Plastics are one of the most widely used materials for the production of objects and components. They are also one of the most versatile and adaptable, capable of being made to take on a vast array of shapes.
This is thanks to a technique known as plastic injection molding, which uses specialized hydraulic or electric machines to melt, inject and set plastic into the shape of a metal mold that’s fitted inside. The process is highly reliable and extremely fast, allowing for rapid, high-quality manufacturing.
Injection moulding is typically done on a large scale and can be very cost-effective. But, like any manufacturing process, there are certain problems that can occur during production. These can range from simple miscalculations to a complete breakdown of the machine. It’s important to understand the causes of these issues and how to avoid them if you want your injection molding process to run smoothly.
The plastic injection process starts when the pelletised raw material is fed into the machine where it’s melted and injected into the mould at high pressure. The moulds themselves must be tough, designed to withstand the repeated injection of molten plastic, and they must be accurate, down to the nearest 100th of a millimetre.
Once the molten plastic is injected it needs to cool down rapidly so that it doesn’t cause the plastic moulding machine to overheat and shut down. A temperature control unit (TCU), usually located at the injection machine-side, circulates a steady flow of coolant through passages in the injection moulds to help them maintain correct, consistent internal temperatures. This flow carries away the burst of heat created when the IMM delivers a shot and helps to prevent temperature fluctuations in the moulds, helping to ensure that the finished product will have good dimensional accuracy.
As the molten plastic enters the mould it’s subject to a high level of pressure from the screw that drives it forward. This creates friction between the individual molecules of the polymer that reduces their Van der Waals forces, allowing them to move more easily and with less resistance. The screw’s flighting also breaks down some of the pellets, mixing and homogenising their thermal and viscous distributions.
After the molten plastic is injected into the mould it’s held under pressure for a period of time – this ‘holding’ phase can range from milliseconds to minutes, depending on the type of thermoplastic being processed and the complexity of the part being produced. This step is crucial to ensuring that the moulded component sets correctly before it’s ejected from the mould and ready for finishing on the production line.
Injection molding is a complex manufacturing process that requires the correct knowledge and equipment to perform well. Having a partner that understands the intricacies of the process and can offer insight into the best manufacturing practices for your specific application will allow you to minimize costly errors and achieve a quality final product. For example, a partnership that offers design for manufacture (DFM) services can improve the efficiencies of your manufacturing process and reduce the overall cost of production.