To put it in its simplest form, injection moulding is a heat-based manufacturing process with the aim of producing large quantities of plastic parts to exact measurements.

Before we start getting into what exactly thermoplastic injection moulding is and the wide range of sectors it can benefit from, it would be worth revisiting the history of thermoplastics and the types of materials used that led the industry to where it is today.

History of Thermoplastic Materials

Thermoplastics are polymers that can be softened or melted so that they inject into a ready-made mould to cool and become solid, ultimately turning into the plastic parts required.

We can trace back the history of the trade to see that the first condensation polymer, polyester, was created in the mid-1800s by a man named Jöns Jacob Berzelius.

Polyester has similar lightweight properties to nylon, the latter of which would go on to become the commercially preferred alternative for thermoplastic injection moulding, and was used in manufacturing because it was stretch, wrinkle and shrink resistant.

Plastic injection moulding truly began in the late 1800s, when the first moulding machine was patented by Hyatt brothers John and Isaiah.

This would lead to several decades of innovation, particularly during the 1930s and WWII boom for thermoplastics, where polyolefins, polystyrene and PVC were invented as demand for affordable, large-scale manufacturing increased.

In the 1970s, plastic production overtook steel production, with thermoplastic injection moulding now seen as an essential part of electronics, automotive and household appliance manufacturing sectors.

Machinery and Tools Used

Today’s process for injection moulding holds many similarities to the traditional methods of plastic parts manufacturing, although state-of-the-art equipment and advancements in computer technology certainly make life a lot easier.

In terms of machinery used during the process, there is a variety of standard and all-electric based equipment that can be used in thermoplastic injection moulding, with each method defined by the driving systems used; hydraulic, mechanical, electric and hybrid being the most common.

The tools used to create plastic moulds depend largely on the design specifics and production requirements as set out by the client.

For example, steel-based moulds are more costly to produce, but they will often be more durable over a long period of time and is ideal for large-scale production volumes.

Other injection mould tools include aluminium alloy, which is preferred for short to mid-scale manufacturing projects as it tends to be more cost and time-efficient. Although with today’s modern fast machining tool room equipment, along with improved steels, steel tools are just as cost-effective and allow for easier modifications/change at a later date.

Further considerations when it comes to tooling include the option between single or multi-cavity moulds. Again, the decision to use either depends on the requirements of the project, with the difference being the ability to produce either a single product per moulding cycle or more than one product per cycle. Product complexity, material, and product size are also considered at the tool design stage.

If a client’s goal is to produce 1 million products per year, then we would typically recommend a multi-cavity mould of four or eight.

The benefits of a single-cavity mould for shorter or more complex product runs are that there would be a guarantee of one to two million shots (the minimal operation time without additional cost to the client) depending on the material and product design being implemented.

The Thermoplastic Injection Moulding Process

Crafting plastic parts through thermoplastic injection moulding involves injecting a barrel-heated thermoplastic resin into a clamped mould by a screw with an NRV (Non-return valve), that stops the molten material from travelling back up the screw.

We then enter the dwelling phase, where the pressure is held by hydraulic pressure to the plastic, to make sure that the single or multiple cavities are filled and packed to avoid sinkage, warping and distortion.

Next comes cooling, where the plastic is left to solidify within the mould before the mould is separated and ejected through a combination of a movable metal plate and the use of ejector pins/blocks/blades and sometimes aided with an air blast to remove the plastic entirely. it is during this cooling period that the screw in the heated barrel rotates and self feeds the next shot of material ahead of the NRV. The action of the rotating screw ensures a thorough mix of the material whilst being heated to the correct temperature for the mould filling phase.

This then concludes one injection mould cycle before the process is repeated to the number desired by the client.

Advantages of Injection Moulding

There are numerous benefits for manufacturers when it comes to using plastic injection moulding for the production of plastic parts:

  • Waste Reduction and Reduced Environmental Impact – responsible injection moulding companies are committed to green initiatives, meaning any excess plastic generated from the moulding process will always be recycled.
  • Cost-Effective Design and Production Process – using the latest tooling and machinery, our thermoplastic injection moulding techniques are highly cost-effective. Labour costs for the client are greatly reduced in comparison to other types of moulding, ensuring clients receive high-quality parts and high output rates thanks to automation.
  • Ability to Handle Complex Part Designs – a significant benefit of injection moulding is in its design flexibility. From large-scale production of uniform parts through to more complex components of larger items such as those seen in car doors, quality consistency in regard to rib design, corner transitions can be achieved at all levels.
  • Swift Production With Impressive Results – one of the main reasons that thermoplastic injection moulding is so popular among manufacturers is its reputation for efficiency. High production output can see speeds of a few seconds – see the blog Have you ever wondered how DVD Trays are made – between each mould cycle, and longer to suit the part weight, size and complexity.

Which Markets Typically Take Advantage of Injection Moulding?

The aforementioned flexibility of injection moulding means the process is universally applicable to a wide range of manufacturing sectors.

Injection mould shops are worldwide, producing injection mouldings for many applications for both local and export customers. the range of industries and end uses are far too many to list, and we would estimate that you pick up in your hand an injection moulded part every hour, or use a product in your everyday use and life.

Here at the Merriott Group, we produce thousands of injection mouldings every day, for a wide and diverse range of both applications and customers. These customers are here in the UK and worldwide, with their end products serving their customers with well designed, thoughtful and engineered injection mouldings. Contact us, where we can bring our wealth of knowledge and experience to the benefit of your design and company, from a thoughtful and listening key supplier, with facilities in Somerset and Kent.