Learning curves for imperfect production processes with reworks and process restoration interruptions

Many production processes are not defect free, and reworks are unavoidable. This makes the assumption of the Wright’s learning curve [Wright, T., 1936. Factors affecting the cost of airplanes. Journal of Aeronautical Science 3 (2), 122–128] that all units produced are of acceptable quality impractical, suggesting a linkage between quality and learning to be inevitable. The quality learning curve (QLC) developed by Jaber and Guiffrida [Jaber, M.Y., Guiffrida, A.L., 2004. Learning curves for processes generating defects requiring reworks. European Journal of Operational Research 159 (3), 663–672] is a modification of the Wright’s learning curve for processes that generate defects that can be reworked. This paper investigates the QLC for the assumption that the production process is interrupted for quality maintenance to bring the process in control again. New learning curves are developed with numerical examples provided and results discussed.