Design of high accuracy cylindrical profile measurement model for low-pressure turbine shaft of aero engine

Abstract

Coaxiality and cylindricity are the important geometric parameters of the low-pressure turbine (LPT) shaft. And the measurement accuracy of coaxiality and cylindricity directly affect the rotary characteristics of the aero engine. Therefore, a cylindrical profile measurement model with five systematic errors is designed to improve the coaxiality and cylindricity measurement accuracy of the low-pressure turbine shaft in this paper, in which eccentricity, probe offset, probe radius, geometric axis tilt and guide rail tilt are considered. Besides, the influence of systematic error and the shaft radius on the residual error for the stepped low-pressure turbine shaft is analyzed as well. The evaluation results of coaxiality and cylindricity are obtained based on different measurement strategies and models. In order to verify the effectiveness of the cylindrical profile measurement model with five systematic errors in the paper, a rotary measuring instrument with high precision is built. Compared with the traditional cylindrical profile measurement model with two systematic errors, the measurement accuracy of the coaxiality and cylindricity by the cylindrical profile measurement model with five systematic errors proposed in this paper are improved by 2.9 μm and 8.18 μm, respectively in the condition of the optimal measurement strategy for the LPT shaft with large radius. The proposed method is suitable for small probe radius and large eccentricity error, probe offset error, geometric axis tilt error and guide rail tilt error, especially for the LPT shaft with large radius. The proposed method can be applied to error separation and tolerance allocation for multistage rotor.