A possibilistic model for tactical planning of a manufacturing company with demand uncertainty

ALDO VECCHIETTI; MARIA LAURA CÚNICO

Foz do Iguacu

Congreso; EngOpt 2016-5th International Conference on Engineering Optimization; 2016

This work presents a robust possibilistic model for the optimal planning of a manufacturing company where demand uncertainties are modeled using fuzzy set theory. For this case, fuzzy sets used to describe human behavior are adapted to formulate the constraints quantitatively and adapt the problem to the needs of the modeler. The motivations for this work are focused in the requirements of the industries to consider situations when the data are not precise or there are some facts that give vagueness in their operation; some of them can be internal such as failures in the equipments or labor absenteeism, or external, like price fluctuations of the raw materials, delays in materials provision, uncertainties in the markets demands. To overcome those circumstances it is a frequent practice generate a mathematical program to optimize the operations of the manufacturing plant in order to minimize the economical impact of changes in the functional parameters.The study case corresponds to a manufacturing company having two productive sites. In the first plant are made all final products in order to be sold in the markets and also in this one is manufactured an intermediate product for the second plant. In this second facility only final products are made. The model generated is a multiproduct multiperiod one having a horizon time of one year to make operational tactical decisions. The decision variables of the model are the number of units per period to be produced according to the demand, the unsatisfied demand (if there is one) the units transferred from one site to the other. The objective function minimizes fixed and variable costs of: production, inventory and transport, and also penalizes the risk of having product scarcity below a safety stock and the loss of sales. As was mentioned previously the demand vagueness is modeled using fuzzy sets whose characteristics are deduced from market studies and experts in the area. The proposed model is an alternative formulation for imprecise data which penalizes the constraint violations of the uncertain parameter and gives, as a result, a unique tactical plan of the manufacturing company activities feasible for whole range of demand, having robust optimality in the sense that the minimum cost is optimal or close to optimal for all possible demand values.