| The production process of the aluminum melting-casting shop can be described as follows.First,the liquid aluminum from the electrolysis cell is poured into the melting furnace.In the melting process,the appropriate alloy is added to meet customer’s demands of alloy composition.Then,the solid aluminum billet is cast on the casting machine.Finally,the aluminum billet is sent to the rolling shop and is rolled into the aluminum plate product required by the customer.Due to the differences in production capacity of melting and casting production equipment,the production rhythm of melting furnace and casting machine is inconsistent.In addition,the difficulty in material connection is considered which is caused by the series-parallel feeding of the production equipment of aluminum melting-casting shop.Therefore,reasonable production scheduling is of great significance to effectively coordinate the two-stage production process of melting and casting and improve production efficiency.This thesis mainly considers the washing furnace operation brought by the alloy switching and the crystallizer adjustment operation brought by the mold switching.Combined with the actual process constraints and the production equipment layout characteristics of two melting furnaces feeding a casting machine,an integer programming model for the production scheduling problem of aluminum meltingcasting shop is developed.The optimization algorithm based on column generation is proposed.And the production scheduling decision support system for aluminum melting-casting shop is developed.The main research contents of this thesis are as follows.(1)According to the sequence of customer orders on the casting machine,the casting machine is divided into positions.The integrated decision integer programming model is developed with the order-to-location allocation as the decision variable.For large-scale problems,the integrated decision model is difficult to solve.A two-stage modeling method based on hierarchical decision is proposed to reduce the complexity of the solution.In the first stage,an integer programming model is developed by considering the allocation relationship between different alloys of the same size on the melting furnace.In the second stage,an integer programming model is developed by considering the allocation and sequencing decisions of different sizes on the casting machine.Two-stage models are solved sequentially.The solution results of two models are compared and analyzed based on actual production data.The results show that hierarchical decision model has lost some of its optimality,but it greatly improves the speed of solving.(2)For the hierarchical decision modeling method,the defects of the different sizes of the first and last furnace alloys switching are not considered.The alloys of the same size are enumerated to obtain the order cluster.Taking the selection,allocation and sequencing of order sequences in the order cluster as decision variables,an integer programming model is developed.According to the characteristics of the model,the original problem is decomposed into the set partitioning master problem and the price subproblem by using the Dantzig-Wolfe decomposition method.The optimal solution of problem is obtained by using the branch-and-price algorithm based on column generation.Numerical experiments are carried out with instances.The solution results of the branch-and-price algorithm is compared with the solution results of the CPLEX optimization software.The results show that the proposed algorithm can be solved efficiently.(3)Taking the model and algorithm of production scheduling problem in aluminum melting-casting shop as the core,the decision support system for the melting and casting stages of the aluminum casting house is developed.The system realizes reasonable production scheduling for customer orders.The system provides decision support for enterprise production planners.Visual simulation of aluminum melting and casting process is carried out by 3Dsmax software. |
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