Study On Prediction Of Machining Elastic Deformation And Error Compensation For Integral Impeller

Integral impeller is widely used in the field of aerospace engineering, which is beneficial to reduction of total engine parts and improvement of engine performance. It is usually machined by using multi-axis numerical control (NC) milling method. The vanes of most integral impellers have complex surface modeling with thin-walled structure, and they may easily produce deformation caused by cutting force during machining process. Deformation error control of thin-walled vane is always a key and difficult techonolgy to realize precision machining of integral impeller. Although machining process simulation technology is an effective way to solve the above problem, a plenty of research works need to be developed. Therefore, in order to improve machining accuracy of integral impeller, integral impeller geometric modeling, tool path generating, cutting force prediction for five-axis milling process, elastic deformation calculation of thin-walled vane and machining error compensation have been studied in this paper.Firstly, the method of integral impeller geometric modeling and tool path generating is researched to lay a foundation for the following chapters. On the basis of B-spline technique, some common methods of surface editing, such as surface extension, offsetting, trimming and fillet transition are achieved for geometric modeling of integral impeller. And then some works include design of NC milling technological process, tool path planning, tool interference checking and correction and post processing are researched.Secondly, the method of cutting force prediction for NC milling process of free-form surface thin-walled vane is researched. An algorithm for instantaneous engaged cutting edge elements identification is proposed to ascertain upper and lower limits of the integral in a cutting force model. This identification algorithm involves two key techniques:one is the generation of the tool swept volume; the other is establishment and the update of Z-map model. Based on the envelope theory, the equation of envelope curve at each cutter location point is derived, and then tool swept volume surface for five-axis NC milling is constructed by B-spline fitting. The Z-map models of workpiece and tool swept volume are established by an intersection algorithm between line and free-form surface, and then update of the workpiece is realized by a boolean operation between workpiece Z-map model and tool swept volume Z-map model. According the cutter location characteristics of free-form surface thin-walled vane milling process, an empirical formula considered tool inclination angle of average cutting force is established, the undetermined coefficients is calibrated by carrying out an orthogonal test, and then the validity of this empirical formula is verified by using the AdvantEdge PM software.Thirdly, the method of elastic deformation calculating and error compensation for NC milling process of free-form surface thin-walled vane is researched. Considering the coupling relationship between cutting force and elastic deformation, an iteration format for calculating elastic deformation of free-form surface thin-walled vane is presented with cutting depth, cutting width and tool inclination angle as feedback variables, and then elastic deformation at each cutter contact point of a free-form surface thin-walled vane example is calculated in accordance with this iteration format by using Matalb and Ansys software. Base on this, the error compensation of the thin-walled vane example is studied by applying mirror method.Finally, in order to verify validation of the methods proposed in this paper, some works such as machining experiment of integral impeller, measuring experiment of vane and analysis of vane machining error are developed successively. During machining experiment of integral impeller under five-axis CNC machine with dual rotary tables, two adjacent vanes are selected as sample pieces, one is without error compensation, and the other is with error compensation proposed in this paper. Data measurement of impeller is carried out by using a3D scanner, and then surface reconstruction of the sample pieces is completed by applying Geomagic software. Comparison analysis of machining errors from two sample pieces is done, and the results indicate that the methods proposed in this paper are effective and valid.