How Does Plastic Injection Molding Work?

Injection molds must have a high precision match between the two mold halves in order to perfectly control the material flow. Creating the mold is crucial to building a seamless, precision product.  Injection molds are typically constructed using steel or aluminum, and precision machined to form the features of desired product.
The injection molding process is fairly repetitive once a functional, errorless mold has been produced. It also has a low scrap rate relative to other manufacturing processes such as CNC machining which cut away considerable portions of the original material blank in a subtractive process.
The Plastic Injection molding process is highly repeatable and reliable for high volume production. Once the first part is produced, the second is going to be practically identical, due to the ability to make multi-cavity injection mold parts, where multiple parts are made with one cycle. Other advantages are the wide range of material selection, low labor costs, minimal scrap losses, and minimal requirements to for post-molding finishing operations.
The major disadvantages of injection molding are the initial costs of the mold design, which tends to be high due to design, testing, and tooling requirements and the longer required lead times. Some custom complex parts may encounter problems during the injection molding process such as warpage or surface defects. Therefore, injection molded parts must be designed with careful consideration to any change in geometry as they cool and the material selection to assure stability.

Conclusion

The process of injection molding may seem like a complex one, but it’s the most common manufacturing method because of its capability and efficiency to produce a plethora of custom plastic parts. Injection molding is one of the most cost effective ways to build both functional prototypes and end use products.

(source:https://www.hthc-tech.com/how-does-plastic-injection-molding-work/)