STABILITY AND VIBRATION SIGNAL ANALYSIS IN HARD TURNING

摘要

The machining of hardened materials has attracted a great interest as an alternative to conventional grinding processes. Also, the machining of hardened materials without coolant offers many possible benefits such as lowered costs, environmental friendly production and better surface integrity. Hard turning applications have been remaining slow due to the existence of surface damage such as chatter marks. Prediction of stable cutting regions is a critical requirement for hard turning operations. The chatter marks on a machined component surface could be found only after machining. This postprocess scenario imposes a potential danger to subsequent product performance such as fatigue life. Therefore, real-time monitoring of hard turning operation has significant economical and durability importance. Hard turning creates high pulsating pressures on the insert seat and shim. The shim acts as a shock absorber for the insert and workpiece. The shim protects both insert and tool holder from damage due to high cutting forces. In this research, the shim material is replaced with different damping materials. Also in this study an attempt is made to develop a chatter model for predicting chatter stability conditions in hard turning. A linear model is developed and stability analysis based on Tlusty and Polacek mode-coupling theory is used to determine the critical stability parameters. To validate the model a series of experiments have been carried out to determine the stability limits. The improvement in quality of surface finish is investigated by real time observations using the vibration data collector. The experimental results show that the surface finish of the workpiece is significantly improved after replacing Carbide shim with constrained layer damping and Poly tetra Fluoro Ethylene coated Brass shim.