Logistieke beslissingen in de bedrijfsvoering

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The effect of workload control on order flow times

Situations where single components are manufactured with a relatively high frequency, where production capacity can be considered as homogeneous and where the manufacturing of a component requires the performance of a relatively large number of successive operations are considered. A model is presented of the dynamic behaviour of the system on an aggregate level. For two control modes, the variance and the steady state deviation of the order flow time from the norm is calculated. Typical differences are revealed between workload control by means of capacity variations and by means of order release variations. It is shown that the flow-time norm is a major determinant of the control effectivenes

A hierarchical approach to structuring the production control in multi-product multi-phase production systems

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Performance prediction and diagnosis in two production departments

In complex, job-shop-like production departments it is usually very difficult to predict the near-future logistic performance as well as to explain or diagnose objectively why and how a certain performance has been achieved. Presents a prediction and diagnosis method that has been developed and tested in two production departments. Describes how the method provides realistic logistic performance targets in the short term with respect to the throughput of a production department and order completion times. The method also quantitatively determines ex post the impact of occurred disturbances on the realized performance. In the pilot project the method provided a clearer insight into relationships between logistic key variables, gave decision support to the capacity allocation decision, and generated reliable performance targets for the short term. More importantly, the actual performance became more open to discussion due to the objective explanation of the achieved performance, which opens the way to performance improvements

Evaluation of three control concepts for the use of recipe flexibility in production planning

Process industries often obtain their raw materials from mining or agricultural industries. These raw materials usually have variations in quality which often lead to variations in the recipes used for manufacturing a product. Another reason for varying the recipe is to minimize production costs by using the cheapest materials that still lead to a satisfactory quality in the product. A third reason for using recipe flexibility is that it may occur that at the time of production not all materials for the standard recipe are available. In earlier research we showed under what conditions the use of this type of recipe flexibility should be preferred to the use of high materials stock to avoid materials shortages. We showed that the use of recipe flexibility to account for material shortages can be justified if the material replenishment leadtime is long, the demand uncertainty is high and the required service level is high. In this paper we assume that these conditions are satisfied and we investigate three different concepts for coping with the certainty and uncertainty in demand and supply. The first concept optimizes material use over the accepted customer orders (assuming that the customer order leadtime is small compared to the material replenishment leadtime); the second concept optimizes material use over the customers orders plus expected customer orders over the material replenishment leadtime; the third concept optimizes material use of the customers orders taking into account the effect of the remaining stock positions on the future recipe costs, based on knowledge of the distribution function of demand. These three concepts are investigated via an experimental design of computer simulations of an elementary small scale model of the production planning situation. The results show that the third concept outperforms the second and first concept. Furthermore, for a realistic cost structure in feed industry under certain circumstances the use of the third concept might lead to a 4% increase in profit. However, this improvement must be weighted against the cost incurred by the operational use of this complex concept. Based on this considerations and the numerical results in this paper, we may expect that for most situations in practice the use of the first simple myopic concept, optimizing material use only over the available customer orders, will be justified from an overall cost point of view

Evaluation of three control concepts for the use of recipe flexibility in production planning

Process industries often obtain their raw materials from mining or agricultural industries. These raw materials usually have variations in quality which often lead to variations in the recipes used for manufacturing a product. Another reason for varying the recipe is to minimize production costs by using the cheapest materials that still lead to a satisfactory quality in the product. A third reason for using recipe flexibility is that it may occur that at the time of production not all materials for the standard recipe are available. In earlier research we showed under what conditions the use of this type of recipe flexibility should be preferred to the use of high materials stock to avoid materials shortages. We showed that the use of recipe flexibility to account for material shortages can be justified if the material replenishment leadtime is long, the demand uncertainty is high and the required service level is high. In this paper we assume that these conditions are satisfied and we investigate three different concepts for coping with the certainty and uncertainty in demand and supply. The first concept optimizes material use over the accepted customer orders (assuming that the customer order leadtime is small compared to the material replenishment leadtime); the second concept optimizes material use over the customers orders plus expected customer orders over the material replenishment leadtime; the third concept optimizes material use of the customers orders taking into account the effect of the remaining stock positions on the future recipe costs, based on knowledge of the distribution function of demand. These three concepts are investigated via an experimental design of computer simulations of an elementary small scale model of the production planning situation. The results show that the third concept outperforms the second and first concept. Furthermore, for a realistic cost structure in feed industry under certain circumstances the use of the third concept might lead to a 4% increase in profit. However, this improvement must be weighted against the cost incurred by the operational use of this complex concept. Based on this considerations and the numerical results in this paper, we may expect that for most situations in practice the use of the first simple myopic concept, optimizing material use only over the available customer orders, will be justified from an overall cost point of view

Production control in engineer-to-order firms

During the last decade many engineer-to-order firms have tried to implement MRP II systems, however, the little or no success. The choice of a MRP II system is often based on the wide availability of MRP II software and the fact that the exact reasons why this software is not suitable for engineer-to-order firms are not understood. Therefore, the many implementation failures are not surprising. In the first part of this paper we will discuss the main differences between engineer-to-order manufacturing and the make-to-stock manufacturing (which was the basis for the development of MRP II software). Important characteristics of the engineer-to-order situation are: the important role of the customer order, the customer-specific product specifications and the product and production uncertainty. These characteristics of the engineer-to-order production situation differ substantially from the basic assumptions of MRP II. An engineer-to-order situation thus asks for a completely different production control system. In the second part of this paper we will present a production control framework which better suits the specific characteristics of the engineer-to-order situatio