Unpaced production lines with three simultaneous imbalance sources
| Published date | 27 September 2011 |
| DOI | https://doi.org/10.1108/02635571111182746 |
| Date | 27 September 2011 |
| Pages | 1356-1380 |
| Author | Tom McNamara,Sabry Shaaban,Sarah Hudson |
| Subject Matter | Economics,Information & knowledge management,Management science & operations |
Unpaced production lines
with three simultaneous
imbalance sources
Tom McNamara
Department of Finance and Operations,
ESC Rennes School of Business, Rennes, France
Sabry Shaaban
Department of Economics, Strategy and Organization,
Groupe ESC La Rochelle – Cerege, La Rochelle, France, and
Sarah Hudson
Department of Finance and Operations,
ESC Rennes School of Business, Rennes, France
Abstract
Purpose – The purpose of this paper is to investigate the performance of unpaced reliable production
lines that are unbalanced in terms of their mean operation times, coefficients of variation and buffer
capacities.
Design/methodology/approach – Simulations were carried out for five- and eight-station lines
with various buffer capacities and degrees of means imbalance. Throughput, idle time and average
buffer level performance indicators were generated and statistically analysed.
Findings – The results show that an inverted bowl allocation of mean service times, combined with a
bowl configuration for coefficients of variation and a decreasing order of buffer sizes results in higher
throughput and lower idle times than a balanced line counterpart. In addition, considerable reductions
in average inventory levels were consistently obtained when utilizing a configuration of progressively
faster stations, coupled with a bowl-shaped pattern for coefficients of variation and an ascending
buffer size order.
Research limitations/implications – The results for these specific experiments imply that
resources expended on trying to achieve a balanced line could be better used by seizing upon possible
enhanced performance via controlled mean time, variability and buffer imbalance. Results are valid for
only the line type and parameter values used (simulation results are specific and not general).
Practical implications – Guidelines are provided on design strategies for allocating labour and
capital unevenly in unpaced lines for better performance in terms of increased throughput or lowered
idle time or average buffer levels.
Originality/value – This paper might be viewed as one of the first simulation investigations into the
performance of unpaced production lines with three sources of imbalance.
Keywords Optimized production scheduling, Operations and productionmanagement, Simulation,
Unpaced productionlines, Means imbalance, Variabilityimbalance, Buffer imbalance
Paper type Research paper
1. Introduction
Research shows that in the design of unpaced asynchronous serial production lines,
there are a number of issues to be considered if performance is to be improved. First,
the operators at each station along the line work at different average operation time
The current issue and full text archive of this journal is available at
www.emeraldinsight.com/0263-5577.htm
IMDS
111,9
1356
Received 26 March 2011
Revised 11 May 2011
Accepted 3 July 2011
Industrial Management & Data
Systems
Vol. 111 No. 9, 2011
pp. 1356-1380
qEmerald Group Publishing Limited
0263-5577
DOI 10.1108/02635571111182746
rates from each other and so the placement of these operators along the line becomes an
important consideration. In addition, the variation in the time taken by an operator to
complete a task can differ quite considerably. People in general cannot perform a task
or a series of tasks differing in complexity and specificity again and again at exactly
the same speed over a length of time, so the positioning of operators with different
coefficients of variation (CVs) is yet another important consideration.
Another influence on performance is the buffer size and placement. In theory, the best
way to allocate buffer space along a line is evenly. However, this is not always possible
for technical reasons and a manager may have to distribute buffer capacity unevenly.
Finally, line length and the total buffer space available along the line have an influence
and so an investigation into the combined influence of mean operation time, CV and
buffer imbalance at different levels of total buffer capacity and at different line lengths is
performed.
As far as unpaced lines are concerned, there has been a large amount of research
devoted to balanced production lines, with the underlying assumption that these types
of line, where workstation processing times and variability are equal and where buffers
are evenly allocated, lead to the best performance.
However, a growing body of publications has shown that line imbalance with regard
to buffers, mean times or coefficients of variation, rather than being an unwelcome fact
of life for these unpaced lines can in some cases actually enhance performance. This
investigation contributes to this line of research by reporting on the results of simulation
experiments on the effects on performance of various combinations of three sources
of imbalance. Simulation of unpaced lines with simultaneous multivariate effects on
performance still remains a fairly understudied area, and this approach can yield
interesting insights into the behaviour of specific lines in defined conditions.
The contribution of the work presented here is twofold. First, we will see that a few
of the imbalanced lines simulated in the experiments actually perform better than
the corresponding balanced line, a counterintuitive result which supports findings by
previous research in this area. Second, the effect of three simultaneous sources of
imbalance on performance in terms of idle time, throughput and average buffer level has
not to our knowledge been reported before, and will add to the body of work in thisarea,
since the nearer that modelling mirrors real life conditions,the more useful the results are.
This paper is organized as follows. In Sections 2 and 3 the relevant literature is
reviewed and the research objectives are stated. Section 4 discusses the methodology
and experimental design aspects. The simulation output data and analysis are exhibited
in Section 5. A summary of the findings and conclusions, along with a discussion, are
presented in Sections 6 and 7.
2. Literature review
Owing to the importance of unpaced serial production lines in the production of many
goods and services, a considerable number of investigations have been conducted to
study their operating behaviour and to determine ways of improving their efficiency
(Hillier and So, 1996; Chan and Ng, 2002; Shaaban and McNamara, 2009a).
There are different approaches to this area, including for example the development of
algorithms for optimal performance and subsequent testing through simulation of
specific patterns of imbalance in a variety of operating conditions and for differing
performance indicators, such as throughput, costs and so on. Another approach looks
Unpaced
production lines
1357
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