Taguchi Methods for Manufacturing Process Control

What is the definition of quality? Responses frequently given include: "conformance to specifications," "zero defects," or "meeting client requirements."

Dr. Taguchi promotes a different, more holistic view of quality. Quality relates to cost and "loss" in dollars, not just to the manufacturer at the time of production, but to the consumer and to society as a whole.

What is "loss" and who pays for it? We usually think of loss as additional manufacturing costs incurred up to the point a product is shipped. After that, it is society, the client, that bears the cost or loss due to poor quality. When the client stops bearing this loss, the manufacturer is out of business.

Initially, the manufacturer pays warranty costs. After the warranty period expires, the client must pay for repair on a product. But indirectly, it is the manufacturer who will ultimately "foot the bill" as a result of negative client reaction and costs that are difficult to capture and account for such as:

• client complaints and dissatisfaction
• Time and money spent by clients
• Loss of client faith and loyalty
• Damaged reputation
• Eventual loss of market share

These intangible losses, along with other tangible losses (rework, defects, down time, etc.), make up the quality level of a product or process. In Taguchi Methods for Manufacturing Process Control, the first key is using Dr. Taguchi's Quality Loss Function to measure quality in monetary terms.

Once quality is expressed in monetary terms, the remaining task is to economically justify process control activities. Traditional implementation of process control focuses on "whatever it takes to achieve quality." As a result, cost of implementation often becomes excessive due to unnecessary (non-value added, just-in-case) activities. On the other hand, it indicates the lack of activities if the quality loss is greater than the process control cost. This application of Taguchi Methods focuses on how to cost-effectively conduct process control activities during the manufacturing stage. These methods help:

• Diagnose the health of a process
• Minimize production of defects
• Determine the optimal process checking intervals and control limits
• Establish optimal preventive maintenance systems
• Design the best process connection systems toward the goal of full automation in the future
• Rationalize inspection systems
• Achieve an equilibrium between being "quality conscious" and being "cost conscious"

All are evaluated using Taguchi's Loss Function, a cost-based analysis tool. In contrast to the early quality control methods, which are based on rather vague economic principles, "monetary evaluation" is a consistent and mandatory feature of Dr. Taguchi's methods.