Free and regular mixed-model sequences by a linear program-assisted hybrid algorithm GRASP-LP

A linear program-assisted hybrid algorithm (GRASP-LP) is presented to solve a mixed-model sequencing problem in an assembly line. The issue of the problem is to obtain manufacturing sequences of product models with the minimum work overload, allowing the free interruption of operations at workstations and preserving the production mix. The implemented GRASP-LP is compared with other procedures through a case study linked with the Nissan’ Engine Plant from Barcelona.Peer ReviewedPostprint (author's final draft

Incorporating working conditions to a mixed- model sequencing problem

Partiendo de una variante de un problema de secuenciación en líneas de productos mixtos (MMSP-W: Mixed-Model Sequencing Problem with Workload Minimisation), se proponen dos nuevos modelos que incorporan condiciones laborales a los puestos de trabajo de la línea. El primero tiene en cuenta la limitación de la saturación de los puestos de trabajo, mientras que el segundo contempla, además, la activación de los operarios a lo largo de la jornada laboral. Se realizan sendas experiencias computacionales, empleando un caso de estudio de la planta de motores de Nissan en Barcelona, con dos propósitos: (1) estudiar la repercusión que ocasiona la limitación de la saturación sobre la caída de la productividad de la línea, y (2) evaluar la recuperación de la productividad de la línea, mediante la activación de los operarios, manteniendo la misma calidad en las condiciones laborales conseguida al limitar la saturación.Beginning with a variation of the sequencing problem in a mixed-products line (MMSP-W: Mixed-Model Sequencing Problem with Workload Minimization), we propose two new models that incorporate the working conditions into the workstations on the line. The first model takes into account the saturation limit of the workstations, and the second model also includes the activation of the operators throughout the working day. Two computational experiments were carried out using a case study of the Nissan motor plant in Barcelona with two main objectives: (1) to study the repercussions of the saturation limit on the decrease in productivity on the line and (2) to evaluate the recovery of productivity on the line via activation of operators while maintaining the same quality in working conditions achieved by limiting the saturation. The obtained results show that the saturation limitation leads to suppose an important increase of work overload, which means average economic losses of 28,731.8 euros/day. However, the consideration of activity reduces these losses by 62.7%.Preprin

Mixed integer linear programming models for minimizing ergonomic risk dispersion in an assembly line at the Nissan Barcelona factory

We present a variant of the approach to the assembly line balancing problems, with the aim of reducing the ergonomic risk for operators of mixed-model assembly lines (MILP-3). Specifically, the MILP-3 model is focused on minimizing the average range between ergonomic risk values of workstations. Using a case study from Nissan’s plant in Barcelona, not only are the differences between levels of ergonomic risk of stations reduced, but we attempt to reduce the average maximum ergonomic risk of the assembly line. The new model is compared with two others, MILP-1 and MILP-2, which minimize the average maximum ergonomic risk and the average absolute deviation of the risks, respectively.Postprint (published version

Mejores soluciones del conjunto de instancias Nissan-9Eng.I para el problema MMSP-W/pmr/free

Estado del arte 2016/06 MMSP-W/pmr/freeEn este documento se recogen las mejores soluciones actuales de las instancias Nissan-9Ing.I, para el problema de secuenciación de modelos mixtos con mínima sobrecarga, restricciones sobre el mix de producción y libre interrupción de operaciones. Dichas soluciones proceden de 3 fuentes: programación dinámica acotada mediante programación lineal, programación lineal entera mixta y algoritmos GRASP hibridizados con programación lineal (GRASP-LP). El documento recoge también las 23 mejores secuencias, correspondientes a las instancias Nissan-9Ing.I, que ofrecen los algoritmos híbridos GRASP-LP.Postprint (published version

GRASP para secuencias regulares de modelos mixtos con sobrecarga mínima e interrupción forzada de operaciones

Presentamos un algoritmo GRASP para resolver un problema de secuenciación de productos mixtos en una línea de montaje. El objeto del problema es obtener una secuencia de fabricación de modelos que genere la mínima sobrecarga con interrupción forzada de las operaciones, que sea regular en producción y que el mix de producción mantenga la propiedad quota en toda la secuencia. El GRASP implementado se compara con otros procedimientos usando instancias de un caso de estudio de la planta de fabricación de motores de Nissan en Barcelona.Postprint (published version

A case study at the Nissan Barcelona factory to minimize the ergonomic risk and its standard deviation in a mixed-model assembly line

This work examines a balancing problem wherein the objective is to minimize both the ergonomic risk dispersion between the set of workstations of a mixed-model assembly line and the risk level of the workstation with the greatest ergonomic factor. A greedy randomized adaptive search procedure (GRASP) procedure is proposed to achieve these two objectives simultaneously. This new procedure is compared against two mixed integer linear programs: the MILP-1 model that minimizes the maximum ergonomic risk of the assembly line and the MILP-2 model that minimizes the average deviation from ergonomic risks of the set of workstations on the line. The results from the case study based on the automotive sector indicate that the proposed GRASP procedure is a very competitive and promising tool for further research.Peer ReviewedPostprint (published version

Mixed integer linear programming models for Flow Shop Scheduling with a demand plan of job types

This is a post-peer-review, pre-copyedit version of an article published in Central european journal of operations research. The final authenticated version is available online at: http://www.doi.org/10.1007/s10100-018-0553-8This paper presents two mixed integer linear programming (MILP) models that extend two basic Flow Shop Scheduling problems: Fm/prmu/Cmax and Fm/block/Cmax. This extension incorporates the concept of an overall demand plan for types of jobs or products. After using an example to illustrate the new problems under study, we evaluated the new models and analyzed their behaviors when applied to instances found in the literature and industrial instances of a case study from Nissan’s plant in Barcelona. CPLEX solver was used as a solution tool and obtained acceptable results, allowing us to conclude that MILP can be used as a method for solving Flow Shop Scheduling problems with an overall demand plan.Peer ReviewedPostprint (published version

Transformación de una línea de montaje de modelos mixtos en un taller de flujo regular: Caso de estudio en la factoría Nissan de Barcelona

En este trabajo aplicamos dos modelos de Programación lineal entera mixta, sobre problemas de taller de flujo regular con demanda generalizada de tipos de trabajos, con el propósito de transformar una línea de modelos mixtos en un taller de flujo regular. Para ilustrar dicha aplicación, presentamos un caso de estudio basado en una línea de motores mixtos de la factoría de Nissan en Barcelona. En el estudio se comparan los costes de producción de los dos sistemas productivos enfrentados, llegando a la conclusión de que el sistema taller de flujo regular sin bloqueos entre estaciones es el más competitivo. Como herramienta de resolución hemos empleado el solucionador CPLEX con resultados satisfactorios. Para llevar a la práctica la transformación de la línea de producción en un taller de flujo regular, proponemos un conjunto de requisitos, así como la asistencia al sistema productivo con un sistema de información basado en tecnologías IoT en el marco de la Industria 4.0.Postprint (author's final draft

An expert system to minimize operational costs in mixed-model sequencing problems with activity factor

One of the major issues in industrial environments is currently maximizing productivity while reducing manufacturing cost. This can be seen clearly reflected in mixed-model assembly lines based systems, where obtaining efficient manufacturing sequences is a key to be competitive in a dynamic and globalized market. However, this continuous cost reduction and productivity growth should not penalize the welfare of employees. This work is intended to address this lack of compatibility between the economic and social objectives through the study of the mixed-model sequencing problem from both the business and labor perspective. This is done by considering the possibility of reducing or increasing processing times of operations by varying the work pace of line's operators within the permissible legal boundaries. Thus, depending on this flexible activation time of operators, the amount of completed work and idle time will be one or the other and, consequently, the productivity of the line will also improve or get worse. In this regard, we propose new approach to the sequencing problem without incurring cost increases and providing a safe working environment, in accordance with applicable law. This new approach leads to obtain efficient manufacturing sequences, in terms of both productivity and labor conditions. Specifically, the objective of the new problem is minimizing the unproductive costs of the line by incorporating the possibility of increasing production through the variation of the work pace of line's operators. Increasing the work pace of operators, the amount of non-completed work or the preventable idle time can be reduced and therefore, their associated costs too. In addition, and without losing sight of the effort involved in working with a work pace above the normal, we propose several economic criteria to compensate the activation of workers where necessaryPeer ReviewedPostprint (author's final draft

Minimizing the ergonomic risk and its dispersion in a mixed model assembly line using GRASP

Postprint (author's final draft