TOLERANCING FOR FUNCTION AND MANUFACTURING 1 E. Chirone 1 , S. Tornincasa 2 1 Dipartimento di Ingegneria Meccanica, Università di Brescia 2 Dipartimento Sistemi di produzione ed Economia dell’Azienda, University of Turin e-mail: tornin@polito.it Abstract Dimensioning and tolerance values could be established by manufacturing capability or by the product functional requirements? The product function should be the primary focus in establishing dimensional relationship and tolerance on drawing, allowing a designer to assure the widest possible tolerance maintaining part functionality. This concept is illustrated by examples that demonstrate the importance of functional approach satisfying most of conditions required during production and inspection. The designer may assign relatively tight tolerances to each part to ensure the expected design function, but this normally requires higher manufacturing cost. Enlarging tolerances on each component, on the other hand, reduces costs, but can result an unacceptable loss of quality and poor performance, leading to customer dissatisfaction. These conflicting goals between design and manufacturing have an enormous influence on the final cost of a manufactured product. Further examples are proposed to show a direct interface between a parametric CAD system and the functional dimensioning environment developed in order to create datum selection, based on the function of the part and an automatic tolerances analysis and allocation. 1. INTRODUCTION In mechanical industry, blueprints were often the only means to determine how a part would be manufactured and placed into an assembly. Following the blueprint, the part was produced and inspected, and when the components did not fit together properly, the blueprints went back to the engineering design in order to recalculate the dimensional or geometrical variations that allowed the suitable fit. The tool for such a performance is proper dimensioning, that is founded on technological and functional requirements. Technological, or manufacturing, requirements depend on materials, machinery and tooling, and, since play a major role in the development of the manufacturing cost, have a leadership in particular for the assignation of dimensional tolerances (so often called manufacturing tolerances). Blueprints are actually considered as working schedule (as they are) but with the implication that manufacture is what imposes 1 From “Atti XI Convegno Nazionale ADM, Palermo, 1999 “ , vol. C