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Quality Scan: Six Sigma Isn't Lean






Lately I have been seeing the term Lean Sigma appear more and more, and I'm getting more and more confused. You see, I know what Six Sigma is, and I know what Lean is, but how do you combine the two?

Six Sigma is a mathematical, data-driven approach for the detection of defects in any process. The six sigma measurement system describes quantitatively how a process is performing. To achieve 6, a process must not produce more than 3.4 defects per million opportunities. A six sigma defect is described as anything outside customer specifications. A six sigma opportunity is thus the total quantity of chances for a defect. This description can apply to any process—manufacturing or transactional—and to either products or services. The objectives of six sigma methodology are the mathematical analysis of variables present in any process, quantification of these variations, and the ability to predict the possibility of errors or mistakes happening. It's a great, powerful tool!

On the other hand, Lean is the psychological belief in people being able to rationally make decisions based on training and the use of appropriate tools. It is the synergy that develops when people work as a team instead of individuals; it is the desire for recognition and rewards that are ego-driven. It is the conviction that Continuous Improvement is a way of life, not just a statement read from a sign on the wall.

Most Lean initiatives and ideas are based on the Toyota Production System, which has 14 fundamental concepts:

  • Genchi Genbutsu Shugi. (Practical hands-on experience is valued over theoretical knowledge.)
  • Visual Management. (Charts, graphs, pictures and signs.)
  • Normal or Abnormal. (Quality check sheets track performance and are graphed to show variations.)
  • Total Productive Maintenance. (The inclusion of operators in the maintenance program.)
  • Kaizen. (Work operational kaizen, equipment kaizen, and process kaizens.)
  • Find Problems. (Analysis of data to find problems. This is where six sigma may be used.)
  • Leadership by Example. (Workers will follow good leaders not those that only tell them what to do.)
  • 5S. (Sieri, sort; Seiton, straighten/arrange; Seiso, scrub and shine; Seiketsu, standardize and stabilize; Shitsuke, sustain)
  • Safety, (First priority of all workers.)
  • Cross-train. (Be able to perform multiple tasks in the workplace.)
  • Self-education. (Team members strive to attain a higher level of education and skills.)
  • Teams. (Basic concept that teams are more productive than individuals.)
  • Communication. (At all levels, all the time.)
  • Quality Circle. (Plan—Do—Check—Act routine.)

In addition to the basic concepts, there are the Seven Basic Tools, which are: histograms, Pareto diagrams, cause and effect diagrams, run charts, scatter diagrams, flow charts, and control charts.

These are the tools which the strongest, best-run, most profitable companies use. When volumes are large, then six sigma is used to drill down deeper to analyze a process even better, but nowhere is six sigma used as an operating philosophy, as is the Toyota Production System.

In my home I have a Persian cat and a Poodle dog; each does its own thing. My dog barks and chases balls, the cat purrs and sleeps a lot. Combining Lean and six sigma would be like cross-breeding my cat with my dog and trying to get a Catoodle. There is no need to have a Catoodle, it serves no purpose.

In most of the attempted cross-breedings, an attempt is made to add reference to six sigma by including numbers or simple formulas that are supposed to make you think that somehow those numbers are related to six sigma analysis, and will help you attain six sigma. In reality, the Toyota Production System already has provisions for collecting all the right numbers you need to be successful. And since six sigma needs high quantities to work, how can Lean Sigma work when the quantities are small? It can't!

Six Sigma is not a stand-alone philosophy which the average worker on the floor can embrace, like the Toyota Production System. It's a management tool for a very select few, certainly not worth the effort required to train an entire workforce on how to use or apply it. Like the Catoodle, there is no Lean Sigma.


This article was first published in the July 2006 edition of Manufacturing Engineering magazine.

Published Date : 7/1/2006

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