Rough Mill Analysis Model (RAM) software, developed by Dr. Rado Gazo with Dr. Philip Steele at Mississippi State University, was described in the previous LFPL Newsletter. In this issue we will discuss one of the many uses of this program: determining yield, processing time and machine utilization differences between processing sorted and unsorted lumber.
Many rough mills purchase mixed grades of lumber and process this lumber without sorting by lumber grade. Information is not available on the benefits of sorting mixed lumber grades prior to processing. Cutting long parts from higher grades and short parts from lower grades is generally considered to maximize yield and reduce waste. Processing efficiency may also be increased if the appropriate size parts are cut from the specified lumber grades. Therefore, processing of unsorted lumber grades may not allow cut-up operators to make optimal decisions producing yields which may be lower and processing times longer than for the processing of sorted lumber grades.
Both crosscut-first and rip-first rough mill systems were simulated using the RAM software. Results for sorting lumber and crosscuting-first in a rough mill were as follows. An increase in yield of about 1 percent was obtained even though total processing time was not influenced . The actual machine utilization also increased by 9.4 percent, but the salvage crosscut saw decreased by 16.7 percent.
Sorting lumber prior to processing for the rip-first rough mill also increased yield by 0.3 percent and decreased total processing time by 2.0 percent. The actual machine utilization increased by 25 percent for the crosscut saws, decreased by 1.8 percent for the sorting operation and increased by 13.5 percent for the salvage straight-line rip saws.
Although this study found a positive influence by sorting lumber prior to rough mill processing in two actual rough mills, it is not feasible to obtain a general result for all rough mills. The results may differ for each rough mill since yields and processing times are influenced by specific lumber grades and their specific grade mix for cutting orders being filled. Simulation of each rough mill is therefore required to determine specific values and incorporate individual rough mill variables. For more information about this program call Rado Gazo at (504) 388-6432.
