Research On Dynamic Characteristics Of Automotive Panel Splicing Die During Hard Milling

In the process of machining automobile cover die,because parts of the surface shape fluctuation,it has special hardness requirements in local position resulting in uneven mold cavity,it is necessary to improve the machining efficiency by using different hardness splicing workpiece according to the stress and heat characteristics of different parts.Different hardness of the insert block after quenching and then splicing into a whole piece to ensure the technology of splicing block,and improve the life of the mold.Because of the influence of the hardness difference,the milling force amplitude changes obviously and the vibration is aggravated during the milling process,thus the workpiece surface quality and the tool life are reduced.How to make a smooth transition in stitching over seam is a problem to be solved urgently.Based on the above problems are mainly around the impact of milling splicing workpiece,the dynamic modeling of milling system and the prediction of the stability of hardened steel milling with multiple hardness,the prediction model of milling force due to the hardness difference and the stability prediction curve are obtained,and the accuracy of the model is verified by milling test.Firstly,the force coefficient method of instantaneous milling is used to obtain the milling force coefficient of simulation.The influence of cutting parameters on the instantaneous milling force coefficients is obtained by milling test,and the parameters of the milling system are obtained by modal analysis and modal test,which provides the basis for the simulation of milling dynamics.Based on the above theory,the influence of the mutation force caused by the workpiece hardness difference in the milling process is deeply studied.The single degree of freedom contact collision model is introduced into the milling force modeling to realize the prediction of milling force at splicing,which provides theoretical basis for improving the surface quality of workpiece,improving cutting efficiency and prolonging the service life.Secondly,based on the milling characteristics of ball-end cutter,the dynamic model of milling and the instantaneous thickness-cutting model of splicing seam are established.In this paper,a four-order Lunge-Kutta method is proposed to solve the vibration differential equation to get the prediction curve of the stability of the splicing die milling process,and the minimum envelope method is used to judge the stable region.The minimum enveloping curve formed by the minimum envelope point of each stable lobe is regarded as the final stable boundary,and the result is the theoretical basis for the selection of milling process parameters of large automobile panel.Finally,based on the research method of milling vibration characteristics to study the correlation between hardness difference and vibration characteristics of milling process,the effects of milling direction,path of cutter,hardness difference and cutting parameters on the vibration characteristics of milling process are studied.According to the above research results,the problem of milling force mutation caused by hardness difference is solved by choosing a reasonable path and cutting parameters to improve the tool life and the surface precision of the splicing mould,and also help the development of the die processing of the large automobile cover parts.