We wake up, check our phones. We make coffee with our coffee machines. Then we start working on our laptops. What do these three actions—and most of the things we do throughout the day—have in common? Plastic injection moulding. Phones, coffee machines, laptops, showers, chargers, GPS modules, domestic appliances, you name it, and it’s probably partly made using plastic injection moulding.
What is plastic injection moulding?
Plastic injection moulding is a process used to manufacture products—from medical devices to garden chairs. First, plastic pellets contained in a loader are dropped onto a screw, which drives them forward in a heated barrel. Consequently, the pellets (thermosetting/ thermoplastic polymers) melt, and the resin accumulates in front of the screw. Finally, when there is enough malleable resin, the screw injects the resin through a runner into a mould, which solidifies to create the final product.
After one complete cycle, the mould opens, and the product is removed. The process is repeated as many times as necessary. Plastic injection moulding allows identical products to be made quickly and at scale.
What is resin?
Resin is an industrially produced rigid polymer (or thermoplastic) that comes as equally sized pellets. When they are fed into the plastic injection moulding machine, the pellets are melted, injected into the mould, and become the final product.
The right type of resin to choose depends on the final manufactured product. For example, a medical device that must be FDA (U.S. Food and Drug Administration) approved requires a different resin from a plastic toy. Choosing the correct resin is a critical plastic injection moulding consideration and is key to the product’s success.
There are over 100 varieties of resin, but here are the most commonly used ones:
- Acrylonitrile-Butadiene-Styrene (ABS)
- Nylon (PA)
- Polycarbonate (PC)
- Polypropylene (PP)
- Polystyrene (GPPS)
What are moulds?
Moulds are generally made from a specific grade of stainless steel and are created to be the desired shape of the product. They are hollow so that the resin can be injected inside.
Choosing the right steel grade is crucial to the project’s success in terms of overall cost, tool maintenance, and production volume.
What are runners?
Runners are like plastic taps that either cool or heat the part. A heated runner can maintain a steady temperature, making the process faster but more costly. Conversely, cold runners are more cost-effective and can work with a broader range of resin.
Why use plastic injection moulding for electronic products?
Using plastic injection moulding to make parts for electronic products has a whole host of benefits in terms of the manufactured part's physical properties, the manufacturing process, the environment, and the ability to sell products. Here are the most significant advantages.
Reduces the final cost
The final plastic product is lightweight compared to any other material that could be used to make the same product—steel, for example. Therefore, the process is the cheapest way to make various shapes at high volumes. Of course, specific materials are required for some products used in specialist areas like aerospace. Still, for the majority of products, the unit price of manufacturing plastic products is the best and cheapest option.
Makes products energy-efficient
The plastic injection moulding process is less energy intensive than processes using other materials such as metal or wood.
Provides heat insulation
Overheating electrical appliances are a danger for factories, offices, and homes. Household electrical appliances cause 38 fires a day in England alone. Heat and electronics are a dangerous mix.
However, using plastic components at specific points of electrical appliances is beneficial as plastic is a poor conductor of heat. Also, the manufacturer can use a special flame-retardant plastic during the plastic moulding process to make electrical appliances safer and reduce the impact of fires. The UL94 standard of flammability is used to define the flame retardancy of different thermoplastics.
Provides electrical insulation
Plastic is a poor conductor of heat and electricity, meaning that it acts as a sound barrier between a potentially deadly electrical current and a user.
Again, choosing the correct resin is essential for electrical insulation, as certain plastics are recommended for products that contain electrical wiring.
Creates durable products
Metals can corrode, organic materials can rot, but plastic is resistant. Choosing a strong resin will make electronic products long-lasting. And you can also select resins that are resistant to chemicals, meaning the products can be used in demanding environments.
Creates lightweight products
Original electronics manufacturers (OEMs) are always looking to create lighter products. And one way of making them lighter without sacrificing durability (see above) is to make them from plastic. Different types of plastics can be used inside and on the exterior to create a lightweight product.
Creates hygienic products
Although not usually a concern for most electronic products, plastic is a hygienic material as it is easy to clean germs and dirt from the surface.
This is an important consideration for electronic healthcare products, such as diabetics' insulin pens.
Manufactures products quickly
Plastic injection moulding allows you to produce high volumes of a product very quickly—the cycle time is from two seconds to five minutes, depending on product complexity. Compared to materials such as cast iron—for which cycle times can be over 15 minutes—creating plastic items is rapid, meaning more products can be produced in less time.
Positive environmental outcomes
Plastic has a bad reputation. And while it is undoubtedly true that plastics have not been managed well globally, plastic injection moulding can have positive environmental benefits when compared to other processes.
For example, the process is energy efficient, so it has a low carbon footprint due to the quick cycle times.
Also, it is relatively simple to use recycled plastic in the plastic injection moulding process. There is always a slight colour variation when using recycled plastic, so it cannot be used for important external parts; however, it is a good option for many internal parts.
Plastic runners, which would otherwise be discarded, can be re-grinded and mixed with virgin plastic. The process reduces the cost of purchasing more new plastic, saves time, and is energy efficient. However, it is always important for OEMs and their EMS (electronics manufacturing services) partners to discuss this option before the start of the project, as the exact ratio of runner to virgin plastic that can be used depends on the final product.
Aesthetically pleasing
Although the plastic used inside and outside electronic products are highly functional—the type of plastic used on the outside also helps sell the product. It's not just used to cover up the hardware; it makes the product attractive, so people want to buy it.
While beauty is subjective, plastic injection moulding can contribute to making attractive shapes and designs that are generally aesthetically appealing. For example, a computer mouse can be made from plastics with different textures and a high-gloss finish on one side. This is likely to be more attractive to the customer.
Plastic injection moulding facilitates the designing and manufacturing of plastic products. The process allows designers to be innovative and creative when bringing new products to market. If you are looking to make your product stand out by creating it in a different shape, colour, texture or by making it transparent, then plastic injection moulding is an excellent option. You can also mix many additives into the plastic to give the final products a 'special' quality.
Conclusion
Plastic injection moulding is an excellent choice for high-volume electronics manufacturing when products need to be made quickly. The process is not particularly resource or labour-intensive, and even products with tight specifications can be made easily by the right supply chain partner. What's more, the unit cost associated with injection moulding is low as moulds can be used extensively before needing to be changed.
