Determination of the chip geometry, cutting force and roughness in free form surfaces finishing milling, with ball end tools

Abstract

CAD/CAM systems offer various possibilities for finishing milling of parts such as dies and moulds, turbine blades and other high quality components, but most of them do not take into account the surface topomorphy expected, which is significantly affected, among others, by the milling kinematics and the contact conditions between the tool and the workpiece. In order to predict the workpiece roughness in multiaxis finishing milling with ball end tools, the computer supported milling simulation algorithm ‘ ballmill’ was developed. By means of this algorithm, considering the individual movements of the cutting tool and of the workpiece due to the milling kinematics, the undeformed chip geometry, the cutting force components, the tool deflections and the final surface topomorphy expected are determined. Numerous investigations concerning the parameters mentioned above, with various workpiece materials have been carried out in order to determine the correlation of the experimental results with the corresponding calculated ones with the aid of the ballmill algorithm. Moreover the algorithm validity was extensively evaluated in milling of free form surfaces of large hydroturbine blades. The convergence between the experimental and the related calculated surface topomorphies by means of the ballmill computer program was found out to be satisfactory. Thus, the prediction of appropriate cutting conditions and milling kinematics to fulfill surface topomorphy requirements was enabled.