Capacity requirements planning— a systematization

Abstract

The central problem of manufacturing planning is to reconcile clue dates, derived from customer delivery timetables, with schedule dates, developed from production capabilities. Conventional capacity planning techniques utilize the technological sequencing of material flow in order to build up production schedules. As they ignore interactions between work stations, and override due date requirements, these techniques are often unsatisfactory. Wight and Belt have suggested a new approach to the problem, and this paper presents a systematic methodology based on their ideas, to characterize and analyse the flow of work through a work station, and relate this flow to the nominal capacity of the station. Operation of the station is measured by work in process, delay and underload (operation below nominal capacity); flow between stations is measured by queue length and lead times (process plus wait time). Performance is evaluated by the degree of underload and overload planned for the station—the degree to which available capacity is utilized, and the degree to which lead times, imposed by the Material Requirements Plan, can be achieved. Achievable average and maximum lead times are shown to be a function of both nominal work station capacity and the input work load profile—not a constant value for the work station. A more correct study of plannable lead times, as production loads vary, allows the necessary connection to be made between due dates and schedule dates.