Why Is Plastic Injection Molding Important?

Everywhere you look, most of the plastic items in the world around you are made using injection moulding. Plastic injection moulding has been a reliable and well-established manufacturing process for many years. The first injection moulded part was invented by John W. Hyatt back in 1872 and the industry has come a long way since then. The design flexibility and cost-effectiveness it offers allow for many different use cases across different industries. Here's what you should know before deciding if this manufacturing process is right for your project.

What is injection moulding?

Injection moulding is a manufacturing process that produces parts by injecting molten plastic resin into a mould cavity. The rate and pressure at which the material is injected into the mould affect the desired shape.

How injection moulding works

Injection moulding begins with the manufacture of a tool, also known as a mould, which is precision machined from steel or aluminium. The machine operator places the tool into the injection moulding machine. The injection moulding machine feeds thermoplastic resin pellets through a hopper. When the injection moulding machine is started, these thermoplastic pellets are pushed forward by a screw into the barrel of the machine and melted until liquefied. This liquid resin, called a projectile, is collected in a chamber at the front of the barrel. The machine then injects the thermoplastic resin ejected from the chamber into the tool cavity. The machine applies pressure until the resin fills the tool. After cooling, the resin re-solidifies to form the part. Finally, the part is ejected from the machine and moves on to the next production step.

So is injection moulding the right choice for my project?

Before you make the effort to produce parts through injection moulding, consider the following points.

Start with financial considerations

You need to determine the number of parts that will be produced when injection moulding becomes the most cost-effective manufacturing method.

From there, you need to determine the number of parts you want to produce to break even on your investment (taking into account the costs of design, testing, production, assembly, marketing and distribution as well as the expected selling price point). Establish a conservative margin.

And don't forget the cost of entry. Preparing a product for injection moulding manufacturing requires a significant initial investment. Make sure you understand this key point in advance.

Next, let's talk about design considerations

When it comes to part design, you want to think about injection moulding from day one of designing the part. Simplifying the geometry and minimising the number of parts as early as possible will pay dividends in the future.

When designing a mould, the first priority is to prevent defects from occurring during production. For a list of 10 common injection moulding defects and how to fix or prevent them, read here. Consider gate locations and run simulations using mould flow software such as Solidworks Plastics.

Getting injection moulding production right

Cycle times are critical here. Keep cycle times as short as possible. Using machines with hot runner technology and well-thought-out tools will help. When you are producing millions of parts, small changes can make a big difference and cutting your cycle times by a few seconds can translate into significant savings.

Related to production is the assembly process. You need to design parts to minimise assembly. Much of the reason for injection moulding in South East Asia is the cost of assembling simple parts during the injection run. To the extent that you can design the assembly outside the process, you will save a lot of money on labour costs.

Injection moulding: the bottom line

Injection moulding is a great technology for the mass production of finished products. It is also useful for final prototypes for consumer and/or product testing.