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Prior-use knowledge can lead to past and effective solutions and at the same time the
better material or manufacturing process solutions could be omitted.
Knowledge and experiences are the key factors to top-level product contrarily the lack
of both could lead in other direction. The invitation to the expert at material or
manufacturing process selection is a regular practice in SMEs' to disseminate
company's knowledge and experiences.
Availability of the material is a very important point at material selection as some
characteristics of the design could not be implemented with some always available
cheaper materials.
4.1 Material selection methods
Material selection is a significant stage of the 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 general, material selection methods can be, according to Ashby
(Ashby & 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.
4.2 List of must and want properties in engineering praxis
List of must and want properties method can be characterized mostly as Selection by
Analysis however it could be also applied as Selection by Synthesis or Selection by
Similarity. Usually this method 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)
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