Onderdelenvoorziening in de landbouwmechanisatie : een operationele analyse

The procurement of spare parts in Dutch agricultural mechanisation has been investigated at wholesale and retail level.

At wholesale level the importers are the main distributors of equipment and spare parts and here the main objective is to treat stock control as a feedback system, with the degree of service as principal performance indicator. This gives rise to a number of organisational and operational problems, related to lead times, definition of service and forecasting. The proper control of lead times is a prerequisite for stock control of spare parts and therefore the lead time variability should be taken into account. The registration of the achieved level of service depends on the way service is defined. For every article a reorder level is calculated using a probability density function to guide it to its desired service level. Particularly in the case of spare parts supply, where machines are waiting for repair, not only should the measure of service take into account the number of items short, but also the duration of shortages. With regard to the necessary short term forecasting of demand, it has been pointed out that for non-seasonal demand simple models suffice, but special models are required for both recognition and forecasting of seasonal consumption of spare parts e.g. for harvesting equipment.

When the need for information processing at the dealers' level was investigated, improper management with the dealers was found to be the cause of many of the inventory problems with the importers. Introduction of electronic dataprocessing techniques opens the way to automatic information exchange between importers and dealers. Once a data exchange network has been established for the updating of article data and automatic ordering, the next development is to use this as a basis for the exchange of spare parts. In this way surplusses at one place are used to compensate for shortages at another.

Exchange of information and material in an organised way may lead to integral stock control. The effects of the latter were investigated by means of a discrete simulation model with a multi-echelon structure. Simulation of the situation whereby shortages at dealers' level can be quickly filled by exchanges from other dealers not only showed a dramatic reduction of rushorders at wholesale level, but also a reduction of the waiting times for customers in case of shortage with both importer and dealer.