Study on general analytical method for CNC machining the free-form surfaces

Free-form surfaces are widely used in CAD systems to describe the surface of parts, such as molds and dies. The surfaces are often produced by a 3-axis CNC machine tool using ball-end or face-end cutters. The current methods for machining those part surfaces require some important human decisions, such as determination of the precise interval between successive tool-paths. A tool-path interval that is too large can result in a rough surfaces; one that is too small can increase machining time, making the process inefficient. The purpose of this paper is to establish a systematic general analytical method for CNC machining the free-form surfaces, and develops the postprocessor to obtain the NC code. The method comprises five steps: (1) to find the equation of surface, (2) curvature analysis, (3) the selection of tool, (4) the error calculation of the linear incremental kinematics and (5) the calculation of the tool-path interval. To use the ball-end or face-end milling cutters for the convex or concave of surfaces, respectively. Through the verification by the solid cutting simulation software, it confirmed the effectiveness of the proposed algorithm.