A computer-implemented method for CAD volume extrusion operator detection in a CAD 3D model representing a mechanical part. The method includes obtaining a segmentation of the CAD 3D model. The CAD 3D model includes a skin representing an outer surface of the mechanical part. The segmentation comprises segments each representing a skin portion. The method further includes iteratively grouping segments. Segments of a pair are grouped when: each segment of the pair is an extrusion surface and a union of the segments is an extrusion surface having a same extrusion axis as the segments, or each segment of the pair is an extrusion surface and one of the two segments is a closing plane for the other segment. The method further includes determining one or more CAD volume extrusion operators, each corresponding to a respective group.