Improving the cutting rate in turning operations of flexible stepped shafts with a linear parameter-varying controller using the electromagnetic actuator

The stability requirement in turning operations of uniform and stepped shafts limits the cutting depth to avoid chatter. There is no solution so far for the problem. The recent trend is to generate stability lobe diagrams and the depth of cut is selected in such a manner the chatter regions are avoided. Hence, the cutting rates are very low due to the limited depth of cut. Normally, the workpiece is considered rigid and active chatter control techniques are applied to reduce vibrations of flexible cutting tools. In our work, both the workpiece and cutting tool are considered flexible in appropriate directions. The novelty of the work is the combination of theory and practical applications. As the material is removed during cutting, natural frequencies of the shaft are changed. Fixed parameter controllers lose their effectiveness under these changing conditions. Linear parameter-varying controller has been designed and implemented so that the cutting stability can be maintained in the total range of parameters. Due to non-contact nature of electromagnetic actuators, control forces can be applied from a distance and hence stability can be maintained. Theoretical solutions are investigated for feasibility of the control process through simulation. The productivity of the process is improved as the cutting depth has been increased from 72 to 250 μm in a case study.