| With the globalization of IT and manufacturing, The demand of intelligent processing and network transmission efficiency is increasingly high. The ISO 6983 interface which used to define a simple tool movement and low-level switch programming brings many problems such as not compatible between systems, programming difficulties and low intelligence level greatly, and greatly limits the development of modern CNC production. It is fail to reflect IT (information) technology and MT (manufacturing)technologies.Therefore, a new data model and a new CNC programming method (STEP-NC) has been proposed. It is the extension of the STEP standard to CNC field, re-enacts the interface between CAD/CAM and CNC. At the same time, NURBS (Non-uniform Rational B-Spline) method is defined as STEP standard curve and expressed the only form of surface by the advantage of its good mathematical characteristics. It not only can describe free curve surface, but also can precisely represent conic arc and the second surface. A significant feature of STEP-NC is the support for complex surface machining and spline interpolation. The technology of surface processing tool path is also asked a new requirement by STEP-NC CNC system. Addtionally, especially the wide application of surface parts, so there is a urgent need for a new method of expressing tool path way which can improve the quality of surface machining and processing efficiency and meet development of modernization. NURBS tool path can not only improve the surface smoothness and processing efficiency, but also greatly increase the system stability. Therefore, as the NURBS surface for example. This paper research the processing of STEP-NC tool path generation technology, because of the good mathematical properties of NURBS, NURBS curve tool path generation for algorithm is proposed and make verfication.Firstly, This paper deeply analyze the model NURBS curves and surfaces based on STEP standard data; Make corresponding EXPRESS entities mapped to C++classes after in-depth analysising the NURBS curves and surfaces data model in the STEP standard; Developed small systems for extracting NURBS curve and surface geometry information,and then test and verify whether the extracted information is correct through surface can reapper or not; Make geometry processing for the extracted data; Calculate the surface math expression, and prepare for the follow-up tool path planning.In the study of NURBS curve toolpath technology, Based on in the parameter line algorithm, this paper presents a kind of toolpath generation algorithm which can control u,v directions at the same time, obtained the tool contacting path mathematical expression of surface; But because of for the freedom curves and surfaces, new curves and surfaces that generated after offset offseting are no longer identical with the original NURBS expression,which determine by the geometric properties of NURBS expression, so we can not directly get the cutter point toolpath. Put the surface into MASTECAM software and then output cutter location file which is expressed by small line segment, extract parts of the cutter location points and fit NURBS curve, also known as reverse path. To obtain NURBS expression tool path.Researching NURBS curve tool path technology based on STEP-NC not only provides extended function for existing CNC which is used to machine complex curved surface, but also provides the core technical support for the next generation of STEP-NC CNC system development, consequently provide the solid foundation for the realization of manufacturing network. Not difficult to imagine, a large number of digital product model database in network-based manufacturing,Digital Manufacturing will appear more diversified.
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