Injection moulding is a mass production process capable of creating multiple quantities of solid plastic parts repeatedly at fast cycle times. Consequently, it is very suited for high volume manufacturing.

Explore the basics of injection moulding 

With many advantages over other plastic moulding processes, injection moulding allows products to be produced in complex and intricate detail that would otherwise be too costly or difficult to make. Furthermore, with the capacity to manufacture multiple parts at the same time, the high production output is beneficial to company labour costs.
 

 

Faults in the finished product can also be rectified easily, therefore little material is wasted, adding to the cost-saving benefits of the entire process. With a wide range of materials available for use, from polypropylene to high-performance engineering polymers, the possibilities to create bespoke products that are unique to your requirements are endless.

The injection moulding process

Step 1 – The mould tool is securely mounted into a moulding machine of relevant size, with the two halves of the tool held into place by clamps. A machine setter prepares for production by entering the specific tool settings into the machine.

Step 2 – Plastic pellets are fed into the moulding machine using a hopper and passed into a heated barrel to melt the granules. Within the barrel a reciprocating screw plasticises and compresses the material, driving the molten plastic towards the mould tool.

Step 3 – A nozzle forms a seal between the barrel and the mould tool. Under high pressure the molten plastic is passed from the barrel, through the nozzle, and into the cavity of the mould tool. Tools can contain multiple cavities to produce more than one part each time.

Step 4 – Temperature controlled water or oil circulates the body of the mould tool for a specific length of time to cool the plastic within. As the plastic cools it solidifies to the shape of the mould cavity or cavities.

Step 5 – The moulding machine uses its moving platen to open the mould tool and ejector pins extend into the mould cavity to push the part out. Often a robot collects the finished moulding from the mould and places it on a conveyor belt or final working area. They then retract to their original position allowing the mould to be closed and the cycle repeated.

The cycle time of the injection moulding process is defined by the time it takes to make a complete part from closing the tool, injecting the plastic, cooling the polymer under pressure, opening the tool and ejecting a full part. A short cycle time will improve manufacturing efficiency, allowing more parts to be made for the customer in a shorter time. A short cycle time is also paramount to achieve a competitively priced component.

Each tool can consist of one or multiple cavities. These can be identical to each other or unique to allow one tool to produce differing sets of components. For high volume requirements, it is ideal to design a tool that will make more than one identical part at a time.

For example, pre-form plastic components for making plastic bottles are produced in tools of up to 160 identical cavities. Accurate tool-making and precise process control are required to ensure that all cavities are created equally in multi-cavity moulds.

There are a number of additional processes to compliment a plastic injection moulded part, many of which are available at RGE.

Automatic application of self-adhesive labelling is available at RGE on many injection moulded parts. Alternatively, detailed markings and stunning graphics can be applied to cooled components using Computer Controlled Pad (Tampo) Printing. This method offers a premium finish to any product.

Simpler decoration can also be added, such as company logos or product markings. These can be carried out with the application of hot-foil blocking, usually during the cooling cycle of the plastic injection moulding process.

Plastic components can be assembled using ultrasonic welding or linear vibration welding. RGE make complex base components for products such as tumble-dryers using the linear vibration welding technique. The method joins a lower and upper part with a water tight welding joint to make a stable and accurate complex plastic component.

RGE’s experience stretches across many other plastic moulding and welding applications and we produce in excess of 23,000 tonnes of injection moulded plastic components every year from over 160 injection moulding machines. With an injection moulding machine clamp force capacity ranging from 25t up to 3150t, RGE can cover the full spectrum of any injection moulding requirement 

We’re all aware of the black and white mindset that’s becoming increasingly popular lately with regards to plastic use. However, whilst this view does have some merit, using plastic is something that needs to be viewed and thought about critically. Find below some of the key environmental benefits to plastic injection moulding:

Low Waste

As the plastic injection moulding process involves injecting plastic into an exacting mould, only the exact quantities of material are used to create and shape the final product. Any excess in channels or air vents can be re-ground, melted, and used to create the next moulding. This means that aside from the creation of the mould tool, there is little-to-no waste in the entire production process, and as one tool could be used to create hundreds or thousands of products, this is an amazing amount of waste saved.

Shaping similar products out of more natural materials like wood or metal will not only produce excessive waste, each item will also take much longer to produce, especially the more complicated shapes; things that could be shaped using a single piece of plastic may take several parts that would need to be individually created which increases the costs of production.

Many natural materials are also harder to clean and will decompose over time. This is suitable for some products, but for long-lasting items that will be in regular use it does not seem worthwhile if five separate products made from natural materials (and the associated waste) have to be produced to match the life of a single plastic product.

Ease of Recycling

Products made using thermoplastics (which can be re-ground and set an infinite number of times) can easily be reused to create a new product once it reaches the end of its life. The same plastic granules could be recycled into multiple different plastic products over the course of their lifetime (which as we know with plastics is hundreds of years).

This is an especially efficient way to recycle single-use plastics, the biggest source of plastic pollution. Provided thermoplastics and not thermosets were used in their creation, they could easily be cleaned, reground, and reused in new products.

Product Durability

Products made using plastic also last longer under a wide range of conditions than their natural alternatives. Whilst things like wood and metal will decompose or rust, plastics only do so on a much longer scale. While this is detrimental to the environment when unused plastic is piling up, it can be beneficial if used correctly.

Smooth plastic surfaces are far easier to maintain than even their closest counterparts. This makes them ideal for use in industries like medical where objects need to be regularly disinfected.

Also a lot of items made from plastic injection moulding are rarely single-use. Things like school chairs and storage boxes are designed to be durable and last for years. This process also achieves high levels of consistency in end products. This is advantageous both because it creates less scrap