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International Journal of Production Research Vol. 47, No. 21, 1 November 2009, 6145–6158

Real time production improvement through bottleneck control
Lin Lia*, Qing Changb, Jun Nia and Stephan Billerb
a b

Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, USA; Manufacturing Systems Research Lab, General Motors R&D Center, Warren, Michigan, USA (Received 24January 2008; final version received 23 May 2008) Variability is a key characteristic for evaluating the performance of a process. Small variability for a bottleneck machine can generate high production variability. Short-term production analysis and bottleneck identification are imperative for enabling optimal response to dynamic changes within the system. In comparison to the rich and abundantliterature available on long-term analysis, only a small section of the literature addresses the dynamic bottleneck control policies, which may be used to maximise sustainable benefits. In this paper, a real time bottleneck control method is introduced to efficiently utilise the finite manufacturing resources and to mitigate the short-term production constraints by using two practical approaches:initial buffer adjustment and maintenance task prioritisation. The objective for real time bottleneck control is to obtain a continuous production improvement towards a balanced-line status to increase the throughput efficiently. The benefits of this method are presented by considering an industrial case study of an automotive assembly line. The results obtained from this case study show significantproduction improvements as compared to traditional approaches. Keywords: real time bottleneck control; short-term; balanced-line status; bottleneck inertia phenomena; initial buffer adjustment

1. Introduction Throughput is an important parameter to evaluate production performance. Extensive work has been done in the area of throughput analysis (Dallery and Gershwin 1992, Gershwin 1994, Goviland Fu 1999, Hopp and Spearman 2000). A machine is defined as a throughput bottleneck if the performance of the machine is the most sensitive to the overall performance of a manufacturing system. The existing work in bottleneck detection can be categorised into analytical methods (Gershwin 1994, Wang et al. 1999, Blumenfeld and Li 2005) and simulation-based methods (Law and McComas 1998, Bonder andMcGinnis 2002). Most of the bottleneck studies using analytical methods are restricted to long-term steady-state bottleneck detection because of their statistical and probability distribution assumptions for machine performance. Also, developing analytical closed form solutions for complex lines is difficult. As compared to analytical methods, discrete event simulation may be used to understandcomplex layout and study their dynamic performance. The major drawbacks of the simulation approach are system specific knowledge, relatively less flexibility to layout changes, long development time and possible

*Corresponding author. Email: lilz@umich.edu
ISSN 0020–7543 print/ISSN 1366–588X online ß 2009 Taylor & Francis DOI: 10.1080/00207540802244240 http://www.informaworld.com

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misinterpretations of simulation results. These factors greatly impede the wide application of simulation-based methods. Different approaches have been developed for long-term steady-state bottleneck control. Adams et al. (1988) described an approximation method for solving the minimum makespan problem of job shop scheduling through the shifting bottleneck procedure. Computationaltesting shows that the proposed approach yields consistently better results than other procedures discussed in the literature. In Pourbabai (1993), an optimal operational strategy is used to optimise the system utilisation while controlling the bottleneck problem in a finite capacity integrated assembly line system. Lawrence and Buss (1995) critically analysed production bottlenecks from an...