Genichi Taguchi Robust Design and Loss Function

Question 1

Taguchi Robust Design Principles

Answer 1

Taguchi demonstrated robust design from the below three method concepts:

1. Concept Design
2. Parameter Design
3. Tolerance Design

Question 2

Taguchi Robust Design Approach

Answer 2

Robust design is the key development in design process during recent years. Robust approach in design is key aspect as it produces reliable design both during manufacturing and also during product use.

The basic concept of robust design is that parameters control that makes designs strong enough that does not cause failure due to random “noise.”

Processes or products are controlled by various factors to get the desired response:

1. Signal factors
2. Control factors
3. Noise factors

Question 3

Signal Factors

Answer 3

The signals used to get the desired response

E.g. pressure valve setting to get the required air pressure in the line

Question 4

Control Factors

Answer 4

These factors produce the response based on noise in the process and also these are controlled by the designer.

e.g. Heat shrinks or thermo couples will respond based on the heat generated in the process. Sometimes these factors add cost to the design hense these are also called Tolerance Factors

Question 5

Noise Factors

Answer 5

These are random events in the process, only mean and variance can be predicted but are not controllable by designer.
E.g. Voltage fluctuation, air pressure variation, etc.

The noise factors impacts the response and leads to errors hence designers to focus on appropriate control factors to produce maximum response to signal factors

3 Noise Categories:

1. External Noise: Variations in the environment where the product is used
2. Deterioration Noise: Wear and tear inside the unit
3. Internal Noise: Deviation from target values

Question 6

Taguchi Robust Design Principles

1. Concept Design

Answer 6

A process of selecting product or process based on competing technologies, customer, price or any other important considerations. Moreover the most advantage of this method is that organizations can product high quality products with low production costs.

Question 7

Taguchi Robust Design Principles

2. Parameter Design

Answer 7

• Refers to the identification of control factors for the process and also to determine the optimal (target) level of each factor.
• Initially in this method design is developed using low cost parts and manufacturing methods. Afterwards response is optimized to minimize the noise.
• Furthermore, the ultimate goal of this method is to find the efficient process (functionality robust) and service design.

Question 8

Steps to perform Parameter Design

Answer 8

1. Identify signal factors and noise factors and also respective ranges
2. Select as much as possible control factors and also levels of the factors, and then dispense these levels to suitable orthogonal arrays (to identify main effect with minimal number of runs). Functionality can be improved by adjusting different levels of control factors.
3. Determine the S/N Ratio, Signal to Noise
4. Identify the optimal condition from the experimental data, for this maximum S/N ratio to be used for each level of control factors.
5. Finally, perform real production runs.

Question 9

Signal to Noise (S/N) Ratio

Answer 9

An equation that indicates the magnitude of an experimental effect above the effect of experimental error due to chance fluctuations.

• r is the measurement of magnitude of input signal
• Sβ sum of squares of ideal function
• Ve mean square of nonlinearity
• VN error term of linearity and nonlinearity

Question 10

Taguchi Robust Design Principles

2. Tolerance Design

Answer 10

Step beyond Parameter Design as it impacts the budget such as material change, equipment, etc. Apart from economics, it also considers the other important factors like constraints due to safety factor, material property, an and design choice etc.

In other words, Tolerance design maintain the balance between quality and cost design. Thus, Tolerance design creates metrics allowing designer to compute the tolerances that can be adjusted to meet customer needs and expectations while delivering a cost effective product.

Question 11

Tolerance

Answer 11

-An acceptable limit of deviation in a parameter’s dimension or value and this must be determined for all system components.

The maximum and minimum limit values a product can have and still meet customer requirements.

Question 12

Taguchi’s Quality Imperatives

Answer 12

1. The basic quality losses are due to poor design
2. For any new products, plan experiments to get the parameter targets
3. Consider customer environment conditions to develop robust products
4. Robustness is a function of product design
5. Quality losses are loss to society
6. Robust products have a strong signal to noise ratio
7. Manufacture the products that are consistent by reducing variation
8. Tolerances should be set prior to manufacturing and also Quality Loss Fuction can be measured

Question 13

Quality loss function

Answer 13

A parabolic approximation of the quality loss that occurs when a quality characteristic deviates from its target value.

• The quality loss function is expressed in monetary units: the cost of deviating from the target increases quadratically the farther the quality characteristic moves from the target.
• The formula used to compute the quality loss function depends on the type of quality characteristic being used. The quality loss function was first introduced in this form by Genichi Taguchi.

Question 14

Taguchi’s Loss Function