Using case outcome to integrate customer feedback into the Quality Function Deployment process D.A. Adams1, C. Irgens1, B. Lees2, E. MacArthur3. 1
Department of Mechanical and Manufacturing Engineering. Department of Computer Information Systems. 3 Department of Mathematics and Statistics. University of Paisley, High Street, Paisley, PA1 2BE, UK. Contact: David Adams, Email:
[email protected], Phone: ++44 141 848 3553, Fax: ++44 141 848 3555. 2
Abstract Quality Function Deployment (QFD) is a product development methodology which is aimed at increasing customer focus in product development. Industrial research has suggested that, in variant design, the provision of customer feedback information, from fielded products similar to the product under development, could be useful to the new development. This paper investigates the use of case outcome in the capture and utilisation of customer feedback information in the QFD process. We also consider extensions to the approach in which feedback information is captured from various activities which are affected by the decisions made in the initial stages of the QFD process.
1.0 Introduction Quality Function Deployment (QFD) is a methodology used in the development of new products which supports adherence to the requirements of the customer throughout the product development cycle. (5, 6). In QFD, the principal stage is the initial stage in which a set of customer requirements are translated from the customer’s language into an appropriate technical description (5). This is referred to as the organisation’s language. This technical description then goes on to drive the remainder of the process. This initial stage, however, is frequently problematic due to the subjective nature of the translation process which is often conducted arbitrarily by the designer (6). This can lead to a ‘hit or miss’ product development process since there is the opportunity for a particular customer requirement to be translated in a number of different ways. It is proposed that Case-Based Reasoning could be applied beneficially to this situation. In this approach the set of customer requirements is used to access a case library of previous products developed using QFD and retrieve those cases which have similar customer requirements to the new case. The translations that were used in the previous case then provide a starting point for the translations to be made in the new case. Novel to this approach is the capture of customer feedback information relating to fielded products and its use as a form of case outcome. This effectively places a measure of success or otherwise on the solution used in the previous case. Therefore, when selecting a retrieved case we base the selection on the degree of similarity and the results of a feedback assessment measure which is based on customer feedback information. Section 2 briefly presents background information on QFD whilst sections 3 and 4 consider our approach in more detail specifically considering the incorporation of customer feedback into the case.
2.0 Quality Function Deployment 2.1 Background Quality Function Deployment (QFD) is a product development methodology which was developed in 1966 in Japan by Yoji Akao. Akao defines QFD as being "a method for developing a design quality aimed at satisfying the consumer and then translating the consumers' demands into design targets and major quality assurance points to be used throughout the production stage." (1). Benefits obtained from the successful adoption of QFD practices have been reported as: an increased level of team working including providing a communication platform for concurrent engineering, a reduced time to market, a reduced amount of re-work, and an increase in quality of the product (6, 13, 12). The process of QFD and the House of Quality - one of the most important QFD steps and the focus of our prototype system - are reviewed below. 2.2. The QFD Process In general the process of QFD comprises four main stages: Product Planning, Design Deployment, Process Planning, and Production Planning (10, 12). Each of these stages consists of a translation process between the input to the stage and the output from the stage. The output from one stage is the input to the following stage. The initial input is the customer requirements with the final output being a manufactured product. If the translations undertaken in the intervening stages are accurate, then the final output, i.e. the product, should satisfy the initial input, i.e. the customer requirements. The process is shown in figure 1. Matrix methods are normally used in each stage of the QFD process to relate the 'Whats' to the 'Hows' (5). In the first stage of the process a special matrix known as the House of Quality (HoQ) has been developed (7, 5) . This is discussed below.
Product Characteristics (‘How’)
Input Customer
Customer Requirements (‘Whats’)
Product Planning
Design Characteristics (‘How’)
Product Characteristics (‘Whats’) How much? (Target Values)
How much? (Target Values)
QFD
Customer Satisfaction? Production Requirements (‘How’)
Production Planning
Process Planning Process Parameters (‘How’)
Process Parameters (‘Whats’)
Product Output
Design Deployment
How much? (Target Values)
Design Characteristics (‘Whats’) How much? (Target Values)
Figure 1: The QFD Process (Ranky)
2.3 The House of Quality The main purpose of the HoQ is to provide a structure for relating customer requirements to measurable product characteristics. An outline of a HoQ is shown in figure 2 The use of the HoQ involves the following steps: 1. Obtain Customer Requirements and their degree of importance. ('Whats') 2. Determine any trade-offs between the customer requirements (optional). (Requirements matrix) 3. Determine the required product characteristics. ('Hows') 4. Determine the relationships between the 'Whats' and the 'Hows'. This is called the Relationship Matrix. 5. Determine any trade-offs that may exist between product characteristics. This is done in the 'roof' of the HoQ and is known as the Correlations Matrix. 6. Determine product goals or ‘How Much’. The target value-product characteristic pairing is the output from the HoQ.
5 Trade-offs (correlations matrix) Product Characteristics 3 (voice of engineer)
1 Customer Requirements (voice of customer)
4 How relations (relationship matrix) Product goals (target values)
Requirements Correlation 2
6
Figure 2: The House of Quality
The ‘quality’ of the completed House of Quality is extremely important because the output from this stage goes on to drive the remainder of the QFD process. Any decisions made at this stage should therefore be made based upon the best information that is available. Such information, we believe, has two dimensions: (i) Experience of what worked in the past based on an evaluation of the outcome of previous House of Quality charts, i.e. a product, by the intended customer of the chart, i.e. consumers; (ii) Knowledge of known constraints and organisational capabilities.
2.4 An example of the House of Quality The following example is taken from Wasserman (14) and concerns the characteristics of a hypothetical pencil. The House of Quality for the pencil is shown in figure 3. As can be seen from the figure, the customer requirements of ‘easy to hold’, ‘does not smear’, ‘point lasts’, and ‘does not roll’, have each been assigned a degree of importance which indicates how important each requirement is perceived to be to the customer. Using knowledge of the domain and experience the engineer has determined a set of product characteristics which have some impact upon the desired customer requirements. The impact, or relationship, each product characteristic has with each customer requirement is formalised in the House of Quality via the symbols shown in the diagram. Based on market research and bench-marking, a target value is assigned to each product characteristic. The importance of achieving each product characteristic is also required. In this example the importance of each product characteristic has been determined in both absolute and relative terms via equations (1) and (2). The product characteristics, their target values, and their derived importance ratings are then passed to the next stage of the QFD process and take the place of the customer requirements in a further chart similar to - but not the same as - the House of Quality (the HoQ is only used in the first stage of QFD).
m ,n
impabsj = i ∑j di•Ri , j (1), , =1
impabsj
imprelj =
∑ imp
× 100 (2),
absj
where di = degree if importance of customer requirement i, I = 1,2,…, m. Ri,j = relationship value between customer requirement, I, and product characteristic, j, I = 1,2,…m; j = 1,2,…, n. impabsj = absolute importance for product characteristic j, j = 1,2, …, n. imprelj = relative importance for product characteristic j, j = 1,2, …, n.
Correlation symbols: ++: strong positive corr. + : positive corr. -- : strong negative corr. - : negative corr.
+ ++ +
Product Characteristics Customer Requirements Degree of importance
Easy to hold
Does not smear
15
25
Point lasts
45
Does not roll
15
Measurement units
inches
classification
degrees
Mg/cm2
minimal
