Written by Muqi Wulan
Quality Function Deployment (QFD) is a comprehensive method of matching customer requirements to engineering characteristics. As known, the core structure in QFD is the House of Quality (HoQ). Its most complete configuration is shown in Figure 1. There are 8 “Rooms” or sections to be filled in. Each labelled “Rooms”, from 1 to 8, is a structured, systematic expression of a product development team’s understanding of an aspect in the overall planning process for a new product or service. The information required for the HoQ is constructed in a step-by-step process, which consists of 8 steps.
Figure 1 – The HoQ converts customer requirements into engineering characteristics (Dieter and Schmidt 2009: 101)
In the previous material for Level 1, the former 4 steps have been presented.
Step 1: Identify customer requirements (CRs) in Room1.
Step 2: Identify engineering characteristics (ECs) in Room2.
Step 3: Build a correlation matrix of ECs in Room 3.
Step 4: Build a relationship matrix between CRs and ECs in Room 4.
The rest 4 steps for HoQ will be described in the following so that the whole HoQ is completed.
Step 5: Rank the importance of the identified ECs (CRs) in Room 5.
It is to determine which ECs are of critical importance to satisfying the CRs listed in Room 1. Those ECs with the highest rating are given special considerations because these ECs have the greatest effect upon customer satisfaction. The ranking has two categories: absolute importance and relative importance.
As in Figure 2, these values of importance are inserted in two columns – “Weight/Importance” is for the absolute importance of ECs, and “Relative Weight” for the relative importance. The absolute importance of each EC is calculated in two steps.
– Multiply the numerical value in the EC of the relationship matrix by the associated CR’s relative weight;
– Sum the results for each column and place the total in the row of “Weight /Importance” in Room 5. (e.g., 6.7×0+13.3×0+33.3×0+26.7×0+20.0×9=180.0)
Then the value of the relative importance of each EC can be calculated based on the absolute importance of all the ECs and listed in the row of “Relative Weight”.
Figure 2 – The calculations of importance ranking in Room 5 (QFD Online 2011)
Step 6: Analyse the product with other competitive products in the market in Room 6.
This step is involved in the competitive analysis or customer assessment of competing products. A table is designed to record how the top competitive products rank with respect to the customer requirements listed in Room 1 of the HoQ. This information comes from customer surveys, industry consultants, and market departments. Figure 3 shows the competitive analysis in the case of chocolate chip cookies.
Figure 3 – Competitive analysis in Room 6 (QFD Online 2011)
Step 7: Estimate the technical advantage and difficulty of each EC in Room 7.
No organisation would invest in the development of a product or service without knowing enough about the competition to be sure that their design is competitive (Cohen 1995). So Step 7 deals with Room 7 – technical assessment or benchmarks. Each of the ECs, which are identified as important features of the product, will be measured for both the company’s own existing products and the other available competitive products. Generally a scale of 1 to 5 (best) is used. Room 7 may also include a technical difficulty rating that shows the ease in achieving each of the ECs, and an estimate by the design team of probability in attaining the desired value of each EC. In the example (Figure 4), a scale of 0 (easy to accomplish) to 10 (extremely difficult) is employed to denote technical difficulty.
Step 8: Assign the target value to each EC in Room 8.
The final step in constructing a HoQ is to set target values to ECs in Room 8. It is the ultimate output of the HoQ, and a set of engineering target values to be met by the new product design. For example (Figure 4), “tensile yield strength” is one of the ECs. Its target value is assigned 0.01MPa.
Figure 4 – Technical assessment (Room 7) & Target values (Room8)
(QFD Online 2011)
Until now you may have known how to construct a fully configured House of Quality (HoQ) step by step in the early stage of design. The next example is of designing engineering attributes of a car door using a HoQ (Figure 5).
Figure 5 – House of Quality for a car door (Cross 2008: 133)
In different applications of HoQ for QFD, their terms and codes are not the same, such as in the examples of chocolate chip cookies and a car door. It is recommended that the terminology and coding scheme should be consistent inside a project in order that common understanding can be achieved among multi-disciplinary development teams.
Summary
The aim of the QFD method is to set targets to be obtained for the engineering characteristics of a product or service so that they satisfy customer requirements. The House of Quality (HoQ) is the basic structure in QFD. The complete information required for a HoQ needs to be established in a step-by-step process, which consists of 8 steps in accordance to the featured rooms of the HoQ. The procedure is as follows:
Step 1: Identify the customer requirements (CRs) in Room 1.
Step 2: Identify the engineering characteristics (ECs) in Room 2.
Step 3: Build the correlation matrix of ECs in Room 3.
Step 4: Build the relationship matrix between CRs and ECs in Room 4.
Step 5: Rank the importance of the identified ECs (CRs) in Room 5.
Step 6: Analyse the product with other competitive products in the market in Room 6.
Step 7: Estimate the technical advantage and difficulty of each EC in Room 7.
Step 8: Assign the target value to each EC in Room 8.
Back to QFD
Back to Planning and Clarification
Back to MAE Design Model
Selected References
QFD Online (2011) House of Quality (QFD) example [online] available from <http://www.qfdonline.com/qfd-tutorials/house-of-quality-qfd-example/> [26 July 2011]