Rocío Alfaro-Pozo

Models for assembly line balancing by temporal, spatial and ergonomic risk attributes

Assembly lines with mixed products present ergonomic risks that can affect productivity of workers and lines. Because of that, the line balancing must consider the risk of injury in regard with the set of tasks necessary to process a product unit, in addition to other managerial and technological attributes such as the workload or the space. Therefore, in this paper we propose a new approach to solve the assembly line balancing problem considering temporal, spatial and ergonomic attributes at once. We formulate several mathematical models and we analyze the behavior of one of these models through case study linked to Nissan. Furthermore, we study the effect of the demand plan variations and ergonomic risk on the line balancing result.

Maximizing comfort in Assembly Lines with temporal, spatial and ergonomic attributes

We aim at maximizing the comfort of operators in mixed-model assembly lines. To achieve this goal, we evaluate two assembly line balancing models: the first that minimizes the maximum ergonomic risk and the second one that minimizes the average absolute deviations of ergonomic risk. Through a case study we compare the results of the two models by two different resolution procedures: the Mixed Integer Linear Programming (MILP) and Greedy Randomized Adaptive Search Procedures (GRASP). Although linear programming offers best solution, the results given by GRASPs are competitive.

Consideration of human resources in the Mixed-model Sequencing Problem with Work Overload Minimization

MMSP with work overload minimization and improvement of working conditions.Compliance with saturation conditions of workers imposed by collective agreement.Increase of work pace factor of workers to reduce production losses.Auxiliary processors to complete the required work and to fulfill all conditions.Case study linked to the Nissan Powertrain Plant in Barcelona. 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 a set of working conditions in regard with human resources of workstations on the line. These conditions come from collective agreements and therefore must be respected by both company and labor unions. 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 both activation of operators, while maintaining the same quality in working conditions achieved by limiting the saturation, and auxiliary processors. By results we state that saturation limitation leads an important increase of work overload, which means average economic losses of 28,731.8 Euros/day. However, the productivity reduction may be counteracted by the work pace factor increase, at certain moments of workday, and/or by the incorporation of auxiliary processors into the line.

A hybrid dynamic programming for solving a mixed-model sequencing problem with production mix restriction and free interruptions

In this article, we propose a hybrid procedure based on bounded dynamic programming assisted by linear programming to solve the mixed-model sequencing problem with workload minimization with serial workstations, free interruption of the operations and with production mix restrictions. We performed a computational experiment with 23 instances related to a case study of the Nissan powertrain plant located in Barcelona. The results of our proposal are compared with those obtained by mixed integer linear programming.

Minimizing Lost-Work Costs in a Mixed-Model Assembly Line

Mixed-model assembly lines present two issues due to differences in processing times from product types; these issues are the work overload or unfinished work and the useless time or unproductive time. Within this context, we present, in this paper, a new mathematical model for the mixed-model sequencing problem. This model minimizes the costs by lost production and idle productive time. The model also allows processors carry out their workload with a factor activity greater than the normal, in order to reduce the work overload if it is necessary. Obviously it is also considered to provide economic compensation to workers based on their level of activation. Finally, the model is evaluated by a computational experience linked to a real case from the automotive industry.

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.

GRASP Approach to a Min-Max Problem of Ergonomic Risk in Restricted Assembly Lines

A Greedy Randomized Adaptive Search Procedure GRASP is proposed to solve an extension of the assembly line balancing problem. The problem focuses on minimizing the maximum ergonomic risk of the assembly line when the space required by workstations, the cycle time, and the number of workstations of the line are given. To evaluate the GRASP procedure a case study linked to Nissans engine plant in Barcelona is used and the obtained results are compared with those obtained by Linear Programming.

Mixed-Model Sequencing Problem Improving Labour Conditions

It is presented an extension of the mixed-model sequencing problem that considers some working conditions agreed between companies and trade unions. In particular, it is formulated a mathematical model with saturation limits which an operator can have throughout his workday and with the possibility of increasing the work pace of the operators at certain times of the workday. In this way, it is possible to improve labour conditions and line productivity simultaneously. In fact, the proposed model is evaluated by means of a computational experience that allows to observe that an increment of \(3.\overset{\lower0.5em\hbox{

Ergonomic Risk Minimisation in Assembly Line Balancing

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Productivity Improvement, Considering Legal Conditions and Just in Time Principles in the Mixed-Model Sequencing Problem

}}{3} \;\%\) on the work pace factor of processors reduces the work overload by 62.6 % while the saturation conditions imposed by collective agreements are satisfied.