Tolerance elements: an alternative approach for cost optimum tolerance transfer

Abstract

This paper presents a method for cost optimum conversion of functional tolerances into machining tolerances transferred to one or more datum reference frames. A new concept—that of the Tolerance Element—is introduced as a machining process-related geometric entity with attributes associated with the accuracy cost. The accuracy-getting capabilities and cost per Tolerance Element are recorded for a particular machine shop through an appropriately designed database feedback form. The Tolerance Elements methodology, once adapted for this machine shop through processing information of the database feedback form, automatically creates application-focused cost-tolerance functions. The latter, in conjunction with the tolerance transfer principle and the machining axes accuracies, are used for the formulation of the problem objective function for cost optimum tolerancing. The system database needs expert updating only when changes occur in the machine shop facilities and/or expertise. The proposed method is demonstrated and discussed by means of an application example.