Cost-based scheduling of workers and equipment in a fabrication and assembly shop

Many manufacturing firms that use Material Requirements Planning (MRP) cannot deliver products on schedule and within budget. Faced with bewildering bottlenecks, erratic process flows, and unrealistic due dates, they are unable to develop accurate schedules for their raw material acquisitions, workforce, and equipment. Their MRP plans must be translated into a workable schedule, one which determines when individual tasks will be performed by workers at work centers. There is a clear need for such an enhancement to MRP, a means to operate on detailed task data, yet capable of producing a schedule that directly relates to the MRP plan, the master production schedule, and the resource plan. The authors describe a method for determining feasible and cost-effective schedules for both labor and machines in a job shop. The method first sequences tasks at resources and then minimizes overall earliness and lateness cost by solving a series of maximum flow problems. By using the model as an enhancement to a company’s MRP system, the authors simulated the cost effects of redeploying its workforce. Although the model was not used for real-time scheduling, it served a strategic role in workforce expansion and deployment decisions.