Modeling flank wear of coated carbide inserts during turning

Sammanfattning

This thesis investigates flank wear behavior in coated carbide inserts during orthogonal and longitudinal turning of bearing steel. An abrasive model was used to model wear based on cutting forces and calculation of wear volume from tool geometry. A multi-layer abrasive wear model is proposed based on multi-phase wear of Al₂O₃ and Ti(C,N) layers. The specific wear rate of a multi-layer component is conjectured to be the weighted harmonic mean of the specific wear rate of each layer. The model is compared to a single-layer abrasive wear model. Longitudinal and semi-orthogonal turning was performed on Ovako 825B steel at a cutting speed of 200 m/min and feed rates of 0.15 and 0.2 mm per revolution and microscopy imaging in between operations was used to measure flank wear progression. Scanning electron microscopy (SEM) and energy dispersive spectroscopy of etched inserts were conducted to examine layer composition and identify coating breakthrough. The surface ratio of Al₂O₃ to Ti(C,N) was measured in SEM after wear progression which aligned well with predictions based on insert geometry and the measurement of Al₂O₃ layer thickness. Focus variation microscopy was used to create depth profiles of inserts before and after turning to analyze the character of wear on the rake and the flank faces. Turning tests were compared to historical data for tests with similar workpiece and machining parameters. The time to reach a flank wear width of 0.12 mm was found to be six times longer in newer inserts, reflecting advancements in coating technology over the past 12 years. The multi-layer model fit closer to experimental results than a single-layer and the results support the use of harmonic mean-based models for layered coatings and highlight the potential influence of cutting operation duration on wear behavior.