Quality function deployment – DDL Wiki

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Quality Function Deployment (QFD) is a structured method of defining customer needs or requirements and compares them with product specifications or requirements. In short, it is a way to capture “the voice of the customer.” Once the customer specifications are recorded using a variety of methods, the customer requirements are plotted in a weighted matrix and the interactions between those requirements and product specifications/requirements are easily visible. This provides an understanding of what elements of the product satisfy the needs of the customer, and thus helps ensure a product of high quality .

Capturing the Voice of the Customer

Before any product planning can fully go underway, designers need to survey customers and stakeholders so that they can understanding the requirements necessary for designing a product of high quality. The voice of the customer can be captured in a variety of ways, including surveys, discussion, field research, observations, etc. Marketing programs and discrete choice analysis are analytical methods of determining the utility and thus importance of these product attributes in the eyes of the customer, which aids in the QFD process when the interaction of customer requirements and product requirements is considered during the product planning stage. Once enough surveying methods are recorded, a list of customer attributes and requirements are composed and weighed in terms of importance.

Product Planning Matrix

A product planning matrix or “house of quality” is a matrix that organizes customer requirements and product design requirements into a structure and analyzes the interactions between those requirements. The specific customer requirements are weighed in terms of importance, the strength of the interactions are inputted into the matrix, and the result is a rating of importance and target specification for the product requirements. The matrix may also include an evaluation of competitor products in terms of customer requirements so that a designer can establish where they rank among competitors (When analyzing competition it is necessary to produce more surveys and field research). Below is an example of a product planning matrix (Figure 1).

Figure 1: Product Planning Matrix

Product Planning Matrix Components

Customer Requirements: The customer requirements are listed to the left along with their importance in the next column. This column is a list depicting the “voice of the customer” which was captured in the surveys and research done. The column numerically valuing the importance of each requirement is specified by the constructor of the matrix.

Product Design Requirements: The product design requirements are listed as the column headers of the matrix. They are established to respond to the customer requirements and are organized into categories that are related to the requirements. In order to fully exercise the advantage of this matrix, the design requirements should be measurable, meaningful, and globally conveyed. It is important to make sure that all the requirements are related to customer requirements and that all requirements have been addressed appropiately. It is not helpful to make eight requirements that measure up to two customer attributes and have only a few relate to the rest.

Relationships: The key on the upper right of the example describes the measurements for relationships between customer and product design requirements. In this example, there are three degrees of relationships: strong, moderate, and weak. The matrix then plots the relationship values in each cell of the customer requirements vs. product design requirements matrix. Relationships of requirements that are not related are left blank.

Interactions: The Interactions are listed on the top of the row of product design requirements. They describe the importance of interactions between each of the product design requirements with respect to themselves. It is also notable that this listing of interactions is in the form of a triangle which resembles a roof to a house, thus explaining the nick name “house of quality.” The key in the upper left of the example describes the measurements of the interactions. In this case there are four values: strong positive, mid positive, mid negative, strong negative. The cells of the triangle are filled in accordingly (non-related interactions are left blank). It is important to understand the value of these interactions. Positive interactions are optimal because it means that both product requirements can be implemented without trade-offs. However, too many positive interactions can mean redundancy in the product design requirements. The negative interactions are the key ones to look for because the trade-offs will have substantial effect on the quality of the product design depending on the weight of the customer requirements and the relationship between customer and product requirements.

Competitive Evaluation: The right side column evaluates the current product against competitor products in terms of customer requirements. This chart can be advantageous in terms of seeing strengths and weaknesses in the competitors and establishing breakthrough attributes of your product to result in an optimal market entrance.

Technical Evaluation: The fourth to bottom row states the relationship between the current product and the competitors in terms of the product design requirements. This is used in junction with the competitive evaluation column to help determine the competitor’s strength and weaknesses and establish breakthrough attributes of your product to close the gap with competitors.

Target Value: Preliminary target values for the product requirements.

Technical Difficulty: A rating of difficulty for each product design requirement. Though this is not weighted with the relationship values, it is important to realize which design requirements are more difficult to accomplish when analyzing product costs and time management in future steps.

Importance Ratings: These values are the total values of the product between the weight factor and relationship value for each column of product design requirements. The value of the relationship is user defined (for example, strong could be 5, moderate is 3, and weak is 1).

Once the product planning matrix is completely constructed, one can analyze the components and calculations of the matrix to develop product developing strategies. What trade-offs need to be made, and should the target values be adjusted depending on the technical difficulties? These are a few questions to consider when analyzing the matrix.

Future Steps: Concept Selection

Once the product planning matrix is completed and developing strategies are considered, one may begin to further analyze the quality of product concepts. These concepts would be compared in a concept selection matrix and given normalized values for each product design requirement taken from the product planning matrix. Each concept would have different values (for example, one concept may have product requirement A and B with a high and low relationship value respectively, and another concept may have product requirement A and B with a medium and high relationship value respectively). The importance ratings for each product requirement (taken from the product planning matrix) would be included in this matrix and the product of relationship values with importance ratings would be added up for each concept. Therefore one may see the overall score for each concept and use that to base which concept would have a high quality.

Figure 2: Concept Selection Matrix

IMPORTANT
While both the product planning matrix and concept selection matrix are helpful tools goal towards successful product selection, it is not recommended to base product design judgement entirely on these tools. It is important to consider feasibility of concept designs, market costs and profit analysis, fatigue, sigma six and statistics of failure, manufacturing processes, failure modes and effects analysis (FMEA) , and other third variables that may affect the decision making process in product design. These tools are simply available to provide guidelines, organization and direction towards making these design decisions.

References

• Crow, Kenneth, “CUSTOMER-FOCUSED DEVELOPMENT WITH QFD” , [1]
• Ullman, D.G. (2003) The Mechanical Design Process, McGraw Hill.