DECISION SUPPORT TO POLYMER MATERIAL SELECTION

Urška Sancin and Bojan Dolšak

Faculty of Mechanical Engineering, University of Maribor, Smetanova ul. 17, SI-2000 Maribor, Slovenia

Keywords: Product development process, Design, Material selection, Plastics, Human cognition, Decision support

system.

Abstract: To succeed means to develop and produce a product with optimal properties for considerable lower price in

comparison to similar products on the market. Material selection is one of crucial decisions in product

development process affecting quality as well as price of future product. In technical praxis, the designer

has to evaluate the information gathered from material data sheets and simulations, engineering analysis and

animations of future product performance in virtual environment. Afterwards, he or she has to seek

interdependences between them and finally choose the optimum from the broad list of materials. Wide

spectrum of various polymers at disposal should be outlined here, as it presents a problem to the designer at

polymer material selection process. The proposed decision support system model is an attempt to solve this

dilemma and will focus on function, technical features and shape of developing product. Other criteria, like

serviceability, technical feasibility and economic justification are going to be considered accordingly. The

major benefits concern inexperienced designers along with small and medium sized enterprises (SMEs’).

1 INTRODUCTION

Material selection is one of many stages in product

design process. The engineer has to progress through

this process in order to design a model, semi-product

or a final one. Within this process the designer has to

take numerous decisions at all stages of design like

material selection, process selection, analyses and

simulations, diverse evaluations of the developing

product, tool design and industrial design where

ergonomic and aesthetic attributes should be

considered.

Product development process is decision making

process since the engineer has to take considerable

amount of decisions whilst designing. Younger

inexperienced design engineers have major

difficulties at solving this query. One product

development phase, material selection, will be

discussed here in order to overcome decision making

barrier, the decision support system for plastic

product design is proposed. This computer aid will

offer recommendations and guidelines according to

the required parameters, shape or/and function of the

product and could also be helpful for experienced

designers using the system as a verification tool.

What is more, it is expected that small and medium

sized enterprises (SMEs’) will characterize proposed

system as a major acquisition as they could

economize at human resources and benefit on

financial field.

This article presents an explanation of material

selection methodology and polymer material

selection in praxis, all collected in Section 2. Section

3 envisages the intelligent decision support system

with graphic mode as Section 4 represents the

implementation of proposed decision support system

for polymer material products’ design. Conclusions

are tersely collected in Section 5.

2 MATERIAL SELECTION

Material selection is a significant stage of design

process and a complex task, whose execution varies

from enterprise to enterprise in accordance with staff

and the economic aptitude of the company. In this

section material selection methodology is described

and divided in four general approaches to polymer

material choice upgraded with presentation of this

process in praxis.

2.1 Material Selection Methodology

In general, material selection methods can be, accor-

707

Sancin U. and Dolšak B..

DECISION SUPPORT TO POLYMER MATERIAL SELECTION.

DOI: 10.5220/0003293107070710

In Proceedings of the 3rd International Conference on Agents and Artiﬁcial Intelligence (ICAART-2011), pages 707-710

ISBN: 978-989-8425-40-9

 2011 SCITEPRESS (Science and Technology Publications, Lda.)

ding to Ashby and Johnson (2005), arranged in four

different selection methods called Selection by

Analysis, Selection by Synthesis, Selection by

Similarity and Selection by Inspiration. All methods

require input data in the form of design requirements

specific for each method.

Selection by Analysis is the most systematic and

robust as input requirements are objectives,

functions, and constraints, and furthermore, they are

precisely defined and unambiguous. Its deficiency

derives from this particular distinctiveness, which

causes the method to fail in the case of imprecise

inputs or imperfectly formulated rules. Previous

experience and analogy are key factors in the

Selection by Synthesis method, where design

requirements appear in the form of intentions,

features, and perceptions. This method is used, when

knowledge of the solved cases can be exploited and

transferred to other product with some features in

common. Selection by Similarity is the selection

method, where input is already known or potential

material solution and its purpose is to find

substitutive material for an existing product, often

initiated by design requirement changes due to e.g.

environment legislation. The less uniformed method

is Selection by Inspiration, where input is pure

curiosity and the designer’s task is to examine and

analyse other solutions for a specific feature, in a

systematic way. This method is used when no

scientific method is helpful. All material selection

methods and their variations are implemented in

numerous variations as engineering praxis.

2.2 Polymer Material Selection

in Praxis

Usually the methodology of material selection

involves making a list of properties that you must

have for future application and the list of properties

that are desired for this particular application. These

must and want properties are then matched with the

properties of available polymer materials on the

market. In engineering praxis, four basic groups of

material properties are reviewed:

 Physical (specific heat, coefficient of thermal

expansion, thermal conductivity, heat distortion

temperature, glass transition temperature)

 Chemical (composition, additives, fillers,

crystallinity, environmental degradation, spatial

configuration, molecular weight, flammability)

 Mechanical (tensile and compressive properties,

heat distortion, pressure-velocity limit, toughness,

stress rupture resistance, creep resistance)

 Dimensional considering manufacturing condi-

tions (manufacturing tolerances, stability, available

sizes, moldability, surface texture)

In order to illustrate the importance of polymer

materials’ idiosyncrasies (Budinski and Budinski,

2010), each group of followed properties should be

described.

2.2.1 Physical Properties

Physical properties are material characteristics that

pertain to the interaction of these materials with

various forms of energy and human senses.

Generally they could be measured without

destroying the material. Density is a physical

property determined with weighting or measuring

the volume of the product. Physical properties like

feel and colour are even easier to determine while

they affect the customer as he or she only looks at it.

Nevertheless, they are not marginal material

properties and their importance rises in today’s

consumer oriented society. The designer has to

acknowledge that plastic feels different from metal

and yellow is happier colour in comparison to

brown.

2.2.2 Chemical Properties

Chemical properties are related to the structure of

polymer material, its formation from the elements of

which the material is made, its reactivity with

chemicals and environments. These properties

cannot be visually inspected and are measurable in

chemical laboratory.

2.2.3 Mechanical Properties

Mechanical properties are the features of material,

which are put on view when it is exposed to a force.

They are related to the elastic or plastic behaviour of

the polymer and they often require destruction for

measurement. Term mechanical is used because they

are usually used to indicate the suitability of the

material for use in mechanical applications – parts

that carry a load, absorb shock, resist wear, etc.

2.2.4 Dimensional Properties

Dimensional properties include as well

manufacturing considerations like manufacturing

tolerances and moldability. This category concerns

also the surface texture and its roughness, which is

measurable and essential for many applications.

Available size, shape, finish and tolerances of the

product are also important polymer material

selection factors.

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3 DECISION SUPPORT

IN GRAPHIC MODE

FOR POLYMER MATERIAL

SELECTION

In recent years, many decision support systems

where developed and some successfully launched in

real applications (Turban et al., 2004). The

significance of material selection dilemma is

obvious as several models were developed to

support the designers at this stage of design (Đurić

and Devedžić, 2002).

Building the decision support system in graphic

mode presented in this paper aiming at a successful

and efficient performance is a complex assignment.

The development methods included in research are a

combination of special domain knowledge expertise

in the field of polymer materials and human

cognition in the field of design knowledge. Human

knowledge useful for problem solving is of special

importance and is in the form of rules relating to

modern plastic materials’ selection and correlated

manufacturing processes, assisted by the field of

Design for Manufacturing (DfM) (Molcho et al.,

2008).

A graphic mode of proposed system will be

related to three major groups of polymer materials:

thermoplasts, thermosets and elastomers, which will

all be arranged and presented in individual circles.

Within the framework of each circle several

technical features carefully selected to cover all

essential material properties described in Section 2,

will be assigned:

 Mechanical properties (strength, bending

strength and working temperature),

 Production process (injection moulding,

compression moulding, spin casting and extrusion),

 Chemical properties (resistance to base, acid,

gas/oil, hot water),

 Working environment (internal/external use, fire

resistance).

 Optical properties (colouring possibilities).

All three circles will have the same framework so

the parameters, introduced to the system by the user

will reflects trough all of them.

The system model will provide polymer material

suggestions in discussed case, e.g. the designer

receives two polymer material results, epoxy and

diallyl phthalate (DAP), whose properties are

introduced in the outer ring of the circle.

The significant feature of the system is two level

solutions. The primary result will be the possible

plastic material choice, many of them or none. The

database of the polymer materials will play the key

role here. Afterwards, the system’s knowledge base

containing human cognition of plastic material

selection and DfM will be of special importance as

the system will be able to evaluate the candidates for

potential material choices, which were just over the

boundaries created by introduced parameters. Thus,

some polymers are going to become a secondary

solutions presented to the designer in form of notices

containing recommendations about the advantages

of each suggested solution. Considering the

described decision support system with graphic

mode, the enterprises will be able to compete at the

global market by selecting the optimal material for

their product.

4 IMPLEMENTATION

OF DECISION SUPPORT

SYSTEM MODEL

The decision-making process is a constant for every

designer aiming at a successful and efficient

performance. Alternatively to experts’ acquired

domain knowledge, we decided to develop an

intelligent decision support system (Edwards and

Deng, 2007) in order to overcome the bottle neck -

plastics material selection.

The knowledge base will contain human

cognition useful for problem solving in the form of

rules relating to modern plastic materials’ selection

and correlated manufacturing processes, assisted by

the field of Design for Manufacturing (DFM).

Different approaches to knowledge acquisition

(McMahon et al., 2004) and the appropriate

formalisms for the presentation of acquired

knowledge within the computer program will be of

special importance.

The potential for transparent and modular IT

rules, whose advantage is neutral knowledge

representation, uniform structure, separation of

knowledge from its processing and possibility of

dealing with incomplete and uncertain knowledge, is

planned to be compared with more flexible

knowledge presentation systems, such as fuzzy

logic, where fuzzy sets and fuzzy rules will be

defined as a part of an iterative process upgraded by

evaluating and tuning the system to meet specified

requirements. Tuning will be the most delicate job

whilst building a fuzzy system as fuzzy sets and

rules should frequently be adjusted during the

DECISION SUPPORT TO POLYMER MATERIAL SELECTION

709

system’s construction. The main goal for the system

is to apply domain knowledge, including human

cognition, relations and experiences in the

knowledge base of the system, which will, together

with the data base, serviceable for a complex

reasoning procedure behind the inference engine

leading to qualified design recommendations and

guidelines for designing plastic products.

The user interface will be developed with a

special attention, in order to enable transparent and

efficient system application. Two different

application modes have been anticipated, in regard

to the type of input and output data. Question and

answer guided mode will be used mostly at the

beginning, when the first set of parameters has to be

presented to the system. During the data processing

phase, the system may present additional questions

or ask for more parameters. In this case, guided and

graphic modes will be used to present the problem to

the user. The solution in the final phase will also be

presented in graphic mode.

5 CONCLUSIONS

Human cognition along with experiences is

engineer’s main advantage. Consequentially,

inexperienced designers and SMEs’ are kept in the

background here as their decision making process is

aggravated. Decision support system model

proposed here could be of great importance for the

engineering praxis as designers have difficulties at

acquiring expert knowledge and experiences.

Proposed system model will be able to offer some

recommendation and design guidelines on the field

of design and knowledge expertise in the field of

polymer materials. The designer will benefit much

due to faster, less experience dependent design

process, consecutively higher efficiency and

friendlier working environment.

REFERENCES

Ashby, M., Johnson, K., 2005. Materials and Design,

Elsevier.

Budinski, G. K., Budinski, M. K., 2010. Engineering

Materials, Pearson Prentice Hall, 9

edition.

Đurić, M., Devedžić, V., 2002. I-Promise—intelligent

protective material selection. Expert Systems with

Applications, 23, 219-227.

Edwards, K. L., Deng, Y.-M., 2007. Supporting design

decision-making when applying materials in

combination. Materials & Design, 28, 1288-1297.

McMahon, C., Lowe, A., Culley, S., 2004. Knowledge

management in engineering design: personalization

and codification. Journal of Engineering Design, 15,

307-325.

Molcho, G., Zipori, Y., Schneor, R., Rosen, O., Goldstein,

D., Shpitalni, M., 2008. Computer aided

manufacturability analysis: Closing the knowledge gap

between the designer and the manufacturer. In CIRP

Annals - Manufacturing Technology, 57, 153-158.

Turban, E., Aronson, J. E., Liang, T. P. 2004. Decision

Support Systems and Intelligent Systems. Prentice

Hall.

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