Research On The Integration Problem Of Order Scheduling And Inventory Planning For The Cold Rolling Line

Cold rolling line is the tail process of whole steel production process and also a complicated production operation process with high variety of products,complex logistics,and high production cost.This makes the production operation management for cold rolling line very complicated.Taking cold rolling production process as a background,this thesis studies the integration problem of order scheduling and inventory planning for the cold rolling line.The production cost,load balance,and inventory balance are simultaneously considered in the problem to improve the production efficiency and increase the profits of steel complex.The main works of this thesis are presented as follows.1)Taking cold rolling production process as a background,an integration problem of order scheduling and inventory planning is proposed.The problem is to decide in which time slots the orders should be processed and the production sequence of orders for each production unit in the cold rolling line in order to reduce production cost,and guarantee the balance of unit production load and inventory.Different from the existing problems,the decisions in this problem are to determine the production sequence of orders for multiple production Lunits in multiple time slots.Therefore,the problem is very complicated and difficult to be solved.Based on the analysis of the key factors that affect the smooth of production and logistics of cold rolling process,the main optimization objective and technical constraints are concluded to prepare for a problem formulation.2)For the integration problem of order scheduling and inventory planning for the cold rolling line,with the consideration of the practical production constraints and the production capacity constraints,a mixed integer programming model is formulated.The objective is to minimize production cost,the production load deviation cost,and the inventory deviation cost.The model can be directly solved by MIP solver CPLEX.The computational experiment on the randomly generated instances is conducted to test the performance of the proposed model3)Due to the fect that CPLEX can only solve the small scale instances,an improved differential evolution(DE)algorithm is developed to solve the large scale problem in a reasonable time.In the algorithm,the real number coding and decoding strategy is designed to overcome the difficulty that the classical DE solves problems with discrete variables.In addition,a new repairing strategy factor is developed,which can obviously improve the convergence rate of DE,and avoid the algorithm from being trapped into a local optimum.The efficiency of the proposed DE is tested by comparing it with CPLEX and the manual approach based heuristic.4)Based on the requirements by production operation management of the cold rolling line,by embedding the proposed model and algorithm,a support decision system for the integration problem of order scheduling and inventory planning problem is designed and developed for the cold rolling line.Combining with the good human-computer interaction interface,the system can automatically dertermine the order schedules for each production unit in the cold rolling line with the consideration of production and inventory balance.