Tolerancing for manufacturing: a three-dimensional model

This paper proposes a three-dimensional (3D) model on manufacturing tolerancing for mechanical parts. The work presented relies on research conducted at the LURPA on the computation of 3D tolerance chains for mechanisms. Starting from these works, the authors propose a formalization of the problem within the more specific context of manufacturing tolerances. Models of the workpiece, the set-ups and the machining operations are provided. The main originality is to model the machining set-up as a mechanism. The concept of the small displacements torsor (SDT) is used to model the process planning. It opens up the way for the 3D integration product/process because of the similarities between the concepts used in both points of view. The first part recalls the principle of the modelling of surface variations with SDT as well as its application to the modelling of mechanisms. The second part introduces the use of the concept in the case of manufacturing tolerancing. A third part shows the modelling of the problem with the help of an example. At last, a detailed computer implementation is described.