Constructing and processing of NC instruction for 5-axis machining of NURBS surfaces

A new Numerical Control(NC)instruction(G code)for the direct interpolation of Non-Uniform Rational B-Spline(NURBS)surfaces was proposed.The mechanisms of the transferring of surface information and of the information processing were also presented.NURBS surfaces information which was described in the form of Initial Graphics Exchange Specification(IGES)could entirely be input into Computer Numerical Control(CNC)system from Computer Aided Design(CAD).The proposed method solved the problem of the loss of the normal vectors of cutter contact points and the tangent vectors of tool path on the surfaces to be machined as a result of the approximation of the surfaces into a number of smaller straight lines and curves during the machining of NURBS surfaces,which enabled CNC systems to implement the 3D online cutter compensation and the intelligent control.The simulation experiment was conducted to test the effectiveness and accuracy of the proposed method.