Plastic Injection Molding: Definition, Process, And Environmental Impact

Injection molding is a manufacturing process for producing a wide range of parts and items by injecting liquefied raw materials into a mold. The process initially began in the 19th century, and it still is one of the best methods to fabricate intricate items for a reasonable price. Injection molding is a multipurpose process, permitting a broad range of various materials and finishes. That makes it a common choice in many industries with entirely diverse requirements and goals.


Whether you are a manufacturer who needs a limited number of items or you’re looking for a reliable technique to produce large quantities of pieces quickly, injection molding is a perfect choice if you are working with materials such as plastics.

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Plastic Injection Molding

Plastic injection molding is the process of fabricating plastic parts by injecting molten plastic into a metal mold. The process started in 1872 when an American creator named John Wesley Hyatt invented the first plastic injection molding machine. After the machine’s creation, the plastic injection molding industry developed quickly, from manufacturing simple and small plastic parts such as buttons to producing complex medical apparatus. Manufacturers all over the globe utilize injection molding to produce all sorts of goods. The most extensive use of plastic injection molding is for making non-consumer items for applications where visual interest is not significant.

This article is guiding you throughout the process of this manufacturing technique. So, continue reading to find out more about this great method that today’s manufacturers highly implement for different purposes.

The Process Of Plastic Injection Molding: A Step-by-Step Guide 

The production cycle of injection molding is, as a rule, very shortusually between two seconds and two minutes, and it includes the following stages:


Before the injection of the material into the mold, the two parts of the mold must be firmly closed by the clamping device. Each part of the mold attaches directly to the injection molding machine and only one of the parts slides. The hydraulically actuated clamping device pushes the mold parts together and applies adequate force to keep the mold firmly closed while the material injects. The time needed to close and clamp the mold depends on the size of the machine.


The raw plastic material (commonly in the shape of granules) is catered into the injection molding machine and pushed towards the mold by the injection device. During this procedure, heat and pressure melt the material. Afterward, the melted plastic is injected into the mold very fast and the accumulation of pressure packs and holds the material. The material that is injected is referred to as ‘the shot’. The injection time is difficult to estimate precisely because of the complicated and varying flow of the melted plastic. However, the injection time can be calculated by the shot quantity, injection pressure, and injection force.


The melted plastic that is inside the mold starts to cool once it comes in contact with the internal mold surfaces. As the plastic cools, it solidifies into the form of the desired object. During the cooling phase, some shrinking of the object can occur. The packing of material in the injection phase allows extra material to flow into the mold and decreases the amount of shrinkage. The mold must remain closed until the needed cooling period elapses. The cooling time may be calculated from the few thermodynamic qualities of the plastic and the highest wall width of the object.


After enough time has passed, the cooled object can be ejected from the mold by the ejection unit, which is attached to the back part of the mold. When the mold opens, a mechanism pushes the object out of the mold. Force should be applied to eject the object because throughout the cooling phase the object shrinks and sticks to the mold. To ease the ejection of the object, a mold releasing agent can be sprayed on the surfaces of the mold cavity before injecting the material. 

The period that is needed to open the mold and eject the object may be calculated from the dry cycle time of the machine and the time the object needs to fall out of the mold. Once the object is ejected, the mold can be shut tightly for the following shot to be injected.


After the injection molding cycle ends, some post-treatment is usually required. In the cooling stage, the plastic material in the mold solidifies attached to the object. That excess material should be trimmed from the injected object by using cutters. For several kinds of materials, like thermoplastics, the shred material that results from the trimming can be recycled by using a plastic grinder called a regrind machine or granulator which regrinds the shredded material into granules. Due to degradation of the material characteristics, the granules must be blended with raw material in proper regrind proportion to be reused later.

Plastic Injection Molding And Its Impact On The Environment

Energy consumption is something that is very important and affects the environment. For this reason, with a focus on the impact on the environment, the plastic injection molding advancements in engineering allowed the injection machinery to use 20-50% less energy in comparison to a decade ago.

Because of the plastic’s lightweight nature, many manufacturers are picking it instead of metal to fabricate their products. Plastics are now included in vehicles and aircraft because the weight change positively affects fuel and energy savings. Furthermore, companies use plastics today for building materials and processes like insulation and double glazed units. All of this adheres to saving and producing energy. Presently, plastic injection molding is a regular procedure in manufacturing. Due to its latest advances, it provides main advantages, not only to the market’s economy but the environment as well.

Final Words

If you are a manufacturer who is thinking of implementing plastic injection molding, you should try it immediately. As you can acknowledge from the above-given information about the process itself, you will benefit from this low-cost manufacturing procedure. What’s even more important, you will also help the environment.