Fault identification, diagnosis and compensation of flatness errors in hard turning of tool steels

The motivation of this paper is to minimize the flatness errors in hard turning (facing) operations of hardened tool steel F-5211 (AISI D2) discs using Polycrystalline Cubic Boron Nitride (PCBN) tools with finishing cutting conditions. To achieve this, two strategies have been developed. First an on-line Conditional Preventive Maintenance (CPM) system based on monitoring a parameter that correlates well with the geometrical error, namely, the passive component of the force exerted by the workpiece on the tool. The second strategy is more sophisticated and consists of the development of an on-line Error Compensation System that uses the error value estimated using the first strategy to modify the tool trajectory in such a way that flatness errors are kept within tolerances. Moreover, this procedure allows the life of the tools to be extended beyond the limit established by the first CPM system and also the reduction of part scrap and tool purchasing costs.