Justifying Six Sigma Projects in Manufacturing Management

This paper develops and illustrates a case in manufacturing management, using the instance of justifying quality improvement of ball bearings—a common precision product whose correct manufacture and assembly greatly affects their efficiency, utility and life. Mass-produced at high speed, bearings extend a fertile domain for benefiting from QA apparatus including Gage R&R, ISO standards, sampling, and SPC to Six Sigma DMAIC (Pyzdek 2000). However, when large investments are involved, it becomes imperative that besides the obvious, the hidden costs of quality be located and sized. This paper provides methods to examine and quantify such shortfalls—many being preventable by reduction of quality variance and/or part variety. Statistical and numerical models have been used. Thus, targeting beyond scrap and rework, this paper invokes modeling methods to quantify such not-so-visible constraints that limit productivity and profits of high-volume high-speed processes.