Modelado y resolución de variantes del problema de secuenciación de modelos mixtos con minimización de la sobrecarga (MMSP-W)con factores de actividad y regularidad en la producción

Resumen

In this thesis it is studied the mixed-model sequencing problem with work overload or uncompleted work minimisation (MMSP-W). Indeed, four variants from the original problem are estudied with the aim of leading the problem from the literature to both the productivity improvement and the improvement of working conditions of the line operators. Because of this, different aspects from real situations that occur in the current production systems are taken into account. The first studied variant considers workstations arranged in series, the possibility that several homogenous processors can get together at the same workstation and the possibility that any workstation can hold any product unit a time greater than the cycle time in order to complete all the requiered work. Two equivalent mathematical models are the fruit of this variant and they will serve as the starting point of the following studied variants. These models focus on optimising the work overload or the uncompleted work. The second variant incorporates concepts from the JIT management ideology. In fact, in addition to minimise the work overload or maximise the completed work, this variant considers the advantage of obtaining product sequences with an homogeneous distribution of the required work, completed work or work overload, throughout time. The result of this study will be a set of mono and multi-objective models whose purpose will be to minimise the work overloads avoiding undesirable excess efforts for human resources and regularising the product sequence. The third variant considers variable processing times of the operations regarding the work pace of workers throughout the workday. Thus, based on the idea that the activity or work pace of workers is not constant over time, differents functions for the activity factor are defined. These functions will force an increase of work rythm of operators at certain moments of the workday and therefore the operators will be able to complete more requiered work, at the same time, and therefore, the work overload will be reduced.In the last proposed variant, taking into account the presence of human resources at workstations, the labour conditions agreed between company and trade unions are considered. Indeed, we have considered working conditions with respect to the saturation or ocupation level of operators of the line. Thus, new mathematical models for the MMSP-W are formulated. These models respect the maximum values of medium and maximum saturation of the processors of workstations which have been established by collective agreements. Finally, note that all the variants studied are evaluated through a case study related to the Nissan engine plant in Barcelona. Thus, it is possible to compare the results obtained by the reference models with the models proposed in this thesis from a computational, economic, social and legal perspective.