Prediction Of Workpiece Surface Topography In The Ball-end Milling Process

CNC machining is the typical process technologies in modern industry. Some workpiece with complex surface have been widely used in aerospace, vehicles and energy field. CNC machine tools are usually used for those workpiece. However, most classical process technologies generally consider the CNC machining of workpiece with complex surface simplified into a cylindrical or spherical milling cutter, and rarely take into account the influence of the cutter edge, the spindle of tool, tool swinging and other factors on the surface topography, which made it difficult to control the surface precision of workpiece according to the traditional model. In this paper, taking the process of ball-end cutter as research objective, predicting the surface topography and the influence of machining parameters on the surface topography are studied. It will provide the suggestion on how to select the machining parameters.First, introducing the cutter coordinate system. Based on the relationship between the cutter helix angle and the warp of cutting edge, we formulate the mathematical expression of the cutting edge. The reason inducing the tool axis rotation eccentricity error is analyzed and the model of rotary eccentric error is presented. Considering the influence upon the topography of inclination angle in the machining and the way of cutter feeding, the trajectory equation of cutting edge relative to workpiece is derived.Secondly, the movement of any point on the edge of the cutter and the process of milling a workpiece are researched. The traditional methods in judging the relationship between the cutting edge and the surface of the workpiece need to use the numerical approximation method. In order to avoid this problem, an improved algorithm is presented. The sweep surface of cutting edges of cutter in the milling process interpolated based on Biharmonic spline and the mathematical matrixes that represent the surface topography of workpiece are got through the Boolean calculating method.The feasibility and effectiveness of the algorithm are demonstrated by comparing several computer simulation results with the actual processing experimental results under different experimental conditions.Finally, the commonly processing parameters of ball-end milling are studied by using the prediction model proposed in this paper. According to the simulation results, the curve of the rule related to the simulation parameter is drafted.