40 research outputs found
Hierarchical mathematical programming for operational planning in a process industry
Scheduling techniques for discrete manufacturing industries do not fit in many process industries. A technique that often is used in process industries is mathematical programming. However, mathematical programming is used mostly for strategic or tactical planning. This article describes a problem at the operational planning level in a process industry. The (large) problem is decomposed into smaller problems, which can be solved separately with use of mathematical programming. The resulting models are less complex and require less calculation time than a large model. The decomposition is based on the uncertainties for raw materials and customer orders that exist for future time periods. In this way a Decision Support System is developed which has an acceptable calculation time
Enige in Nederland verkrijgbare personal-computer-softwarepakketten voor mathematische programmering
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
Balancing stocks, flexible recipe costs and high service level requirements in a batch process industry : a study of a small scale model
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 not all materials for the standard recipe are available. If variations in supply and demand are large, keeping sufficient safety stock to cope with these variations may incur prohibitive high costs. This means that the costs of keeping safety stock should be balanced with the costs of sometimes using more expensive recipes. The question now is for what situations and to what extent the use of recipe flexibility is justified. In this paper we study this question by means of a small scale model. For this simple situation we derive a decision procedure to balance safety stock costs and flexibility costs. This procedure is applied to a range of different situations, that are characterized by a set of parameter values, in order to determine for which situations recipe flexibility should be used