Monthly Archives: March 2012

Process Stability – it all starts here.

Many of us have used the common statistical tools of ppk and cpk for determining how capable our processes are. Many times we blindly input our raw variable data into a statistical software such as Minitab and admire our statistical genius without first making sure our process producing the data is stable. Some of the Minitab tools (capability 6 pack) will tell us if our data is stable via the probability plot and the control chart functions, but many do not take this step first of actually looking at the data with these tools. In a nutshell unless your process is stable the statistical probability behind the ppk and cpk formulas are not valid with non stable data.

Lean implementation has some similarities with this example in that we should first install a stable, repeatable process before we can begin to realize the true benefits that Lean or the Toyota production System (TPS) offer us with other tools in the toolbox like kaizen. The “House of Lean” is built upon the premise of “stability”. If we do not first install and develop a process that is done the same way every time, using the same repeated steps and same tools we cannot truly expect to reap the benefits. If our process being studied is not stable and repeatable how can we expect to analyze it to find the areas for improvement. That is why a true Lean initiative (in my opinion) should be started with standardization, 5S and value stream mapping (current state). Only once we have a stable process can we move onto the other tools available such as Just-in time (kanban), quality at the source, poka-yoke (mistake proofing), etc… Once these are installed the kaizen process can be repeated again and again to bring our process to higher and higher levels.

Stability (as is the case in many areas in life) is the key. If your day (work or home) is a chaotic frenzy then you cannot hope to focus on the proactive areas.