Taguchi's Robust Design Method

Taguchi’s robust design method:

Taguchi’s methods are used for product quality improvement. Earlier methods relating to quality assurance of a product depended on inspection of the products as and when they rolled out of the production process and those products which did not meet the product specifications or standards were rejected. As per Taguchi, product quality cannot be determined upon inspection alone rather quality has to be embedded as a design into the product right from the production process.
Robust design is a product improvement engineering technique in research and development phase so that high quality products can be produced quickly and at a low cost. The concept behind robust design is quality improvement of a product, minimizing

It represents a paradigm shift to the way which manufacturers consider whether the product is of appropriate quality or not. It is very different from the traditional approach which used step function to ensure that performance lies within the upper specification limit and lower specification limit.

Taguchi’s quality loss function is expressed in terms of quadratic relation:
L = k (y - m)^2.
Where y and m are the nominal values of the product specifications.
K is a constant which depends on the cost of the specification limits.

This function identifies the deviation of the parameter from the specification limits which contributes to the deteriorating performance of the product eventually resulting in a loss to the customer. The basis is that the product engineers have a sound knowledge of the nominal size of the specification. The usual upper and lower specification limits for the tolerance of a design parameter can be changed to a continuous function representing any other parameter value than the nominal as a loss. The loss function mentioned is referred as Nominal is

Tolerances of factors having the greatest influence on variation are adjusted after the parameter design stage. Engineers associate quality with better tolerances but strict tolerance limits increases the cost of the product or process as it requires better components, parts, materials and machinery. Taguchi’s approach allowed quality improvement without the need of better parts or materials which makes it possible to decrease cost and improve quality at the same time.

Taguchi’s Parameter Design Approach:

There are two types of factors which affects product’s functional characteristics i.e. the noise factor and the control factor.

Noise factors: These factors are impossible or expensive or difficult to control. There are three types of noise factors: inner noise, outer noise and between product noise. These are responsible for causing a product’s performance to deviate from its expected value. So parameter design identifies settings of the control factors that make the product insensitive to variations in the noise factors and hence making the product robust without eliminating the variation causes.

Control factors: These factors can easily be controlled such as cycle time, material choice, or temperature in an injection molding process. Examples of Noise