3D computer aided geometrical modeling and simulation of process planning

In the context of tolerance allocation in process planning, our interest is the 3D modeling of the manufacturing defects. This paper presents two approaches for the geometrical manufacturing simulation. The concept of small displacement torsor is used to modelize geometrical defects of part surfaces. The first approach uses a CAD modeler in order to extract the geometrical data used then to generate the equations needed for a mathematical processing with a symbolic computational software. The model that we developed for manufacturing considers each manufacturing get-up as a mechanism constituted (a machine-tool, a part-holder, manufacturing operations and the workpiece). We have defined a chart representation which we use to express the geometrical manufacturing conditions of the process plan as a torsor chain (like a chain of dimensions by using a traditional ID model). The second approach aims at using the functionalities of an industrial CAD/CAM system in order to reproduce and deploy this model. Each element is modeled with its defects to lead to the part in its final geometrical state with the resulting defects. Thus, the 3D model of the simulated workpiece is usable to check the conformity of the finished part. The results of the simulation integrated into the CAD/CAM system are coherent with those resulting from the mathematical calculations.