The Mechanism And Control Method Of The Non-coaxiality In Robotic Drilling Of The Stacked Aircraft Fuselage Structures

In the robotic drilling of aircraft fuselages,the manufacturing errors and the different deformations of the stacked structures usually cause interlayer gaps,which lead to the interfacial burrs and non-coaxiality of the stacked holes,thus to bring adverse effects on the hole qualities and assembly conditions.However,the researches on interlayer gaps are still lack and the studies on the non-coaxiality has seldom been reported.As a result of lacking the help of both theoretical and technical researches in industrial manufacturing,large amounts of fasteners are adopted to keep the stacks together to reduce the interlayer gaps and the non-coaxiality,which limits the drilling quality and efficiency in robotic drilling.According to the typical characteristics of the stacked structures in aircraft fuselages,the experimental stacked structures which contain two lower lathy plates and an upper broad plate are designed to imitate the aircraft stacks.After the stack drilling experiments,the diameters of the upper hole,the lower hole and the stacked hole at the interface are measured and the non-coaxiality of the stacked holes are discovered.Then,a simplified mechanical model of stack drilling is built in 2-D and the appearance of the non-coaxiality is revealed.The non-coaxiality is classified to three types by the deformation characteristics,which are Type I caused by pure bending of the stacks,Type ? caused by the different displacements of the stacks at the horizontal direction and Type ?I caused by the different local deformations at the hole edges and the hole axis.Then,the quantitative evaluation method,a convenient calculation and a measurement method of the non-coaxiality is proposed,thus to providing theoretical foundation for future researches.Then,single factor studies are conducted to study the influences of different stacked structures on the interlayer gaps and the non-coaxiality.As the results show,the influence of the lower layer at the drilling location is far more remarkable than the upper layer,thus a method to predict the tendency of the interlayer gaps and the non-coaxiality by studying the deformations of the lower layer is proposed.Then the broad plates,the cantilevered lathy plates,the framed stringers are studied.The results show that the stacks of two broad plates are suitable for researching on the interlayer gaps but not suitable for researching on the non-coaxiality.The stacks of cantilevered lathy plates and broad plates can imitate the non-coaxiality in the stack drilling of actual aircraft assemblies.For the stacks of framed stringers and broad plates,the non-coaxiality are more serious with the stringers being lathier,more convex curved and with the drilling location being further to the fixed location.On the other hand,the interlayer gaps are more serious with the stringers being broader and with the drilling location being further to the ribs.With the method to predict the tendency of the interlayer gaps and non-coaxiality by studying the deformations of the lower layer,the methods to decrease and control the interlayer gaps and the noncoaxiality in stack drilling can be better designed for different kinds of structures in aircraft assemblies.At last,the influence of the pressing forces is studied and the method of obtaining a suitable pressing force is proposed.The theoretical accuracy of the normal direction measurement with four laser displacement sensors of a rhombus layout is solved,thus to optimize the layout of the displacement sensors for higher precision and to minimize the influences of the drilling directions on the non-coaxiality.More importantly,the effects of the fasteners on reducing interlayer gaps and non-coaxiality are revealed in the 2-D simplified mechanical model of stack drilling,and an optimized layout of the pre-installed fasteners is proposed,thus to achieve a high efficiency and a high quality in the robotic drilling of aircraft fuselages.