13 Feb 2020
The metal plates of a plastic injection mold

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The plastic injection molding process


The basics of injection molding: melted plastic is injected into a metal mold. The material cools inside the mold and hardens into the finished product. The product is released when the two halves of the mold separate and the product is ejected. 


How does injection molding work?


Put simply, injection molding is a process used to inject liquid plastic or metal into a mold in order to create a product. Injection molding is used to create pieces quickly and efficiently at the lowest possible cost.  

You can read more about the basics of molding process here.


What is injection Molding used for?


Injection molding is most often used when a producer needs to manufacture a large number of plastic products, usually over 100 pieces. The process offers a number of advantages, most namely a low cost per unit. Plastic molding creates an incredible number of everyday products; in fact there’s a good chance that you’re near one right now. From computer mice to car parts, plastic injection molding is an integral part of our lives. 


Injection molding process steps


  1. Melt plastic
  2. Inject the molten plastic into a mold
  3. Let the molten plastic cool to a solid state
  4. Remove the hardened product from the mold


Injection molding process control 


When it comes to the quality of molded products, there are a number of specific processes that must be accounted for and controlled. 

Key to the injection process as a whole, temperature has a huge impact on a mold’s performance. The temperature must be adjusted to suit the material being used, as each material has a specific melting point. 

Another factor that is monitored and controlled is pressure, applying to both the injection and the mold cavity. Too much will cause material to be extruded from the mold while too little can cause the product to be incomplete.  


Problems that arise


If you’re wondering where to turn for plastic molding services, it’s important to understand the problems that can arise during the process. Some issues are inevitable, but by making an informed choice, molders can limit the slowdown these problems cause. 

  • Short shot – The mold doesn’t fill completely and the part is incomplete
  • Splay – visible gray or silver streaks on the finished product caused by excess moisture in the material
  • Weld line – a line or seam that forms where liquid material comes together
  • Burning – Burn marks on the product caused by air trapped in the mold
  • Flash – Plastic that escapes out of the cavity, creates a thin layer of plastic sticking off of the part that must be trimmed
  • Sink – A dimple or depression in the part, caused by low pressure in the mold


From start to finish


The plastic manufacturing process can seem daunting at first, but understanding the steps involved can help to clear the matter up. If you have questions about manufacturing a product using this process, contact us for more information. 



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