Research On Multi-stage Flexible Flowshop Scheduling With Batching Features

Steelmaking,continuous-casting and hot-rolling are the main production process in iron and steel industry which can product the steels of railway,steel sheet pile,all kinds of steels and so on.Furthermore,it has greatly promoted the development of the national economy,and plays an important role in the whole production process.Based on steelmaking-continuous casting-hot rolling production process in iron and steel industry,the problem of scheduling n jobs in a multi-stage flexible flowshop with batching features is studied which not only need to meet a series of constraints in iron and steel industry,but also has the characteristics of batch processing.The multi-stage flexible flowshop with batching features require all jobs in the same batch to be processed on the same machine according to the known priority order.It is the extension of the classical flexible flowshop problem.Based on the reality,the complex flexible flowshop problem is analyzed.Thus this paper gives a comprehensive introduction of flowshop problem in the application field,and at the same time,does the analysis of the related domestic and foreign literatures.Through analyzing,the status of the application of flowshop problem is summarized and the research questions of this paper are identified.The problem of scheduling n jobs in a multi-stage flexible flowshop with serial batch production at a certain stage is studied which based on steelmaking-continuous casting-hot rolling production process in iron and steel industry.A mathematical model is formulated to minimize the total weighted completion time with the consideration of various constraints in actual production.Firstly,analyzing the structure of continuous casting-hot rolling production process,which can be regarded as flexible flowshop,and the first stage consists of multiple serial batching machines in parallel and the other stages contain discrete machines.The improved self-adaptive genetic algorithm is used to solve the problem with the consideration of transportation time among the adjacent processing stages.Based on steelmaking-continuous casting-hot rolling production process in iron and steel industry,the problem of scheduling n jobs in a multi-stage flexible flowshop with batching machines at some middle stage is studied.The batching production stage consists of multiple serial batching machines in parallel and the other stages contain discrete machines.A mathematical model is formulated with the consideration of job dynamic arrival,transportation time between the adjacent stages and machine setup time.Computational experiments test a large number of random data for up to 240 and 150 jobs in view of different problems.The results show that the proposed algorithm can find the better solutions within a shorter period of time,as compared with the general genetic algorithm.The comparison with Lagrangian relaxation shows that the improved genetic algorithm performs better on solution quality for medium and large sized problems.