Key Injection Mold Components You Should Be Familiar With

If you’re planning to produce a plastic part using injection molding, you’ll need to familiarize yourself with the essential injection mold components. From the primary flow path to the sub-runner and exhaust port, each component plays a vital role in the injection molding process. However, if you’re new to injection molding, you may find yourself lost in a sea of technical jargon and unfamiliar terms.

We have you covered whether this is your first time learning about the injection molding process and its components or you’re independently venturing into this business with little understanding.

In this article, we’ll explain the various injection mold components, and when they’re utilized, so you know what you’re getting into. So, without further ado, let’s get into the specifics.

Some injection mold components

8 Key Injection Mold Components

So what determines the quality and specifications of the plastic product you set out to manufacture using injection molding? The components of injection molding determine the quality, efficiency, design accuracy, finishing, and performance of the product. Choosing the right components during the injection mold process ensures that your product complies with the necessary production checklist.

Let’s explore some primary components in detail among the multiple injection mold components below.

Primary Flow Path

It is a segment of the runner that connects the injection nozzle of the injection molding machine to the shunt runner or the cavity in the mold. To connect with the nozzle, the highest point of the primary flow path is concave.

To prevent overflow and blockage caused by an inappropriate connection between the two, the diameter of the entrance of the main flow path should be slightly wider than the diameter of the nozzle (0.8mm). This will ensure that the two do not interfere with one another. The size of the product determines the diameter of the inlet, typically between 4 and 8 millimeters.

Casting Component

It refers to the section of the flow path that comes after the nozzle but before the plastic enters the cavity from the main flow channel. This section includes the runner, the gate, the main flow path, and the cold material hole. The molding quality of plastic items and the production efficiency of those products are intimately correlated to the casting system.

Cold Material Tole

It is a hole located at the end of the main flow channel and is used to catch the cold material produced between the two injections that take place at the end of the injection nozzle. This is done to prevent the obstruction of the shunt runner or the gate. After the cold material has been blended into the cavity, it will be simple to induce internal stress in the items.

Furthermore, the cold charging hole has a diameter of between 8 and 10 millimeters and a depth of 6 millimeters. In most cases, the bottom of the de-molding rod is carried by the de-molding rod itself to make the demolding process easier.

Temperature Regulation System

A temperature-regulating system is needed to regulate the mold temperature to meet the requirements of the injection process for mold temperature. For thermoplastic injection mold, the cooling system is mainly designed to cool the mold.

Now the common method of mold cooling is to set up a cooling water channel in the mold, using circulating cooling water to remove the mold’s heat. The heating of the mold can use not only hot water or steam in the cooling water channel but also install electric heating elements in and around the mold.


Within the multi-groove die, the channel individually connects the primary flow path to each cavity. The distribution of the sub-runners on the mold should be symmetrical and evenly spaced out to achieve the desired result of having the melt fill the cavities at the same rate. The flow of the plastic melt, the level of difficulties associated with product de-molding, and the manufacture of molds are all affected by the form and size of the cross-section of the sub-runner.

In this process, a circular section will have a lower flow resistance if the flow rate remains constant. Unfortunately, the cylindrical channel’s relatively low specific surface area is not an effective method for cooling the debris contained within the sub-runner. As a result, a shunt channel with a cross-section of a trapezoid or a semicircle is frequently utilized.

injection mold sub runner

This channel is typically arranged on a half mold with a de-molding rod. It is necessary to polish the runner surface to lessen the resistance to flow, resulting in a faster filling speed. When determining the size of the runner during the manufacturing process, the type of plastic, as well as the size and thickness of the product, all play a role.

 However, it is noteworthy that the section width of the shunt channel for most thermoplastics is not more than 8 millimeters. So an extra big one can reach 10–12 millimeters, and the extra tiny one can reach 2-3 millimeters.

Exhaust Port

It is a groove-style air outlet that has been opened up in the mold. Its purpose is to release the gas that was originally present and the gas introduced by the melt. When the molten material is injected into the mold cavity, the air that was originally stored in the mold cavity as well as the gas brought in by the melt, must be discharged to the outside of the mold through the exhaust port that is located at the end of the material flow.

If this is not done, the products will have air holes, poor connections, insufficient filling of the mold, or even the accumulated air will burn the products due to the high temperature caused by compression. In most cases, the vent hole can be situated either after the flow of molten plastic within the mold cavity or on the mold surface that separates the two halves. The second step is to open a shallow groove on one side of the die.

Additionally, the depth of this groove should be between 0.03-0.2mm, and the width should be between 1.5-6mm. So during the injection molding process, no significant amount of molten material leaks out of the vent hole. It is primarily because the molten material cools and solidifies there to block the channel. This will prevent a significant amount of leakage.

Gate & Sprue

The passageway links the primary flow path, also known as the sub-runner, to the cavity. The channel’s cross-sectional area can occasionally be the same size as the primary flow path of the sub-runner, but more often than not, it is less. Thus, it is a relatively insignificant component of the flow passage system as a whole. The form and dimensions of the gate have a significant bearing on the overall quality of the items.

Controlling the rate at which the material flows is one of the sprue’s primary functions. Having said that, due to the early setting of the molten material in this section, it is possible to prevent backflow while the injection is being performed. Because of the intense shearing, the temperature of the molten material moving through is raised, lowering the apparent viscosity and increasing the fluidity.

Molding Parts

Molding parts refer to all kinds of parts forming the shape of products, including moving die, fixed die and cavity, core, forming rod, and exhaust port. The forming part consists of the core and die. The core forms the inner surface of the product, and the concave die forms the outer surface shape of the product.

Later, after the mold is closed, the core and cavity form the mold cavity. According to the process and manufacturing requirements, sometimes the core and die are composed of several pieces. Sometimes they are made as a whole, and only insert parts that are easily damaged and difficult to process are used.

injection mold parts


Overall, it’s safe to say that plastic manufacturing would be impossible without injection mold components. For smooth and efficient mold operation, it is crucial to use key components like base, cavity inserts, and ejector pins.

Some other important elements that can affect the quality and durability of the mold components include the materials used, the accuracy of the manufacture, and the care with which they are maintained.

Companies today can make plastic goods that are up to snuff, thanks to their knowledge of the relevance of these parts and their collaboration with seasoned and trustworthy producers. Injection mold components will remain critically important to the plastics sector even as technology and materials advance.

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