Quality Function Development
The Quality Function Development theory was first defined by Yoji Akao in 1966, and its initial application took place at the Kobe shipyard of Mitsubishi in 1972. They introduced a matrix that placed customer demands on the vertical axis and the methods by which they would be met on the horizontal axis. From this simple basis, the system has evolved to encompass a broad range of activities within most manufacturing and service organizations. The comprehensive application of this technique has been defined as:
A system for translating customer requirements into appropriate company requirements at every stage, from research through product design and development, to manufacture, distribution, installation and marketing, sales and service.
It is equally valid to think of QFD as a way of identifying the true voice of the customer at an early stage and making sure that it is heard through the design/production/delivery process to achieve high levels of customer satisfaction. QFD is not truly a quality technique; it is rather a planning technique used to focus teamwork where it matters on customer satisfaction.
According to Dr. Yoji Akao, “Quality Function Deployment (QFD) is a method to transform user demands into design quality, to deplay the functions forming quality, and to deploy methods for achieving the design quality into sub-systems and component parts, and ultimately to specific elements of the manufacturing process”.
According to Sullivan, “QFD is the main objective of any manufacturing company to bring new (and carryover) products to market sooner than the competition with lower cost and improved quality”.
It is a structured approach to defining customer needs or requirements and translating them into specific plans to produce products and or services to meet.
Quality Function Development Tools
Some Quality Function Development tools and techniques have been refined or enhanced for SQD. A few are briefly explained below:
1) Data Flow Diagrams
Data Flow Diagrams (DFDs) have supplanted flow charts for analysis purposes in software circles over the last ten years. While flow charts were widely used twenty years ago, DFDs have emerged as powerful tools for software applications and non-software purposes. They are utilized in software engineering to analyze organizational activities and do not necessarily require technical expertise.
Table: Tools of QFD
|Data flow diagram
2) Software Support
Software is available to support most of the individual tasks of SQD, but only part of the process. Existing Computer-Aided Software Engineering (CASE) tools reasonably help the software engineering aspects but still need to address the quality deployment side. Given the highly competitive nature of this market, one should expect this to change in the next few years. Enhancements to QFD for SQD are a prime example of continuous improvement applied to the tools, techniques, and improvement processes.
3) Precedence Diagrams
In Japan, the arrow diagram (the activity-on-arrow diagram) is taught as one of the 7-MP tools accompanying QFD. The arrow diagram was the first project management diagram developed for the Program Evaluation Review Technique (PERT) in the late 1950s. Later, the activity-on-node diagram was created for CPM. Today, project management professionals prefer the (time-scaled) precedence diagram, readily available from PC-based software packages.
4) Analytic Hierarchy Process
An essential aspect of QFD is prioritizing customer (user) demands. However, asking people to rank isolated items along an arbitrary scale is a process vulnerable to many biases. The Analytic Hierarchy Process (AHP) is a more robust approach, which employs pairwise evaluation by hierarchical levels. It facilitates rankings and weightings and measures judgment consistency and sensitivity analysis.
Benefits of Quality Function Development
Quality Function Development has many benefits, especially for companies interested in achieving competitiveness, increasing market share, and improving productivity and the bottom line. Those companies that have adopted QFD have reported significant cost reductions. These benefits are explained below:
The benefits of Quality Function Development are listed below:
- Reduction in Cycle Time
- Lower Cast
- Applied in a Cross-Functional Team
- Maintain a Database for Customer
- Design and Production Efficiency
- Foster Organisational Harmony
- Helps in Decision-Making
- Used to Determine Product Price
- Supports Value-Engineering Analysis
1) Reduction in Cycle Time
Reducing cycle time results in faster product introduction to the market. It lowers start-up costs and improves quality. Additionally, there is a decrease in the number of engineering changes that may be required.
2) Lower Cost
Products are produced at a lower cost due to the reduction in operational costs.
3) Applied in a Cross-Functional Team
QFD is typically applied within a cross-functional team context. For instance, members from various functional areas of the firm collaborate to develop new product concepts. These team members come from diverse backgrounds and can share information effectively while understanding each other’s perspectives.
4) Maintain a Database for Customers
Information gathering is an ongoing process using QFD. Maintaining a database for customer requirements gathered from various sources is crucial. This information can be used repeatedly to design or improve new products.
5) Design and Production Efficiency
QFD enables design and production efficiency achievement. Members of cross-functional teams critically analyse their functions, ensuring integration of customer requirements at every phase of new product development. This ensures that products are designed and produced correctly the first time, thereby reducing production costs, minimising waste, and maximising efficiency.
6) Foster Organizational Harmony
Building cross-functional teams can foster organisational harmony. Rather than competing against each other, functional units work towards a common goal. Such teams promote increased openness and information sharing with the ultimate aim of designing and producing products that result in high customer satisfaction.
7) Assists in Decision-Making
Problems are more easily identified by listening to the “voice of the customer.” These issues can be corrected to ensure a successful product introduction. Moreover, involving significant customer groups in the decision making process helps ensure that products are designed and produced with the customer in mind.
8) Used for Determining Product Price
Market information obtained through QFD can be utilized to determine product pricing, quality, and functionality.
9) Supports Value-Engineering Analysis
Product development is customer-driven and supports value-engineering analysis to cut costs and add value to the product.
Limitations of Quality Function Development
Limitations of Quality Function Development are as follows:
1) Like other Japanese management techniques, applying QFD within the Western business environment and culture can lead to specific problems.
2) Consumer perception is determined through market surveys; if these surveys are conducted well, the entire analysis may be refined for the company.
3) The needs and desires of customers can change rapidly in today’s market. Comprehensive systems and methodical thinking can make adapting to these changed market needs more complex.
4) Subjectivity exists in assessing the strength of relationships between factors and outcomes.
5) A large amount of data input is always required before estimating.
6) Substantial upfront investment is necessary.
7) Specialized training is required.
Quality Function Development Process
Identification of a functional need is a primary input to the QFD process as shown in the image below:
The need must be stated in functional terms to avoid premature commitment to a concept or configuration. Customer surveys, interviews, trend analysis, and competition analysis are often used to identify a valid need. Organizations that can identify and exploit a not-so-obvious need often gain a strategic head start over the competition. The activities comprising the QFD method are discussed in the following subsections:
Step 1: Need Analysis and Identification of Customer Requirements
The initial step involves analyzing the functional need and translating it into more specific customer requirements to understand the perceived deficiency better. Essentially, the purpose of this step is to capture the “Voice of the Customer.” Reference to the “customer” encompasses not only the end-users but also applicable regulations and standards, intermediate distributors, installers, retailers, and maintainers. Therefore, this represents the first significant opportunity to integrate logistics requirements and issues into the mainstream design and development process.
Step 2: Importance of Customer Requirements
Selected requirements often have adverse impacts on each other. For example, a customer may desire ease of opening and closing a car door while also wanting power windows. However, power windows increase the door’s weight, negatively affecting its ease of opening or closing. To address such conflicts, requirements are assigned priorities that must reflect customer preferences. There are several approaches to prioritizing customer requirements, ranging from direct indication by the customer to using the Analytical Hierarchy Process and considering cost and technical factors. Three or five-level priority scales are often employed. While most applications use a simple numerical scale for priorities, linguistic scales (utilizing concepts from fuzzy set theory) have also been developed and applied.
Step 3: Identification of Design Dependent Parameters (DDPs)
Design-dependent parameters, or technical performance measures, are engineering characteristics under a designer’s control. These parameters are manipulated to directly or indirectly influence customer needs. In this context, customer requirements are often called the set of “whats” during the design process. The DDPs should be tangible, describing the product in measurable terms and directly affecting customer perceptions. DDPs guide the analysis and evaluation of design concepts, configurations, and artefacts during the conceptual, preliminary, and detailed system design phases. Therefore, it is essential to identify all relevant DDPs.
Step 4: Correlation of Customer Requirements and Design Dependent Parameters
This step of the QFD process involves populating the correlation matrix within the “house of quality.” Each DDP is analyzed in terms of its influence on customer requirements. Different levels of this correlation are represented in the correlation matrix. Three or five levels of correlation are utilized depending on the level of detail required. Furthermore, the correlation between DDPs and customer requirements may be represented through symbols, as shown in the image below.
Step 5: Check the Correlation Matrix
At this stage, it is necessary to examine the correlation grid before proceeding further. This examination includes checking for the following:
1) Empty Rows in the Correlation Matrix: Empty rows in the correlation grid signify unaddressed customer requirements. In response, the set of design-dependent parameters needs to be revisited, and if necessary, additional DDPs identified.
2) Empty Columns in the Correlation Matrix: Empty columns in the correlation grid imply redundant or unnecessary system-level design requirements. The design team may have included design requirements that cannot be traced back to any customer requirement and could be dropped from further consideration.
Step 6: Benchmarking Customer Requirements
An essential activity involves identifying available systems/products that respond to the functional need (to whatever extent). Customer perceptions are then benchmarked relative to how well these capabilities satisfy the initially specified requirements. The objective is to evaluate the state of the art from a customer perspective. Design and development team members must refrain from influencing this activity, as their technical knowledge will likely bias results.
Benchmarking of customer perceptions is facilitated through tools such as customer surveys, interviews, demonstrations, media information, and feedback from marketing, sales, and service organizations.
Step 7: Technical Assessment of Design Dependent Parameters (DDPs)
This activity involves the assessment of competition from a technical perspective. Engineers and designers actively participate during this step in the QFD process. Cavanagh has identified some methods and techniques to facilitate the effective accomplishment of this step, including:
- Product testing (baseline the system or product, competitive or non-competitive but similar systems or products).
- Informal evaluations (renting competitors’ products).
- Contract laboratories.
Technical assessments are expressed in quantitative and objective terms and often indicate a need for research and technology development if the current state fails to satisfy essential customer requirements.
Step 8: QFD Matrix Inconsistency Analysis
The source, nature, and implications of various inconsistencies in the QFD matrix must be addressed before defining design requirements. For example, if results from the technical assessment activity seem contradictory to results from customer benchmarking, it may signal faulty measures or misinterpretation of customer perception.
Step 9: Definition of Design Dependent Parameter Target Values
This is a critical system design activity, as the DDP target values specify the feasible design space and impact subsequent design decisions. Strategic and pertinent opportunities must be identified and exploited. Experience and familiarity with similar systems are invaluable for effectiveness during this activity. Once again, logistics-related requirements must be integrated into this step for completeness. A comprehensive definition of design requirements facilitates subsequent supportability-related analyses, such as the definition of the maintenance concept, level of repair analysis, failure mode, effects, criticality analysis, maintenance task analysis, etc.
Step 10: Delineation of Design Dependent Parameter Relative Importance
DDP relative priorities must be delineated to facilitate design analysis and evaluation activities. Furthermore, to maintain traceability, relative priorities of design-dependent parameters are computed from the importance levels assigned to customer requirements and the extent of their correlation with DDPs. Along with the activities identified and discussed thus far, a “roof” is often developed over the quality function development matrix. This mechanism allows for the delineation of positive and negative correlations between design-dependent parameters, which in turn facilitates informed trade-offs.