Mold Parts

What is Injection Molding?

Molds are tools that are critical for mass production in the modern manufacturing. It is often used in conjunction with a die, both of which are the key elements in manufacturing applications. For example, mold parts are used in injection mold to shape casting as well as resin, and dies are used in stamping.

Mold parts are essential for injection molding, which have largely contributed to the mass production of products with identical shape and quality in a wide myriad of areas. As a matter of fact, injection molding has always played an important role in the automotive industry.

Understanding all mold components that make up the high quality and precision injection molding can be quite complicated for those who are not of the related area of expertise. It is in fact not easy to find a comprehensive source that will tell you everything that goes into a mold. Therefore, we are going to review the basic parts of a mold in this article so that you will have an idea of what each component entails.

Breaking down Injection Molding

If you did not know what an injection mold is before, you will after reading this section as we are going to help you comprehend each mold component in an easy-to-read language.

Clamp Plates

The clamp plates are used to attach mold halves onto the molding platens. Large bolts used alongside the mold clamps to hold them in piece. More and more molds now utilize magnet force to clamp the mold onto the platen. Some of the advantages of clamp plates using magnetic force include;

● Molds can be easily attached and detached, which will normally take less than a second.
● No energization is required during clamped condition; Energization is only required when switching on and off. Also, there is no heat generation since there is no electricity consumed.
● Magnetic force will not decrease with time, and is in fact maintained for prolonged used.
● Clamp plates are highly durable because they have no moving parts.
● The interior of clamp plate does not require any maintenance.

Sprue Bushing

The sprue bushing is where materials like liquified plastic is injected through the nozzle of the barrel of the molding machine in order to fill the part within the cavity and core. The nozzle is often seated on the sprue bushing and locating ring, which help keeping the nozzle to the center of the mold.

Feed System

Following the above, the liquified plastic is injected through the sprue bushing in a sprue, and then to distinct, individual runner that directs the plastic to the gates – the entry point where material enters and goes to individual cavities. The runners and sprue can be reground, reused, or chopped up. 


Cavities are areas of the mold that enable parts to be molded into desired shape. This entire sequence of event involving the injection of plastic material is called the molding cycle. The cycle starts when the mold closes, followed by the polymer injection into the mold cavity. The number of molds needs to be balanced, thus only certain number cavities are allowed. Once the cavity is filled by the plastic material, a holding pressure is added to make up for the material shrinkage. 

You’d often have a choice between a single-cavity mold and multi-cavity mold. As the name implies, a single-cavity mold produce a single product in one cycle, whereas a multi-cavity mold is able to produce more than one product per cycle. However, keep in mind that multi-cavity mold usually has a longer lead time for mold manufacturer. 

Ejector Pins and Ejector Plate

The ejector system is referred to the sequence of event when parts are pushed off the core using the so-called ejector pins. This is done by the ejector plate pushing the ejector pins forward to push the parts off the cavity or core. The ejector pins are mounted in an ejector plate, and the ejector retaining plate is responsible for holding the pins into the ejector plate.

Locating Ring

The basic function of a locating ring is responsible for “locating” and aligning the orifice of the cold or hot sprue with the hole in the stationary platen of the machine. The locating ring is usually located in the center of the mold, but is often subject to being offset by several inches to lessen the size of the mold base. Contrary to popular belief, the most standard or basic type of locating ring is actually not very user-friendly, especially in large molds. 

Final Words

In conclusion, understanding all parts of an injection molding is the first yet very important step to do if you happen to be a product designer or in the relevant business. As injection molding is more intricate than you think, both the terms and the function of each mold parts may be overwhelming. But you’d still need to know all of this information if you are, for example, to share your CAD drawings with your engineers to confer about the potential tweaks.

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