mathematics

Quality function deployment

Quality function deployment is a mathematics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Quality function deployment rather than just read about it. In short: Quality function deployment (QFD) is a method developed in Japan beginning in 1966 to help transform the voice of the customer into engineering characteristics for a product. Yoji Akao, the original developer, described QFD as a "method to transform qualitative user demands into quantitative parameters, to deploy the functions forming quality, and to deploy methods for achieving the design quality into subsystems an…

Key takeaways

Quality function deployment belongs to mathematics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Quality function deployment to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Quality function deployment from memory before moving on to harder problems.

Reference excerpt

Quality function deployment (QFD) is a method developed in Japan beginning in 1966 to help transform the voice of the customer into engineering characteristics for a product. Yoji Akao, the original developer, described QFD as a "method to transform qualitative user demands into quantitative parameters, to deploy the functions forming quality, and to deploy methods for achieving the design quality into subsystems and component parts, and ultimately to specific elements of the manufacturing process." The author combined his work in quality assurance and quality control points with function deployment used in value engineering.

House of quality

The house of quality, a part of QFD, is the basic design tool of quality function deployment. It identifies and classifies customer desires (WHATs), identifies the importance of those desires, identifies engineering characteristics which may be relevant to those desires (HOWs), correlates the two, allows for verification of those correlations, and then assigns objectives and priorities for the system requirements. This process can be applied at any system composition level (e.g. system, subsystem, or component) in the design of a product, and can allow for assessment of different abstractions of a system. It is intensely progressed through a number of hierarchical levels of WHATs and HOWs and analyse each stage of product growth (service enhancement), and production (service delivery). The house of quality appeared in 1972 in the design of an oil tanker by Mitsubishi Heavy Industries. The output of the house of quality is generally a matrix with customer desires on one dimension and correlated nonfunctional requirements on the other dimension. The cells of matrix table are filled with the weights assigned to the stakeholder characteristics where those characteristics are affected by the system parameters across the top of the matrix. At the bottom of the matrix, the column is summed, which allows for the system characteristics to be weighted according to the stakeholder characteristics. System parameters not correlated to stakeholder characteristics may be unnecessary to the system design and are identified by empty matrix columns, while stakeholder characteristics (identified by empty rows) not correlated to system parameters indicate "characteristics not addressed by the design parameters". System parameters and stakeholder characteristics with weak correlations potentially indicate missing information, while matrices with "too many correlations" indicate that the stakeholder needs may need to be refined.

Fuzziness The concepts of fuzzy logic have been applied to QFD ("Fuzzy QFD" or "FQFD"). A review of 59 papers in 2013 by Abdolshah and Moradi found a number of conclusions: most FQFD "studies were focused on quantitative methods" to construct a house of quality matrix based on customer requirements, where the most-employed techniques were based on multiple-criteria decision analysis methods. They noted that there are factors other than the house of quality relevant to product development, and called metaheuristic methods "a promising approach for solving complicated problems of FQFD."

Derived techniques and tools The process of quality function deployment (QFD) is described in ISO 16355-1:2021. Pugh concept selection can be used in coordination with QFD to select a promising product or service configuration from among listed alternatives. Modular function deployment uses QFD to establish customer requirements and to identify important design requirements with a special emphasis on modularity. There are three main differences to QFD as applied in modular function deployment compared to house of quality: The benchmarking data is mostly gone; the checkboxes and crosses have been replaced with circles, and the triangular "roof" is missing.

Notes

References Larson, Wiley J.; Kirkpatrick, Doug; Sellers, Jerry Jon; Thomas, L. Dale; Verma, Dinesh, eds. (2009). Applied Space Systems Engineering. Space Technology. United States of America: McGraw-Hill. ISBN 978-0-07-340886-6.

Further reading Hauser, John R. (April 15, 1993). "How Puritan-Bennet used the house of quality". Sloan Management Review (Spring 1993): 61–70. Archived from the original on September 10, 2015. Tapke, Jennifer; Muller, Alyson; Johnson, Greg; Siec, Josh. "House of Quality: Steps in Understanding the House of Quality" (PDF). IE 361. Iowa State University. Archived (PDF) from the original on November 5, 2003. "General principles and perspectives of Quality Function Deployment (QFD)". ISO.org. International Organization for Standardization. 2021. ISO 16355-1:2021.

Worked examples

Example 1 — a first encounter with Quality function deployment

Start with the simplest possible case. Write down what Quality function deployment claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In mathematics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Quality function deployment before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Quality function deployment ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Quality function deployment

In research: Quality function deployment appears in mathematics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Quality function deployment in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Quality function deployment is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1966 introductions, Business intelligence terms, Organizational cybernetics, so understanding it makes those chapters shorter.
In everyday life: Look for Quality function deployment outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Quality function deployment in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Quality function deployment means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Quality function deployment out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Quality function deployment in simple terms?

Why does Quality function deployment matter?

Because it connects several mathematics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Quality function deployment?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Quality function deployment.