AIJSTPME (2009) 2(2): 35- 42 © King Mongkut’s University of Technology North Bangkok Press, Bangkok, Thailand 35 From the nominal model to a model of manufactured parts in a CAD context Vignat F. G-SCOP Laboratory, University of Grenoble, France Villeneuve F. G-SCOP Laboratory, University of Grenoble, France Kamalinejad M. G-SCOP Laboratory, University of Grenoble, France Abstract Product design today mainly involves CAD software’s. In this context, the designers create a nominal model of the product and the process. Mainly, simulation and assessment are made based on this model. In this paper a model of the manufactured i.e. a model with deviation defects is proposed, the MMP model. One utilisation of the MMP is then presented, the functional tolerance analysis. This analysis is presented from the modelling of the tolerance by a virtual gauge to the numerical resolution by a Monte-Carlo simulation. Keywords: Tolerance, Manufacturing and Simulation 1 Introduction Product design today mainly involves CAD softwares. In this context, designers create a nominal model of the product and the process. On one hand, the simulations of the product behaviour (FEA, Kinematics …) are performed using this nominal model so that we can say that these are nominal simulations. On the other hand, the product will not be manufactured similar to this model. The manufacturing process chosen to produce the parts will generate deviations that will change the behaviour of the product in term of performance expectations. Therefore, it is necessary to predict this loss of performance and limit deviations in order to keep them in the acceptable range. The limitation of the deviations is usually done through functional specifications. It is therefore necessary to have, in the CAD environment, additional information about the manufacturing of the part. To answer this question, we propose a 3D model of manufactured parts (MMP) [1], based on the nominal CAD model, where deviations are described relative to the surfaces of the nominal part by the way of a small displacement torsor. These deviations are determined by simulation of the manufacturing process[2][3]. The MMP obtained contains information about the manufacturing process: the process plan, the elementary defects by the way of parameters, the combination of these defects and their range of variation by the way of constraints. This MMP model can then be used to analyze the impact of the production process proposed on the functional tolerances of the part. It is also possible to assemble number of MMP to evaluate the behaviour of a system in terms of functional requirement that must comply. In the present paper we propose to remind the MMP structure, the defects determination and the process simulation. The modelling of functional tolerances as virtual gauges is presented and. the description of the process plan (set-up, positioning and manufactured surfaces) is reminded. An analysis method, applied to functional tolerances and/or to functional requirements, I then exposed. It uses the parameters of the Model of Manufactured Parts combined to a Monte Carlo simulation of the parameters variation.