29-12-2012, 03:17 PM
SIX SIGMA
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SIX SIGMA
Seminar Report on Six Sigma
Amey P. Deshmukh
WHAT IS SIGMA?
SIGMA is a term used in statistics to represent standard deviation, an indicator of the degree of variation in a set of a process.
WHAT IS SIX SIGMA?
Six Sigma (6σ) is a business-driven, multi-faceted approach to process improvement, reduced costs, and increased profits. With a fundamental principle to improve customer satisfaction by reducing defects, its ultimate performance target is virtually defect-free processes and products (3.4 or fewer defective parts per million (ppm)).Therefore, defects or problems in the processes have been removed to the point where the quality of the output is near perfect. Six Sigma is seen as the ultimate goal in achieving near perfect processes through continual improvement.
NEED FOR 6S:
Specification limits are the tolerances or performance ranges that customer’s demand of the products or processes they are purchasing. Figure 1.8 illustrates specification limits as the two major vertical lines in the figure. In the figure, LSL means the lower specification limit, USL means the upper specification limit and T means the target value. The sigma quality level (in short, sigma level) is the distance from the process mean () to the closer specification limit. In practice, we desire that the process mean to be kept at the target value. However, the process mean during one time period is usually different from that of another time period for various reasons. This means that the process mean constantly shifts around the target value. To address typical maximum shifts of the process mean, Motorola added the shift value ±1.5σto the process mean. This shift of the mean is used when computing a process sigma level as shown in Figure 1.10. From this figure, we note that a 6σquality level corresponds to a 3.4ppm rate. Table 1.1 illustrates how sigma quality levels would equate to other defect rates and organizational performances. Table 1.2 shows the details of this relationship when the process mean is ±1.5σshifted.
TOOLS USED FOR SIX SIGMA:
The most common tool used for Six Sigma improvement is the Define-Measure-Analyze-Improve-Control (D-M-A-I-C) cycle. This approach focuses on ensuring that the improvement is clearly defined and measured, through a data-driven and disciplined approach. Data is analyzed to identify problems and the improvement is consolidated through process controls.