Six Sigma and Lean manufacturing

Definition

Six Sigma is a structured management methodology which purpose is to improve processes efficiency and to eliminate processes defects.

It is a registered trademark of Motorola, "Inventor" of the method in 1987.

At first highly quality connoted, Six Sigma was first of all used on manufacturing industrial processes and then extended to any types of process. The actual context of globalization of the companies’ strategic vision leads to a more complex management where such a tool can be very useful.

In statistics, the Greek letter sigma σ represents the standard deviation. Six Sigma thus means « six times the standard deviation ». The term six sigma comes from the fact that if there is, for a given process, 6 times the standard deviation between the average performance and the worst acceptable performance, virtually no product will be produced outside wished performance.

Principles of Six Sigma

Six Sigma is a structured process based at the same time on customer needs (inquiries, polls) as well as on measurable and reliable data.

It is split generally into two sub processes:

• The DMAIC, for existing processes improvement to answer customer’s expectations.
• The DMADV, for new processes because existing processes cannot be improved to answer customer’s expectations.

DMAIC is the acronym of the following 5 stages:

• Define: the improvement objective based on customer’s expectations and company’s strategy.
• Measure: current process performance and gather necessary data for a future comparison
• Analyze: exhaustive search for the causes / effects relations.
• Improve: the process according to the progress tools and axes identified during the analysis
• Control: continuously to avoid that a difference turns into a default and to compare

The DMADV is the acronym « for Define, Measure, Analyze, Develop and Verify ».

The principle is the same but improvement is replaced by creation (Development).

A process created with this method is said to be "DFSS" (Designed for Six Sigma)

Six Sigma actors

The method six Sigma needs to implicate all the company’s hierarchy, but it also leans on proper human resources with a defined role:

• The Green Belt, are part-time staff on improvement projects management (approximately 25 %).
• Black Belt, full-time on the improvement (project management, Green Belts and the other Black Belts training). They have to master the whole method. They are specialized either in DMAIC, or in DMADV.
• The Master Black Belt, trainer of Blacks Belts, guarantor of the method respect, is the hierarchical manager of the Blacks Belts.
• Deployment Leader, in charge of the strategy establishment, training supports, budgets, etc…