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May 3, 2010


In lean manufacturing there are many techniques but now we will talk about taguchi methods (equation).In 1989, the Japanese engineer, Dr. Genichi Taguchi was awarded the prestigious Purple Ribbon by the emperor of Japan for his contribution to the development of industrial standards.

Taguchi, unlike other leading quality gurus, focuses more on the engineering aspects of quality rather than on management philosophy or statistics. He emphasises the importance of designing quality into products and processes rather than depending on inspection after manufacture. A distinctive feature of Taguchi's approach to quality lies in the application of statistical methods, not to quality control where they have already found wide application, but on improving products and processes (Naylor, 1996). He applied statistical methods in novel ways to:

1- Make products less sensitive to variations in their components and in the environment in which they are made.
2- Improve reliability.
3- Improve testing procedures.
Taguchi methods employ statistical techniques to evaluate the combined effects of environmental variations and manufacturing tolerances on the performance of the product. Dr. Taguchi is widely recognised for adding greatly to our understanding of the importance of properly designed engineering experiments in quality improvement and is therefore often considered the most important contributor to quality engineering concepts and methods.

Quality Loss Function
Traditional definitions of quality usually refer to the conformance of the product or service to requirements. Dr. Taguchi, however, defines quality as: “…..the loss a product causes to society after being shipped, other than any losses caused by its intrinsic functions.” Taguchi attempts to quantify this loss imparted to society by means of his Quality Loss Function (QLF). The QLF is a mathematical function used to calculate the loss to society in financial terms. Investigation of the QLF reveals that any deviation of the quality characteristic from its optimal value results in increased loss to society, whether or not the tolerance limit has been exceeded.
Taguchi proposed the Quality Loss Function to underline the need to aim close to the target (Naylor,1996). It estimates the total cost in the long run of poor quality resulting from a product moving away from exactly matching the target value. The cost covers all losses from the time the product is delivered, including those incurred during use and the consequent effects of failure.