There are many parallels between the Six Sigma and lean philosophies. Both are focused on the process and process improvements. The techniques of each one complement the other and provide enhanced results.
Comparing the Two Methodologies
Six Sigma focuses on improving existing processes to give results that are essentially defect‐free. A CTQ characteristic or CTQ that reaches the Six Sigma level will have only 3.4 DPMO. There are two ideas at work here: first, preventing defects is more cost effective and reduces the need for inspection and rework; second, all products and services have multiple CTQ characteristics. If each CTQ reaches the six sigma level, then the product or service will work as the customer expects.
The reality is that Six Sigma can lead to an improved process with mechanisms to maintain the improvements, but there are still inefficiencies in the process. All of the benefits of eliminating non‐value‐added steps may not yet be evaluated or addressed. Also, the flow throughout an organization that is integral to the pull systems of lean may not have been considered. What we know today as lean manufacturing began with the concepts that Ford Motor Company pioneers at the Rouge facilities in Michigan. Based on the idea of raw steel coming in and finished cars going out, the Rouge facility had taken production to new heights. Then Toyota took this idea a step further. The brilliance of lean was to move beyond craft and mass production techniques to short runs with essentially no setup time required. With short runs and small batch sizes, quality problems would be noticed immediately and there would be no backlog of interior parts or materials. Small batches made quality immediate visible and led to quality improvements (see Table 8.4).
Waste of time, waste of materials, and the waste of money – all drive the lean concepts. A number of offshoots of the original lean ideas have emerged. Eliminating wasted efforts by removing non‐value‐added steps in a process has led to VSM. Eliminating excess inventory and small batches has led to a “pull” system of production. All of the lean efforts are directed toward removing wastes of various types in the production systems. A lean approach opens up the opportunity to achieve reductions in time to market and in costs while improving product quality.
Both concepts focus on the process. Lean techniques may well be the ones to use to achieve the improvement in quality and cost reduction that are the objectives of the Six Sigma initiative. Six Sigma may well provide the statistical techniques that will take the lean initiatives to the next level. They both are critical and if orchestrated in concert can be much more effective than either one individually (Snee and Hoerl 2003).
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