Research On Key Technology Of Aircraft Sheet Metal Part Forming Technique For Precise Assembly

Along with continuously upgrade of the aircraft performance and innovation of assembly process,the aircraft assembly is changed from manual repairment to precision assembly.The stringent demand for forming precision of sheet part is proposed recently.As an important component of aircraft part family,the manufacturing quality of the metal sheet directly relates to the flight performance and service life of the aircraft.In recent years,the aviation industry has obtained considerable development in our country.However,there still exist some gaps in the forming technology of some key metal sheet parts with advanced international standards.The precision and quality of metal sheet is the neckbottle of aircraft digital manufacturing and precision assembly.The precision,flexible and digital forming of metal sheet is the urgent problem to be solved.The aircraft frame,rib and skin are most used component in the aircraft assembly procedure.The solution of rubber bladder forming and precision skin stretch forming is proposed.Some key technologies,such as blank fast design,forming process simulation,precision skin stretch forming and flexible clamping for skin edge trimming are achieved.The relative software system and hardware system are developed.The main research contents and results are as follows:1)The fast blank design method based on one step inverse forming for rubber bladder forming of metal sheet is proposed in this paper.The Rubber Blank Size Estimation(RBSE)system of the initial blank has been developed.First,the geometrical relationship and constitutive equations of one step inverse forming are established.The calculation method of element node internal force and equivalent node external force separately by adopting the triangle elements and the Newton-Posen method iterative format of one step inverse forming are studied.Then,a kind of fast and accurate blank shape predict algorithm of aircraft sheet metal rubber bladder forming based on one step inverse forming is proposed,and the RBSE system with CATIA/CAA secondary development tool by using the algorithm of one step forming inverse solution as the core algorithm is developed.Finally,the verification of the system with the parts of subsidence and rib is carried.The results indicate that the system can predict the size of the rubber bladder forming accurately,which improves the precision and efficiency of the metal sheet forming.2)The springback compensation method of rubber bladder forming by displacement mapping is proposed.The simulation system of rubber bladder forming process is developed.First,the material model and stress modification are established by the governing equation and space finite element discretization.The springback compensation method of rubber bladder forming is built by displacement mapping,iterative processing and surface reconstruction based on the displacement adjustment algorithm and forward springback algorithm.Then,the technological process of rubber bladder forming is designed.The quick design of the die surface,forming simulation and springback compensation technology are studied.The accurate forming technological process of the sheet metal rubber bladder forming based on the springback compensation is proposed.Finally,the rubber bladder forming simulation system which combined with PAM-STAMP 2G and CATIA/CAA secondary development platform is developed.By take a typical rubber bladder forming part as example,the simulation analysis of rubber bladder forming is carried out.The result verifies the reliability of the simulation system.By the way,the influence of the related parameters on the simulation springback is researched3)The stretch forming process design method based on the reconfigurable flexible multi-point die is proposed.Based on the development of the relative technology,such as spatial orientation of curve surface,die surface supplement,nail height calculation,blank size and stretch forming path calculation,the numerical control technology of reconfigurable flexible multi-point die design system by the CATIA secondary development technology(CAA)is developed.It can be used to solve the problems,such as springback compensation and surface optimization of the reconfigurable flexible multi-point die.The dynamic simulation system of FET600 and VTL1000 CNC stretch forming machine on the basis of the solution of stretch forming tracks and movement parameter conversion algorithm is developed by the CATIA secondary development technology also.4)The dynamic multi-point position method based on N-2-1 principle and position parameter calculation is proposed.The flexible clamping equipment based on digital control vacuum sucker is developed.Firstly,the skin edge trimming process and fixture based on flexible clamping are studied.The dynamic multi-point position method of skin edge trimming based on N-2-1 principle is proposed.The virtual fixing of curved part by flexible fixture is implemented by geometric restrain relationship.The position parameters of flexible fixture are calculated also.Secondly,the key technologies,such as design,manufacture and control of the flexible clamping equipment based on vacuum sucker are achieved.The digital control flexible clamping fixture based on vacuum sucker is implemented for the actual practical application.The fast blank design technology,the forming process design and simulation system of rubber bladder forming,the stretch forming process,simulation,flexible multi-point die and flexible clamping fixture are verified by practical test.The practical result shows the above technologies and system can be used in engineering to achieve precision successfully.