Total Quality Management

September 9, 2009

Quality Function Deployment

A key to improving quality through TQM is linking the design of products or services to the processes that produce them. Quality Function Deployment (QFD) is a means of translating customer requirements into appropriate technical requirements for each stage of product or service development and production. Bridgestone Tire and Mitsubishi Heavy Industries originated QFD in late 1960s adn early 1970s when they used quality charts that take customer requirements into account in the product design process.

In 1978 Yoji Akao and Shigeru Mizuno published the first work on this subject, showing how design considerations could be “deployed” to every element of competition. The core of this approach is a chart called house of quality, which is a conceptual map for inter-functional planning and communications.  See the following chart that shows a house of quality chart for improving the quality of a car door.

House of Quality Chart

House of Quality Chart

The above chart was constructed by answering the following six questions:

  1. Voice of customer: What do our customer need and want? Customers were asked to list attributes of car-door quality they felt were important. Customer attributes were grouped into two categories-“easy to open and close the door” and “isolation”-as shown in the above chart. The relative importance to the customer is listed as a percentage to the right of each attribute.
  2. Competitive analysis: In terms of our customer, who well we are doing relative to our competitors? Customer perceptions of our car doors and those of our competitors for each attribute are listed on the right-hand side of the chart. For example, our car has an advantage over the other cars with respect to “no road noise,” but nine of the cars has advantage regarding “stay open on a hill.” The evaluations provide a place to start looking for ways to gain an advantage over the competition.
  3. Voice of the engineer: What technical measures relate to our customers’ needs? The engineering characteristics that are likely to affect one or more of the customer attributes are listed along the top of the chart. The plus sign means that the engineers would like to increase the level that characteristic, and the minus sign mean that engineers would like to decrease the level. For example, our engineers would like to decrease the level. For example, our engineers would like to increase “road noise reduction” and decrease “energy to open the door.”
  4. Correlation: What are the relationships between the voice of the customer and the voice of the engineer? The nature of the relationship between customers’ needs ad engineering attributes needs to be specified. For example, reducing the amount of energy required to close the door will make closing the door easier, but increasing the door seal resistance will make closing the door more difficult.
  5. Technical Comparison: How does our product or service performance compare to that of our competition? Comparing our door with those of the competition for each engineering characteristics allows the technical difficulty of working on each one to be assessed. For example, our door requires the greatest energy to close (11 ft-lb) and the greatest peak closing force (18 lb). A scale of 1 to 5 (where a rating of 5 means most difficult) conveys the relative technical difficult of improving each dimension. In addition, the importance of each characteristic in responding to customer concern can be assessed. For example, “easy to close the door from outside” has high relative importance to customers and has a strong positive relationship with “reducing the energy to close the door” receives the highest imputed  importance (10 % points) of all the engineering characteristics. Estimated costs, again expressed as percentages, indicate relative importance. Finally,  in this step targets are assigned for the various engineering characteristics. Note that reducing the  “energy to clsoe the door” from 11 ft-lb to 7.5 ft-lb makes our car very competitive with the other cars. Other targets for the “open-close effort” category also were changed to improve the door.
  6. Trade-offs: What are the potential technical trade-offs? Note that no changes were targeted in the current measures of engineering characteristics relating to the category “sealing insulation.” The reason is that those engineering characteristics and the ones included in the “open-close effort” category have some strongly negative relationships. These relationships are depicted at the top of the chart. For example, though “increasing road noise reduction” would have a strong positive impact on “no road noise,” it would have strong negative impact on “reducing the peak closing force” and “reducing energy to close the door.” Because customers gave a low priority to “no road noise,” no adjustment were made to “increasing road noise reduction.

The house of quality method provides a way to set targets and debate their effects on product quality. Engineering uses the data to focus on significant product deisgn features. Marketing uses this input for determining marketing strategies. Operations uses the chart to identify the processes that are crucial to improving product quality in the eyes of the customer. As a result, the house of quality encourages inter-functional communication for the purpose of improving the quality of products and services.

Source: Operations Management: Strategy and Analysis, Fourth Edition, by Krajewski/Ritzman


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