SCHEDULING FLEXIBLE MANUFACTURING SYSTEMS FOR APPAREL PRODUCTION

In mid to high volume apparel production, garments are typically group ed into production lots, and each lot is processed in its own manufact uring cell, A flexible manufacturing system used in this environment e nables quick cell configuration, and the efficient operation of cells. The scheduling problem is to decide when to set up a cell and consequ ently begin garment production in the cell, and to decide the quantity of machines to allocate to each cell, under the constraints of limite d machines, The time to process a production lot depends on the quanti ty of machines allocated to the cell in which the lot will be processe d, and thus scheduling and resource allocation are highly coupled, Pas t approaches separate the resource allocation and scheduling decisions because the combined problem is too complex to be solved in a practic al amount of time,In this paper, an accurate and low-order integer pro gramming model is developed which integrates scheduling and resource a llocation, Insight is provided into how the model relates to the opera tion of a real factory, The model is solved using the Lagrangian relax ation methodology, and a new bundle method is used for optimizing the Lagrangian dual function, The combination of an accurate low-order mod el, Lagrangian relaxation, and the bundle method is shown to be very p ractical, Testing is performed using data from a real factory producin g 10 to 40 lots per week (between 4500 and 8900 garments total) on 105 machines of nine different types, Numerical results show that one-wee k schedules are generated in less than 3.5 CPU min on a 60 MHz persona l computer, and the schedules are within 16-29% of optimal.