Multi-objective optimization of rolling schedule for tandem cold strip rolling based on NSGA-II

A multi-objective optimization model of rolling schedule based on NSGA-II algorithm was presented, and three objective functions are defined as motor power balance, good flatness and preventing slippage. The experimental results show the excellent performance of NSGA-II in obtaining non-dominated front which could suggest several alternative solutions to rolling schedule in a single run of the algorithm. Additionally, considering that the rolling load distribution strategy dynamically adjusts are required to balance the impact of roll surface condition changes on the rolling process, a model of weighted-sum approach with variable weight coefficients based on rolling length was proposed. In this model, a roll change cycle was divided into four optimization stages which are given different weight coefficients. Moreover, a smooth correction model of weight coefficient was proposed to ensure the quality of strip flatness. Compared to the traditional weighted-sum approach, the presented model on the basis of variable weight coefficients can make full use of Pareto set, and has better adaptability to changing rolling conditions. Finally, the proposed model was applied to the multi-objective optimization model above, the results showed that the final optimal solutions have better performance in almost all objective dimensions than the empirical one. The practical application has further confirmed the effectiveness of the multi objective optimization for rolling schedule.