Using discrete-event simulation to study the influence of log yard sorting on sawmill processing efficiency of small-diameter timber Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2n49t509p

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  • A sawmill is similar to other manufacturing enterprises when it comes to making decisions, scheduling production and meeting customer demands. In order to help sawmills achieve their goals, and because there is such a high degree of variability in the raw material used in this industry, computer simulation has proven to be a very valuable tool to help improve productivity and processing efficiency. Raw material variability is expected to be an increasing issue in coming years due to an increase in small-diameter timber on the market resulting from the thinning of overstocked forest stands. These changes are expected to result in a significant decrease in production for mills that are not equipped to process this type of material. As a means of analyzing the influence of these changes, this thesis details the development and use of a discrete-event computer simulation model of the Warm Springs Forest Products Industries sawmill in Warm Springs, OR. This research is part of a larger project in which other improvement scenarios were studied (Salichon 2005). The simulation model was first used to identify some possible areas of improvement and to optimize the current overall process and production of the sawmill while operating with its current log distribution. The study identified a number of opportunities for improvement. It was demonstrated that increasing the unscrambler maximum capacity up to 800 boards resulted in an increase in piece count production ranging from 2.6 to 5.3%. The influence of machines downtimes as well as the influence of having a second operator assisting at the horizontal resaw were also investigated. Past studies have shown that log sorting is an essential condition to achieve high production in a sawmill. The simulation model was used to evaluate sorting strategies that would minimize the decrease in production resulting from introducing small-diameter timber (5 to 7 inches) into the log supply. Different small-diameter distributions were tried and different sorting solutions were tested for each of the log distributions. It was shown that the mill would suffer a decrease in piece count production ranging from 10.1 to 13.1% if their current two decks sort is retained. However, it was demonstrated that implementing a three decks sort would considerably reduce this drop in production to only 4.7 to 6.4%. Simulation has been shown to be a very valuable tool that sawmills can use to investigate production and other log supply issues. While piece count production was sufficient for analyzing current mill efficiency changes, the introduction of smaller diameter logs will also reduce the board feet per piece ratio. Due to the loss of the trimmer data during the test run, no information can be provided about board footage and thus the results and statistics in this research were based on piece count only. However, future work could be done with log breakdown models like BOF or SAW3D to determine board footage. Future research could also focus on studying the influence of the trimmer's downtimes on the unscrambler queue and other machine utilization rates as well as testing mathematical algorithms that will search for other optimized sorting and feeding strategies.
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