Study On Surface Topography Characteristics And Drag Reduction Performance Of Ball End Milling

There is a close relationship between the topographical features of the surface of a part,such as the topographical size features and topographical categories,and its surface properties.Therefore,some specific morphologies can be prepared on the surface of a part to obtain better performance.In recent years,it is a hot topic in the field of surface performance to obtain the geometric features of the target topography by using the idea of bionics and applying it to the surface of parts to obtain excellent performance.This paper starts from the background of reducing energy consumption and improving energy efficiency,and is devoted to explore a new method to reduce the resistance loss of parts through the combination of bionic theory and ball end milling.Therefore,this paper takes the surface topography of ball end milling as the research object,and establishes the mapping relationship between milling parameters and surface topography element size in transverse and longitudinal dimensions respectively.A series of high speed milling experiments under the influence of different factors were designed to modify the topography and size model.On this basis,the topography model under the influence of multiple factors is established.Finally,the drag reduction characteristics of the topography model at different flow rates were analyzed,and the drag reduction mechanism was given from the aspects of shear stress,velocity field and near-wall flow field characteristics.The research in this paper is of great value to enrich the drag reduction theory of non smooth surfaces and the design of parts with drag reduction requirements.Firstly,the biological surface structures with excellent drag reduction characteristics in nature were analyzed,and the surface morphologies after ball end milling were compared with the bionic prototype surface structures.By analyzing the machining process of ball end milling,the mapping relationship between the longitudinal dimensions of plane and small curvature surface topography and milling parameters was established respectively.The arrangement of different topography elements was defined by the definition of topography angles.On this basis,the mapping relationship between transverse dimensions and milling parameters was established when the topography angles were 60°and 90°.Secondly,through high-speed milling experiments,the effects of feed rate,row spacing,milling depth and rotation speed on the dimensions of surface topography elements in both transverse and longitudinal directions were analyzed respectively.The topography parameters S_a and S_dr were selected to characterize the topography distribution of the machined surface in two dimensional directions,and the range analysis was carried out using them as indexes to obtain the strength relationship of the influence of milling parameters on the topography characteristics.According to the experimental data,the position coefficient of the typical concave topography model was modified,and the established topography size-milling parameter model was verified.Thirdly,in order to explore the drag reduction characteristics of ball-end milling surface,the boundary layer characteristics of gas-solid interface were analyzed according to the basic theory of boundary layer,and three kinds of boundary layer thickness were defined.According to the idea of micro-element,the calculation model of friction resistance and drag coefficient of gas-solid contact surface in turbulent state was established.On this basis,the calculation model of the resistance of a single surface topography element was established.Through the error comparison between the theoretical results and the CFD results,the practicability of the simulation for the resistance analysis is analyzed.Finally,according to the mapping relationship between topography size and milling parameters,the topography models of the machined surface under the influence of different factors were established respectively.By means of numerical simulation,the drag reduction characteristics of ball end milling surface were investigated.The effects of the shape Angle,feed rate per tooth and row spacing on the drag reduction characteristics of the machined surface at different flow rates were analyzed.According to the numerical simulation results,the drag reduction mechanism of the surface topography in ball end milling was analyzed from the aspects of wall shear stress,turbulent kinetic energy,velocity field and near-wall flow field characteristics.