Plastic Injection Molding Process

Plastic Injection Molding ProcessAs we know, plastic injection molding is the most common manufacturing process to obtain plastic parts. It’s widely used for various kind of products like automotive, medical, industrial, electronics and other related fields. Since injection molding is so important to us, we would like to discuss how the actual injection molding is.


Basically the injection molding requires a serial of facility including injection molding machine, mold tooling, and raw plastic material. While raw plastic material is melted in the injection molding machine, so as to be filled into the mold tooling, where the plastic parts come out. Here below are some key elements of injection molding process.

1. Mold tooling  

Prior to the injection molding process, you must prepare the relativemold tooling, where the molded part will be filled and come out. It normally takes about 15~45 days to build a plastic mold tooling as the custom mold tooling is very complicated and requires a systematic fabrication period. To build a accurate mold tooling, you should have both good mold design and mold manufacturing process. Each process should be completed by sophisticated mold designer and mold makers. Moreover choosing a high quality mold steel is also another key point that determines the mold tooling quality. The better steel, the longer use time the mold would be. Finally number of cavity will affects the cycle time of injection molding, as well the molding cost.

2. Mold Clamping

It’s a preparation job to get mold tooling clamped onto the injection molding machine. As we know, a mold tooling is mainly consist of two half(cavity side and core side), these two sides must be separately and securely fastened on the injection machine. So that each half can move accordingly when the machine is move to open and close. The hydraulically clamping pushes the mold cavity and core forth and back, and gives sufficient clamping force to keep the mold securely closed while the raw material is injected. But different mold size requires different clamping force, for surely, the larger tonnage of injection machine runs larger clamping force.

3. Material filling

The material filling of injection molding is a core process that the injection machine give force to push molted material through machine to reach mold cavity. We also call this process injection molding. Before the injection process, we should prepare the pre-heated raw material onto injection machine, during this process, the molten plastic material is then injected into the mold cavity very quickly under high injection pressure. And those injected material will stay in the mold to become the idea shape. This process is referred to shot or injection cycle. For most of plastic products, the injection cycle time takes 20 seconds~2 minutes.  The cycle time can be calculated based on the shot volume, injection pressure, and cooling time.

4. Cooling Time

After the molten plastic material is shot onto the mold tooling, the cooling system(usually by water or oil) of mold tooling will cool down the mold temperature instantly. So as to solidify the final molded parts. The tooling time normally takes few seconds or longer, it depends on material type and cooling structure of the mold tooling. During this stage, some of plastic defects might occur, like shrinkage, deformation, or venting marks. So we should consider and prevent these problem when mold design. In case these problem happens, we can also troubleshoot them by adjusting the injection parameter.

5. Ejection

After the desired parts is solidified on the mold tooling, we should have a automatic structure to take off the parts. Normally the mold tooling will be designed for ejection pin or ejection plate that push the molded parts out of the mold tooling. After the plastic parts ejected to drop off, the mold tooling will be clamped to close for next cycle of injection molding process.


After reading our article above, I think you must have some basic knowledge on plastic injection molding process. Once you still have some question, or any plastic project to run, please don’t hesitate to contact Inno Molding team for help, we will always here to help.