Modélisation et évaluation de l’incertitude de mesure lors de l’utilisation de MMT avec des pièces déformables

Abstract

Abstract. In the automotive and aerospace industries, the use of plastic parts is frequent. To validate these parts, the methodology used to realize the measurement takes into account some specific elements as departure elements: points or surfaces (datum elements of the plastic part). The method also considers a thin wall associated to the theoretical geometry of the part (CAD model). The Cartesian coordinates of control points are then measured by using a Three-Dimensional Measuring Machine. We can then compare the position of these points to the nominal CAD. This paper presents a new approach to define a method of control for deformable parts. We use simultaneously simulation software and simplified control equipment. This simple measurement fixture defines the setting in position of the part and the points that need to be clamped. It's represents the way the part will be assembled into the car. The implementation of this method consists in measuring different parts without any clamp or constraint (free state) to quantify the variation of the position of selected datum points. The choice of these points is linked to the setting in position we defined and the clamp of the workpiece on the simplified control device. This measurement may be done by using a laser scanner or CMM. The variations obtained will be specified as geometric tolerances in the simulation software (3DCS). This simulation tool includes a module of calculation with the finite elements method. This allows calculation of the deformation of the workpiece clamped on the simplified control assembly. The deformation is different for each part, due to the geometric variations of the parts in the free state. Virtual measurements can then be performed on the workpiece in position and constrained on the control device. This method is applied to an industrial part.