Stability Research And Applications On Turn-milling Of Large-sized Shaft Parts

Landing gear is the typical large-sized shaft parts and the key parts of the plane used for takeoff and landing.It’s manufacturing technology effect the development speed of China’s aviation industry.With the large numbers of advanced fighters loaded and general aviation developed,the landing gear’s processing efficiency has become an urgent problem.The characteristics of large dimensions and high surface hardness result in the large material removal rate and cutting force,complex process system,and occurrence of chatter.Thus,the machining parameters are conservative and machining efficiency is low.Turn-milling machining of landing gear has multi machining conditions and complex dynamics of process system.For the machining parameters optimization of landing gear,the dynamics of machining system were identified and analyzed,the tool frequency response function under operational conditions was identified,the cutting force prediction model of orthogonal turn-milling with considering variable cutting depth and thickness was studied,the milling stability prediction model with considering multi-modes and cross FRF was established,the three-dimensional milling stability prediction model with considering workpiece dynamics was established.The updated full-discretization method was developed for improve the solve efficiency.Based on those theories,the stability prediction is applied on machining parameters optimization of landing gear.The major characteristics of landing gear turn-milling machining were analyzed,and every characteristic’s dynamics of process system was measured and analyzed.After obtained the dynamics,the common key technologies were summarized.An identified method based on RCSA for tool end FRF was proposed for considering the influence of operational condition on dynamics of process system.The structure of spindle-holder-tool is divided to two substructure by using the RCSA method and the equilibrium equation of the structure and substructure in frequency domain were established.According to the constraint condition of structure and substructure,the tool FRF prediction algorithm under operational condition only using the FRF with spindle head response and finite element analysis was established.This method avoids expensive equipment(non-contact equipment),complex experiment process and data processing.The cutting force prediction model with consider variable cutting depth and cutting thickness and eccentric distance was established for orthogonal turn-milling of the Landing gear’s cylinder.The relationship between cutting chip shape and spindle speed,workpiece rotating speed and diameter was established according to the geometrical movement characteristic.After dispersing the tool along axial direction,the start angles and angles of every cutting edge element on cutting thickness and depth were calculated.The cutting force of every cutting edge element was calculated base on mechanical force model and integrated along axial direction to form the cutting force of the tool.For the 300M steel,the cutting force prediction model was verified by the cutting experiments.And,the influence of workpiece-tool diameter ratio and eccentric distance on the turn-milling cutting force was analyzed.For the multi-modes and cross frequency response functions,a time domain model for milling stability prediction simultaneously considering multi-modes and cross frequency response functions effect was established.Mechanical mobility and impedance transformation method dealing with frequency response functions is proposed to establish the dynamic matrix equation.The approaches of multiple modal parameters normalization on the tool tip and reducing the vibration variable number in modal space are described.By predicting the stability milling boundary,the influence of multi-modes and cross frequency response functions on stability boundary was analyzed.For the machining of landing gear’s flank where far away the axle wire,the stability prediction model with considering dynamic behaviour of tool and workpiece was established by introducing the dynamic behaviour of workpiece to the dynamical equation.the influence of different machining position and stage on workpiece dynamic behaviour and stability boundary was analyzed.An updated full-discretization method was proposed for milling stability prediction based on the high-order interpolation of both the state item and the time-delay term.The second-order interpolation of both the state item and the time-delay term was proved has better effect on prediction accuracy than only third-order interpolation of the state item.Meanwhile,the direct approach of establishing the state transition matrix has better effect on saving computing time.The solve efficiency of stability model in time domain is improved by the improvement of the computational efficiency and accuracy.The machining parameter optimization software for landing gear turn-milling machining was developed by integrating the FRF identified method under operational condition,cutting force prediction of turn-milling,stability prediction simultaneously considering multi-modes and cross frequency response functions effect,stability prediction model with considering dynamic behaviour of workpiece and the solving algorithm of stability model.The machining parameter optimization method was applied on the landing gear turn-milling machining.