ORIGINAL ARTICLE Balancing–sequencing procedure for a mixed model assembly system in case of finite buffer capacity Daria Battini & Maurizio Faccio & Alessandro Persona & Fabio Sgarbossa Received: 22 July 2008 / Accepted: 27 October 2008 / Published online: 9 December 2008 # Springer-Verlag London Limited 2008 Abstract In the last decades, the necessity to make production more versatile and flexible has forced assembly line production systems to change from fixed assembly lines to mixed model assembly lines, where the output products are variations of the same base product and only differ in specific customizable attributes. Such assembly lines allow reduced setup time, since products can be jointly manufactured in intermixed sequences (Boysen, Flieder, Scholl. Jena Research Papers in Business and Economics, Friedrich-Schiller-Universitat Jena, 1;1–11, 2007a; Boysen, Flieder, Scholl. Jena Research Papers in Business and Economics, Friedrich-Schiller-Universitat Jena, 2;1–33, 2007b). Unfortunately, the installation of customization options typically leads to variations in process times, and when the cycle is exceeded within a certain station, an overload is created, forcing other stations to wait and idle. Normally, process time variation in an un- paced line are absorbed by buffers, but in some industrial application the buffer dimensions are critical not only for the reduction of work in progress but also in reducing other constrains (space, technology, model dimensions, etc.). The problem of balancing mixed model assembly lines (MALBP), in the long term, and that of sequencing mixed model assembly lines (MMS), in the short term (Merengo, Nava, Pozetti. Int J Prod Res 37:2835–2860, 1999), are the two major problems to solve. The object of this paper is to illustrate an innovative balancing–sequencing step-by-step procedure that aims to optimize the assembly line perfor- mance and at the same time contain the buffer dimensions in function of different market demand and production mix. The model is validated using a simulation software and an industrial application is presented. Keywords Balancing problem . Sequencing problem . Buffer dimension . Assembly 1 Introduction and literature review A mixed model assembly line consists of different work stations assembling different models connected in series. In the un-paced assembly lines, the stations are decoupled by buffer stocks. Buffers have the function to hold work pieces when the following station is still working on the previous item and is not ready to receive new pieces. Such buffer becomes critical when the assembly activities may take different times per different models, and for this reason, in a mixed model, buffers are normally present. The buffer location and size has a strong influence on the production rate of the line, on the storage space, on material handling, and inventory costs (Scholl [2]). In general, companies consider the buffer to be a production constrain, especially when the available space is limited and the products have large dimensions. From this point of view, it is important to reduce the buffer dimensions and at the same time improve the production rate. For the purpose of this study, we assume that the buffers are located between each couple of stations (typical of un- paced mixed model assembly line system) and we aim to Int J Adv Manuf Technol (2009) 44:345–359 DOI 10.1007/s00170-008-1823-8 D. Battini : A. Persona : F. Sgarbossa Department of Management and Engineering, University of Padova, Stradella San Nicola, 3 36100 Vicenza, Italy M. Faccio (*) Department of Innovation in Mechanics and Management, University of Padova, Via Venezia 1, 35131 Padova, Italy e-mail: maurizio.faccio@unipd.it