Integration strategy of on-machine measurement (OMM) and numerical control (NC) machining for the large thin-walled parts with surface correlative constraint

Abstract

There is a kind of large thin-walled parts in aerospace industry, the machining target surface of which is tightly associated with another specific surface (named correlative surface). And it is always the primary machining objective. However, the preformed correlative surface is significantly different from its original design model due to large profile and thickness errors. Thus, part-referenced machining is necessary to ensure the correlative constraint accuracy. In this article, an integration strategy of OMM and NC machining for the large thin-walled parts with surface correlative constraint is systematically developed. Generally, the integration process consists of correlative constraint analysis, on-machine measurement, machining target surface redesign, and NC machining. Firstly, an isoplanar-based on-machine scanning method is presented for large surface profile information extraction. Then, a unified target surface redesign model is established according to surfaces accompanying relation analysis. Further, to compensate stress-induced monotonic structural deformation, a partitioned measuring and machining approach has been employed. Finally, the liquid rocket engine nozzle as a typical part was employed to verify the validation of the proposed strategy. Coolant channel machining experiments were conducted on a special dual-spindle machine tools. For a nozzle with machining area about 8 m2, the correlative accuracy could be controlled in the range of ±0.1 mm. It has been proved that incorporating dimensional metrology feedback to machining process could consistently improve machining quality and efficiency of large thin-walled parts.