Real World Use of Statistical Process Control (SPC)

(Courtesy: wallpapers-xs.blogspot.com)

If you read many books on lean six sigma, you quickly realize that much of the focus is on data collection and analysis.  If you are like me you wonder if there are any real world applications and how can using the data collection techniques improve a process.

Early on in my earlier life as a design engineer at Boeing, I was part looking into a tolerance study of stringers on the B-2 bomber program.  These stringers were attached inside the wing and serve to transfer load from the wing skin to the underlying frames and ribs.  There were issues with the location of the stringers being out of position and our engineering group sought to determine why the stringers were out of position.

A generic configuration showing the long slender stringers as they sit in a wing box - courtesy of avcom.co,za 

We took location measurements of where the stringers were actually resting on the wings stored in the factory.  We then used the +/- tolerances as the upper control limits.  We then gathered data and plotted the stringer locations as measured to try to determine if there were any significant common trends (i.e. at a particular stinger number, at  certain coordinates in a wing, etc.)

Unfortunately I left that group shortly thereafter and I lost track of the final outcome.  At that time six sigma was not nearly as accepted as today, so I don't think we even knew what else to do and how to go into much greater analysis.  But I gained a quick indoctrination into six sigma and know it can show how to improve a process or product if used effectively.