Research On Dynamic Performance Of Automobile Panel Die Milling And Machining Error Control

With the continuous development of economy,cars have become the necessities of daily life for people.With the continuous improvement of consumers' demand for automotive performance and personalization,car manufacturers need to constantly update the appearance of the car.As one of the most important parts of the automobile production process,its design and manufacturing process accounts for2/3 of the entire automotive R & D cycle.In order to ensure the high quality production of automotive panels,how to improve the durability and accuracy of the die is particularly important.This paper aims at improving the precision and efficiency of automobile panel die by using complex surface milling force prediction model,analysis of stability in machining process and analysis of machining system stiffness distribution.Then,machining error prediction and compensation is completed base on on-machine inspection.The above research can be used to guide the optimization of machining parameters and the reasonable planning of the machining path.The specific research contents include:(1)In order to solve the problem of uneven load on the die surface milling,the spatial contact between cutting ball-end milling tool and workpiece during the milling process is described by using the mechanical model method.The axial immersion angle and radial immersion angle in the milling process are redefined.The influence of the curvature of the surface on the cutting contact axis and the radial immersion angle of the tool workpiece are analyzed.The prediction model of instantaneous milling force under the influence of many factors such as curvature of surface,tool geometry and machining parameters is built.Then,the milling force of hardened steel dies is predicted based on the model.At the same time,the fractaldimension is used to analyze the nonlinear characteristics of cutting force.(2)In order to solve the problem of chattering in milling process of die surface,dynamic equations are established by considering the influence of die surface curvature and tool rake angle on the dynamic undeformed chip thickness.The stability of milling under parameters near the stability boundary(which obtained by the full discrete method)are explored by taking the ratio between dynamic cutting thickness and static cutting thickness as the threshold.The vibration signals of different processing parameters are analyzed based on phase plane,Poincare cross section and spectrum,in order to determine whether flutter is occurring in the milling process under different parameters.Subsequently,the stability prediction method is verified through the milling experiment of automobile panel die.(3)In order to analyze the influence of the comprehensive stiffness of the machining system on the machining quality,according to the theory of multi body small deformation,through the point transfer matrix and Jacobi matrix,the comprehensive stiffness field modeling of the sampling system is completed base on the sampling points of the die surface.At the same time,the force ellipsoid is introduced.The force ellipsoid is used to analyze the key parts of the rigidity performance of the machining system,such as the beam of machine tools,the joint of the tool spindle and milling cutter,milling cutter and the surface of die.Subsequently,the influence of milling cutter space position and die face curvature on the comprehensive stiffness field of the machining system is analyzed.It can guide the tool's spatial position and cutting path planning during the milling process of automobile panel die.(4)A surface reconstruction method for NURBS surface based on adaptive surface sampling is established,and the machining error is calculated by the machine measurement technology.The method which is based on the adaptive sampling method of the Gauss curvature bending model can accurately reflect the bending degree of the surface.The denser samples are arranged on the region with largercurvature change of the die surface.Under the premise of ensuring the detection accuracy,the method can increase the detection efficiency.(5)The machining error in the process of automobile panel die was predicted by using the processing system error model for complex surface which considering the cutting tool shaft eccentricity,tool system deformation,surface curvature,cutting vibration factors and milling system stiffness field analysis.This model has a high accuracy for predicting the machining error of automobile front panel die surface.The machining error can be effectively controlled by off-line machining error compensation based on the model by considering the influence of the comprehensive stiffness field of milling system and the stability domain of milling process.