Wednesday 3 August 2022

Polymer Material Selection: Defining the Part Requirements as Common Starting Point

Hello and welcome to a new post. Today we discuss the starting point in polymer material selection. 

In general there are several procedures for material selection such as the Ashby methodology or my own developed funnel approach

However, all the selection processes and procedures should have the definition of the part requirements as their common starting point. 

How to do it the best? 

Figure 1: Polymer Material Selection - Estimation of product requirements as common starting point

Covering effectively the product requirements, a combination of functionality questions and selection factor questions can support you to achieve this (Figure 1).

First we have to ask some questions on the functionality of the part. Following questions can help us with this assessment:

-What are the performance requirements (structural, etc.)?

-Do you want to combine multiple parts or functions?

-What will be the structural load of the part (static, dynamic, cycling, impact, etc.)?

-What will be the environmental impact on the part (chemical, temperature, time)?

-What is the expected lifetime of the product?

With the collected answers we can define the part requirements as accurately as possible. Together with the understanding of the differences of thermoplastics (amorphous and semi-crystalline) and thermosets we have an understanding of the performance, thermal and mechanical properties, as well as chemical resistance and processing differences of thermoplastics and thermosets. 

Selection factors - checklist for your material selection 

There are more detailed lists , however in this post we cover the six essential questions on material selection factors. 

1. What is the service environment of your part?

-what is the operating temperature: high, low, duration, thermal expansion

-exposure to chemicals, solvents, lubricants, salt

-exposure to water and humidity

-UV stability for use in outdoor / indoor environment

2. What are the regulatory requirements?

-flammability rating needed such as UL 94 at different wall thickness

-food contact

-fulfillment of medical standards

-any other regulation such as IP 44 for electrical devices

3. What types of load at which service temperature need to be fulfilled?

-continuous load represented by Young modulus and creep resistance

-intermittent load represented by tensile strength

-impact load represented by impact strength

-fatigue represented by cycles to failure for example over a Wöhler curve

4. Other considerations such as: 

-dimensions and tolerances which need to be met

-electrical properties such as CTI, electrical breakdown strength

-wear and friction 

-thermally conductive materials with or without electrical isolation

-aesthetics and colour (relevant for application with food contact, and toys)

-painting and printing 

-life time needs 

5. What is the processing and fabrication method?

-injection moulding, extrusion, thermoforming

-assembling by using screws, laser welding, or adhesives

-secondary operations

6. What are the economic and commercial considerations

-useful to make when material short-list is available


The combination of questions on part functionality and selection factors will help to facilitate your polymer material selection, together with fundamental data in a systematic way. 

Thank you for reading and #findoutaboutplastics



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[1] GE Plastics - Product Guide



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