Presentation of a Novel “Simultaneous Three Axis Turning” Process for Time and Cost Efficient Machining of Turbine Components Made of Difficult-to-Machine Super Alloys

To increase the efficiency of turbines and jet engines, novel materials are developed continuously. Although such materials are beneficial regarding the turbine efficiency, disadvantages emerge regarding the machinability. Due to the enhanced physical and chemical properties these materials are very difficult to machine. Typical machining processes like milling or turning reach their limits very fast when these materials are machined. Thus, machining is very costly and time intensive, which reduces the cost saving potential of novel material developments. To be able to machine complex, rotational symmetric turbine components made of novel super alloys cost and time efficiently, a novel three axis turning process was developed, which is presented in this paper. By enhancing the two already existing translational x- and z axes in turning with a third additional rotation axis, the flexibility and the efficiency of turning can be increased significantly. The additional moving axis provides major benefits when turning geometrically complex parts made of difficult-to-machine materials such as turbine discs, mandrels, casings etc., especially regarding tool consumption and machining time. However, in this paper the novel turning process “Simultaneously three axis turning” is presented for the first time. It is shown that by simultaneous three axis turning the tool consumption can be decreased significantly by more than half when machining turbine disks made of super alloys like TiAl6V4 or Inconel 718. Due to the possibility of adapting the tool inclination optimal to the workpiece geometry and cutting conditions, tools can be used more efficiently. The paper also shows how major process results like surface generation, process forces and in particular tool wear depends upon the temporal movement of the third axis. Finally a method based on experimental results, which can be used to design and implement simultaneous three axis turning processes in industrial manufacturing of turbine components is presented.