Eliminating Constraints, Enhancing Flow, Improving Quality (ToC, Lean, Six Sigma)
Robert Spector has married the Theory of Constraints to Lean and Six Sigma in his article. The Theory of Constraints is a continuous improvement strategy developed by Eliyahu Goldratt (www.goldratt.com). ToC is used to identify key leverage points within a production or service value stream. These constraints may be resources, policies, markets or vendors which limit the performance of the value stream relative to its goal. Dr Goldratt uses five focusing steps to describe the implementation of the ToC process: Identify the constraint within the value stream; Decide how to exploit it, Subordinate everything else to this decision; Elevate the value stream constraint; and Loop. So when Spector says we should focus first on throughput improvement, ToC is a valuable tool to accomplish this.
Monroe's article then addresses value streams broadly. This follows Spector's advice to focus on inventory reduction and recognizes inventory's place as one of the most pernicious of the Lean wastes. GP Deltapoint recognizes eleven forms of waste: Complexity, Labor, Overproduction, Space, Energy, Defects, Materials, Idle Material, Time, and Transportation (Their convenient mnemonic is "Hold all waste in a CLOSEDMITT").
If we follow Monroe's methodology, we will have an excellent understanding of the constraints within the target value stream. Six Sigma tells us that these constraints may be causes of performance that does not meet average target levels or of performance that suffers from excess variability (every process suffers from variation in "noise" inputs: what is critical is to make the process robust against this variation and control the remaining ones). Lean gives us specific tools to improve flow and reduce waste. Together, ToC, Six Sigma and Lean enable us to pinpoint areas for improvement, elucidate root causes for missing customer needs, test improvement ideas, implement them and then hold the gains, preventing the backsliding that Spector deplores. Too often, practitioners hew to one of the improvement methods alone, missing the opportunity for a powerful coherent, robust approach that uses all these tools and that will stand the test of time.
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