The shape of protective capacity in unbalanced production systems with unplanned machine downtime

Several studies have shown that when both statistical fluctuations and dependent events exist, unbalanced production lines out-perform balanced lines. By definition, unbalanced lines have some amount of protective capacity built into them; however, little research exists to address the question of quantity and position of protective capacity necessary to counteract the impact of variation on system performance. This research seeks to improve our understanding concerning the shape of protective capacity in unbalanced lines when faced with variation in the form of unplanned machine downtime. Both Kanban and drum-buffer-rope (DBR) controlled lines are investigated. Results show that balancing the protective capacity yields superior results over both increasing and decreasing protective capacity shapes (holding average protective capacity equal). Results also show that Kanban lines behave differently than DBR lines.