Six Sigma is a business methodology of eliminating variation in a product. By eliminating variation, you eliminate defect, and every single product (be it a circuit board or car part) works perfectly, just like the one before it. But, eliminating variations is a long and involved process. Lean Six Sigma borrows tools from lean manufacturing, a practice of eliminating waste, and generally produces results more quickly.
Elements of Six Sigma
The Six Sigma methodology involves a five-step process called DMAIC: define/measure/analyze/improve/control. (The project planners define a challenge, measure the variations, analyze the results, improve the process and control the process to eliminate variation. The goal is to achieve at most 3.4 defects per million opportunities. This is a “rigorous and proven problem-solving approach” and a “data-driven approach to improving processes in a logical and methodical way,” notes the authors of "Rath & Strong’s Six Sigma Leadership Handbook." Thus, it is lengthy--a Six Sigma project may take several months to achieve sustained improvement. Finally, Six Sigma relies upon highly-trained and certified individuals, called Black Belts, Green Belts and so on.
Lean Six Sigma
Lean Six Sigma is a methodology based on the Toyota Production System or TPS, and chiefly targets eliminating waste. Lean Six Sigma recognizes seven forms of waste or “muda” (the Japanese word for waste). Defects are one form of waste; the others are overproduction, overprocessing, motion, transportation, inventory and waiting.
Lean Six Sigma leaders typically receive some training and certification, by recognized educators like the Lean Enterprise Institute and the Lean Learning Center, but the Lean Six Sigma process involves employees at every level to improve a process. The theory is that a machine operator is best suited to identify the waste surrounding that machine. Employees participate in kaizens (a sort of quality circle) to eliminate all the waste along the process of delivering to customers. Everything left over is meaningful and profitable work. Generally, the employees themselves are empowered to recognize the need for an improvement, and to make that change immediately.
Six Sigma as well is far more data-driven than Lean Six Sigma (and Lean). A Six Sigma level is, again, 3.4 defects per million; a Five Sigma level is 233 defects per million, and so on. As Michael L. George describes, every Six Sigma improvement requires "a measure to define the capability of any process." This reliance upon precise measurement is what makes the DMAIC process lengthy; a DMAIC project may require thousands of measurements before project leaders can analyze the results. Lean Six Sigma does not ignore measurement where it is required, but does not rely upon it absolutely.
Lean Six Sigma and Time to Delivery
Author Michael L. George in “Lean Six Sigma: Combining Six Sigma Quality with Lean Speed” advises that companies must first solve the quality problems that affect the customer. Time delays are chief among those problems, and Six Sigma typically does not target time delays, while Lean Six Sigma does. On-time delivery is quality, where the customer is concerned.
George describes how companies like Caterpillar, GE, Honeywell and Northrop Grumman have each implemented Lean Six Sigma for near-immediate process improvements. George described a Tier One supplier to the Ford Motor Company, which reduced manufacturing lead times from 14 to 2 days (thus, beginning work on every job 12 days sooner); and increased its profit margin by 12 to 19.6 percent.
Lean Six Sigma is not confined to manufacturing. The practices of design for Lean Six Sigma (DLSS) identifies defects in the design of any product or process, eliminating them before the product or service ever reaches a customer. And, service organizations including Bank One, Stanford Hospital and Starwood Hotels have also implemented Lean Six Sigma to provide faultless delivery of services.