The significance of materialized prototypes from CAD generated mechanical parts has been recognized since more than a decade. Despite the ever increasing quality and speed of graphical visualization methods, solid 3D hard copies from designs remain essential for certain stages in the creation process. Especially during the phase of conceptual geometric design, when alternative shape proposals must be quickly judged, automatic, fast and inexpensive production of replica is of importance. However, for such a kind of prototyping in conjunction with CAD, traditional methods based on CAM and NC technology turn out not adequate. To support conceptual design, several extensions and optimizations, mainly in the software area, need to be effected. In this paper an autonomous NC-milling process generator TLCOR is presented. It evaluates and analyzes surface/solid models based on NURBS, determines the physical constraints of the 3D milling devices (represented in a technical database) and finally produces an ISO-standard control statement sequence. The system selects the appropriate machining method (parametric and/or geometric algorithms) and tools, and breaks up the process into different stages of non-planar path planning with interference avoidance. The user will never be confronted with any aspect concerning the NC. The designer only needs to express his or her wish to obtain a milled copy of the actual CAD model. Extension of TLCOR to shape models defined neutrally (STEP/PDES based) and to multi-axis and robot milling is in progress.