An open CNC for machining NURBS surfaces based on STEP-NC

Generally, free-form surfaces are machined using the following procedures: by a CAM postprocessor a free-form surface is approximated into a number of smaller straight lines or curves to send a CNC system in the form of G/M code, which focuses on the constant speed of cutter location point instead of the constant speed of cutter contact point. These methods lead to low machining efficiency and accuracy. To overcome these limitations, a method for machining of NURBS surfaces based on STEP-NC is proposed, by which a CNC system can deal with the NC program which includes entire NURBS surface geometric and technological information in the form of STEP-NC. An open CNC which can realize the machining of NURBS surfaces is developed based on PC. Simulation experiment has been finished to test the proposed method.