ORIGINAL ARTICLE Redesigning an assembly line through lean manufacturing tools Roberto Álvarez & Roque Calvo & Marta M. Peña & Rosario Domingo Received: 18 March 2008 / Accepted: 19 September 2008 / Published online: 17 October 2008 # Springer-Verlag London Limited 2008 Abstract The implementation of a lean manufacturing strategy represents a robust contribution to the phase sequence that leads to operational excellence and the continuous improvement through the elimination of non- value-added activities. Therefore, lean practices contribute substantially to plant operational performance. This paper studies the use of value stream mapping (VSM) as a tool in lean manufacturing implementation and a framework of improvement activities, in particular for an efficient introduction of kanban and milkrun techniques. A case study illustrates VSM use, as well as kanban and milkrun systems application on an assembly line. Finally, the results obtained show the path of improvement, measured through the lean rate (LR) and dock-to-dock time (DtD). Keywords Lean manufacturing . Value stream mapping . Parts flow . Kanban . Assembly line 1 Introduction The implementation of a lean manufacturing strategy allows strengthening the phase sequence that leads to operational excellence, a continuous improvement, and the elimination of nonvalue-added activities [1]. Thus, the influence of lean practices contributes substantially with the operating performance of plants [2, 3] and the use of lean tools allows the improvement of results [4]. The tool value stream mapping (VSM) is applied as a way to progress toward lean manufacturing and as a formula to lead the activities of improvement [5–9]. In this sense, the contribution of internal transportation and its scheduling is specially important. Kanban card has been used to identify problems of production flow, maintaining the synchroniza- tion of inventory and material flow among production cells [10]. We can find that practical approaches to determine the optimal kanban size via simulation have been established [11] and some real applications have been published [12– 14]. However, the literature does not include authentic industrial applications showing the integration of kanban and internal transportation and its effects in the strategic productive factors. Moreover, it is necessary to study the empirical lean situations [3, 15, 16] to contextualize the lean concepts. This paper is focused on the analysis and use of the VSM to get improvements by means of kanban and milkrun, implemented in an efficient way. Their strategic influence is measured by means two lean metrics: lean rate (LR) and dock-to-dock time (DtD) [6]. These metrics are important to establish gains and identify areas for further improvement. Some authors have demonstrated their relevance to system performance in pull environment [17, 18]. LR is a key, fundamental, and paradigmatic metric and it should be reduced. It is useful to find and tally inventory accumulations where the flow of value has to be interrupted due to process problems. DtD depicts the material flow through the value stream. Therefore, it is a measure of the ability to deliver on time and it is generally a good indicator of the effectiveness of lean initiatives to improve the flow. Int J Adv Manuf Technol (2009) 43:949–958 DOI 10.1007/s00170-008-1772-2 R. Álvarez : M. M. Peña Department of Engineering, Universidad Antonio de Nebrija, C/Pirineos 55, E-28040 Madrid, Spain R. Calvo : R. Domingo (*) Department of Manufacturing Engineering, National Distance University of Spain (UNED), C/Juan del Rosal 12, E-28040 Madrid, Spain e-mail: rdomingo@ind.uned.es