Centre cone generation and its force performance in single-point diamond turning

Abstract In single-point diamond turning (SPDT), vertical tool centre error owing to the tool feed trajectory is higher or lower than the workpiece centre will result in the conical or cylindrical appearance on the centre of machined surface. Different from the residual centre cylinder under tool below centre error existance, the interference between the tool and the workpiece when tool above centre error exists will cause interference zone around the formed centre cone, which greatly affects the form accuracy of the machined surface and the optical functions it owns. In order to explore the evolution and force performance of the central cone during tool interference, and realize the online identification of tool above centre error, this paper analyzed the relation between the centre structure mophology and the cutting force form under the existence of the tool above centre error. Meanwhile, the influence of the secondary interference between the tool clearance face and the centre cone generated from previous face turning was studied. Then, by establishing the geometric model of the tool clearance face, round platform and centre cone during the turning process, a interference spatial curve model between tool and workpiece was derived. Finally, a force model reflected by the mapping of extrusion area of tool and workpiece was established, whereby the mapping relation between the cutting force and the morphology of the interference zone was further clarified, and the tool above centre error could be online identified based on the cutting force forms. Theoretical and experimental results show an exact correspondence between the cutting force and the morphology of interference zone, the online identification of the tool above centre error can be potentially realized by the established cutting force model, which greatly improves the cutting efficiency of SPDT.