Research On Allowance Optimization For Adaptive Machining Thin-wall Cabin Based On Measurement

The aerospace craft cabin is a key component for loading and connecting various functional parts,and its manufacturing precision has an important impact on the performance of the aerospace craft.With the continuous development of the aerospace industry,the requirement for lightweight aerospace craft is becoming more and more urgent,so the whole thin-walled structure is widely used in the cabin.At present,the cabin structure is mainly processed by a hybrid machining process of casting/welding and precision numeric control(NC)machining.Due to the thermal cycle in the casting process,the cabin experiences poor accuracy in external shape,bad stability in structure thickness,uneven distribution in machining allowance.The traditional NC processing technology has the problems of long processing time and low processing efficiency.In this paper,the adaptive optimal allocation of machining allowance for thin-wall cabin is studied for the cabin processing requirements,which integrates the key technologies of three-dimensional digital measurement,shape matching,quick NC programming.Main researches included in this paper are as follow:(1)Based on the structural characteristics and dimensional accuracy of the cabin,the threedimensional digital measurement technology is studied.On-machine measurement system for complex external shape and on-machine ultrasonic thickness measurement system for thin-wall cabin are established respectively.and measurement plans have been developed for the shape and thin-wall thickness to ensure efficient and accurate measurement of the blank of the cabin.(2)Based on the actual measurement data,the model registration idea adapting to the structural characteristics of the cabin is proposed.The fast rough registration algorithm based on PCA and the ICP exact registration algorithm based on unit quaternion are studied,which improve the efficiency and accuracy of registration and provides a good posture for subsequent constraint registration.(3)Based on the registration results of the measured data and the theoretical CAD model,the distribution of the machining allowance is analyzed,three processing conditions of the thin-wall blank is analyzed,and the allowance optimization method under the profile and the wall thickness constraint is study for the distribution of the margin.(4)According to the programming requirements of the personalized cabin,a fast adaptive NC programming solution based on the overall rigid transformation of the template-based tooling point is proposed.The method of generating and extracting the template-based tooling point is studied,and an algorithm for calculating the unit normal vectors of tool positions is present.The tool offset is applied based on the tool axis normal to generate the final machining tool path.The machining experiment of the thin-wall cabin testing part is carried out.The dimensional accuracy of the processed test pieces is analyzed.The experimental results verify the feasibility of the adaptive optimal allocation of machining allowance for thin-wall cabin.