In this paper, lean buffering (i.e., the smallest level of buffering necessary and sufficient to ensure the desired production rate of a manufacturing system) is analyzed for the case of serial lines with machines having Weibull, gamma, and lognormal distributions of up- and downtime. The results obtained show that: (1) the lean level of buffering is not very sensitive to the type of up- and downtime distributions and depends mainly on their coefficients of variation, CV{sub}(up) and CV{sub}(down); (2) the lean level of buffering is more sensitive to CV{sub}(down) than to CV{sub}(up) but the difference in sensitivities is not too large (typically, within 20%). Based on these observations, an empirical law for calculating the lean level of buffering as a function of machine efficiency, line efficiency, the number of machines in the system, and CV{sub}(up) and CV{sub}(down) is introduced. This empirical law leads to a reduction of lean buffering by a factor of up to 4, as compared with that calculated using the exponential assumption on up- and downtime distributions.
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