30079_19.pdf

CHAPTER 19

TOTAL QUALITY MANAGEMENT IN

MECHANICAL DESIGN

B. S. Dhillon

Department of Mechanical Engineering

University of Ottawa

Ottawa, Ontario, Canada

19.4.5

Taguchi's Quality Philosophy

Summary and Kume's

Approach for Process

Improvement

19.1 INTRODUCTION

475

19.2 TQMINGENERAL

476

480

19.2.1 Total

476

19.2.2 Quality

476

19.2.3 Management

476

19.5 QUALITY TOOLS AND

METHODS

480

19.5.1

Fishbone Diagram

480

19.3 DEMING'S APPROACH TO

TQM

19.5.2

Pareto Diagram

481

477

19.5.3

Kaizen Method

481

19.5.4

Force Field Analysis

481

19.4 QUALITY IN THE DESIGN

PHASE

19.5.5

Customer Needs Mapping

Method

477

482

19.4.1 Product Design Review

477

19.5.6

Control Charts

482

19.4.2 Process Design Review

478

19.5.7

Poka-Yoke Method

482

19.4.3 Plans for Acquisition and

Process Control

19.5.8

Benchmarking

483

479

19.5.9

Hoshin Planning Method

484

19.4.4 Guidelines for Improving

Design Quality

19.5.10 Gap Analysis Method

484

479

19.1 INTRODUCTION

In today's competitive environment, the age-old belief of many companies that "the customer is

always right" has a new twist. In order to survive, companies are focusing their entire organization

on customer satisfaction. The approach followed for ensuring customer satisfaction is known as Total

Quality Management (TQM). The challenge is to "manage" so that the "total" and the "quality"

are experienced in an effective manner. 1

Though modern quality control dates back to 1916, the real beginning of TQM can be considered

the late 1940s, when such figures as W. E. Deming, J. M. Juran, and A. V. Feigenbaum played an

instrumental role. 2 In subsequent years, the TQM approach was more widely practiced in Japan than

anywhere else. In 1951, the Japanese Union of Scientists and Engineers introduced a prize, named

after W. E. Deming, for the organization that implemented the most successful quality policies. On

similar lines, in 1987, the U. S. government introduced the Malcolm Baldrige Award.

Quality cannot be inspected out of a product; it must be built in. The consideration of quality in

design begins during the specification-writing phase. Many factors contribute to the success of the

quality consideration in engineering or mechanical design. TQM is a useful tool for application during

the design phase. It should be noted that the material presented in this section does not specifically

deal with mechanical design, but with the design in general. The same material is equally applicable

to the design of mechanical items. This chapter presents topics such as TQM in general, Deming's

approach to TQM, quality in design, quality tools and techniques, and selected references on TQM

and design quality.

Mechanical Engineers' Handbook, 2nd ed., Edited by Myer Kutz.

19.2 TQMINGENERAL

The term quality may simply be defined as providing customers with products and services that meet

their needs in an effective manner. TQM focuses on customer satisfaction. The three words that make

up this concept—"total," "quality," and "management"—are discussed separately below. 1

19.2.1 Total

This calls for the involvement of all the aspects of the organization in satisfying the customer, a goal

that can only be accomplished if the usefulness is recognized of having partnership environment at

each stage of the business process both within and outside the organization, as applicable. With

respect to the outside stage of the business process, the important critical factors for a successful

supplier-customer relationship are

1. Development of a customer-supplier relationship based on mutual trust, respect, and benefit

2. Development of in-house requirements by customers

3. Customers making suppliers clearly understand their requirements

4. Customers selecting their potential suppliers with mechanisms in place to achieve zero defects

5. Regular monitoring of suppliers' processes and products by the customers

19.2.2 Quality

Any company or organization in pursuit of TQM must define the term quality clearly and precisely.

It may be said that quality is deceptively simple but endlessly complicated, and numerous definitions

have been proposed, such as "quality = people + attitude"; "providing error-free products and

services to customers on time"; and "satisfying the requirements and expectations of customers".

Another definition is offered here: "quality means providing both external and internal customers

with innovative goods and services that meet their needs effectively."

This definition has three important dimensions:

1. It focuses on satisfying the needs of customers

2. Organizations using this definition provide both products and services, which jointly deter-

mine the customer's perception of the company in question

3. The concerned companies have both external and internal customers

According to a survey reported in Ref. 1, 82% of the definitions indicated that quality is defined

by the customer, not by the supplier. The top five quality measures identified by the respondents

were customer feedback (22.92%), customer complaints (16.67%), net profits (10.42%), returning

customers (10.42%), and product defects (8.33%).

19.2.3 Management

The approach to management is instrumental in determining companies' ability to attain corporate

goals and allocate resources effectively. TQM calls for a radical change in involving employees in

company decision-making, as their contribution and participation are vital to orienting all areas of

business in providing quality products to customers. It must be remembered that over the years the

Fortune 1000 companies in the United States have reported such benefits of employee-involvement

as increased employee trust in management, improved product quality, improved employee safety/

health, increase in productivity, improved management decision-making, increased worker satisfac-

tion, improvement in employee quality of work life, improved union-management relations, improved

implementation of technology, improved organization processes, eliminated layers of management,

and better customer service.

Companies considering the introduction of TQM will have to see their employees in a new way,

for the change in management philosophy needed to truly manage total quality is nothing short of

dramatic. Furthermore, it is important that the managment infrastructure lay the foundation for in-

volving the entire workforce in the pursuit of customer satisfaction.

The Senior Management Role

Senior management must show enthusiasm for improving product quality if employees are to seri-

ously consider its importance. The following steps by management are useful in gaining commitment

to total quality: 3

• Announce absolutely clear quality policies and goals and ensure that these are explained to

everyone involved.

• Regularly show management support through action.

• Ensure that everyone in the organization understands his or her necessary input in making

quality happen.

• Eradicate any opportunity for compromising conformance.

• Make it clearly known to everyone concerned, including suppliers, that they are an important

element in contributing to the quality of the end product.

19.3 DEMING'S APPROACH TO TQM

One of the pioneers of the TQM concept has expressed his views on improving quality. His fourteen-

point approach is as follows: 4

1. Establish consistency of purpose for improving services.

2. Adopt the new philosophy for making the accepted levels of defects, delays, or mistakes

unwanted.

3. Stop reliance on mass inspection as it neither improves nor guarantees quality. Remember

that teamwork between the firm and its suppliers is the way for the process of improvement.

4. Stop awarding business with respect to the price.

5. Discover problems. Management must work continually to improve the system.

6. Take advantage of modern methods used for training. In developing a training program, take

into consideration such items as

• Identification of company objectives

• Identification of the training goals

• Understanding of goals by everyone involved

• Orientation of new employees

• Training of supervisors in statistical thinking

• Team-building

• Analysis of the teaching need

7. Institute modern supervision approaches.

8. Eradicate fear so that everyone involved may work to his or her full capacity.

9. Tear down department barriers so that everyone can work as a team member.

10. Eliminate items such as goals, posters, and slogans that call for new productivity levels

without the improvement of methods.

11. Make your organization free of work standards prescribing numeric quotas.

12. Eliminate factors that inhibit employee workmanship pride.

13. Establish an effective education and training program.

14. Develop a program that will push the above 13 points every day for never-ending

improvement.

19.4 QUALITY IN THE DESIGN PHASE

Although TQM will help generally to improve design quality, specific quality-related steps are also

necessary during the design phase. These additional steps will further enhance the product design.

An informal review during specification writing may be regarded as the beginning of quality

assurance in the design phase. As soon as the first draft of the specification is complete, the detailed

analysis begins.

Some of the important areas assocated with quality in design are discussed separately below. 5

19.4.1 Product Design Review

Various types of design reviews are conducted during the product-design phase. One reason for

performing these reviews is to improve quality. Design reviews conducted during the design phase

include preliminary design review, detailed design reviews (the number of which may vary from one

project to another), critical design review (the purpose of this review is to approve the final design),

preproduction design review (this review is performed after the prototype tests), postproduction design

review, and operations and support design review.

The consideration of quality begins at the preliminary design review and becomes stronger as the

design develops. The role of quality assurance in preliminary design review is to ensure that the new

design is free of quality problems of similar existing designs. This requires a good knowledge of the

strengths and weaknesses of the competing products. The following approaches are quite useful in

ensuring quality during the design phase.

Quality Function Deployment (QFD), Quality Loss Function, and Benchmarking

Quality function deployment is a value-analysis tool used during product and process development.

It is an extremely useful concept for developing test strategies and translating needs to specification.

QFD was developed in Japan. In the case of new product development, it is simply a matrix of

consumer/customer requirements versus design requirements. Some of the sources for the input are

market surveys, interviews, and brainstorming. To use the example of an automobile, customer needs

include price, expectations at delivery (safety, perceived quality, service ability, performance, work-

manship, etc.), and expectations over time (including customer support, durability, reliability, per-

formance, repair part availability, low preventive maintenance and maintenance cost, mean time

between failures within prediction, etc.).

Finally, QFD helps to turn needs into design engineering requirements.

The basis for the quality loss function is that if all parts are produced close to their specified

values, then it is fair to expect best product performance and lower cost to society. According to

Taguchi, 6 quality cost goes up not only when the finished product is outside given specifications, but

also when it deviates from the set target value within the specifications.

One important point to note, using Taguchi's philosophy, is that a product's final quality and cost

are determined to a large extent by its design and manufacturing processes. It may be said that the

loss function concept is simply the application of a life cycle cost model to quality assurance. Taguchi

expresses the loss function as follows:

L(x} = c(x - T v ) 2

(19.1)

where x = the variable

L(JC) = the loss at x

T v = the targeted value of the variable at which the product is expected to show its best

performance

c = the proportionality constant

(x—T v ) = the deviation from the target value

In the formulation of the loss function, assumptions are made, such as zero loss at the target

value and that the dissatisfaction of customer is proportional only to the deviation from the target

value. The value of the proportionality constant, c, can be determined by estimating the loss value

for an unacceptable deviation, such as the tolerance limit. Thus, the following relationship can be

used to estimate the value of c:

c = |

(19.2)

where L a = the amount of loss expressed in dollars

A = the deviation amount from the target value T v

Example 19.1

Assume that the estimated loss for Rockwell hardness number beyond 56 is $150 and the targeted

value of the hardness number is 52. Estimate the value of the proportionality constant. Substituting

the given data into Eq. (19.2), we get

150

C ~ (56 - 52) 2

= 9.375

Thus, the value of the proportionality constant is 9.375.

Benchmarking is a process of comparing in-house products and processes with the most effective

in the field and setting objectives for gaining a competitive advantage. The following steps are

associated with benchmarking: 7

• Identify items and their associated key features to benchmark during product planning.

• Select companies, industries, or technologies to benchmark against. Determine existing

strengths of the items to benchmark against.

• Determine the best-in-class target from each selected benchmark item.

• Evaluate, as appropriate, in-house processes and technologies with respect to benchmarks.

• Set improvement targets remembering that the best-in-class target is always a moving target.

19.4.2 Process Design Review

Soon after the approval of a preliminary design, a process flowchart is prepared. In order to assume

the proper consideration being given to quality, the quality engineer works along with process and

reliability engineers.

For the correct functioning of the process, the quality engineer's expertise in variation control

provides important input.

Lack of integration between quality assurance and manufacturing is one of the main reasons for

the failure of the team effort. The performance of process failure mode and effect analysis (FMEA)

helps this integration to take place early. The consideration of the total manufacturing process per-

formance by the FMEA concept, rather than that of the mere equipment, is also a useful step in this

regard. For FMEA to produce promising results, the quality and manufacturing engineers have to

work as a team. Nervertheless, FMEA is a useful tool for performing analysis of a new process,

including analysis of receiving, handling, and storing materials and tools. Also, the participation of

suppliers in FMEA studies enhances FMEA's value. The following steps are associated with the

process of FMEA: 8 - 9

• Develop process flowchart that includes all process inputs: materials, storage and handling,

transportation, etc.

• List all components/elements of the process.

• Write down each component/element description and identify all possible failure modes.

• Assign failure rate/probability to each component/element failure mode.

• Describe each failure mode cause and effect.

• Enter remarks for each failure mode.

• Review each critical failure mode and take corrective measures.

19.4.3 Plans for Acquisition and Process Control

The development of quality assurance plans for procurement and process control during the design

phase is useful for improving product quality. One immediate advantage is the smooth transition

from design to production. The equipment-procurement plan should include such items as equipment-

performance verification, statistical tolerance analysis, testing for part interchangeability, and pilot

runs. Similarly, the component-procurement quality plans should address concerns and cooperation

on areas including component qualification, closed-loop failure managment, process control imple-

mentation throughout the production lines, and standard and special screening tests.

Prior to embarking on product manufacturing, there is a definite need for the identification of the

critical points where the probability of occurrence of a serious defect is quite high. Thus, the process

control plans should be developed by applying the quality function deployment and process FMEA.

These plans should include items such as

• Acceptance of standard definitions

• Procedures to monitor defects

• Approaches for controlling critical process points

19.4.4 Guidelines for Improving Design Quality

During the product design phase, there are various measures concerned professionals should take to

improve quality. These include 10 ' 1 1 designing for effective testing, simplifying assembly and making

it foolproof, designing for robustness, minimizing the number of parts, reducing the number of

different parts, using well-understood and repeatable processes, minimizing engineering changes to

released products, eliminating adjustments, selecting components that can withstand process opera-

tions, and laying out components for reliable process completion. These factors may be taken into

consideration during designing and/or during design reviews.

Past experience has shown that guidelines such as those listed above lead to many benefits,

including

• Increase in part yield

• Decrease in degradation of performance with time

• Improvement in product reliability

• Reduction in part damage

• Better serviceability

• Improvement in consistency in part quality

• Reduction in the volume of drawings and instructions to control

• Lower assembly error rate

Today, many engineering systems use computer technology, to varying degrees. This means that

it is important not only to have good-quality hardware, but also good-quality software. The software-

development environment possesses certain characteristics that may adversely affect its quality, in-

cluding outdated support tools, cost and time constraints, complex hardware, variations in programmer

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