Making a product conform to the functional requirements indicated by the
customer suppose to be able to manage the manufacturing process chosen to
realise the parts. A simulation step is generally performed to verify that the
expected generated deviations fit with these requirements. It is then necessary
to assess the actual deviations of the process in progress. This is usually
done by the verification of the conformity of the workpiece to manufacturing
tolerances at the end of each set-up. It is thus necessary to determine these
manufacturing tolerances. This step is called "manufacturing tolerance
synthesis". In this paper, a numerical method is proposed to perform 3D
manufacturing tolerances synthesis. This method uses the result of the
numerical analysis of tolerances to determine influent mall displacement of
surfaces. These displacements are described by small displacements torsors. An
algorithm is then proposed to determine suitable ISO manufacturing tolerances