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A New Model
of the Conceptual Design Process Using QFD/FA/TRIZ
by Dr. Noel León-Rovira
and Ing. Humberto Aguayo, MSC
Instituto Tecnológico y de
Estudios Superiores de Monterrey
Ave. Eugenio Garza Sada # 2501, Col. Tecnológico
CP 6409, Monterrey, NL, Mexico
email: nleon@campus.mty.itesm.mx
CONTENTS:
Abstract
An integrated model of the
Conceptual Design Process is presented, which is based on QFD, Functional
Analysis and TRIZ. It is analyzed how to use TRIZ, starting from the QFD-Diagrams
and continuing through Functional Analysis during the conceptual design
stage of new products. The information obtained during the Functional
Analysis is used to identify the product structure which reveals the
technical parameters needed for the QFD process. Two cases are presented
and analyzed on how the "roof" of the "House of
Quality" may be used as an interface to the Technical Contradictions
Matrix in TRIZ, as contradictory parameters are identified and the design
conflicts may be solved based on the Technical Contradictions Matrix.
1.
Introduction
This paper is the first of a
series of papers about the research work that is being undertaken at the
Center for Integrated Manufacturing Systems of the Monterrey Institute of
Technology in Monterrey, Mexico, looking for the integration of different
design tools and methodologies.
This work is based on the
experience gained of several real product design projects that have been
undertaken since 1995 on a contractual basis together with industrial
enterprises in Mexico which are looking for the improvement of their
products to compete in the international market.
Some of these product design
projects have been undertaken by student teams of the master degree
program on Manufacturing Engineering, as part of an effort to change the
way design is taught, providing hands-on experience in classes involving
students in full-scale product development resulting in functional or
virtual prototypes. In these paper two cases are discretionary presented
to illustrate the approaches applied.
The main scope of our research
work is to search for synergy between existing design methods and tools
while evaluating the results of the design process through measuring the
competitive advantage gained by the enterprises for which the projects are
being developed.
This first paper is aimed at
the integration of QFD, Functional Analysis and TRIZ, because the
integration of these tools may improve the performance of the early stages
of the design process, which, as most specialists agree, determine more
than 75 % the cost of the designed products [1]
Today companies are attempting
to understand quality better, and to predict product performance, but the
lack of integration of these tools increases cycle time. This was stated
at the workshop held at Gold Canyon, Arizona, from May 22 - 25, 1995 and
supported by the National Science Foundation, with the purpose to
determine research priorities in engineering design by examining industry
and education needs,
One of the conclusions of this
workshop is that greater demand for product efficiency, reliability,
quality, compactness, variety and customization combined with cycle time
reduction of 60 to 90% are needed to stay competitive in the future.
The workshop participants also
concluded that research areas that will have the greatest impact on
engineering design over the next 10 years are: Collaborative Design tools
and techniques, Prescriptive models/methods, System Integration
Infrastructure/Tools, and Design Information Support Systems. [2]
One further conclusion was
that there is a need for more generalists in product design who can
understand the big picture, not just some specialized problems. However,
currently much integration is being done by engineers lacking a real
understanding of the integration problem and at the same time, the
knowledge burden on the designer keeps increasing as more materials and
more options become available.
Work in prescriptive models
has been taking place largely in Europe especially in Germany [3,4, 5].
However, such systematic prescriptive methods are not based on any
theoretical foundations, and in fact, some doubt that there is sufficient
evidence that prescriptive methods produce better results. Work on
experimental validation is just beginning in Germany.
U.S. and Latin American
industry (and even academia) is relatively unaware of the German
systematic methods, but Taguchi methods and other techniques such as
Quality Function Deployment have been imported from Japan and used in
practice.
2.
QFD and Functional Analysis
QFD is a very important tool
to improve market share by reducing the gap between the customer's desires
and the product's performance. The fundamental principle of QFD is to
drive the design of a product or service by gathering all relevant
information about the customers’ wishes through surveys, interviews,
tests, benchmarks, etc. [6]. That means that the primary function of QFD
is to identify the most important issues and parameters of the products
and to link priorities and target values back to the customer.
As long as it is known how to
satisfy the wishes (WHATs) from the customers through the properties,
parameters and attributes of the products (HOWs ) this primary function
may be fulfilled.
But QFD is not a
problem-solving tool, although it is very useful in identifying what
has to be solved or improved in order to increase market share.
But before the correlation
between WHATs and HOWs in the QFD-matrix may be established, the
functional structure of the products has to be decomposed on to its basic
components. In each case each one of the identified relevant WHATs should
be supported by at least one of the basic components of the functional
structure of the already existing products.
To achieve this, the
functional tree structure, as described by Clausing [7] and Pahl and Beitz
[4] (Figure 1), is a very useful tool. The primary or global useful
function of a system is decomposed in sub-functions at different
hierarchical levels. In this case the term function is defined as the
input/output relation in one technical system that has to fulfill a task.
Sub-functions are therefore also input/output relationships that fulfill
sub-tasks in the technical system. Functions are then described in terms
of actions fulfilled on objects, where the actions are described by verbs
and the objects by parameters or substantives: i.e. "to increase
torque" "to transfer load" "to decrease rotational
speed" "to cut metal" etc.
Figure 1. Functional
tree structure
As stated earlier, the
functional tree should be developed so far, that each sub-function might
be stated as an action on a functional parameter. Furthermore at least one
parameter should be determined that is related to each and every one of
the WHATs identified in the first stage of the QFD process. This is a
non-trivial task and requires experienced designers that are able to
identify those correlations.
While applying QFD techniques
we concluded that it is a mistake to try to establish the functional
parameters or HOWs of the new products as part of the QFD process, without
first establishing the relationships between WHATs and HOWs of the already
existing products.
As QFD is not a problem
solving tool huge difficulties arise when trying to simultaneously define
the relationships between the wishes from the customers and the functional
structure and parameters of the new products being designed.
In appendix 1 a resumed QFD
matrix is shown about the Railroad Brake Beam from ACERTEK1.
The wishes of the customers were stated through market research of the
enterprise. Later our design team identified the relationships of the
wishes captured from marketing personnel with the structure and design
parameters of the brake beams that have been marketed during the last
years. The parameters were stated through functional analysis.
Therefore one conclusion of
our research work is that the first stage of applying the QFD methodology
is to identify the relationships between customer satisfaction and prior
existing product structure, before attempting to synthesize a new
product structure through the QFD matrix.
In the mentioned product
design projects, QFD approach has proved to be extremely useful in
understanding the strengths and weaknesses of prior existing products from
the viewpoint of the customer satisfaction. This understanding is
indispensable for further product development in a competitive
environment. However, attempts to use the QFD’s House of Quality as a
problem solving tool in other product design projects have caused
increased development time and costs, without real gain in customer
satisfaction and product quality.
Based on this, we changed our
approach and now recommend that QFD process and the construction of the
House of Quality (HOQ) should begin before a new product
design process is started.
This approach allowed us to
gain a better understanding of the market and customer needs and of its
relationships to the existing product structure and parameters. Later,
this better understanding could be applied when new product design
processes were started. As one of the features of the HOQ diagram shows
the directions in which product parameters has to change, or which
parameters should remain unchanged for a better customer satisfaction, the
new product design process may then focus on how to achieve this changes
to gain bigger market shares.
3. TRIZ
On the other side TRIZ has
proved to be a very strong tool in helping to solve difficult technical
problems that requires inventive thinking; that means problems where one
or more technical contradictions are involved and which do not have known
ways or means of solution
Altshuller began his work on
TRIZ in 1946. He studied the experience of inventive creativity from a
fundamental point of view and brought out the characteristics features of
good solutions and what distinguished them from bad solutions: "the
solution of inventive problems turned to be good if it overcame the
technical contradiction contained in the problem presented and bad if the
technical contradiction was not revealed and eliminated" [8]. From
Altshuller’s point of view a technical contradiction exists if when
using certain methods to improve one part, function, sub-function or
parameter of a technical system it is inadmissible for an other part,
sub-function or parameter to deteriorate in the process [9].
Of course, not every one of
the wishes of the customers involves an inventive problem. Most of the
work on identifying how to satisfy the needs from the customers has to be
solved based on the existing expertise of the designers. That means that
designers have to have enough knowledge and experience about the behavior
and structure of their products in order to be able to establish the links
among WHATs and HOWs in the QFD correlation matrix.
From the TRIZ point of view
that means that the biggest part of the problems that arise has solutions
from levels 1 or 2.
TRIZ is not originally a tool
that belongs to the classical product design methodologies and its place
in the product design process has yet to be better identified in order to
increase its efficiency. Some work has been already undertaken in this
direction by Savransky [10], who tries to find the links between TRIZ and
other methodologies of the classical German school.
A new terms denoted as
Inventive Engineering as a further Step from Design Engineering has been
coined in a Web publication from Arciszewski and Zlotin [11], denoting the
need to introduce innovative concepts in new product design to remain
competitive.
Terninko [9] has also
identified several links between TRIZ and QFD in his analysis of the
connection of these tools.
Although not yet a
comprehensive approach for the integration has been established and
further work is being undertaken, several opportunities of synergy and
need of improvement have been recognized between QFD/Functional Analysis
and TRIZ
3.1.
The Ideal Final Result Concept
At the kernel of TRIZ lies the
Concept of Ideal Final Result, which states that the ideal solution of a
technical contradiction should be that which enables to increase the
usefulness of the product without introducing new harmful effects,
maximizing the ideality. Ideality may be expressed as:
Ideality = Benefits / (
Costs + Harm)
The Ideal Final Result
describes the solution to a technical problem, independent of the
mechanism or constraints of the original problem. It is the upper limits
of the "ideality" equation, and can be visualized as
"ideal": The ideal system delivers benefit without harms (no
undesired side effects.)
By removing the mental
constraints of existing solutions, it gets people to think "out of
the box" and encouraging breakthrough thinking by enabling designers
to define the roadblocks they had been facing. [12]
At our design projects, the
first step after having a complete description of customer needs and
wishes, has been to formulate the IFR of the product being developed. A
written formulation of the IFR proved to be helpful in breaking the
psychological inertia.
However, attempts to formulate
the IFR as a target of the design process lead to inhibition of designers
in maximizing ideality. One thinking aid that has been helpful was to
start from the functional tree, eliminating all harmful effects and the
functions that are used to correct or eliminate harmful side effects.
3.2.
The Contradiction Matrix
As stated earlier in this
section the elimination of technical or physical contradictions is the
basic evaluation criteria for good innovative design solutions.
One of the first tools
developed by Altshuller was the Contradiction Matrix, where inventive
principles screened from the patent analysis were classified based on the
technical contradiction that were solved.
As at the roof of the HOQ are
identified the contradictory relationships among the design parameters, it
seems straightforward to use these identified contradictory parameters to
find a link to Altshuller’s Technical Contradiction Matrix.
In Figure 2 a simplified
representation of the link between the QFD-diagram and the contradictions
matrix is shown.
Figure 2. Simplified
representation of the link between QFD-diagram and TRIZ's contradiction
matrix
As during the last semester 8
student teams worked on the same number of design projects, a systematic
analysis was undertaken in each case: those parameters between which
contradictory relationships had been identified in the QFD diagram, were
then compared with the 39 general parameters from the Contradictions
Matrix. The intention was to find a match among the contradictory
parameters from the HOQ and the 39 Altshuller's parameter and to identify
inventive principles that could be applied to solve the technical
contradictions that had been stated.
It was concluded that
Altshuller’s Contradiction Matrix is useful in finding inventive
principles to solve technical contradictions. Several useful ideas were
derived from the use of the contradiction matrix, during the conceptual
design stage of the nopal-cactus dethorning machine. The inventive
principles segmentation, previous action, mediator, use of hydraulic and
pneumatic construction have been used to increase the Ideality of the
solutions applied in this project.
However, in other cases the
usefulness was only to a limited extent because several of the parameters
that had been identified in QFD diagrams could not be matched with any of
the 39 general parameters defined in the Matrix. For example such
parameters as the degree at which items has to be previously ordered or
aligned before processing them and inventive principles to solve technical
contradictions related to this parameter are not included.
In other cases, solution
principles that were used to solve design problems are not included in the
matrix, as for example increasing the inertial moment of structural
sections to solve the technical contradiction between strength and weight.
Other authors [13, 14] have
recognized the need to enhance the Contradiction Matrix with new
parameters and inventive principles that improve the success rate in using
this tool.
In our group, further work is
being developed in this direction. As in each product design project a
thoroughly patent search has to be completed, students are being
encouraged to identify if the found patents solve any technical
contradiction. When this is the case, the parameters and inventive
principles applied in those patents should be identified and compared with
those of Altshuller’s Matrix. In a later paper the achieved results will
be published.
3.3.
SUH diagrams
SUH diagrams from the
Innovation Workbench have been widely used, because they allow an
extensive analysis of the possible solutions in order to increase
Ideality. SUH diagrams have proved to be a useful tool if applied
carefully without exaggerating its use.
The connection between SUH
diagrams and Functional Analysis is straightforward. As Functional
Analysis allows to recognize the different useful functions and the
derived lateral harmful effects, it proved to be a very important step in
building the SUH diagrams to classify the decomposed functions in useful
ones and those that are needed to eliminate or reduce lateral harmful
effects.
Attempts to develop SUH
diagrams without determining first the functional structure was not as
useful and clear as those made after the functional tree structure was
first thoroughly identified, and the functions classified according to the
described criteria.
In Figure 3 the schematically
relationship between the functional tree and the SUH diagram is shown.
Figure 3.
Relationship between functional tree and the SUH diagram
Figure 4 shows one of the SUH
diagrams developed during the design of the new optimal brake beam.
Figure 4. SUH
diagram for the new optimal brake beam
4.
Conclusions
Synergies may be found among
QFD/Functional Analysis and TRIZ, which allow improving the structure of
the design process and shortening cycle time reducing design iterations by
solving complex design projects where inventive thinking is needed.
Successful results were achieved in several complex design projects that
were developed during the last 2 years.
Students and research
assistants participating in these projects agree that the combined and
systematic use of these tools facilitated their tasks and helped them in
finding better solutions.
Common sense has also proven
to be very useful in identifying the tasks where different methods and
inventive tools are more efficiently applied. For example using
conventional design tools as morphological matrix or simple design rules
where no innovative or inventive solutions are needed, has proven to be a
more efficient way because less time and effort is required. Innovative
efforts may then be concentrated on the more relevant parameters
accordingly to the evaluation rates in the HOQ Diagrams. In those cases
TRIZ tools, specially SUH diagrams, and Contradictions Matrix have proven
to be very useful.
The concept of Ideal Final
Result has shown to be a universal and robust way to lead to better
solutions, as psychological inertia and creativity inhibitions are
eliminated.
Opportunities have been also
identified of improving some TRIZ tools. For example the need was
recognized to enhance and further complete the Contradiction Matrix adding
new parameters and inventive principles.
5.
References
[1] Pugh, Stuart, Total
Design: Integrated Methods for Successful Product Engineering,
Wokingham, England: Addison-Wesley Pub. Co., 1991.
[2] Shah J. Shah et. al.,
"Research Opportunities in Engineering Design," NSF Strategic
Planning Workshop, Final Report, April 1996, Arizona State University.
[3] Verein Deutscher
Ingenieure, "VDI Guidelines – Systematic Approach to the Design of
Technical Systems and Products," VDI 2221, 1987.
[4] Pahl, G., and Beitz, W., Engineering
Design: A Systematic Approach, Springer, 1988.
[5] Leon, N. and Soucek, R., Beitrag
zur Verallgemeinerung der Ordnungsebenen Theorie in der Konstruktionslehre,
Wiss. Zeitschrift der Technischen Universität Dresden 32 (1983) H.4 Pag.7
- 19.
[6] Terninko, J., "The
QFD, TRIZ and Taguchi Connection: Customer-Driven Robust Innovation,"
The Ninth Symposium on Quality Function Deployment, June 10, 1997.
[7] Clausing, D.P., Total
Quality Development: A Step-by-Step Guide to World Class Concurrent
Engineering, ASME Press, New York 1994.
[8] Alshuller, H.S., Creativity
as an Exact Science: The Theory of the Solution of Inventive Problems,
New York: Gordon and Breach, 1995.
[9] Derrick, T. and Nordlund,
M., "Synergies Between American and European Approaches to Design,
Integrated Design and Process Technology," IDPT-Vol 1, Pag.
103- 109.
[10] S.D. Savransky, http://www.jps.net/semyon/savransky-triz-papers.htm
[11] Arciszewski, T., and
Zlotin, B., "Ideation/TRIZ:
Innovation Key to Competitive Advantage and Growth."
[12] Ellen D., "How to
Help TRIZ Beginners Succeed," http://triz-journal.com.
[13] Williams, T., "Reversability
of the 40 Principles of Problem Solving," http://triz-journal.com,
May Issue, No. 1.
[14] Savransky, S.D., "A
Few Words About Altshuller's Contradiction Matrix," http://triz-journal.com,
August 1997.
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