Group Scheduling Problem Considering Learing&Forgetting Effects And Preventive Maintenance

With the development of the diversification of customer needs，groupmanufacturing has become an important manufacturing form for small andmedium volume production. This paper focuses on sing-scheduling groupscheduling problem. And an integrated single-machine group schedulingmodel incorporating both learning&forgetting effects and preventivemaintenance planning is proposed. Considering operators gain experiencefrom previous and the similarity between jobs, learning and forgetting canoccur in group production, so leaning and forgetting effects are taken intoconsideration in group scheduling problem. In this paper, three learningfunctions under different circumstances are proposed to deduce thevariable processing time of each part, considering the learning effect whenconsecutively producing identical or similar parts, together with theforgetting effect when transferring jobs interrupts the production processand makes retrogress in learning. In reality, machine breakdown can give agreat loss to company. So PM is taken into consideration. For maintenancepolicy, preventive maintenance can be performed only after one kind ofproducts is finished, and when the machine fails due to degradation,minimal repair is performed to restore the machine to be “as bad as old”.Based on these policies，a model containing sequence-dependent setuptime, actual processing time, planned preventive maintenance time andexpected repairing time is formulated. The objective is to minimize theexpected makespan by optimal job sequence and preventive maintenancedecisions. The search algorithm for the model is developed, and thenumerical example is studied. The computational results and sensitivity analysis show that this improved group scheduling model can well balancethe machine resource requirements from different practicalmanufacturing-related activities.