Study On Key Techniques Of Wing-fuselage Joints Machining In Digital Aircraft Assembly

Forced localization and clamping are often adopted in conventional jig-based aircraft assembly. Wing-fuselage joints can not be measured accurately with high efficiency. Thus finish machining of wing-fuselage joints is carried out involving a certain degree of risk. In order to guarantee the quality and security of aircraft assembly, a wing-fuselage joint finish machining method for digital join-assembly of large aircraft components is proposed. Several key problems are studied and analyzed deeply.Domestic and foreign development states of aircraft final assembly techniques are summarized. Development of aircraft wing-fuselage joint finish machining techniques is analyzed in detail. Shortcoming of domestic techniques is indicated. Considered general process and layout design of digital assembly system for mating and joining large aircraft parts, design and realization method of the system used for wing-fuselage joint measurement, evaluation and finish machining are put forward. According to the demands of measuring and finish machining wing-fuselage joints, object performance parameters of each special NC machining center are determined. And main measures taken to guarantee their performance are illustrated. Realization method of main functions of wing-fuselage joint measuring, evaluating and machining system are presented.The digital coordination mechanism of aircraft final assembly is designed. A method for analyzing wing-fuselage joints'posture error relative to the reference frame of assembly system is put forward. A posture error model of wing-fuselage joints is built using matrix perturbation method. The span of each source error is determined according to results of fuselage posture alignment experiment or performance parameters of correlative equipments. Distribution of posture error of wing-fuselage joints is learned by Monte Carlo simulation. Cutting allowance of wing-fuselage joint hole in the worst case is calculated using extremum analysis. According to the calculation results, we can draw a qualitative conclusion that it's a possibility that allowance of some wing-fuselage joint holes is insufficient for finish machining.To avoid possible security problems, two kinds of safety checking measures for finish machining of wing-fuselage joints during digital join-assembly of large fuselage parts are proposed. Three-coordinate measurement of wing-fuselage joints is performed on spot by special machining center. Basing on measured data, the model of actual wing-fuselage joints is built through automatic parameterized modeling. Machining process simulation is performed to find out possible problems, such as wrong codes in NC programs, over travel of machining center or interference between machining center and fuselage. A feasibility evaluating model of finish machining is put forward based on measured data of wing-fuselage joints. This model can find out four kinds of possible problems, namely initial joint hole remaining after finish machining, distance between object hole and side face of joint running out of tolerance, overcutting at the root of joint flange and initial matching surface of joint flange remaining after finish machining. Thus fatal damage of wing-fuselage joints can be avoided.If actual cutting allowances of some wing-fuselage joints do not meet the condition to begin finish machining, fuselage posture should be realigned. To gain optimum posture realignment object, a nonlinear optimization model is built based on measured data of wing-fuselage joints and points used for evaluating fuselage posture. Constraints on posture error of integral fuselage, position errors of posture measuring points, and allowance errors of wing-fusel age joints are considered in this model. The relative importance of all residual errors is analyzed according to their nature. Then weights used in objective function are configured through analytic hierarchy process. All residual errors can be redistributed by adjusting these weights. Thus optimum objective posture meeting all constraints can be obtained finally.To replace conventional wing-fuselage joint machining method with NC machining method in digital assembly of large aircraft parts, the characteristics and difficulties of wing-fuselage joint finish machining are analyzed. Three technical measures are taken to solve this difficult machining problem, namely designing the digital assembly system aim at wing-fuselage joint machining, improving the machining technic and optimizing cutting parameters by test. An on-line digital checking method for finished wing-fuselage joints is proposed to overcome the limitation of traditional method using joint gauge. Position errors of unmachined joints are calculated using measured data from laser trackers. An on-line assembly accuracy evaluation model of integral fuselage is built by summing up all errors with appropriate weights.Finally, summary of the whole work in this dissertation is given, and the future work is discussed.