Six Sigma

 SIX SIGMA

Prerequisite Discussion

Six Sigma is a set of techniques and tools for process improvement. It was developed by Motorola in 1986, coinciding with the Japanese asset price bubble which is reflected in its terminology.

Six Sigma seeks to improve the quality of process outputs by identifying and removing the causes of defects (errors) and minimizing variability in manufacturing and business processes. It uses a set of quality management methods, including statistical methods, and creates a special infrastructure of people within the organization ("Champions", "Black Belts", "Green Belts", "Yellow Belts", etc.) who are experts in these methods.

WHAT IS SIX SIGMA?

·        Six sigma stands for six standard deviation from mean (sigma is the Greek letter used to represent standard deviation in statistics).

·        Six sigma, similar to Zero Defect (ZD), is a philosophical benchmark or standard of excellence proposed by Philip Crosby.

·        Six sigma methodology provides the techniques and tools to improve the capability and reduce the defects in any process.

·        It was started by Motorola in 1987, in its manufacturing division.

·        Six sigma strives for perfection. It allows for only 3.4 defects per million opportunities (or 99.999666 percent accuracy). Here a defect can be anything from a faulty party to an incorrect customer bill.

·        Six sigma improves the process performance, decrease variation and maintains consistent quality of the process output. This leads to defect reduction and improvements in profits, product quality and customer satisfaction.

·        Six sigma incorporates the basic principles and techniques used in business, statistics and engineering.

The objective of six sigma principle is to achieve zero defects products/process. It allows 3.4 defects per million opportunities.

WHY DO WE NEED SIX SIGMA?

(Three sigma quality is not enough. Why?)

We know that, the three sigma quality, i.e., the natural variability (x ± 3s) is equal to tolerance (= upper specification limit – lower specification limit). It means, in normal distribution curve, only 0.27% of the output would be expected to fall outside the specifications limits.

The real meaning of 3s concept: A medium aircraft consists of 10,000 different parts. At 3s quality, 27 of those parts in an assembled aircraft would be defective. So three sigma quality level cannot be accepted as good enough quality level. So we have to increase the sigma level (i.e.,

reducing the number of defectives). In fact, even four sigma quality also not sufficient for the aircraft case. That’s why six sigma quality level is preferred than 3σ and 4σ quality levels.

CONCEPT

Six Sigma – A vision of quality which equates with only 3.4 defects per million opportunities for each product or service transaction. Strives for perfection.

DMAIC methodology provides a structured framework for solving business problems by assuring correct and effective process execution.

This methodology has 6 phases in which, in the case of Six Sigma, teams take total employee involvement approaches to complete the cycle of process management and use self-diagnosis skills to fulfill the goals of each phase.

DMAIC

DMADV

DMAIC – It is used for improving existing processes/products.

DMADV – It is applied to a new processes/products.

Example: (Need for Six Sigma)

• Aircraft consist 10000 different parts. 

• At 3 sigma level27 parts will be defective. 

• It cannot afford to fail 27 parts in million at 3 sigma level. 

• Similarly 1). Failure in surgery. 2). Testing of nuclear plant. 

• Therefore increased to six sigma level. (reduce the number of defects) 

Significance:

Each Six Sigma project carried out within an organization follows a defined sequence of steps and has quantified value targets, for example: reduce process cycle time, reduce pollution, reduce costs, increase customer satisfaction, and increase profits.