Injection Moulding: Applications and Materials

May 18, 2021
EngineeringClicks

While many people may not be aware, injection moulding is used to create a whole range of the everyday products we use. The applications of injection moulding take in everything from automotive parts to electrical switches, medical devices to simple plastic lids and much more. Even though there are some restrictions regarding the shapes and complexity of products made using injection moulding, there are many different materials which can be used.

Numerous articles on this subject have looked at specific components made using the injection moulding process; we are going to take a different approach. There are many different materials which can be used as part of the injection moulding process, offering an array of different characteristics. Each will suit different products as you can see below.

Matching materials with products

The majority of applications of injection moulding will use a type of plastic (often referred to as a polymer) which can vary in:

Strength
Durability
Flexibility
Cost

In a moment we will take a look at some of the more commonly used types of plastic, their particular characteristics and which plastics best suit which type of product. It is safe to say you will be surprised, if not amazed, by some of the products which are made using the injection moulding process.

Benefits of injection moulding

Before taking a look at the array of plastics and applications which use injection moulding, it is worth reminding ourselves of the benefits of injection moulding. These include:

Design flexibility
Low wastage
Mass production
Product consistency
Highly efficient
Fast production
Low labour costs
Enhanced strength
Reduced finishing required

The main drawbacks of injection moulding include relatively high tooling and start-up costs, although the impact of these is mitigated further down the line. Products made by the injection moulding process should avoid designs with cuts and sharp edges where possible.

Nylon

You may be surprised to learn that nylon is a type of plastic which is actually derived from crude oil. While the material is put through an intensive chemical process before being used in the injection moulding process, it has some very useful characteristics:

Extremely tough
High melting point
Able to accommodate significant wear and tear
Chemical resistance
Relatively lightweight

Due in the main to its relative strength, nylon is used to produce an array of products such as:

Packaging
Plastic fasteners
Cookware
Toothbrushes
Gears
Plastic bearings
Bushings
Components for engines

While many people predominately see nylon as a simple material, as you’ll see above, it is used in a whole range of different products. This is one of the more common materials used in injection moulding.

Acrylic

Did you know that acrylic was first produced in 1928, and is still in use today? This will give you an idea of its importance in the injection moulding industry. There are many reasons why acrylic is used today which include its:

Resistant to numerous different chemicals
Impact resistance compared to ordinary glass
Ability to withstand variations in temperature
Optical clarity and transparency
Light weight

When you take into account the transparency, weight and ability to withstand significant temperature variations, acrylic is used across a whole range of different products. These include:

Windows
Lighting equipment
Alternatives to glass
Refrigerators
Food storage containers

It is worth noting that acrylic is perfect for food preparation and storage products because it doesn’t contain Bisphenol A (BPA). BPA is a controversial synthetic compound which has been linked to a number of different medical conditions, although opinion is very much divided.

Polyoxymethylene

While polyoxymethylene is not something that you might come across in your everyday life, it is an extremely popular material for injection moulded products. The many benefits of polyoxymethylene include:

Extremely strong
Retains properties in the temperature range -40°C up to 140°C
Excellent dimensional stability
Impressive wear and tear characteristics
Creates a high-gloss surface
Low moisture absorption

After reading the characteristics of polyoxymethylene it is not difficult to guess a number of different products which may benefit. These include:

Gear wheels
Ball bearings
Fasteners
Knife blades
Locking systems
Ski bindings

The strength and durability characteristics of polyoxymethylene are very similar to many types of metal, as demonstrated in the above products. This makes it a very popular material when considering the many applications of injection moulding.

Polystyrene

When we think of polystyrene, many of us automatically think of the white material more commonly used in packaging and insulation. There are two specific types of polystyrene, known as high-impact polystyrene and general purpose polystyrene. High-impact polystyrene is more commonly used with injection moulding and has the following characteristics:

Easy to machine/fabricate
Good insulator
Easily processed
Able to paint and glue
Relatively low cost
Extremely sturdy
Durable with strong impact resistance

While high-impact polystyrene is used across a range of different sectors, it is commonly used for the injection moulding of electronic and medical applications. These include:

Petri dishes
Waste canisters
TV housings
Computer housings
Toolboxes
Freezer/refrigeration appliance housings

You only need to look at your toolbox to see how sturdy, compact and durable it is. This is likely to be made of high-impact polystyrene, using the injection moulding process.

Acrylonitrile Butadiene Styrene

Acrylonitrile Butadiene Styrene is certainly a challenge to pronounce, so it is no surprise to learn it is more commonly known as ABS. There are numerous useful characteristics to ABS which include:

Exceptional rigidity
Electrical characteristics
Hard surface
Tensile strength
Dimension stability
Abrasion resistant
Impact resistant
Chemical resistant
Heat resistant

As you might have guessed, due to the many useful characteristics of ABS, it can be used across a wide range of injection moulding processes including products such as:

Lego
Sports equipment
Compressors
Gardening tools
Medical applications
Automotive dashboard components
Door liners/handles
Seatbelt components
Instrument panels

In all honesty, we are literally just scratching the surface with regards to the range of products which can be created using ABS.

Polypropylene

If there is one plastic polymer you will come across in everyday life, it will be polypropylene. As you will see in a moment, the range of products which are compatible with polypropylene is huge. However, before we look at the products let’s take a look at the characteristics of this polymer:

Chemical resistant
Moisture resistant
High impact strength
High elasticity
Extremely tough

This is a material which does not degrade when washed in hot water and is therefore common in the food products industry. Some of the specific products made using polypropylene include:

Homeware such as cups and saucers
Bottle tops
Flexible packaging
Car bumpers
Interior trim
Plastic trays
Petri dishes
Intravenous bottles
Pill containers
Pans

There are very few materials which offer this level of impact resistance and toughness with a high degree of elasticity. The range of products which can be made with polypropylene injection moulds is substantial.

Polyethylene

Polyethylene is yet another plastic polymer which has a range of different characteristics that make it perfect for injection moulding components. Some of the more common benefits associated with polyethylene include:

Protection from moisture and gases
Lightweight
Extremely durable
Highly level of flexibility and/or rigidity

When looking at injection moulding components, high density polyethylene is also safe when used with food and drink. Some of the more common items made from polyethylene include:-

Containers
Pallets
Crates
Packaging
Bottle tops
Automotive components
Toys
Drainpipes

Even though we are just scratching the surface with the above list, it does give you an idea of the ways in which polyethylene can be used in the injection moulding process.

Thermoplastic Polyurethane

When you look at the characteristics of thermoplastic polyurethane it is not difficult to see why it is so popular for injection moulding products. The main advantages of using thermoplastic polyurethane includes:

Abrasion resistant
Impact strength
Toughness
Flexibility
Elasticity similar to rubber
Protection against oil, grease and other similar fluids

Unfortunately, we don’t really have enough space to list all of the ways in which thermoplastic polyurethane can be used. However, it is the flexibility, while able to maintain an overall rigidity, which makes it so useful. It is used with injection moulding products such as:

Sports footwear soles
Car bumpers
Gaskets
Bearings
Mobile phone protective coverings
Computer components
Floatation devices
Protective goggles

When you think of sports footwear, such as football boots, where the sole requires a degree of rigidity and flexibility, thermoplastic polyurethane is just perfect.

Injection moulded products are all around us!

The applications of injection moulding take in everything from footwear to car bumpers, protective goggles to food containers, pallets to bottle tops and much more. While the initial injection moulding setup process can be relatively expensive, once the mould is complete and the production line in order, there are potentially huge long-term cost savings.

There are also dozens of different types of plastic polymers you can use during the injection moulding process, matching their characteristics with the requirements for each component. In the early stages, it is important to not only ensure the mould is correct but that you are also using the most appropriate plastic polymer.