The 4 Stages of Plastic Injection Molding

Last Updated on October 12, 2023 by assistant

When you get a project for plastic fabrication with high accuracy, which manufacturing method is your best option? Injection molding. It applies thermoplastic material to make high-volume plastic parts with high efficiency and lower cost.

Injection molding components have a variety of applications in daily life, including computer casings, mice, toys, chargers, household appliances, etc. Do you know the specific production process of injection molding? This article can give you more insight into the details of injection molding.

Preparations before injection molding:
1. Design the mold. The first step we need to do is design the mold according to the customer’s 3D and 2D files. Once we have confirmed the final files with the client, we will transfer them to the engineering department.

Mold designing

The professional engineers will analyze the files and design the appropriate molds. Mold designing is also a critical step for the whole injection molding process. The quality, precision, and size of the finished plastic parts are determined by the designed mold.


2. Make the mold. During the process, we may need to make the parts of the mold by an array of manufacturing techniques including CNC machining and EDM machining. We tend to apply CNC machining to produce the main frame of the mold.

Molds Making

At the same time, EDM (Electrical Discharge Machining) is a preferred technique to finish the parts with more complex patterns. By polishing the tool several times, the preparations for mold processing are completed.


3. Select the material. Different materials vary in hardness, cost, and weight and the selection of material depends on the product’s design and end-use. We need to select the most suitable material for your unique injection molding project.

Material Range for Injection Molding

Among a variety of materials for injection molding, thermoplastic may be the most commonly used material for it. It not only softens easily but also hardens easily. The common thermoplastics for injection molding include ABS, PC, HDPE, Nylon, POM, PMMA, etc.


What are the four steps of injection molding?
In general, injection molding consists of four steps: melting the material, injecting the material, cooling, and ejecting.

(1) Melt the material. After designing and creating the mold is finished, the first step is to put the granular material into the hopper. These materials will be heated until fully melted. Then, the melt thermoplastics are pushed forward in preparation for injection.

Melting the material for injection molding

(2) Injecting the melt. When the mold is closed, the injection step begins. The molten plastic is filled throughout the mold by the pressure inside the mold to ensure that it takes the shape previously envisioned.

(3) Cooling. After the material injection is completed, the next step is to wait for cooling. After the molten plastic enters the inner mold, it gradually cools, forms with a specific type, and solidifies. During the whole process of injection molding, the time required for cooling may be the longest one. The length of cooling depends on the wall thickness and material properties of the part.

(4) Ejection. When the cooling is completed, the ejector pin of the mold will open the mold and eject the parts, and the robotic arm will take out the plastic parts one by one and put them on the automatic assembly line for the next injection molding process.

Ejection for injection molding

The above is a basic introduction to the process of plastic injection molding. And Ruitai Mold is willing to be your plastic injection molding partner. There are over 15 sets of injection molding machines at Ruitai. We are pretty confident to deliver high-performance plastic parts to you.