Taguchi Methodology

Introduction

Taguchi’s methodology is a statistical innovative approach to total quality

management developed by Genichi Taguchi of Japan. When Japan began its

reconstruction efforts after World War II, it faced an acute shortage of good quality raw

material, high quality manufacturing equipment and skilled engineers. The challenge was to produce high quality products and continue to improve the quality under those circumstances. The task of developing a methodology to meet the challenge was assigned to Dr. Genichi Taguchi. Through his research in the 1950s and the early 1960s, Dr. Taguchi developed the foundations of Robust Design methodology and validated its basic philosophies by applying them in the development of many products.

The Methodology

Robust Design is an engineering methodology for improving productivity during research and development so that high quality products can be produced quickly and at low cost. Its use can greatly improve an organization’s ability to meet market windows; keep development and manufacturing costs low, and deliver high quality products. The fundamental principle of this methodology is to improve the quality of a product by minimizing the effect of the causes of variation without eliminating the causes. This is achieved by optimising the product and process designs to make the performance minimally sensitive to the various causes of variation. The quality of a product is measured in terms of these characteristics. Quality is related to the loss to society caused by a product during its life cycle. A truly high quality product will have a minimal loss to society as it goes through this life cycle. Taguchi recognizes the customer’s desire to have products that are more consistent, part-to-part, and a producer’s desire to make a low cost product. The loss to society is composed ofthe costs incurred in the production

process as well as the costs encountered during use by the customer (repair, lost

business, etc.). To minimize the loss to society is the strategy that will encourage

uniform products and reduce costs at the point of,production and at the point of

consumption. The primary goals of this methodology are :

1. Reduction in variation of product/ process design to improve quality and lower

the loss to society.

2. A proper product/ process implementation strategy, which can reduce variation.

Taguchi addresses quality in two main areas namely offline quality control and online

quality control. Offline quality control refers to improvement of quality in product/

process development stages. Online quality control refers to monitoring of current

manufacturing process to verify quality levels of product. The engineering optimisation of a process or a product is carried out in a three-step approach - system design, parameter design and tolerance design. In a system design, a basic functional prototype design including product design stage and process design stage is developed. In product design stage, the selection of materials, components and tentative product parameter values are determined. The process design stage examines processing sequences, the selection of the production equipment and the tentative process parameter values. Since system design is an initial functional design, it may be less than the optimum in terms of quality and cost. The objective of parameter design is to optimise the setting of process parameter values for improving quality characteristics and to identify the product parameter values under the optimal process parameter values. The tolerance design is used to determine and analyse the tolerance around the optimal settings recommended by parameter design. The tolerance design is required if the reduced variation obtained by The parameter design does not meet the required product performance. It involves

tightening tolerances on the product/ process parameters whose variations result in a

large negative influence on the required product performance. Tightening tolerances

means to increase cost. Thus the parameter design is the key step in Taguchi method to

achieve high quality without increasing cost. This approach includes the following steps:

1. Identify the quality characteristics and process parameters to be evaluated.

2. Determine the number of levels for the process parameters and possible

interactions between these parameters.

3. Select the appropriate orthogonal array and assign the process parameters

to the array.

4. Conduct the experiments based on the arrangement of orthogonal array.

5. Analyse the experimental result using Analysis Of Variance.

6. Select the optimum levels of process parameters. The objectives that can be achieved through parameter design are:

a. Determine the optimal parameters for a process or product

b. Estimate the contribution of each process parameter to the quality

characteristics.

c. Predict the quality characteristics based on the optimum process parameters. The two major tools used in this methodology are:

a. Signal to Noise ratio, which measures the quality

b. Orthogonal arrays, which are used to study many design parameters 

simultaneously.