By Fabien Gaussorgues

Do you need to manufacture a plastic part in China? The first question is usually ‘what is the best material?’ comes before prototyping and before deciding on a manufacturer.

The most common plastics used in China are acrylic (PMMA), acetal (POM), nylon (PA66), polycarbonate (PC), acrylonitrile (ABS), thermoplastic (PET), polypropylene (PP), low density polyethylene (LDPE), and polyetheretherketone (PEEK).

There is usually no straightforward answer. Many criteria have to be considered, and a compromise often needs to be chosen.

The most common criteria clients mention are listed below:

• Resistance to wear
• Strength
• Transparency
• Food or flame grade
• Hardness
• Price
• Tolerances
• Melting temperature

To make this choice more complicated, it is possible to mix some materials — for example ABS/PC, or adding some fiber glass for a better fit to the final product.

There are also significant differences between Chinese “no name” raw material and branded offers coming from China (e.g. Chimei), Taiwan (e.g. Formosa), Germany (e.g. BASF, Bayer) and the USA (e.g. Dupont, Sabic).

When the performance is critical and is close to the limit of what the material can achieve, it is important to control its source and to identify the material origin. For example, for high precision, you might want a plastic with low shrinkage, and adding fiber will improve performance.

There are two more reasons for controlling the source:

• You need to ensure the plastic is the same from one batch to the other.
• The tolerance for changes is low when a mold is involved. Most of the time, changing the material will mean changing the mold and scrapping the old one! Material selection and expected performances should be part of the product specification before deciding on a manufacturer.

There are many resources available online to help the user find the right raw material. However, it is also important to rely on the manufacturer’s experience (assuming you have found a manufacturing partner you can trust). They can suggest solutions you might not have thought of.

What else? Sometimes, you might simply want to reuse the same plastic as an existing product with similar performance requirements. How to ‘reverse engineering’ it and discover what plastic they used? The solution is to burn it!!!

Most plastics have different behaviors, and product families can be identified this way. See more details here if you are curious.

Side note:

This method can also confirm if your supplier used the right type of plastic. The temptation to save on purchasing costs is very high, especially if they think you will not pay for expensive laboratory tests.

We listed a few other simple tests that can be carried out to check a plastic’s flexibility here.

Here are some useful online resources regarding the choice of the right polymer for injection molding:

• Shortlist of main plastics, and main selection criteria
• Database of material properties — a huge database to find what plastic will be a good fit for your project

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• How to get the design and engineering right

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