From Start to Finish: Injection Molding Process Steps

Every manufacturing process has its own standard set of proper steps and order of operations in order to be completed. Injection molding is certainly no different. The injection molding process steps follow a logical sequence that starts off with material selection and ends with ejection.

Walk through the complete manufacturing process with Metro Plastics as we highlight all of the injection molding process steps.

Material Selection and Preparation

Metro Plastics’ knowledge of material application and preparation can elevate your project to new heights by providing you with the necessary specifications to allow you and your team to make the most informed decision for your project.

Best practices for material selection include having a high-level understanding of your components’ intended design and knowing key parameters such as environment, need for durability, and targeted lifecycle.

Material preparation starts off with plastic pellets, sometimes referred to as granules, loaded into what’s called a hopper. A hopper is what feeds the material into the injection molding machine.
As the pellets are fed into the machine, they are moved into a heated barrel where they are met by a rotating screw.
The heat from the rotating screw causes the once solid pellets to melt, which serves as the material that is injected into the mold.

Injection Molding Process Steps Feature Clamping and Mold Closing

The injection molding process involves a carefully sequenced series of steps to ensure parts are produced correctly. Once material preparation is complete, the process moves to the next stage: clamping and mold closing.

The mold is mounted by the injection molding machine and then forcefully clamped at varying tonnages. Clamping happens with varied tonnage levels because it is intended for the mold to resist injection pressure.
Once the mold has been successfully clamped and closed, it’s onto the next part of the process.

Injection

This is where injection molding gets its name. Injection is also one of the most critical injection molding process steps.

The same screw that was used to heat up the plastic and melt it now serves as a plunger that injects a measured shot of the melted plastic through the nozzle, down the runner system and into the mold cavity.
It’s essential that pressure is maintained throughout this part of the process to ensure uniform shots, which also helps minimize defects such as shrinkage, internal voids, or air bubbles.

Cooling and Solidification Are Critical Injection Molding Process Steps

Injection molding happens at high temperatures and high pressures, but eventually both have to come down in order for the final injection molding process steps to occur.

In cooling, there are designed cooling channels within the mold to help control temperature as material solidifies within the mold itself.
Molds remain closed until the part is firm enough to be ejected without any defects. Cooling time is largely dependent upon material selection and design aspects such as wall thickness.

Mold Opening and Ejection

The final step of the injection molding process is the mold opening and ejection from the machine.

Once properly cooled, the clamp opens the mold as ejector pins, sleeves, or plates push the part and its attached runners out of the mold.
When the finished product has been ejected from the mold, any excess material is removed and the cycle is complete.

Contact Metro Plastics and Trust Us With Each of the Injection Molding Process Steps

For over 50 years, Metro Plastics has performed injection molding services for a variety of industries and along the way, we’ve honed in on the injection molding process steps. We know that while every order we take is different, the process largely remains the same.

We proudly hold an ISO 9001:2015 certification, ensuring that your components are of the highest quality when they leave our facility.

When it comes time to place your plastic parts order, trust Metro Plastics to correctly follow the injection molding process steps and contact us today.