Chatter model with structure-process-control coupled and stability analyses in the cold rolling system
In the cold tandem rolling process of high-strength thin plates, the chatter usually brings significant influences on equipment safety, production efficiency and product quality. The higher the rolling speed is, the more frequently and seriously the chatter occurs. Considering the equivalent elastic-plastic stiffness within the rolling gap, an eight Degree-of-Freedom (DOF) centralized mass model in the vertical direction for a six-roller mill is proposed, and a dynamic model of rolling process is established based on the Slab method. Then the structure-process coupling model is constructed and validated by calculating the equivalent stiffness and the rolling force. Subsequently, both the feed-forward control of entry thickness and the feed-back control of exit thickness are considered, and a hydraulic Auto Gauge Control (AGC) unit is modeled, which links with the established structure-process model to form a complete structure-process-control coupling model. Furthermore, by applying the Routh stability criterion to the presented structure-process-control coupling model, a threshold calculation model of rolling speed is derived, which is determined by the strip specification, technique condition and control parameter. Additionally, it is found that the experimental signals monitored from the actual rolling process are almost entirely consistent with the theoretical calculation, and more details involved in the vibration signals are demonstrated. Therefore the newly proposed structure-process-control coupling model is expected to be valuable for instability prediction and chatter suppression of the cold tandem rolling.