Abstract

Objective
The aim of the doctoral thesis “MODELOS Y MÉTODOS PARA EL PROBLEMA DE PROGRAMACIÓN DEL LOTE ECONÓMICO CON COPRODUCCIÓN DELIBERADA Y CONTROLADA (DCC-ELSP)”, by Ms. Pilar Isabel Vidal Carreras and directed by Dr. Mr. Jose Pedro García Sabater, is to analyze and model scheduling problem with controlled and deliberate coproduction, in the context of sector automotive supplier, which is similar to the ELSP - Economic Lot Scheduling Problem. For this, it requires the definition of different methodologies and algorithms to solve them satisfactorily.

Interest of the Problem                                    
The source of the problem of this thesis is the result of continuous and extensive contact of the thesis director, Dr. Mr. José P. García Sabater and latest PhD, Ms. Pilar I. Carreras Vidal, with companies supplying the automotive industry (Garcia-Sabater et al., 2006a; Garcia-Sabater and Marin-Garcia, 2009; Garcia-Sabater et al., 1999; Garcia-Sabater, 2000; Garcia-Sabater and Vidal-Carreras, 2010; Garcia-Sabater et al., 2006b; Miralles et al., 2005; Vidal-Carreras and Garcia-Sabater, 2005). Deliberate and controlled co-production, this is the option to make or not (intentionally) two products simultaneously in a controlled manner, in this setting occurs frequently. To cite an example comment as automobiles contain many parts symmetrical for left and right side of the vehicle (mirrors, doors, lights, etc). These production processes are often designed to produce the left and the right side at the same time. This situation does not seem a problem when producing parts for a new car. However, the same manufacturing facilities used to produce spare parts to replace damaged parts.
The thesis is a brief summary of relevant aspects of production scheduling in companies supplying the automotive industry that directly affect the problem of deliberate and controlled coproduction (DCC) . Is part of the literature by the state of the art, as an interesting contribution, since the problem of coproduction had not been treated so far from this point of view.

Methodology
An analysis analytical problem, for two pairs of coproduct a and b, are done resulting the algorithm DCC-ELSP-2P. This algorithm allows to define the parameters that minimize the costs of coproducing two products, with demand not replaceable. We present a numerical application to improve understanding of the dynamics of the models and algorithms designed.
Created heuristics are described to model the phenomenon of co-production in the environment of the problem of economic lot scheduling for a multi-item mixed. In this environment there are products that can co-produce or not. Heuristics are relatively simple design, while others are more elaborate and complex and dynamic parameters considered in time.
The proposed heuristics are applied to a benchmark classic in the literature of the ELSP (Bomberger, 1966) with various machine load uses (Oner and Bilgic, 2008). To do this, you need a complete experimental design.

Results
The analysis of the results allows the extraction of interesting conclusions. According to the stability of the system with respect to its utilization level, heuristics and combinations to use to get the best results would be different. For stable systems with high utilization, better heuristics are presented as simple to implement in practice, since they produce the amounts calculated in accordance with maximum and minimum levels of inventory, a non-preemptive. Production orders are being implemented in a period, not altered by imbalances in inventories of products not being produced at that time. However, if you work in an environment that can ensure stability, or the application or in the production rates of the products, the best thing is to use a heuristic flexible and adaptable to new system use requirements. These heuristics are more elaborate and require a dynamic recalculation cycle time, but this allows better adapted to new situations. By the time this review cycle, allowing to mitigate the effect of the imbalance of the costs of setup or change of heading, by changing the rate of use of the facility. Actually, the setup costs in a system with or without coproduction, should be a measure of system capacity and in turn, allow for adjustment thereof. The approach outlined in (Segerstedt 1996) for inventory management in multi-stage environment stating that setup costs are the result of limited system capacity, appeared clearly on this issue DCC-ELSP-2P. Regarding the design parameters, we can conclude that, using appropriate heuristics with the correct parameters is achieved adequately model the phenomenon of deliberate and controlled coproduction, achieving a balance between the costs of setup and inventory.
Throughout the study task has been made, have had to have to make decisions, leaving many areas of research for future work. Is remarkable considering both the DCC-ELSP-2P to the same classical ELSP the idea of adjustable setup costs of the system capacity.