SYNTHESIS REGARDING THE PRODUCT CONCEPTUAL DESIGN METHODS AND TOOLS

Felicia BANCIU1, George DRAGHICI1, Andreea MIHARTESCU1

1 Politehnica University of Timisoara, Integrated Engineering Research Centre, {fbanciu, gdraghici, amihartescu}@eng.upt.ro

Keywords: product design, conceptual design, design methods and tools

Abstract: The presented researches refer to the product’s conceptual design phase. The paper is part of a wider theme having as final aim the development of a platform for product conceptual design. This platform will include the main design methods and their software supports. To solve the proposed goals, we started with the analyses of the theoretical bases, which define the main concepts, some of the methods and their software supports. These software supports can follow different ways to finalize a study, according to AFNOR or APTE norms. Because we choose an APTE approach, we presented first APTE method and Functional Analysis based on APTE method, and then FMEA method. Finally, we presented the software that applies these methods: TDC Need, TDC Structure and TDC FMEA.

1. INTRODUCTION

Engineering design is a creative activity which starting from expressed needs and

existent knowledge has as aim to define a material or immaterial object, named also artifact, which satisfy these needs and which can be industrial realized [1]. Engineering design is a key factor for the new product’s development process.

Product design can be defined as an entirety of activities and processes which allow us to pass from the idea of a new product (or improving an existent one) to information (drawings, programs, etc) which allow the production launching and ensure the product’s use and maintenance [6], [8].

Among design models the most representative is the model of Pahl and Beitz [5], which is based on a design seen as a hierarchical, sequenced phases, the predominant logic being the convergence. At the origin of each new technical object, there is a specific problem to solve and a goal to focus on. The first phase of design consists in establishing the desired technical and economical specifications. The next phases consist of comprehending the design as a process of an increasingly defining process of adopted solution or like a bridge from a function (abstract form) to a solution (certain form). In the conceptual design phase, after a functional analysis and a study of possible technical alternatives available for each function and sub-function a concept for the design object is usually chosen. The goal in the embodiment design phase is to determine the shape and the dimensions of the artifact. During the detail design phase are mentioned the components of the product and are formalized the papers needed for preparing the supply and manufacturing the components.

The presented researches refer to the products conceptual design phase. The paper is part of a wider theme having as final aim the development of a common platform for product conceptual design. This platform will propose a conceptual design methodology based on the most usual methods and software tools: Functional Analysis – FA (TDC Need, TDC Structure), Value Analysis – VA (Valorise), Quality Function Deployment - QFD (QFD Designer), Structured Analyses and Design Technique – SADT (AI0WIN), Failure Modes and Effect Analysis – FMEA (TDC FMEA), Theory of Inventive Problem Solving –TIPS (TRIZ Explorer).

In the paper we deal with Functional Analysis (AF) method, used in software TDC Need to elaborate the Functional Specifications Conditions (FSC) and in TDC Structure so

that we can functionally decompose the products. Taking into account that a FMEA can be made starting from a product’s decomposition in functions that have to be achieved by the product itself or from the decomposition of systems in subsystems, components, functions, we continued with the FMEA method.

To solve the proposed goals, first, we started to analyze the theoretical bases that define the main concepts, some of the methods and their software supports. These software supports can follow different ways to finalize a study, according to AFNOR or APTE standards. Because we choose an APTE approach, first, we presented the APTE method and Functional Analysis based on APTE method, then FMEA method. Finally, we presented the software, which apply these methods: TDC Need, TDC Structure and TDC FMEA.

2. SHORT OVERVIEW OF THE CONCEPTUAL DESIGN METHODS

2.1. APTE Method The definition of APTE method is: “It is a judgment method with a technical-

economical characteristic which refers to the fact that in a product, proceeding, organization, is included only what is considered to be absolutely necessary concerning the material, resources, wok force, energy to satisfy the exact need of those who use this product, proceeding, organization” [2]. The approach consists of four stages:

Expressing the study’s goals and limits,

Emphasizing the uses of the product,

Emphasizing the absolutely necessary elements which will express the absolutely necessary concept regarding that what is necessary, the design function .

Finding the solution which will render the service and is more closer to the absolutely necessary, meaning with a minimal cost

APTE method proposes seven judgment principles [2]:

Writing the objective specifications – the solutions are not compared to each other, each solution is compared to the services that it has to render to the user;

The judgment taking into account the external utilization environment – the solutions are independent from the ways in which they are solved;

Using the judgment power offered by the analysis – the functions are independent and so they offer a analysis background;

Distinguish between what is useful and what is useless: in all the solutions to attain the goal a part of the used resources is absolutely necessary to the user and the rest depends on the design characteristic of this solution, named as design function;

From an economical point of view, to think cash-flow – each judgment has to be followed by a thought about the economic matters in terms of input and output;

Searching the solution applying a judgment with reference to the functions – the functions are not related to the solutions, thus, their manifestation makes possible the issuing of a multitude of possible solutions, it has to be at the basis for an organized research, offering the best solution by using the quality and cost criteria;

Realizing the synthesis, then the analysis. The characteristic features of APTE method consist in synthesizing the contributions

of different thoughts and scientific researchers: functional approach, the systemic analysis, operational research, economy, and generally engineering sciences. The appliance of the APTE method requires a multidisciplinary work group, which has to have a leader.

Next APTE stages are unfolded [2]. The first three stages are found again in the software presented in the second part of the paper.

The first stage express the limits and the goals of the study and the used instruments are bête à cornes (Figure 1 (a)) and validity control. The results of this stage are information that is used by those that design or change a product, process, or organization.

The second stage expresses services that have to be rendered through FSC, is used to express the service that has to be rendered by the studied object to its users. It contains the list of the object’s functions that have to be expressed, validated, quantified, and qualified through value criterions. FSC is the expression of the goals independent by the used means to reach them and represent an objective reference of the quality (rendered services to user).

The functional specification conditions (FSC) definition (NF EN 1 325-1:1996) is: „A document through whose mediation the person which expresses the needs (or the person which has the mission to express the needs) in terms of service functions and constraints. For each function, there are defined appreciation criterions, their levels, each criterion having a flexibility degree.”

To express the functions it is necessary to know the possible contexts in which the product is used and for each of these contexts we have to emphasize and express the service to render. For each context, the object is in contact with a certain number of environment’s elements. These elements are called “external environment” of utilization.

Concerning the formulation of the functions, there are two types: principal functions and constraint functions. The object that’s FSC is realized connects different external environment’s elements. Each relation created between one or more elements of the external environment through the object, has a goal and is the main function. Each demand of the elements of the external environment is considered as a constraint function. It is used the pieuvre scheme (Figure 1 (b)), a graphical tool which helps us to express these functions; in the central part is the object and around it are the elements of the external environment. If there is a relation mediated by the object between two elements of the external environment, then this is a main function and is expressed graphically through a line connecting these two elements and the object. To express the function, there are eight rules.

(a) (b)

Figure 1. The model of Bête à cornes and Pieuvre

Function validity control: The functions are independent of the chosen solutions to realize them but they depend on selected design option to realize them. These options can

Who is the beneficiary of the study?

On what is acting the study?

STUDY

Why? Which is the aim?

Environmental object

Environmental

object

Product

Environmental Object

Environmental object

conduct to the evolution or disappearance of certain functions. So, for each function it has to be made a validity control, consisting in three questions: why does this function exist? What can make it develop?, What can make it disappear?

The third stage consists in selecting the reference solution and in identifying the absolutely necessary cost to realize it. In this stage, it will be made the Functional Diagram Block (FDB) and Functional Analysis Table (FAT). To make this (FDB and FAT) it is necessary to know Functional Analysis (AF) based on APTE method. In the next paragraph are described AF, FDB and FAT.

FSC elaborated after the announcement of the study’s goal represents a reference for the rapid realization of the product. Certain functions expressed in FSC are not totally new; they can be found to other rival companies. We have to find the closest function to that presented in the FSC. Therefore, through comparison of the found solutions to the existent ones, we can determine the lack between the services rendered by the solution and those required, in this way being established the value diagnosis. Through the comparison between what is absolutely necessary to render the services and what is consumed in reference solution, emphasizing the opportunities of resources economy, are named resources diagnosis. The difference between absolutely necessary of resources to respond to FSC and consumed resources into reference solution is considered design function.

2.2. Functional Analysis based on APTE Method

In APTE method to elaborate the FSC it is used External Functional Analysis, and for

the elaboration of Functional Diagram Block (FDB) and Functional Analysis Table (FAT) it is used Internal Functional Analysis. These two ways of analysis are detailed in the following.

According to the AFNOR X50-150 standard [1]: "Functional Analysis is an action which consists of searching, set in order, characterization, hierarchy and/or set a value (quantifying) for the functions".

Connected to functional analysis it has to be specified that there are many methods of AF that is more or less adapted to the analysis that we want to realize. Through these methods are: interactor’s method, (mechanical domain), Functional Tree, FAST Diagram, SADT Method (automation), GRAFCET Method, MERISE Method. These methods have as goal the elaboration and validation of a FSC, the search for solutions that correspond to the real needs the identification of important costs [3].

Functional Analysis can be seen as a bridge between the needs expressed by the customers and the functions that have to render the products, processes, or organizations. Through these features, AF is essentially a way to conduct to the obtaining of the products’ quality. AF can be realized for every specific utilization context of the studied object.

Functional Analysis has two possibilities to be unfolded: External Functional Analysis and Internal Functional Analysis.

External Functional Analysis consists of: analyzing the need, functions identification, identification of the external environment’s elements, identification of the principal functions and constraint functions, functions validity control. These elements were presented before in presentation of the second stage of APTE method. They are processed in TDC Need software [11].

Internal Functional Analysis consists in system’s decomposition, elaborating the FDB and establishing FAT. These elements are processed in TDC Structure software. Internal Functional Analysis is presented in the third stage of APTE method.

To analyze the reference solution it is used FDB. This tool makes easier to emphasize the aggregate of elementary functions and their assignment to basic and design functions. This tool is next completed by FAT. To realize a FDB we have to build a graphic and represent in order [7]:

a) To dispose all the composing elements of the product or subassemblies in contact relation:

external contacts – contacts between different external environmental elements and product’s components to satisfy the basic functions (these are the main functions of the products or constraint functions);

internal contacts - contacts between different product’s components justified by design, which satisfy the design functions (can be real or virtual);

b) To dispose graphically all the external environment’s and system’s elements. c) To dispose the open and close streams:

open streams are relations between external environment and different internal components of the product, to satisfy directly the basic functions;

close streams are relations between different product’s elements because of its designing, it can be external opened streams, which integrate the relations between some of the products components with one or more external environments, respectively internal closed streams which take into account just the product’s components.

Then, it is realized FAT, which allows to estimate the cost for each functional chain. First, it requires to list the element’s functions contented in FDB, identifying those element’s functions in FDB which correspond to FSC and those which correspond to design function, evaluating the absolutely necessary cost for each function in FSC, evaluate each design function’s cost through an analyze of its elements cost. Then it will be calculated the cost for each design function, analyzing the objective cost and possible economies. Next it can be calculated the designing efficiency as ratio between absolutely necessary cost and the solutions cost [2].

2.3. Failure Modes and Effect Analysis (FMEA) Method

FMEA method’s aim is to improve the products quality through an identification of

potential weak points of the analyzed system, identification of the faults, causes and their effects which conducted to the failure, respectively defining and putting into work corrective and/or preventive actions even from the design phase. This method is an exhaustive and rigorous technique of teamwork, extremely efficient because are put together the experience and the competence of each participant [4], [9].

This method was developed in many fields. FMEA can be found at the final of each stage of the life cycle of product [12], [13]:

FMEA product regarding the product in his conceptual phase and allows to check if it accomplishes all the functions for which it was designed;

FMEA process regarding the product in its realization phase and allows to verify the impact of the manufacturing process with the conformity of the product;

FMEA methods regarding the production methods used in the products manufacturing.

To realize a FMEA there has to exist a very good knowledge of the functioning of the studied system or it has to dispose the proper tools to collect the information that we need from those people, which posses the information.

FMEA method is unfolded in five stages [4]: initialization, functional analysis, fault analysis, quoting of faults, proposed corrective actions. A functional analysis of the

elements (product, process, organization that will be the subject of this analysis) is necessary to allow the identification of component elements and their functions. Next are analyzed their potential failures followed by the analyzing of the causes that conducted to them, their possible effects, their critical degree and corrective actions that will be undertake.

Each failure is characterized through probability of appearance, probability of un-detection and severity perceived by the client. Next, it is defined a priority order departing from a critical value to establish if there are necessary corrective or preventive actions [10]. Definition of the terms that appear in methods unfolding:

Cause – cause of failure modes;

Prompt criticality– value that allows to establish if there are necessary corrective or preventive actions;

Failure effect – consequences of each failure modes on correct functioning, functions, user, and is expressed in terms of consequences for final customers;

Failure modes – represents the manner in which a system can interrupt its functioning or to function abnormal, it is expressed in physical terms;

Prompt criticality coefficient – is defined as the multiplication of three values: G/S – gravity coefficient; is the evaluation of the effect of each malfunction experienced by the final customer; this coefficient has as starting point a grid specific for each field; F/O – frequency coefficient; defines the probability with which the cause can determine the falling and also this cause to occur; this coefficient has as starting point a grid specific for each field; D – non-detection coefficient; defines the probability with which the cause (and/or the way) of malfunction already existent has an effect on the customer; this coefficient has as starting point a grid specific for each field.

3. A SYNTHESIS OF THE CONCEPTUAL DESIGN TOOLS

3.1. TDC Need

The elements presented previously referring to the study’s goal and FSC is

synthesized in the software TDC Need, which is used for the elaborate the FSC for existent products (re-design) or totally new ones. FSC allows a better expression of the customers need, to go deeply to the specific character of the customers need through a write dialog between different services: those which design the product defining the need and those in permanent contact with customers – purchase, marketing, improving the quality of the sold service [11].

This software can follow an approach based on retained AF, meaning after one of the EN 1325-1 standards (AFNOR) or APTE method. This thing is possible by the selection of the elements, which we want to be in FSC. In the next example to emphasize the elements of a FSC it was used an example based on APTE method previously presented. The stages necessary to be followed to elaborate a FSC are:

Take into account the utilization contexts;

Take into account the external environment’s elements of the object (PIEUVRE) for each utilization context;

Emphasize the relations created by the object between the external environment’s elements of the object for each utilization context and expressing the goal for each relation;

The identification of constraints functions for each element of the external environment which is not the subject of a principal function;

Validity control of the functions;

Emphasizing the value criterions for each of the validated functions or re-expressed ones;

Qualification and quantification of each value criterion. These seven stages of the FSC are illustrated by TDC Need and will be followed in

the selected stages of the program (Figure 2).

Figure 2. Phases of the Functional Analysis Stages Figure 3. Pieuvre

Functional Analysis stage includes many phases, as can be seen in figure 2. Therefore, the characteristic elements of functional analysis, which is an external one, are emphasize, set in order, characterize, valorization, (capitalization), hierarchy of the functions. Functional Analysis is unfolded for each specific situation of the product (ex: functioning, assembly, etc) these being product’s utilization contexts. In this example it was used a single utilization context, a generally situation. To emphasize the functions it can be used the brainstorming or pieuvre. The software allows the build of pieuvre, the connections created between the product and the elements of its external environment, characteristic to its utilization context, can be seen graphically (Figure 3). Next, the identified functions will be subdued to a validity control followed by the arrangement of functions sub phase where is established their ramifications on levels and sublevels. The functions identified previously will be characterized through the assignation of criterions; levels of each criterion, flexibility class respectively the importance of the discussed function.

3.2. TDC Structure

To realize the internal functional analysis, it can be used the software TDC Structure

that helps us to realize FDB and FAT, described in subchapter 2.2. FDB is used to emphasize the existent relations between product’s component elements, the functions of the product’s elements, reporting on what is internal to product unlike the FSC which take into account just the functions that has to be accomplished by the product, according to the customers enounced need. The concepts used in FDB were defined earlier and they can be identified in software stages presented next. In figure 4, there are presented the stages of the software: emphasize, set in order, characterization of the functions.

Figure 4. Stages of TDC Structure program Figure 5. Functional Diagram Block (FDB)

These three stages are already solved if we used previously the TDC Need software to elaborate the FSC, the stages could be found there. Service functions were identified through the elaboration of FSC with TDC Need. Next, in the second stage it is realized the solutions list. It contains: the product’s components list, their ramification (Figure 4) and characterization (characteristics name, classification, tolerance, units, checking mode, population sample).

Next is realized FDB, which include: contact functions list, the functions list of closed streams which materialize the design functions and the functions defined previous in the stage referring to service functions. All these can be easily represented using the specific way to realize a FDB, namely through the representation of the entire product’s component elements already defined and external environments followed by their setting in the work area (Figure 5). These external environments were also identified in the previous in FSC’s elaboration stage. The external environments are represented as ellipses and the product’s internal elements as rectangles. Taking into account the nature of the identified relations, the existent relations between these can conduct either to contact functions or closed/open streams. These relations are figured through lines that cross or not the product’s elements. A closed stream is represented among these elements that have contact functions among themselves, and their notation is Fb.

After the FDB was realized, the characterization of each contact, stream or service function is made. The product’s component elements participation to realize these functions is centralized in FAT (Figure 6) that has two possible ways of displaying, namely components/functions and functions/components. In this table, we observe that there are centralized service functions and closed stream functions (Fb). For the realization of each of these functions we can identify in the table how many and which of the components contribute to its achieving. By assigning a cost to each identified element it can be analyzed the cost of each function and so it can be identified the expensive or less expensive functions.

Figure 6. Functional Analysis Table (FAT)

3.3. TDC FMEA This software allows a FMEA method (Figure 7). It includes specific modules in which

there are used the notions presented previously in sub-chapter 2.3. FMEA can be fulfilled using a decomposition of product in functions that have to be accomplished or decomposing the systems in subsystems, components, functions. This software support can follow different ways to finalize a study, according to a product or process.

Figure 7. Set in order of the functions Figure 8. Product’s functions

First it is realized the setting in order of the functions, setting in order that was previously realized in FSC. Each function is next included in a table which refers to specific elements of the FMEA, described in subchapter 3.3 as: potential failure, potential effect, category, potential cause, planned actions to be followed, adopted measures, detection, validation, terms, S, O, G coefficients and prompt criticality coefficient named IPR. Depending on the followed type of analyze, a part of the elements present in the tables can be completed with characteristic elements that are kept. Using a default way to make the analyze, there are mentioned product’s functions (Figure 8) that were already identified in software TDC Need and TDC Structure. When it is applied (as an analyze way that uses the product’s decomposition in components) FDB from TDC Structure is useful, fact which emphasizes the functions and the relations between the product’s components relations. The IPR and IPR` coefficients are next calculated and depending on IPR value the correspondent function are colored in green for IPR<60, yellow for 60<IPR<120 and red

for IPR>120. After completion of the table, there is the possibility to display graphically the calculated elements (IPR and IPR’) and to compare them. Depending on the results, decisions are taken.

4. CONCLUSIONS

Realizing the functional specification conditions using the software TDC Need we can

identify, through the use of the marketing department, brainstorming or in workshops, the service functions which answer the customer’s needs, their classification, setting in order, capitalization, hierarchy of the functions, so that for the internal functional analysis, using FDB, we can have the entire picture where there are identified the main functions, the constraints functions, each of them being linked to the degree of importance (the capitalization). These elements of the functional specification conditions are in fact input elements for the software TDC Structure, the first steps being: expressing the service functions, setting in order, respectively their characterization. These have been presented in the functional specification conditions written with the help of the software TDC Need. In the second phase, the solution list is being completed. In this phase, we can distinguish the product’s components list, their ramification, and their characterization. After the realization of the FDB, we can go on with the characterization of each set of contact, service or stream functions. We can use a default way to make the analyze for the realization of the FMEA, using the software TDC FMEA,. There are mentioned the product’s functions that were already identified in software TDC Need and TDC Structure. In the case when it is used a way to make the analyze that uses the product’s decomposition in components, it is useful the FDB from TDC Structure, which emphasizes the functions and the relations between the product’s components relations. Thus, the possible malfunctions, with their causes and effects, can be analyzed and prevented starting with the preliminary conceptual design phase.

5. REFERENCES

[1] AFNOR, (1988). Recommandation pour obtenir et assurer la qualité en conception, Norme X50-127, AFNOR, Paris.

[2] Bretesche, B., (2000). La méthode APTE. Analyse de la Valeur, Analyse Fonctionnelle, Editions Petrelle, ISBN 2-84440-019-1, Paris.

[3] Gabriel, M. (2004). Analiza funcţională, Médiatice (UHP Nancy 1, France), available at: http://www.cyber.uhp-nancy.fr/demos/ROMA-002/general/index.html

[4] Gabriel, M., (2004). AMDEC, Médiatice (UHP Nancy 1, France), available at http://www.cyber.uhp-nancy.fr/demos/ROMA-003/general/index.html

[5] Pahl, G., Beitz, W., (1984). Engineering Design, Design Council, London. [6] Perrin, J., (2001). Concevoir l’innovation industrielle. Méthodologie de conception de l’innovation,

CNRS Editions, ISBN 2-271-05822-8, Paris. [7] Petitdemange, C., (1992). Maîtriser la conception par l’analyse de la valeur, Editions Lavoisier Tec &

Doc, Paris. [8] Prudhomme, G., (2000). Analyse Fonctionnelle et démarche de conception, In: Modélisation de la

connaissance pour la conception et la fabrication intégrées, Drăghici G. & Brissaud D. (Ed.), pp. 7-30, Editura Mirton, ISBN 973-585-216-0, Timişoara.

[9] STAS, (1988). Tehnici de analiză a fiabilităţii sistemelor. Analiza modurilor de defectare şi a efectelor defectărilor, STAS 12689-88, Institutul Român de Standardizare, Bucureşti.

[10] TDC, (2001). Manuel utilisateur TDC FMEA 2001, TDC France. [11] TDC, (2001). Manuel utilisateur TDC Need 2001, TDC France. [12] Tollenaere, M., (1998). Conception de produits mécaniques. Editions Hermès, ISBN 2-86601-694-7,

Paris. [13] Zwingelstein, G., (1996). La maintenance basée sur la fiabilité, guide pratique d’application de la

RCA, Edition Hermès, ISBN 2-86601-545-2, Paris.

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