They have often been considered alternatives, and sometimes antagonists. But in recent years, it has become clear that a synthesis of the two produces a hybrid more vigorous than either is alone.

“The dominant trend in Six Sigma is Lean Six Sigma,” observes Hung‑da Wan, of the University of Texas at San
Antonio’s Center for Advanced Manufacturing and Lean Systems ( http://camls.utsa.edu). “Lean Six Sigma combines the philosophy of Lean Manufacturing with the structured tools of Six Sigma. It is a great integration.”

Tim Donaldson, president of the Donaldson Group ( www.donaldsongroupinc.com ), Wayzata, Minn., a firm that provides services to accelerate profitable growth, agrees, “Today’s economic realities drive organizations to improve quality and reduce costs,” he says. “It is a good time for companies to add Lean Enterprise tools to their Six Sigma repertoire.”

Lean Manufacturing , much of which came out of the Toyota Production System , focuses on improving performance by optimizing the flow of an industrial process. Lean’s mechanism is waste reduction. When all waste has been eliminated, only things that are necessary remain. Flow has the common meaning of throughput, which includes speed, but also conveys the notion of efficiency. And there is an additional subtlety here. In the context of Lean, flow in the factory is explicitly linked to demand in the marketplace. The industrial process is adjusted so that flow is initiated by market pull, not by management targets. Further, cooperative links to factory suppliers are established so that optimal flow can be sustained. These external links make Lean inherently systems‑oriented and responsive to the outside world.

Six Sigma originally focused on improving performance by reducing the number of product defects introduced during shop floor operations. Six Sigma’s mechanism is the scientific method, adapted for use in industry as define, measure, analyze, improve, control (DMAIC).

Practitioners of Six Sigma such as Tim Donaldson soon realized, however, that many product failures resulted from design deficiencies, and that any effective quality program would have to encompass engineering as well as production. For example, says Donaldson, a company that wants to improve throughput for a work center can use DMAIC to define the project and map its processes and current performance statistics. It can also use Single Minute Exchanges of Dies from the Toyota Production System to reduce changeover time, thus creating more capacity and throughput.

Lean Six Sigma

“Lean and Six Sigma have many of the same goals, but tackle problems from different angles,” says Wan. “Six Sigma is highly structured, and Lean is kind of loose. Six Sigma addresses the quality side that is very statistically oriented, while Lean is more of a fundamental philosophy. When we integrate them, the result is a more comprehensive solution.”

The result is more than the sum of its parts. Lean is not well suited to bring a process under statistical control, whereas Six Sigma is. Six Sigma has a hard time dealing with overall process speed, whereas Lean is designed to do so. Together, Lean and Six Sigma synergistically reduce the cost of complexity.

Not only are Lean and Six Sigma complementary, but together they provide good hooks to other relevant knowledge. Design for Six Sigma, for instance, and the “big picture” perspective of Lean make an easy connection to systems engineering via product lifecycle management. And Lean’s emphasis on vendor relationships leads directly to supply-chain management.

The emergence of Lean Six Sigma as a distinct methodology has significant, desirable implications for process improvement—for solving problems that must account for complexity, quality and risk. “It is a natural trend,” Wan concludes.

Marty Weil , martyweil@charter.net, is a freelance writer who covers manufacturing and automation.

Donaldson Group
www.donaldsongroupinc.com

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