Quality function deployment (qfd)
Step 4—Develop an Interrelationship Matrix between HOWs
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Step 4—Develop an Interrelationship Matrix between HOWsThe roof of the house of quality, called the correlation matrix, is used to identify any interrelationships between each of the technical descriptors. The correlation matrix is a triangular table attached to the technical descriptors, as shown in Figure 11–9. Symbols are used to describe the strength of the interrelationships; for example, A double circle represents a strong positive relationship. A single circle represents a positive relationship. A single X represents a negative relationship. A double X represents a strong negative relationship. The symbols describe the direction of the correlation. In other words, a strong positive interrelationship would be a nearly perfectly positive correlation. A strong negative interrelationship would be a nearly perfectly negative correlation. This diagram allows the user to identify which technical descriptors support one another and which are in conflict. Conflicting technical descriptors are extremely important because they are frequently the result of conflicting customer requirements and, consequently, represent points at which tradeoffs must be made. Tradeoffs that are not identified and resolved will often lead to unfulfilled requirements, engineering changes, increased costs, and poorer quality. Some of the tradeoffs may require high-level managerial decisions, because they cross functional area boundaries. Even though difficult, early resolution of tradeoffs is essential to shorten product development time. An example of tradeoffs is in the design of a car, where the customer requirements of high fuel economy and safety yield technical descriptors that conflict. The added weight of stronger bumpers, air bags, antilock brakes, and the soon-to-come federal side-impact standards will ultimately reduce the fuel efficiency of the car. In the case of conflicting technical descriptors, Taguchi methods (see Chapter 14) can be implemented or pure common sense dictates. 
Figure 11–9 Adding interrelationship matrix to the house of quality EXAMPLE PROBLEM Continue the development process of designing a handlebar stem for a mountain bike (see previous Examples) by adding the interrelationship matrix to the house of quality. The interrelationship matrix is constructed by assigning symbols or numbers to represent the degree of correlation (positive or negative) between each of the technical descriptors. For instance, the interrelationship between the technical descriptors of titanium and sand casting would be would be a strong negative (-9) correlation because a titanium part would never be sand cast. Conversely, the interrelationship between the technical descriptors of aluminum and die casting would be would be a strong positive (-9) correlation because aluminum is usually die cast. The interrelationship matrix for designing a handlebar stem for a mountain bike is shown in Figure 11-9. Empty spaces indicate that no correlation exists, either positive or negative. Download 0.94 Mb. Share with your friends:
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