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Injection Moulding: Which Materials?

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Thermoplastic injection is the most common way to manufacture parts. These polymers can be repeatedly molten or softened by heating, or solidified by cooling. Such physical changes take place during the creation of thermoset (plastics cannot be melted again once processed) materials.

Sounds simple, right? Here’s where it gets a mite more complicated for product designers or entrepreneurs looking for the right material to manufacture a product to bring to market. There are 85,000 different types of injection moulding plastic materials.

However, before you start to question how on earth you’re going to choose a plastic moulding that’s tailored to your individual application, it’s easier to choose a material when you consider the overall composition of plastic injection materials. There are six materials that dominate the industry. These are:

  • Polypropylene (PP)
  • Acrylonitrile Butadiene Styrene (ABS)
  • Polyamide (Nylon)
  • High Density Polyethylene (HDPE)
  • Polycarbonate (PC)
  • ABS and PC Blend

Within each of these materials are thousands of variants in composition. However, knowing each of these is superfluous. You only need to know the individual properties of each to identify the right solution for your application.

So, to sufficiently plan your manufacturing process by selecting the best material, you need to know the properties of these materials. This is exactly what we’ll now explain.

Material Flexibility

One common misconception is that all soft materials are flexible whereas all hard materials are rigid. However, as we know, a flexible material isn’t necessarily soft. In simple terms, flexibility is the ability to bend under stress without breaking. Rigid materials are resistant to bending when placed under stress. The stronger the material, the less likely it is to bend when placed under stress.

Take the ABS ruler for example. Even though it’s a harder material, it bends to a certain degree before showing signs of failure. Compare this to a nylon ruler which ruptures soon after a load is applied to it and you begin to see how flexibility and material composition can differ.

It’s important that you consider the tensile strength in addition to the flexibility of any material at the start of any manufacturing process. Only then will you understand which the right material is to use for your application.

Material Hardness

The most common way to measure material hardness (or resistance to indentation) by examining the material hardness of specific products. Soft and harder plastics are categorised on a Shore hardness scale, on which different plastics are graded.

For example, art gum erasers are graded at 30 Shore A which is a soft hardness whereas golf balls are graded at 60 Shore D which is one of the harder material plastics.

Choosing the right material for the right product application is paramount. This will ensure optimal performance in varying conditions, degree and nature of abrasion and even user experience. ABS and PC are considered harder materials, whereas HDPE and PCV are lower on the scale and are therefore softer.

Make sure that you use the material that’s fit for purpose in your injection mould. This is the only way to guarantee not only performance but longevity and durability.

Material Cost

As you’ve probably anticipated, material cost is another important factor when considering what type of materials to use for your injection mould. This is certainly something to be considered when manufacturing a plastic injection mould product, but it’s generally the same for any material.

In general, HDPE and PP tend to be less expensive than PC and nylon. ABS is a little cheaper than HDPE and PP whereas ABS and PC/ABS aren’t overly cheap or excessively expensive.

When considering which plastic moulding is fit for your purpose, make sure that you consider the price of the material. Depending on the scale of operations, costs can quickly escalate and if you’re considering bringing a product to market, keeping a clear eye on your overheads is essential.

Material Weight

The last factor to consider when considering which plastics to apply to an injection mould is the weight of the material. Obviously, the heavier the material the more strain this will place on the tolerance of a moulded material.

Plastic injection moulding can support a range of material weights. This is one of the reasons why the process is so popular amongst products designers and entrepreneurs. However, if you’re working within very specific weight parameters, it might be worth finding out weight difference as this could allow you to further optimise any manufacturing process.

Ultimately, the density of a plastic polymer will determine how heavy or light the end-product will turn out. PVC and PC are generally accepted as being the heaviest polymers whereas PP and HDPE are acknowledged to be the lightest. ABS and PC/ABS fall somewhere in the middle.

The Takeaway

All materials have their own properties. Before deciding which material category to choose, it’s essential that you understand their characteristics – only then will you be able to optimise workflow processes.

Don’t forget to that there are 85,000 types of plastics. Now, we’re hardly suggesting that you trawl through each with a fine-tooth comb to identify the precise material for your needs, however it’s a chance to identify a material that precisely meets your application.

If you need any help or further advice, don’t hesitate to contact Wheatley Plastics. With profound knowledge and years of experience, we can help you to identify the right material for your application.