Research Of Fixturing System With Automatic Collision Avoidance For Large Aircraft Structural Part Machining

With the rapid development of the aircraft manufacturing industry, the requirements of modern aircraft on the performance continuously improve. In the modern manufacture of aircraft products, large monolithic component is widely used instead of the parts combined by riveting and bolt in the past. Compared with the general mechanical parts, we have larger difficulty in aircraft monolithic component machining, not only for the complex entity and high requirements of shape and position accuracy, but also for easy deformation, low stiffness, and high material removal rate in CNC machining process.Multi-point clamping is an efficient and practical approach to ensure the static and/or dynamic stability during aircraft monolithic component machining. However, it is always inevitable that some clamping points are very close to the machined features, such as slots, ribs, holes and so on. In such a situation, tool path and posture planning would be at a loss in the face of the machining motion collision between cutter and clamping points. It is a knotty problem in the aviation manufacturing industry.In this paper, from the view point of parts clamping, an automatic collision avoidance strategy using force-and action-controlled clamping equipment is researched.First of all, the effect of releasing and clamping repeatedly on parts machining status is analyzed numerically using FEA technique. Accordingly, the clamping forces related to raising and pressuring are optimized respectively.And then, a model-based collision detecting algorithm is designed, which can be implemented by comparing the cutter actual position extracted directly through sensor, and the calibrated positions clamping points in machine tool coordinate system. Thus, the automatic collision avoidance will be independent of machining codes.Finally, a modular fixturing system with automatic collision avoidance is designed, manufactured and tested. To verify the validation, an aluminum alloy structural fame with size of 560mm ×110mm x 16mm was used, on which the grids for weight reduction should be machined. The fixturing system was mainly composed of four pneumatic clamping points with maximum controlled force 778N, eight ultrasonic proximity sensors, two ultrasonic displacement sensor, the base and other auxiliary supports. From the machining experiments, it indicates that the proposed fixturing system is highly efficient and very flexible to meet the aircraft structural parts machining requirements.