AMI4900: Engineering Design
Unit 2: Structured approaches to problem solving and process improvement
Section 1: Quality Functional Deployment
Unit Contents
2.1 Quality Functional Deployment
- 2.1.1 What is Quality Functional Deployment?
- 2.1.2 How does Quality Functional Deployment work?
- 2.1.3 Product Planning using Quality Functional Deployment?
- 2.1.4 Concept Selection and Product Design?
- 2.1.5 Process Design
- 2.1.6 QFD Process
2.1.1 What is Quality Functional Deployment?
Figure 2.1.1.1 shows how QFD is used in a quality system: customer needs feed QFD and it translates the voice of the customer into identified key product and process characteristics.
Figure 2.1.1.1
A disciplined approach to quality
Introduced in Japan by Yoji Akao in 1966, QFD is a technique that aims to capture what the customer needs, and work towards how it might be achieved. In 1990 Akao described QFD as ‘a method for developing a design quality aimed at satisfying the consumer and then translating the consumer’s demand into design targets and major quality assurance points to be used throughout the production phase’.
Quality Functional Deployment (QFD) is a technique used in new-product design to link customer requirements to technical specifications.
QFD originated at Mitsubishi in 1972 and was then utilized and developed by Toyota. One of the key figures in QFD is Dr Yoji Akao. Dr Akao lamented the decline of the relationship between the individual customer and the craftsman, or as he put it:
“Time was when a man could order a pair of shoes directly from the cobbler. By measuring the foot himself and personally handling all aspects of manufacturing, the cobbler could assure the customer would be satisfied.”
Dr Akao saw QFD as the way for mass produced goods to have the same individual appeal as bespoke products. QFD works by translating the requirements of the customer into technical specifications which are used by design and manufacturing.
There are five key points to QFD which enable it to understand and develop products to suit consumers and be practical to produce at the same time as providing a competitive advantage.
- Understanding Customer Requirements
- Quality Systems Thinking + Psychology + Knowledge/Epistemology
- Maximizing Positive Quality That Adds Value
- Comprehensive Quality System for Customer Satisfaction
- Strategy to Stay Ahead of The Game
2.1.2 How does Quality Functional Deployment work?
Definition
QFD is a way of listening to customers to learn exactly what they want, and then using a logical system to determine how best to fulfil those needs with available resources. It is a product-development tool that translates customer requirements into design and production requirements. QFD ensures that everyone works together to give customers what they want and it gives everyone in the organisation a road map showing how every step, from design through delivery, interacts to fulfil customer requirements.
QFD’s primary goal is to overcome three major problems in traditional methods: disregard for the voice of the customer, loss of information, and different individuals and functions working to different requirements. In QFD, these issues are addressed by answering the following questions:
- What are the product qualities the customer desires?
- What functions must the product serve and what functions must we use to provide the product or service?
- Based upon the resources available, how can we best provide what our customer wants?
A disadvantage cited by practitioners is the complexity involved in using QFD in large design projects; the number of factors used in each axis of the matrix must be minimised if the process is not to become unmanageable. Conversely, if the number is artificially restricted too severely, important relationships may be overlooked.
The four phases of QFD
The QFD system consists of the four phases that are summarised in Figure 2.1.1.2:
Figure 2.1.1.2
The four phases of QFD
The QFD process involves mapping customer requirements onto specific design features and manufacturing processes through these four matrices. QFD can be employed at two levels:
- To translate requirements of one functional group into the supporting requirements of a downstream functional group
- As a planning and control tool for product development.
The first level typically involves the first of these matrices (Figure 2.1.1.3). This matrix has the most general structure and is often called the ‘house of quality’ (HOQ). Typically applications of QFD are limited to the HOQ, however QFD can play a greater role as a linking mechanism throughout product development through the use of subsequent matrices.
The four phases of QFD help communicate product requirements from the customers to the design team to the production operators. Throughout the phases, all participants are able to assess how solutions would help to satisfy customer requirements. All decisions are based on the highest level of customer satisfaction. The four phases provide a guide through the product development cycle from product design to production.
Each phase has a vertical column of Whats and a horizontal column of Hows. Whats are customer requirements and Hows are ways of achieving these requirements. Hows that are most important, require new technology, or involve high risk are carried forward to the next phase.
In the Design Phase, the customer helps to define the product requirements. The Hows carried over from the Design phase become the Whats for the Details Phase and design specifications are converted into individual part details. In the Process Phase, the processes required to produce the product are developed. The Hows from the Details phase become the Whats for the Process Phase. The Hows from the Process phase become the Whats for the Production Phase and the production requirements for the product are developed.
Figure 2.1.1.3
The House of Quality
First, customers’ requirements (which form the vertical axis of the matrix) are matched with the design attributes (which form the horizontal axis of the matrix). The individual elements of the matrix are used to indicate the degree and direction of influence of the main design attributes on customer needs. To do this some kind of coding scheme is used. This is often pictorial using, for example, circles and triangles. (It is important at this stage to clearly record all assumptions used in judging the nature of these relationships.) The purpose is to make explicit what, without QFD, might have remained unexplained in the design process.
Some benefits include: provides a systematic approach in addressing the customer’s wants and acts as a driver for other techniques such as FMEA, Taguchi, SPC; moves changes upstream where they are more economically accomplished; provides a valuable company record for the next product cycle; promotes teamwork and shared responsibility.
QFD works by considering that quality is designed into a product, not designed into it. The type of quality aimed for in QFD is that which meets the customers needs. As such, quality is a value adding feature.
The “voice of the customer” is key in QFD and includes stated and unstated requirements. These requirements are gathered from sources such as: direct discussion or interviews, surveys, focus groups, customer specifications, observation, warranty data and field reports. The requirements are then fed into a matrix which is the base for QFD.
The matrix used in QFD is known as the “House of Quality”. The House of Quality is not one simple matrix but a combination of different matrices which bring together all aspects of QFD.
The diagram below (Figure 2.1.1.4) shows the four basic phases of QFD and the simple matrices relevant to each phase.
Figure 2.1.1.4
Four-Phase QFD Approach
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2.1.3 Product Planning using Quality Functional Deployment?
The initial stage in QFD is identifying customer needs. Once this has been achieved the House of Quality can begin to be constructed (see Figure 2.1.1.5). The stages for this are shown below:
- Customer requirements are of prime importance under QFD. To this end they are placed on the left hand side of the matrix. Each of the customer requirements is rated from 1 to 5. If the number of customer requirements is greater than 20 items produce more than one matrix. It is important to be able to manage the House of Quality: too many requirements can lead to confusion.
Figure 2.1.1.5 Example of a House of Quality
- An evaluation of previous products, competitive products is carried out to obtain feedback. Evaluation should also include a feedback of competitor’s products to identify key features. A product strategy based on strengths and weaknesses can then be constructed. These strengths and weaknesses in the product then need comparing to customer priorities. It also gives opportunities for development to occur which would allow improvements to exceed competitor’s products and focus development where it will have the greatest payoff.
- Product requirements which respond to customer requirements are then produced. These are organised into related categories. Product requirements need to be meaningful and measurable. Product requirements should be stated so that they do not imply a particular solution and so influence designers.
- Relationships between customer requirements and product requirements need to be developed. These relationships should be demonstrated by using different symbols. The symbol used to identify a ‘strong’ relationship should be used sparingly so that it allows a full design process to occur. It is important to address all customer needs and ensure that there are no product requirements that do not relate to customer requirements.
- A technical evaluation of prior generation and competitive products needs developing so that all products, from all producers, are known and available for consideration in the design process.
- Preliminary targets for product requirements need to be developed.
- Positive and negative interactions between product requirements need developing. If there are too many positive interactions then there is a suggestion that there could well be a potential redundancy in the “critical few” product requirements. Negative interactions should be focused on as these are the interactions where new concepts or technologies can best be employed.
- Importance ratings need calculating. Assign a weighting factor to relationship symbols (9-3-1, 4-2-1, or 5-3-1). Multiply the customer importance rating by the weighting factor in each box of the matrix and add the resulting products in each column.
- Develop a difficulty rating (1 to 5 point scale, five being very difficult and risky) for each product requirement. Technology maturity, personnel technical qualifications, business risk, manufacturing capability, supplier/subcontractor capability, cost, and schedule should all be considered. It is important to avoid too many difficult or high risk items as this will likely delay development and exceed budgets. It is also vital at this stage to assess whether the difficult items can be accomplished within the project budget and schedule.
- The matrix then needs analyzing to develop strategy and product plans. Focus areas and required actions need to be determined and target values need finalising. Items for future QFD deployment can also be identified at this time. To maintain focus on "the critical few", less significant items may be ignored with the subsequent QFD matrices.
NB
The most important factor for a successful QFD matrix is to keep the amount of information in each matrix at a manageable level. With a more complex product, if one hundred potential needs or requirements were identified, and these were translated into an equal or even greater number of product requirements or technical characteristics, there would be more than 10,000 potential relationships to plan and manage. This becomes an impossible number to comprehend and manage. It is suggested that an individual matrix not address more than twenty or thirty items on each dimension of the matrix. Therefore, a larger, more complex product should have its customers needs decomposed into hierarchical levels.
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2.1.4 Concept Selection and Product Design?
Once product planning is complete, a more complete specification may be prepared. The product requirements and the product specification serve as the basis for developing product concepts. New product concepts are gained by benchmarking, brainstorming, and research and development. Once concepts are developed, they are analysed and evaluated. Cost studies and trade studies are performed. The concept selection matrix can be used to help with this evaluation process.
The concept selection matrix shown below lists the product requirements down the left side of the matrix.
Figure 2.1.1.6
Concept Matrix
These serve as evaluation criteria. The importance rating and target values are also carried forward and normalized from the product planning matrix.
Product concepts are listed across the top. The various product concepts are evaluated on how well they satisfy each criteria in the left column using the QFD symbols for strong, moderate or weak. If the product concept does not satisfy the criteria, the column is left blank. The symbol weights (5-3-1) are multiplied by the importance rating for each criteria. These weighted factors are then added for each column. The preferred concept will have the highest total.
This concept selection technique is also a design synthesis technique. For each blank or weak symbol in the preferred concept's column, other concept approaches with strong or moderate symbols for that criteria are reviewed to see if a new approach can be synthesized by borrowing part of another concept approach to improve on the preferred approach.
Based on this and other evaluation steps, a product concept is selected. The product concept is represented with block diagrams or a design layout. Critical subsystems, modules or parts are identified from the layout. Criticality is determined in terms of effect on performance, reliability, and quality. Techniques such as fault tree analysis or failure modes and effects analysis (FMEA) can be used to determine criticality from a reliability or quality perspective.
The subsystem, assembly, or part deployment matrix is then prepared. The process leading up to the preparation of the deployment matrix is depicted below.
Figure 2.1.1.7
Deployment Matrix
The product requirements defined in the product planning matrix become the "what's" that are listed down the left side of the deployment matrix along with priorities (based on the product planning matrix importance ratings) and target values.
The deployment matrix is prepared in a manner very similar to the product planning matrix. These product requirements or technical characteristics are translated into critical subsystem, assembly or part characteristics.
This translation considers criticality of the subsystem, assembly or parts as well as their characteristics from a performance perspective to complement consideration of criticality from a quality and reliability perspective.
Relationships are established between product requirements or technical characteristics and the critical subsystem, assembly or part characteristics. Importance ratings are calculated and target values for each critical subsystem, assembly or part characteristic are established.
An example of a part/assembly deployment matrix is shown:
Figure 2.1.1.7
Part/assembly deployment matrix
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2.1.5 Process Design
Quality Function Deployment continues this translation and planning into the process design phase. A concept selection matrix can be used to evaluate different manufacturing process approaches and select the preferred approach. Using this information the process planning matrix shown below is prepared.
Figure 2.1.1.8
Process planning matrix
The "how's" from the higher level matrix and become the "what's" which are used to plan the process for fabricating and assembling the product. Important processes and tooling requirements can be identified to focus efforts to control, improve and upgrade processes and equipment. It is important for communication between Engineering and Manufacturing to be emphasized so trade-off's can be made as appropriate to achieve mutual goals based on the customer needs.
In addition to planning manufacturing processes, more detailed planning related to process control, quality control, set-up, equipment maintenance and testing can be supported by additional matrices. The following provides an example of a process/quality control matrix.
Figure 2.1.1.9
Process/quality control matrix
The result of this planning and decision-making is that Manufacturing focuses on the critical processes, dimensions and characteristics that will have a significant effect on producing a product that meets customer's needs.
There is a clear trail from customer needs to the design and manufacturing decisions to satisfy those customer needs. Disagreements over what is important at each stage of the development process should be minimized, and there will be greater focus on "the critical few" items that affect the success of the product.
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2.1.6 QFD Process
QFD begins in product and process design - it finishes with a complete package to deliver a quality product to match customer requirements. As such QFD is a multi-function project bringing together development, marketing and manufacturing teams.
Quality Function Deployment, by its very structure and planning approach, requires that more time be spent up-front in the development process making sure that the team determines, understands and agrees with what needs to be done before plunging into design activities. As a result, less time will be spent downstream because of differences of opinion over design issues or redesign because the product was not on target. It leads to consensus decisions, greater commitment to the development effort, better coordination, and reduced time over the course of the development effort.
An essential part of QFD is discipline. Without discipline it is difficult to co-ordinate actions and achieve consensus in planning and decision making. The following points are some which are recommended to successfully carry out QFD and gain the full benefits:
- Gain senior management commitment to QFD
- Establish clear objectives for QFD - use it first on a simple project and perhaps with limited objectives - this is so that experience can be gained before applying it to a critical product.
- Create a multi-functional team with clear objectives and clear commitments.
- Plan regular meetings to maintain focus and keep decision making effective and collective.
- Data does not have to be perfect. Significant information can be held within an organisation in a hidden form - imperfect data can bring this information out more readily than formalised perfect data. Avoid technical arrogance and the belief that company personnel know more than the customer.
QFD is a method to facilitate communication, planning, decision making in a product development team. QFD is not a paperwork exercise - it is a way of thinking to develop products that are closer to customer requirements and to reduce development cycle time and cost in the process.
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