Research On Key Technology Of Nc Machining Of Complex Integral Impeller

The integral impeller is the key part of the aero engine and all kinds of turbine machine. With the increase of the engine capability, the integral impeller becomes more and more complex. The blade becomes thinner and more twisted and the tunnel is narrower. This brought the manufacture of the impeller more barriers. The 5-axis NC machining is flexible, efficient and widely adopted. So it is one of the frequently used manufacturing methods of the integral impeller.This thesis investigates the 5-axis NC machining technique of the integral impeller. Taking an open integral impeller as an example, a set of key algorithms for the integral impeller NC programming is proposed and some key techniques are resolved. The main content and the research result of this thesis are as follows:The foundation algorithms of the 5-axis NC programming are investigated. The peculiar non-linear error in the 5-axis NC machining is analyzed and the non-linear error computation model for general 5-axis NC machines is proposed. Due to the non-linear error in the 5-axis NC machining and the limitation to the tool orientation range by the real NC machine, the tool path computing method for the 5-axis NC machining with meeting the prescribed tolerance is proposed. The smoothing technique of the tool orientations in the 5-axis NC programming is proposed. With considering the tool path character, several key tool orientations are set at a tool path. By the two-phrase interpolation technique, the smooth tool orientation function is built. With this function, the tool orientation and the CL point at the tool path are associated and the smoothed tool orientations are achieved. Finally, the improved secant method is adopted to compute the tool step and the CL files can be obtained.The planning method for the trimmed blade surface is studied. According to the character of the trimmed blade, the remained parameter field is mapped to a normalized one and it is convenient to plan the tool path according the normalized parameter field. Based on the proposed method, the algorithm of the error-meeting isoparamter spiral tool path is presented with adopting the point milling method. The computation method of the integral impeller tool orientations is proposed. Several isoparamter curves along the section direction are selected. The interference-free key tool orientations pointing to the opening of the tunnel at each isoparamter curve are set and the smooth tool orientation function is built. The interpolation along the radial direction of the blade is taken and the global smoothed tool orientations of the integral impeller can be obtained. Due to the large curvature and the rotation angle of the tool orientation around the edges of the blade, it is difficult to ensure the machining quality. The S-shape federate-setting method is proposed to set the federate and the tool transits from the middle of the blade to the edges smoothly and the tool orientation rotating speed is also smoothed. This can increase the quality of the machining of the blade.The rough machining tool path computation method of the blade of the integral impeller is studied. According to the interference of the integral impeller, two kinds of generatrix computation method are given. The offset of the blade section is taken as the directrix and the ruled driven surface for the rough machining of the blade of the integral impeller is constructed. With the ruled surface, the rough machining tool path can be gained. One tool path planning method for the NC machining of the hub of the integral impeller is proposed. According to the feature of the hub, the number of the tool path is obtained and the parameter function of the CC tool path is deduced with the scallop under the specified error. The tool path planning method for the variable radii bend surface is studied. According to the feature of the variable radius bend surface, the minimal bending radius is obtained and the machining tool can be selected. Then, the toolpath of the bend surface can be obtained with considering the geometric conditions and the machining demand.The customized programming modular embedded in UGNX4.0 for the NC machining of the integral impeller is developed by the UPopen apis with the proposed techniques in this thesis. The NC programs are obtained with the modular and applied to the machining test of an integral impeller. The machining test shows that the proposed techniques are validated.