A Basic Approach to QFD

7.2 The QFD Approach

There are several approaches to QFD; each of these approaches makes use of matrices to organize and relate pieces of data to each other.  Many times these matrices are combined to form a basic QFD tool called a “House of Quality”.

The basic approach used here is conceptually similar to the practice followed by most American manufacturing companies. In QFD we typically follow the flow as defined in Figure 7-2.  We start with customer requirements, which may be loosely stated qualitative items such as: looks good, easy to use, works well, feels good, safe, comfortable, lasts long, luxurious or specifically defined requirements. These are important to the customer, but do not represent a product definition. In order to implement a product system engineers need to convert these vague customer requirements into actionable internal company requirements, which we call design requirements. These are generally global product characteristics such that if properly executed the product will satisfy the customer requirements.

 Figure 7-2 The typical flow of applying QFD has five steps

Products are not usually developed at this glo­bal level, but rather at the system, sub-system or part level. The global design require­ments must then be translated into specific product design, company infrastructure and capital investment requirements. Every product has several critical characteristics that determine how good a product fulfills its intended functions. The QFD process allows one to track these critical characteristics throughout the development process. Next determine the required manufacturing operations. This stage is often con­strained by previous capital in­vestment. Development organizations usually do not want to build a new factory or install a new line of equipment to produce a new product ver­sion and this often constrains product design and production methods.

Within the defined operating constraints determine which manufacturing operations are most critical to creating the desired critical product and part characteristics, as well as the process parameters of those operations which are most influential. Think of these process parameters as the knobs or dials of the manufacturing operation that are controllable. The manufacturing operations are then deployed into production requirements, which are the entire set of procedures and practices that enable the production system to build products that ultimately satisfy customer requirements.

These operating procedures determine how the factory operates the manufacturing processes to consistently produce the required critical product/part characteristics. They include a number of ̏soft" issues such as inspection and Statistical Process Control (SPC) plans, preventive maintenance programs, operator instructions and training, as well as identifying the need for mistake proofing devices for preventing inadvertent operator errors

The hierarchical approach described above is not unlike the approach taken for years with varying degrees of success. The problem is that some of the translations are not made properly. There are several key reasons for these improper translations that are the result of the structure of large organizations and the complexity of the product development process.

7.3 Hierarchical Matrices and QFD Phases

There are several approaches to the implementation of QFD.  The QFD method presented here follows the approach taught by the American Supplier Institute (ASI) based upon the “House of Quality” structure. The basic matrix structure consists of various types of matrix and table sections (or “rooms”) linked together to form what has been termed the “House of Quality”.  The ASI approach implements a four phase approach with matrices representing the important characteristics for each phase.  Figure 7-3 illustrates the four phases and how the key characteristics of each phase are deployed to the next phase of development.

Figure 7-3 The four phases of QFD consist of four linked matrices called Quality Tables.

The four phase approach results in a hierarchical series of matrices where each individual matrix is called a quality table and are numbered, e.g. QT-1 thru QT-4.  In the four phase approach a team determines the relationships between customer requirements and product design requirements.  The product design requirements are then deployed to the QT-2 matrix. In QT-2, the team determines the relationships between design requirements and product design.  The product design is then deployed to the QT-3 matrix to determine the relationships between product design and process design. The process design is then deployed to QT-4 matrix to determine the relationship between process design and manufacturing operations.

The four phase hierarchical series of matrices when completed links the customer requirements all the way to the manufacturing operations.   Thus as the manufacturing operations meet their deployed requirements then indirectly the customer requirements are being satisfied.  Therefore the resulting product or system is Customer Driven.