Research On Flexible Flowshop Problem With Missing Stages

As the core of manufacturing enterprises,production scheduling plays a key role in improving the efficiency of manufacturing.As a common scheduling problem in the field of production scheduling,the flexible flowshop problem widely exists in electronics,textile,petrochemical,aircraft engine,and printed circuit board manufacturing workshops.At the same time,the flexible flowshop problem has been proved to be an NP-hard problem,and it is difficult to obtain a satisfactory solution by using deterministic algorithms and heuristic rules.Therefore,exploring the use of intelligent algorithms to solve the flexible flowshop problem is of great significance to both practical production and academic research.In the traditional flexible flow shop scheduling problem,it is often considered that the job needs to be processed in all stages,but in actual production,due to the different processing techniques required for different job,there is a situation where the job will only be processed in some stages,which is called the missing stages.Missing the stages problem is a common phenomenon in the steel processing industry,stainless steel production and plastic production.Therefore,this paper mainly studies the flexible flowshop problem with missing stages.The main research content of this article is divided into three parts.Firstly,the flexible flowshop problem with missing stages is studied under the environment of unrelated parallel machines,and the goal is to minimize the maximum makepan.Assuming that there are multiple uncorrelated parallel machines in each processing stage,an integer programming model is established,and a hybrid genetic algorithm is proposed,which integrates the migrating birds optimization and the adaptive genetic algorithm.Based on the coding scheme assigned by machine,adaptive crossover and mutation operators are designed,the migrating birds optimization algorithm combining three neighborhood search structure is used to further update the better individual.The test results of numerical examples show that hybrid genetic algorithm has better solution efficiency and quality in the same CPU time.Secondly,considering the constraints of transportation time in real production,the flexible flowshop problem with missing stages and transportation consideration is discussed.Build a discrete integer model with the goal of minimizing the total weighted completion time.By introducing a hybrid neighborhood search strategy,an improved discrete migrating birds optimization is proposed,and a machine assignment mechanism combining random programs and shortest processing time rules was proposed to improve the initial solution,neighborhood search is carried out on the obtained better individuals to replace the worst solution and improve the quality of the solution.Finally,simulation experiments are carried out for problems of different scales and various algorithms are compared.The experimental results show that improved discrete migrating birds optimization has obvious advantages in solving problems.Further,for the flexible flowshop problem with missing stages and linear deterioration which is more in line with the realistic production environment,considering the three constraints of unrelated parallel machines,job release time and the transportation time between unmissing stages,a discrete migrating birds and greedy optimization algorithm is proposed to minimize the total weighted completion time.A dynamic initial solution generation mechanism based on real number coding is designed,four neighborhood structures are designed to search the neighborhood of the leader and the follower and finally the solution space is expanded by the greedy heuristic.In order to verify the solution performance of the algorithm,the orthogonal test method is used to set the algorithm parameters and simulation experiments are carried out on different cases.The experimental results show that the discrete migrating birds greedy optimization algorithm has better performance in solving.In this paper,aiming at minimizing the maximum completion time and minimizing the total weighted completion time respectively,to study flexible flowshop problem with missing stages under different constraints and propose corresponding algorithms to solve the problem according to the characteristics of the research problem,which enriches the analysis of flexible flowshop problem with missing stages.The research has certain reference basis for actual production.