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7/23/2019 Module III Lec1

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Module III Product Quality Improvement

Lecture – 1 How QFD helps in product quality improvement?

Quality Function Deployment (QFD) or the house of quality is the foundation to link the voice of

the customers with technical design requirements of a product. In other words, abstract

specifications required by the targeted customers are translated into specific product technical

requirements. Say in summer, customer needs a room to be cool and comfortable. However, how

much cool gives comfort to him/her is not specified. Take another situation, in which, a customer

wants hot coffee. Hot coffee is one of the ‘voice of the customer (VOC)’ [or ‘critical-to-quality

(CTQ) characteristic’] that the customer demands. He /She may not specify the temperature, but

the shopkeeper needs to identify best possible temperature setting for the coffeemaker machine.

The best setting will also differ according to weather conditions/ seasons. In order to translate aVOC (say, comfort temperature range for AC), the AC machine designer must first experiment

and specify the feasible range of temperature setting (say 180C to 27

0C) for varied customers.

Providing varied temperature setting leads to flexibility in the design and helps different

customer to set different comfortable temperature at workplace/ home. There can be more than

one VOC, which can also be interacting. So, as the understanding on customer’s priorities /needs

(VOC) for a product becomes clearer and subsequently freezed, the designer attempts to translate

those into product technical requirements, so as to deliver the best tradeoff solution for

interacting VOC. The next test is to build a product prototype and check real life performance of

the machine. This is a continual design improvement process activity and finalizing a design may

require 30 to 40 prototype experimentation. Subsequently, the product design is approved for

pilot/full production. QFD is a structured framework to translate the VOC to technical

specification of a product. It is not an optimization tool, and does not provide any tradeoff

solution. It only guides the engineers towards developing a robust product design from the

customer’s perspective.

The structure of QFD can be thought of as a house (so-called ‘House of Quality’), and shown in

Figure 3-1.



Figure 3-1: House of Quality

The parts of the house of quality are described as:

The outside walls of the house are shown as the customer requirements and their priorities.

On the left side is a listing of VOC. On the right side is the prioritized customer requirement,which is derived from customer survey. The ceilings of the house contain the technical

descriptors or requirements with expert’s priorities. The central or interior walls of the house

are the relationships between customer requirements and technical requirements. Customer

voices (customer requirements) are translated into engineering requirements (technical

descriptors).

The roof of the house is the interrelationship between independent technical requirements. Here

the trade-offs between similar and/or conflicting technical requirements are identified. The aim

of the house is to determine prioritized technical requirement. Technical benchmarking, reverse

engineering, tradeoff, and target value comparison are mostly used to determine technical

bounds.

This is the basic structure for the house of quality. However, based on this format varied QFD



matrices are proposed.

Building a House of Quality

Quality function deployment starts with a list of goals/objectives. This list is often referred as the

WHATs that a customer needs or expects in a particular product. This list of primary customer

requirements is usually vague and very general in nature. Further definition is accomplished by

defining a new, more detailed list of secondary customer requirements needed to support the

primary customer requirements. In other words, a primary customer requirement may encompass

numerous secondary customer requirements.

Let us consider the development process of designing a handlebar stem for a bicycle.

Let us assume that there are two primary customer requirements, viz. aesthetics and

performance. The secondary customer requirements under aesthetics are affordable cost,

aerodynamic look, proper finish, and corrosion resistance. The secondary customer requirements

under performance are light weight, strength, and durability. This is illustrated in the QFD or

House of Quality diagram (Figure 3-2).



Figure 3-2 House of Quality of a handlebar stem in a bicycle



As the customer needs and expectations are expressed in terms of customer requirements, the

QFD team needs to come up with engineering characteristics (HOW’s)

that will affect one or more of the customer requirements. Each engineering characteristic must

directly affect a customer perception (VOC) and be expressed in measurable terms.

Implementation of the customer requirements in design is difficult until they are translated into

counterpart technical characteristics. Counterpart technical characteristics are an expression of

the voice of the customer in technical language and specifications. For example, a customer

requirement for an automobile might be a smooth ride. This is rather an abstract statement,

which is important from the point of view of selling an automobile. Technical characteristics for

a smooth ride can be appropriate dampening, anti-roll, and stability requirements. These are the

primary technical descriptors or characteristics. Engineering knowledge and brainstorming

among engineering staff’s is a suggested method for determining technical characteristics.

Figure 3-3 shows the different technical requirements which can address all VOC for the bike

stem design.

Figure 3-3 Interrelationship between VOC and Technical Requirements

The next step in building a house of quality is to compare the VOC with technical characteristics



and determine their interrelationships. In this context, engineering knowledge about the product

and historic evidence/ data can provide useful information. Common practice is to use symbols

to represent the nature of relationship between customer requirements and technical descriptors.

Symbols used are:

I. A solid circle represents a strong relationship (scored as +9).

II. A single circle represents a medium relationship. (scored as +3).

III. A triangle represents a weak relationship (scored as +1).

IV. The box is left blank if there is no relationship between VOC and technical

characteristics.

Figure 3-4 provides the interrelationship matrix with type of relationships. Any cell that is

empty implies no or insignificant relationship.

Figure 3-4 Complete Interrelationship between VOC and Technical Requirements

After drafting the relationship matrix, it is evaluated for any empty row or column. An empty

row indicates that a customer voice is not being addressed by any technical descriptors. Thus, the

customer expectation is not being met. Any blank column indicates that the technical

requirement is unnecessary, as it does not address any VOC.



The roof of the house of quality, expressed as correlation matrix, is used to identify any

interrelationships between the technical descriptors (Figure 3-5). Symbols are used to describe

the strength of the interrelationships. Symbols generally preferred are:

I.

A ‘solid circle’ represents a strong positive relationship.

II. A ‘circle’ represents a positive relationship.

III. An ‘X’ represents a negative relationship.

IV. An ‘asterisk’ represents a strong negative relationship.

Figure 3-5 Correlation Matrix and Tradeoff between Technical Requirements



The symbols also describe the direction of the correlation. In other words, a strong positive

interrelationship means nearly perfect positive correlation. A strong negative will indicate nearly

perfectly negative correlation. This type of representation allows the user to identify which

technical characteristics support one another and which are conflicting. Conflicting technical

descriptors are extremely important because they are frequently the result of conflicting customer

requirements and, consequently, represent points at which tradeoffs must be made. Tradeoffs that

are not identified and resolved, while defining specification, will often lead to unfulfilled

requirements, unnecessary engineering changes, increase in cost, and poor quality from the

standpoint of customers. Some of the tradeoffs may require high-level managerial interventions,

because they cross functional boundaries.

An example of tradeoffs in the design of a car is customer requirements of

high fuel economy and safety. These two CTQ and technical descriptors are conflicting.

Addition of stronger bumpers, air bags, and antilock brakes will ultimately reduce the fuel

efficiency of the car.

The customer’s competitive assessment (Figure 3-6) is a pair of table (or graph) that depicts how

competitive products compare with current organization product status on specific VOC. The

customer competitive assessment is the block of columns corresponding to eachcustomer requirement in the house of quality on the right side of the relationship matrix,

The numbers 1 through 5 are listed in the competitive evaluation column to indicate a rating of 1

for worst and 5 for best. The customer competitive assessment is a good way to determine if the

customer voice has been met (as compared to best competitor) and identify areas to improvement

for future design.



Figure 3-6 Competative Assessment of VOC

The technical competitive assessment makes up a block of rows corresponding to each technical

descriptor in the house of quality beneath the relationship matrix. After respective technical

factors have been established, the products are evaluated for each technical factor that addresses

VOC.

Similar to the customer competitive assessment, the data recorded are in a scale of 1 through 5,

to indicate a rating, 1 for worst and 5 for best. The technical competitive assessment is often

useful in uncovering gaps in engineering judgment.



Importance ratings represent the relative importance of customer requirement in

terms of each other.

The target-value of column can be on the same scale as the customer competitive assessment (1

for worst, 5 for best can be used). This column is where the QFD team decides whether they

want to keep their product unchanged, improve the product, or make the product better than the

competitor.

The prioritized technical descriptors make up a block of rows corresponding to the technical

descriptor in the house of quality below the technical competitive assessment as shown in Figure

3-7. These prioritized technical descriptors contain target value and absolute weights.



Figure 3-7 Absolute Weights of Technical Requirements

The last rows of the prioritized technical descriptors are the absolute weight. A popular and easy

method for determining the weights is to assign numerical values to symbols in the relationship

matrix symbols. The absolute weight for the jth technical descriptor is given as

∑=

=n

i

iij j c Ra1



Where,

a j = row vector of absolute weights for the degree of technical difficulty of technical

descriptors

(i = 1, ... , m)

Rij = weights assigned to the relationship matrix (i = 1, ... , n, j = 1, ... , m)

ci = column vector of importance to customer for the customer requirements

(i = 1, ... , n)

m = number of technical descriptors

n = number of customer requirements

The absolute weight for each technical descriptor is determined by taking the dot

product of the column in the relationship matrix and the column for importance to customer. For

instance, for aluminum (see Figure 3-7) the absolute weight is

(9x8+1x5+9x5+9x2+9x7+3x5+3x3) x1 =227.

The greater values of absolute weight indicate higher importance of the technical descriptor toaddress VOC. These weights can be organized into a Pareto diagram to show which technical

characteristics are most important in meeting customer requirements.

In a corrosion problem, a Japanese car company Toyota, during 1960’s and 1970, there was huge

expense on warranty. The Toyota Rust QFD Study resulted in a virtual elimination of corrosion

warranty expenses. The customer requirement on durability was also achieved, with no visible

rust in following three years. It was determined that this could be obtained by including a

minimum paint film build, and maximum surface-treatment. The key process operation that

provides these part-quality characteristics consists of a three-coat process.

module iii lec1

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