UBC Theses and Dissertations
The impacts of sawmill processing variances on lumber target sizes and production revenue Lin, Yingzhong
Although the statistical quality control technique has been applied in the lumber manufacturing industry for more than two decades, many sawmills are still severely over-sizing their lumber due to the inefficiency of their lumber target size control programs in which only the sawing variation is controlled. The shrinkage variation and planing variation which may also contribute significantly to lumber target sizes in the current sawmills are usually not the controlled subjects. This study evaluated the traditional target size control programs and investigated the impacts of all the three processing variances (sawing, drying and planing) on lumber target size control and production net revenue. This was done by: 1) thorough examination of the system variances of an interior B. C. softwood sawmill, and 2) developing a target size estimation program which considers all the three processing variances. The results of empirical study indicated that the variation in drying shrinkage was even larger than total sawing variation and the planing variation of the test mill was more than half of the total sawing variation. The shrinkage variation caused by drying operations other than material itself was found significant. Therefore it was found to be essential to control the drying and planing processes along with controlling the sawing process. The evaluation of traditional target size estimation method showed that this method over-estimates lumber target sizes. The results also showed that the target sizes currently used in the test sawmill were much larger than the necessary target sizes. There is great opportunity for the mill to reduce its target sizes. If the variances of the three sub-processes are strictly controlled, the test mill could expect to realize about three million dollar net revenue per year without reducing current system variation level. The study of the impact of system variation on the target size reduction showed that the reduction in planing variation had greatest impact among the three processing variances. The impact of sawing and drying variation on the target size reduction were similar. In general, it was the variation which was larger in value had larger impact on target size reduction.
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