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What Is Plastic Injection Molding?

Plastic Injection Molding in PET Bottles | KB Delta


An Overview of Plastic Injection Molding

Plastic injection molding is a quick process that is usually used to produce a large number of identical items, like consumer goods. It can also be used to create single items using a unique mold. The latter is the preferred option when it comes to designing and manufacturing both mechanical and medical components, where the precision of each measurement is extremely important.

Out of all of the materials that can be found around us, plastic is one of the most prominent. Try to imagine your daily routine without using any plastic items, you will probably find that it is quite difficult to do so. Approximately 30% of all of the plastic products that you come into contact with on a regular basis will have been manufactured using the process of plastic injection molding.

One of the best things about the process of plastic injection molding in a manufacturing setting is that it enables companies to have a lot of flexibility. It can be used to create simple shapes or intricate shapes, as long as the mold has been designed to do so. It could be used to manufacture everything from toys to the plastic bottles that you can find in supermarkets.


How does the process work?

The exact method that is used during the process of plastic injection molding depends on the company and what they are producing, as some companies do things in their own way. Most of the time, a prototype needs to be designed and approved before the process can begin. Afterwards, the most common method is as follows:

  • Small granules of thermoplastic, thermoset or elastomers are fed into a machine that is referred to as a ‘hopper’. The hopper then forces the granules of material past heaters that cause them to reach an optimum melting point. This point varies depending on the type of material that is being used.
  • The molten plastic is then introduced to something called an injection molding machine. This is where the material will be forced, using pressure, through a nozzle and into a pre-approved mold. The mold itself will already be shaped like the product that is being manufactured.

The next step is easy, as the material in the mold just needs to be left to cool down. This step can be hurried along using either direct or indirect methods. A direct method could involve spraying something like carbon dioxide directly onto the product, while an indirect method could involve having a system of pipes surrounding the mold so that cold water can flow around it to gradually cool the material down.

After the mold has been left to cool down, you will be left with the finished product. Depending on the type of thing that is being fabricated, there might still be a little bit of work to do after. For example, you might need to trim away any excess material that has leaked out of the mold.


What materials can be used?

The materials that can be used in the plastic injection molding process include numerous different types of thermoplastics, thermosets and elastomers. The specific type of material that a manufacturer will choose depends primarily on the product that they are creating. Each material comes with a different set of advantages and disadvantages.

Some of the materials that are frequently used include:

  • Acetal: A material that is commonly used to make everything from bearings to valves. It features an excellent level of chemical resistance, creep resistance and water resistance.
  • Acrylic: This material is usually used to make a wide array of objects, including panels and shelves. It is known for its scratch resistance and rigidity.
  • Polycarbonate: The automotive industry really benefits from using this material. It is commonly used to make everything from helmets to actual mechanical parts. It is known to be tough and temperature resistant.
  • Polyether sulphone: Most of the time, polyether sulphone is used to make valves. This is because it features an impressive level of chemical resistance, making it perfect for difficult environments.


What are the benefits of using these materials?

Over the past few decades, the materials that are used in the plastic injection molding process have been used to replace materials that could be seen as more traditional. There are a lot of benefits that have come with this change. For example, consumer goods that are made out of plastic would not shatter the way that glass would if it were dropped, making them much safer.

Another benefit of using these materials can be seen directly through the eyes of the manufacturer. Plastic injection molding is an incredibly quick process. Usually, you would have to sacrifice either speed or precision to maintain the other. However, this process gets rid of the need to choose either one or the other. This speed can be focused on to keep profit margins at a maximum.

From an environmental viewpoint, thermoplastics and other similar materials are a fantastic option. They can actually be recycled after they have been used and turned into a new product with just a few simple steps, creating a renewable pattern.


Can any problems occur or defects appear during the process?

We would all like to believe that nothing can ever go wrong when it comes to the manufacturing industry, but we all know that problems and defects can occur. Some of the main defects that are known to occur during the plastic injection molding process include:

  • Bubbles: These will usually appear if too much moisture is present in the material that is being used. To avoid this, most companies actually have a machine that will absorb any excess moisture before plastic injection molding begins.
  • Ejector marks: This results in small indentations that can occasionally be caused when the ejection system pushes the plastic out of the mold after it has cooled down.
  • Flash: This occurs when some of the liquid material seeps out of the mold before it has solidified. Whether or not this is a bad thing depends on the scenario. For example, during plastic bottle manufacturing flash is expected so any excess material is trimmed after.
  • Unfilled sections: This is generally something that only occurs if an insufficient amount of material has been injected into the mold, or if the material has not been injected quick enough.

Most of these defects can be avoided as long as protocols are put into place. The defects are usually caused by avoidable scenarios. For example, warping is something that can also occur. However, it usually only occurs when different sections of the plastic cool down quicker than other sections do.

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