Simulating changing diameter distributions in a softwood sawmill

Graduation date: 2006Sawmills are very complex systems that involve many manufacturing processes. The variability of their raw material adds further to this complexity as each log has characteristics that determine its processing path. Therefore, computer simulation is a very useful technique for analyzing sawmill performance. This thesis describes a simulation computer model of the Warm Springs Forest Products Industries sawmill. This model was implemented to improve general sawmill manufacturing processes as well as to quantify the effect of adding more small diameter timber into the mill's raw material log mix. The WSFPI sawmill includes two primary process centers, the headrig for processing large logs and the end-dogging log feeding system, or EDLF, for processing smaller logs (less than 17"). The focus of this study is mainly on the small-log side of the sawmill. For an analysis of the sawmill's large log processing system, see "Using discrete-event simulation to study the influence of log yard sorting on sawmill processing efficiency of small diameter timber" (Pinon 2005). The model was implemented using the Arena discrete-event simulation software package. The influence of log characteristics such as diameter and length was included in the model. The model also included simplifications of the real system to facilitate the mill's simulation. Data was collected for different sawmill Results showed that downtimes had a significant influence on sawmill production. Removing downtimes for the trimmer or the EDLF proved to significantly increase production while the other machines' downtimes had no significant influence on production. Investigations into the effect of increasing the EDLF ' s processing speed were also conducted and showed that for the current log distribution, increasing its speed produced no significant increase in production. However, if more smalldiameter material were processed, a significant increase in production was observed. Increasing the gang edger's speed along with the EDLF's speed was also investigated. A significant increase in production was observed but was limited by the other machine centers that could not process the higher material flow (unscrambler, trimmer, board-edger, and horizontal resaw). Higher percentages of small diameter timber are expected as part of the sawmill's future log supply. Simulation runs were conducted to estimate the production loss due to this change, and they showed a significant decrease in production. Those results suggest that machine center changes would be required to offset the production lost from processing greater amounts of small diameter timber