Int. J. Mathematics in Operational Research, Vol. 4, No. 1, 2012 1 Copyright © 2012 Inderscience Enterprises Ltd. Working time evaluation in assembly lines M. Karimi-Nasab and Unes Bahalke* Department of Industrial Engineering, Iran University of Science and Technology, P.O. Box 1684613114, Narmak, Tehran, Iran Fax: +98-1722233964 Fax: +98-1723336372 E-mail: mehdikariminasab@iust.ac.ir E-mail: unesbahalke@gmail.com E-mail: unesbahalke@iust.ac.ir *Corresponding author H.R. Feili Faculty of Engineering, Department of Industrial Engineering, Alzahra University, P.O. Box 1993891176, Tehran, Iran Fax: +98-2188617537 E-mail: hrfeili@gmail.com A. Sheikhzadeh Department of Industrial Engineering, Amirkabir University of Technology, P.O. Box 1684613114, Tehran, Iran, Iran E-mail: alireza.sheikhzadeh@gmail.com K. Dolatkhahi Department of Industrial Engineering, Iran University of Science and Technology, P.O. Box 1684613114, Narmak, Tehran, Iran E-mail: kasra.dolatkhahi@gmail.com Abstract: Assembly lines are special flow-line production systems which are of great importance in the industrial mass production. This paper introduces the deterioration effects in assembly lines that the aim of the developed mathematical model and the proposed genetic algorithm is to minimise the working time of a product in a cycle of assembly. Task deterioration means that a task processed later consumes more time than the same task when it is processed earlier. At the end several well-known examples are solved and the results proved that the deterioration will affect both cycle time and working time, simultaneously.