Off-axis machining of NURBS freeform surfaces by fast tool servo system

The manufacturing of optical components with complex geometries like freeform surfaces is getting more and more important. Mass production of these optics is enabled by replication methods like injection moulding. For the machining of the required mould inserts with freeform geometries ultraprecision technologies like Fast Tool Servo turning can be applied to achieve the appropriate optical surface quality. For the mathematical description of freeform surfaces NURBS (Non Uniform Rational Basis Splines) are highly applicable. To avoid interpolation errors and to create set points with a continuous and smooth path of motion a trajectory generator directly based on NURBS data has been developed for Fast Tool Servo assisted turning [1], which evaluates the NURBS surface in each position control cycle. An approach of increasing the efficiency of manufacturing freeform surfaces is the off-axis machining of multiple workpieces at the same time. The paper presents the different process steps in simulation and off-axis machining of freeform surfaces using Fast Tool Servo assisted turning in conjunction with NURBS based data processing.