen 12 within the core box 10; positioning the replica 16 within the core box 10; monitoring a condition at one or more screens 12 to determine a state of accretion thereat and generating a signal indicative of the condition; sending the signal to a processor which is in operative communication with a means for cleaning; and activating the means for cleaning within the core box 10 in response to the signal so that flow impediments are cleared from the screens 12 and so that constrictions in fluid flow within the core box 10 are detected in their early stages of development and acceptable production rates may be maintained.