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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


1. Introduction
2. QFD and Functional Analysis
xx3.1 The Ideal Final Result Concept
xx3.2 The Contradiction Matrix
xx3.3. SUH diagrams
4. Conclusions
5. References
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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.


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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