Research On Simulation Of Surface Topography In NC Milling For Dynamic Feedrate

With the rapid development of CAD and CAM technology,the technology of high-speed cutting and five-axis machining has been widely used in aerospace,ship,automobile die and other fields.In CNC machining,the surface topography of workpiece is an important indicator to measure the surface quality.The machining method,machining process,tool,material and cutting parameters in the five-axis CNC milling can affect surface topography.At the same time,in the curve machining or free-form surface machining,the smoothness of tool tip velocity can't ensure the smooth movement of each axis due to the influence of the two rotating axes of the five-axis machining tool.The movement of each axis may exceed the driving limits of the servo motor,resulting in the fluctuation of feedrate,thus changing the 3D surface topography.Therefore,in the environment of feedrate fluctuation,it is important to predict the surface topography parameters based on these factors,especially the cutting parameters.This avoids trial and error method to obtain the desired surface quality.It not only greatly reduces the production cycle and cost of products,but also has great significance in guaranteeing the quality of workpiece processing.At present,most of scholars don't fully consider the formation factors of surface topography and the influence of dynamic feedrate on surface topography.To improve the problems mentioned above,in this study,the generation mechanism of surface topography characteristics under dynamic feedrate is discussed by studying the high-speed cutting principle of five-axis CNC.Firstly,the model utilizes the actual ball-end milling cutter with equal helix angle,and takes full account of the influence of common processing parameters which can be set in CAM software,such as tool inclination,feedrate,cutting depth and pick-interval.The mathematical simulation model of the blade sweeping surface in the workpiece coordinate system can be derived by using matrix transformation of coordinate system.Subsequently,the simulation model of workpiece surface topography is established based on the N-buffer method through the discretization of cutting tool and the meshing of workpiece surface.Combined with the inverse kinematics transformation of machine tool and the multi-constraint adaptive feedrate prediction model,the simulation model of workpiece surface topography is obtained under the condition of dynamic feedrate,and the real surface topography is quantitatively analyzed.The proposed model is suitable for complex free-form surfaces.At the same time,this model gives a good estimation of the local feedrate,so it can simulate the three-dimensional surface topography more accurately.Finally,the three-dimensional surface topography and surface roughness profiles of the experimental results are compared with the simulation results,which verifies the validity and correctness of the simulation model of surface topography in NC milling for dynamic feedrate.