Lean Six Sigma evolved as a combination of the Lean methodology and the Six Sigma methodology.
Six Sigma grew out of Total Quality Management (TQM) and Statistical Process Control (SPC), with a focus on reducing process variation and reducing defects to fewer than four per million opportunities. Lean developed from the Toyota Production System (TPS) and focused on eliminating waste and increasing process speed. Both methodologies have an emphasis on quality as defined by the customer.
Maytag and Allied Signal both began combining the two frameworks in the late 1990's, combining techniques for projects and cross-training employees in the principles and tools of both methodologies. Lean Six Sigma is now spreading throughout manufacturing and service industries, including companies such as GEICO, Best Buy, Xerox and even in health care organizations.
How to Implement
There is now some controversy as to how Lean Six Sigma should be implemented. Some experts support development of both Lean teams and Six Sigma teams, which take on different projects depending on the type and expected time frame. However the integration of skill sets into single process management teams is becoming more popular.
Six Sigma methods, particularly the DMAIC process improvement framework, is employed when the cause of a problem is not clear and the solution for making improvements is not known. DMAIC projects tend to be fairly long-term projects due to the detail involved in each systematic phase. Lean, on the other hand, is preferred when short-term gains are expected. In another perspective, one expert explains that, "Lean creates the standard and Six Sigma investigates and resolves any variation from the standard" (Breyfogle, 2001).
One of the main tools for Lean is Value Stream Mapping (VSM), which is related to the process mapping technique used in Six Sigma. VSM includes clarifying the customer view of quality, delineating the steps in the process being studied, and determining which steps add value and which do not. Steps that are value-added (VA) are those that the customer would pay to have included, whereas others are deemed non-value-added (NVA). The process is then reworked so that it flows smoothly without waste. In this context, waste can take several forms including rework, excess inventory, delays and unnecessary transportation.
Another concept of Lean that is incorporated into Lean Six Sigma is the idea of customer pull. The manufacturing process, for instance, should be driven by customer demand in terms of timing and quantity, minimizing delays, inventory, and other forms of waste.