A computer implemented method for designing a 3D modeled object that represents a mechanical part. The method comprises selecting a group of faces of the B-Rep, defining a trajectory for each respective face of the group of faces, computing, for each face of the group of faces, a respective swept volume, the swept volume corresponding to the volume swept by the respective face with respect to the trajectory, assigning a material removal label or a material adding label to each swept volume, according to the position of the swept volume at the respective face with respect to the interior of the 3D modeled object, and updating the B-Rep with a material removal volume and then a material adding volume. The method improves the design of a 3D modeled object.