Fundamentals of wear mechanisms and wear modelling for unsteady turning processes
Final Report Abstract
As part of the project, non-stationary process control was investigated in the turning of tempered steel. This modulated process control continuously varies the process parameters and thus influences tool load and wear. Stationary and non-stationary processes are designed in such a way that they achieve identical metal removal rates and thus the same productivity with the same average process parameters. The investigations show that the wear rate of coated tools depends primarily on the cutting speed. This causes continuous abrasion on the flank face of the coating and thus determines the failure criterion. Modulations of the process parameters offer potential for reducing this flank wear, especially at low average cutting speeds. Combined modulations of cutting speed and feed rate at a constant metal removal rate, on the other hand, significantly increase wear. An FEM-based simulation model of chip formation was set up for the analysis. The coupling of experimental data with simulation knowledge shows that the process control acts via the temperature-dependent process parameter. Based on this, a wear simulation was developed that calculates temperatures for various combinations of manipulated process parameters a priori. These serve as input variables for a simplified wear model according to Usui. This provides a validated understanding of the mechanisms of action and the wear behavior of non-stationary processes. The simulation agrees well with the experimental results and was used to develop wear-reducing non-stationary processes. With a reduced mean and continuously decreasing cutting speed, experiments showed a lower tool temperature and reduced wear progress compared to stationary processes.
