Taguchi Concepts

The definition of quality given by the Taguchi methodology is customer orientated. Taguchi defines quality in a negative manner -
"Quality is the loss imparted to society from the time the product is shipped"
. This "loss" would include the cost of customer dissatisfaction that leads to the loss of company reputation. This differs greatly from the traditional producer-orientated definition which includes the cost of re-work, scrap, warranty and services costs as measures of quality. The customer is the most important part of the process line, as quality products and services ensure the future return of the customer and hence improves reputation and increased market share. In general, there are four quality concepts devised by Taguchi:
1. Quality should be designed into the product from the start, not by inspection and screening.
2. Quality is best achieved by minimising the deviation from the target, not a failure to confirm to specifications.
3. Quality should not be based on the performance, features or characteristics of the product.
4. The cost of quality should be measured as a function of product performance variation and the losses measured system- wide.
These concepts are detailed hereunder:
Quality Concept One
“At 99, it is still water. When 100, it becomes steam which can provide the power to pull a fully laden freight train”
- AnonQuality should be designed into the product from the start, not by inspection and screening. Quality improvements should occur during the design stages of a product or process, and continue through to the production phase. This is often called an "off-line" strategy. Poor quality can't be improved by the traditional process of inspection and screening (on the production line). According to Taguchi, no amount of inspection can put quality back into a product; it merely treats the symptom. Quality concepts should therefore be developed by the philosophy of prevention; problems are tackled at the source and not down stream. Taguchi emphasises that quality is something that is designed into a product, to make it robust and immune to the uncontrollable environmental factors in the manufacturing phase. This leads us to the next quality concept of minimising variation in a product.
Quality Concept Two
Quality is best achieved by minimising the deviation from the target, not a failure to confirm to specifications. The product should be designed so that it is robust or immune to uncontrollable environmental factors - eg. noise, temperature and humidity. This concept mainly deals with actual methods of affecting quality. Reducing variation is the key to improving quality. By specifying a target value for critical parameters, and ensuring manufacturing meets the target value with little deviation, the quality may be greatly improved.
Quality Concept Three
Quality is not based on the performance, features or characteristics of the product. Adding features to a product is not a way of improving quality, but only of varying its price and the market it is aimed at. The performance and characteristics of a product, can be related to quality, but should not be the basis of quality. Instead, performance is a measure of product capability.
Quality Concept Four
The cost of quality should be measured as a function of product performance variation and the losses measured system-wide. From given design parameters, the deviations from a target are measured in terms of the overall life cycle costs of the product. This includes costs or re-work, inspection, warrantry servicing, returns and product replacement. It is these costs that provide some guidance as to which major parameters need controlling

- Adapted from an article “Taguchi Methods” of Curtin University of Technology, http://kernow.curtin.edu.au/www/Taguchi/SECT3.HTM