Aero-engine Blade In-situ Inspection Method And Its Experimental Study

The aerospace thin-walled blade parts are usually designed as free-form surface. Theseparts have the technical characteristics of variable cross-section, strong distortion, easy todeformation. The geometric deformation in the multi-process machining of these parts is aptto generate. The quality of multi-axis CNC machining of the blades plays an important role onthe performance of aircraft engines. How to fast and efficiently inspect the blades in situ of themachine tools has become one of the vital technical problems in the field of the aviationmanufacturing. In this paper, a certain aircraft engine blade is studied as an example. Themethods and experiment research on the in situ inspection of the blade surface are proposedand implemented. The main research contents are as follows:In this study, the methods of contact measurement, non-contact measurement andcombined measurement are introduced. Some key technology problems on free-form surfaceinspection are analyzed, such as measuring points planning and measuring path optimization.For the problem of measuring points planning of the free-form surface, the basic scheme ondetermining the number of the measuring points is presented and two kinds of measuringpoints planning methods based on the curvature information are proposed: the curvaturedifference method and linear angle method. For the problem of contacting measuring pathoptimization, the calculation methods of the direction vectors of the B spline curve and thedouble three B spline surface are presented and the measuring path planning method based onthe normal vector of the blade surface is proposed.The necessity of the in situ measurement as well as its advantages and disadvantages areintroduced in this paper. The basic working principle of the general in situ measurementsystem and its hardware components are presented. The machining experiments are conductedon the single blade parts, which include the machining processing programming andsimulation. The calibration method and process of the probes are both studied. In the softwareenvironment of the PowerINSPECT OMV, the in situ measuring program of the single bladeparts is programmed, and the corresponding in situ measuring experiments on the Mikronmachining center are conducted. The experimental results are good. The measuring report ispresented with analyzing the experimental data.The preprocessing methods of measuring point cloud data are studied, which contain themeasuring point cloud denoising and the measuring point cloud reducing. The registrationmethods of the measurement model and the design model are analyzed. On the basis of theachievement of the research group, the coarse registration methods based on the characteristicsof the blade surface and the fine registration methods based on the adaptive distance function are studied. The2D cross-section point clouds of the blade surface are extracted. The analysisof the cross-section data is implemented in the software environment of the GeomagicQualify, which include the comparison of the3D error and the2D reverse error. The maincharacteristic parameters of the2D cross-section curves of the blade are extracted and theerror analysis is presented..