Study On High Accuracy Five-axis NC Machining Of Centrifugal Compressor Impeller

Compressor impeller is a type of representative parts with sculptured surface, which is the most important part in the centrifugal compressor. Its design and manufacture precision have large effect on the performance of compressor. With the development of science and technology, the rotational speed, design and manufacture precision of impeller used in the fields of aeronautics & astronautics, shipbuilding and locomotive are increasing. At the present, major compressor impeller is designed and manufactured with advanced import special software and five-axis NC machine tool. The software system of impeller machining is very expensive and closed package, besides it is impossible for us to acquire its key technology. Therefore, in order to improve the performance of compressor, it is necessary to accomplish the high accuracy five-axis NC machining of centrifugal compressor impeller.Taking the five-axis NC machining workflow of centrifugal compressor impeller as the main thread and tool path scheduling algorithm of five-axis machining, post-processing algorithm for special type of five-axis machine tool and error analysis and compensation algorithm as the core contents are studied.Based on the geometry characteristic and processing technique of centrifugal compressor impeller, the tool path of rough and finish machining are scheduled. During the hub surface rough machining, the first is to divide the hub surface into three local areas along with the direction of flow passage, then the different diameter cutters are utilized to remove materials, which supplies a method to improve the machining efficiency. During the blade surface finish machining, the over-cut error is analyzed and by means of rotating initial tool axis vector to control the interference.Therefore, the impeller machining precision is improved.Post-processing programs for the special type of five-axis NC machine tool is developed to make the full use of five-axis machine tool. The special type of five-axis NC machine tool whose tilt rotary axis and translational axis is not parallel, the generic post-processing software can't provide post-processing function of specific mode of motion axes, the post-processing algorithm for special table-tilting and spindle-tilting five-axis machine tools is detailed deduced.Based on viewpoint of post-processing, non-linear error of five-axis NC machining of impeller is analyzed and its influencing factors are presented. The error calculating method using the homogeneous coordinate transformation matrix together with forward and inversekinematics and the corresponding error compensation strategies are proposed. Besides, the concept of tool axis vector smoothing is introduced and the quaternion vector interpolation algorithm is proposed, which can improve the impeller machining precision and surface quality further.Finally, taking centrifugal compressor impeller as an example, the proposed methodology is verified by computer machining simulation and a trial machining with the UG NX software and DMU 70V type five-axis NC machine tool. The results indicate the proposed algorithms are correct and valid.The study on high accuracy and high efficiency five-axis NC machining of centrifugal compressor impeller is accomplished and has a favorable value in the engineering application. In addition, the result from the research can be applied in five-axis machining of other sculptured surfaces for reference.