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Plastic Injection Molding: Understanding the Process and its Advantages and Applications


Plastic injection molding is one of the most common processes in manufacturing. In fact, a large majority of plastic products and plastic components in everyday items are manufactured using this process.

In this post, we’ll help you understand what the injection molding process cycle encompasses and how it can make a difference in your manufacturing process.

Table of Contents

What is Plastic Injection Molding?

Plastic injection molding is a manufacturing process for the fabrication of high-quality plastic parts in large quantities with great speed and precision. To perform this process, an injection molding machine, raw plastic materials, and molds are needed.

The injection molding cycle comprises of 4 main steps:

  • Clamping: The mold is clamped securely within a clamping unit that is powered by a powerful hydraulic engine. This unit keeps the mold closed while the actual injection of plastic takes place.
  • Injection: Raw plastic in the form of grains or pellets are poured into the injection molding machine, which slowly moves toward the clamped mold. While in transit to the mold, these plastic grains or pellets are melted by heat and pressure. The molten plastic is then injected rapidly into the mold; this causes pressure to build up inside the mold, holding the plastic material in place.
  • Cooling: As soon as molten plastic comes into contact with the interior surface of the mold, it begins to cool. The plastic inside the mold solidifies into its desired shape. As plastic tends to shrink during cooling, additional raw plastic is injected into the mold to compensate for this shrinkage.
  • Ejection: After a pre-set cooling time, the ejection system ejects the cooled plastic part from the mold. Force is necessary to remove the part because the plastic may adhere to the sides of the mold. To facilitate this ejection process, mold release agents can be sprayed on the mold cavity surfaces before injection is initiated. Once the part has been ejected, the mold is clamped shut again and the injection molding process repeats.

How Can Plastic Injection Molding Impact Your Manufacturing Process?

While plastic injection molding usually is an integral part of any manufacturing ecosystem, one should weigh the advantages and disadvantages of this process and take them into consideration before adopting it.

Let us begin with the numerous advantages that this process has to offer:

  • Forming parts with complex designs, shapes, and fine details is possible
  • High repeatability, with succeeding parts likely to be identical to the first one – this enhances product quality consistency
  • Excellent surface finish
  • Dimensional accuracy
  • High production rates are achievable
  • Low scrap rates, as excess plastic materials can be recycled
  • Not a labor-intensive process; keeps labor costs low

However, there are also challenges that should be addressed when evaluating how suitable this process is:

  • Upfront costs for product design, testing and tooling requirements prior to plastic injection molding may be higher than the typically-low labor costs required to carry out the process itself; to reduce these upfront costs, manufacturers should avail of cost-effective rapid prototyping technologies to produce low-cost models or samples of the part
  • Only thin-walled plastic parts can be produced
  • Possibility of a longer lead time
  • High cost of equipment for manufacturers who are investing in plastic injection molding machinery in their operations for the first time
  • Although scrap rates are low, regrind plastic materials should not be used for high-quality production parts due to plastic degradation during the injection molding process; instead, regrind materials should only be used in the manufacture of lower quality parts

Despite these few challenges that should be addressed, plastic injection molding is nonetheless vital to the improvement of various manufacturing procedures. With large-scale production runs possible with plastic injection molding, it is capable of manufacturing bulk quantities of plastic parts and products without the diminution of quality.

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