Error compensation for machining of large thin-walled part with sculptured surface based on on-machine measurement

Abstract

Large thin-walled parts are widely used in aerospace. Due to its low rigidity, force- and thermal-induced cutting deformation immediately affects the dimensional accuracy of machined parts. Multilayer milling strategy is usually utilized due to its low rigidity, which results in reduction of machining efficiency. In this work, a typical large thin-walled part, tank bottom of the rocket, is selected as an application object and an adaptive deformation error compensation method for large thin-walled part is proposed. An integrated on-machine measurement (OMM) system is developed to acquire the part’s geometry. Geometry of outer surface is directly measured and constructed by a touch-trigger probe installed on machine tool’s spindle, while the geometry of inner surface is determined by measuring the thickness at each probe point, using an ultrasonic thickness gage. As such, machining error for each layer cutting is identified by comparing with the designed geometry. A deformation prediction model is established to predict the cutting deformation of the next layer based on the calibrated error in previous layer cutting, so as to compute the compensation value. A machining error compensation algorithm is then developed to eliminate the deformation error by modifying the machining toolpath. At last, machining experiment is conducted to verify the feasibility of the proposed methodology.