THE EFFECTS OF BUFFER PATTERNS ON THROUGHPUT IN CONWIP FLOW LINES: A SIMULATION STUDY
Received: May 21, 2007; Revised: Sept 4, 2007; Accepted: Sept 10, 2007
This research was a simulation experiment which aimed to investigate the effects of buffer patterns on the throughput of lines controlled by a CONWIP release mechanism. The hypothetical lines simulated were stochastic 11-station flow lines with the middle station as the bottleneck. ANOVA tests were used for the analysis of the simulation output, followed by Duncan’s Multiple Range tests. There were 6 buffer patterns which were distinguished by the amount of total buffer capacity and the buffer ...view middle of the document...
Thus CONWIP is considered as a pullrelease mechanism where the release rate of new units into the system depends on the true capacity at that time. Other pull-release mechanisms are Kanban (see, for example, Krajewski et al., 1987) and pull from bottleneck (PFB) (Hopp and Spearman, 1996). Under Kanban, each station starts production only when there is a release of a unit at its succeeding station, whereas PFB releases a new unit into the line
Department of Management Technology, Institute of Social Technology, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand. Tel.: 0-4422-4518; Fax.: 0-4422-4521; E-mail: email@example.com Suranaree J. Sci. Technol. 14(4):391-399
Effects of Buffer Patterns on Throughput in CONWIP Flow Lines
upon the completion of another unit at the bottleneck station. The original concept of PFB is a scheduling approach called Drum-Buffer-Rope (DBR), which originated from the theory of constraints (Goldratt and Cox, 1986). Under the PFB release mechanism, the bottleneck stations have to be determined in order to set the correct pulling point, which may be difficult since the bottlenecks may shift around due to the variability in the system and the product type currently processed for mixed-model lines. Hence, Kanban and PFB mechanisms are more complicated than CONWIP. Besides being less complicated, CONWIP was found to outperform other release mechanisms. For example, Spearman et al. (1990) argued that a CONWIP release mechanism could be applied to broader manufacturing environments compared with Kanban. Spearman and Zazanis (1992) demonstrated that, given the same amount of WIP, Kanban is not likely to give a higher throughput than an equivalent CONWIP. Thus, the pulling-everywhere strategy in a Kanban system seemed to be unnecessarily complicated. Duenyas and Keblis (1995) found that CONWIP achieved a target throughput rate with less maximum WIP in the system and also with less average WIP in the system when compared with Kanban. However, those studies on a CONWIP release mechanism assumed no restriction on inter-station buffer capacity or queue size, which may not be realistic since production lines usually have limited space. How the inter-station buffer capacity affects the performance of production lines with a CONWIP release mechanism is not obvious. Thus, the purpose of this research is to explore these effects the results of which could give some suggestions for configuring buffer patterns in the ways that the desired performance can be reached. Although there have been various studies that investigated the methods of allocating limited buffer capacity, those studies explored lines with other release mechanisms, not with CONWIP. For example, Smith and Brumbaugh (1977) found that the best buffer allocation for a three station flow line is to split
buffer capacity equally. Conway et al. (1988) also found that equal allocation is the best approach for production lines with balanced...