Saturday, 30 June 2018

Polymeric Material Selection: In 6 Steps To The Optimal Polymer For Your Application

If you are a designer, application engineer, material engineer, or material purchaser dealing with e.g. automotive parts, you will have one major question in mind to bring forward your projects: which polymeric material fulfills the job based on the set criteria in the optimal way and costs? To take the guess work out, I will show you in this blog post how you can determine the optimal polymeric material in six steps [1]. In this way you can keep track of your material decision making process.

Step 1 - Define key criteria for your part: Main task here is to proper estimate the requirements of the part which can be based on performance criteria, appearance criteria, and cost targets (part costs, tooling costs and equipment costs). Step 2 - Selection of the manufacturing process: there are several things to consider when selecting the manufacturing process of your part. On one hand, it is the part size, part complexity, and allover product volumes. On the other hand, you have equipment costs. For example, costs of an injection moulding machine in case a new one is needed and tooling costs. Production volumes are the driving force here, followed by tooling costs. The material cost can vary from 50% (technical parts) up to 80% (consumer parts) of your manufacturing costs. The economic batch size varies for the different processing techniques:
- Injection moulding: 10^4 – 10^6 units
- Blow moulding: 10^5 - 10^7 units
- Compression moulding: 10^3 – 10^5 units
- Rotational moulding: 10^3 – 10^4 units
- Thermoforming: 10 – 10^3 units
- Polymer casting: 10 – 10^3 units
- Resin transfer moulding: 10^3 – 10^6 units

Step 3 – Create a short list of materials: After we estimated the key criteria and manufacturing process it is time to create a short list of potential material candidates. A grouping into chemical family such as polyolefines, aliphatic nylons, semi-aromatic nylons, polyesters, polysulfones, fluoropolymers, polyketones, polyimides, and so on is useful. Furthermore, grouping by primary additives such as fiber (glass, carbon) reinforcement, tougheners, heat stabilizers, flame retardants is helpful at this stage too. Additionally, you can look for plastic material suppliers in online databases such as Pro-Plast  or you can work with online selection guides such as these ones: Omnexus and PlasticsFinder. Furthermore, CAMPUS material database offers a comparison of hundreds of grades and their properties in an uniform way (every resin supplier who contributes to CAMPUS tests their materials in the same way).

Step 4 – Evaluation of your data: now the feasibility study can start by evaluating the material data of the chosen polymers for mechanical, chemical, electrical, process ability, post-processing capabilities such as laser welding, painting or metallization. Since some load cases of the final part are available, structural analysis can be done too. Cost analysis is crucial for some end markets such as automotive and it needs to be included at this stage. The same is valid for supply chain and global availability of the suggested materials. The complexity of the analysis can vary and timewise it can take days or some months to obtain conclusive results.

Step 5 – Develop your prototypes: now you dive into the product development phase, which has an iterative character. In this phase, the focus is kept on detailed engineering. It is usually the longest phase and it allows you to create prototypes, test them, and re-iterate. Your material selection list will get more focused and some materials might fall off the list. In corporations, this phase can take place in the Research & Development (R&D) departments. There, engineers and scientists test and approve the different materials or they approve a process where the material is integrated. Product development groups have usually the product itself as an output. In some cases, the material needs to be first approved by the R&D for general design use that it can appear on the selection list for certain parts in the Product Development group.

Step 6 – Selection of the material: in the final step, selection takes place. The selection should be already pretty obvious and it should be not a surprise anymore which material will be used in the product. The selected plastic fulfills all the set criteria, including cost effectiveness. Implicit knowledge is turned into explicit results which allow a fact-based decision. If the decision is not yet easy and clear to take, then it is best to revise some of the steps, especially the starting steps. It will cause some time delays and is still better to take the extra loop since a wrong material choice now will lead to potential higher costs in the future. It is always useful to cross-check the results and the suggests with the resin supplier since they have in-house know-how build up on their materials including lots of testing and actual applications.

So, those were the 6 steps for selecting an optimal polymeric material for your application. You can use it as a checklist when you make your next material selection. For further reading I would like to recommend this post dealing with big data and material selection.

Thanks for reading & till next time!
Greetings, Herwig Juster

New to my Find Out About Plastics Blog – check out the start here section

Literature: [1] Eric Larson - Thermoplastic Material Selection: A Practical Guide

Thursday, 28 June 2018

Polymer Processing: Tolerance and Roughness Charts

Hello and welcome to this blog post on tolerance and roughness charts for different polymer processing techniques. This post supports you in the polymer shaping selection as part of the material selection process.

1. Tolerance chart: A part will not be exactly shaped to a specified dimension. There will be a deviation Δx from a desired dimension x which is allowed by the specifier. This is in general referred to as tolerance T which is defined as e.g. x =100 ± 0.1mm, or as 0.01. The bar chart allows selecting different polymer processing techniques to achieve a desired tolerance.

2. Roughness chart: A part will have different surface roughness R, which is measured by the root-mean square amplitude of the irregularities on the surface. A rough surface will have an R < 100 μm and a high polished surface has a R < 0.01 μm. The bar chart allows selecting different polymer processing techniques to achieve a desired surface roughness.

Thanks for reading!
Greetings and till next time,
Herwig Juster

New to my Find Out About Plastics Blog – check out the start here section.

[1] Granta - Material and Process Selection Charts, 2010