Three-dimensional Functional Tolerancing with Proportioned Assemblies Clearance Volume (U.P.E.L : Unions Pondérées d’Espaces de Liberté) : application to setup planning

The topical platforms of Computer Aided Design and Computer Aided Manufacturing (C.A.D/C.A.M) don’t manage the influence of geometric tolerances in the creation of manufacturing process of parts. The aim of this article is to present how a Tridimensional Dimension Chain model can intervene in process planning of machined part. The formulation of Tolerancing Analysis problem is used to study an assembly decomposed into two sub-sets : the machined part and the machine tools. With the « Proportioned Assemblies Clearance Volume (U.P.E.L) » model, we purpose a method to choose the solution which will lead to the least machining deviations. Equivalent mechanical joint between machined part and machine tools is an isostatic joint : six degrees of freedom are eliminated. This equivalent joint can be decomposed into six joints associated in parallel : six « punctual contacts ». We will not study the influence of « punctual contact » location on surface, but only the influence of Geometric Specifications. With the aid of composition rules of U.P.E.L (Union and Intersection), the optimal solution will been chosen. Our model is applicated to an example of machined part. A numerical simulation is presented and we will able to conclude about the best strategy to machine the part shown in our example.