Components in Injection Mold Manufacturing Process

The process of making molds for injection molding is called mold processing. Many molding shops offer mold machining and design as a service on top of full production injection molding. Most of these molds are made of steel, but they can also be made of aluminum.

Mold machining can be a complex challenge because each mold is made up of many different parts. In this article, we will explain the mold manufacturing process and the precise details required with reference to vertical injection molding machines.

Mold Structure

Mold frame:

The mold frame consists of two or more metal plates. These are called cleats and hold all the internal parts of the mold between them. The bottom cleat is located on the insert molding machine table and contains the struts for the ejector plate. The top plate is where the machine's nozzle will press down to receive the plastic resin.

Mold core:

The mold core is what forms the inside of the final part. Similar to the cavity, the core can be found on either plate.
Sometimes, the complexity of the part (e.g., medical injection molded products) requires a loose core insert. The insert is removed from the mold at the end of each cycle, and the part is then removed from the insert.

Ejector plate:

The ejector plate is the moving part that helps eject the molded product from the cavity. The plate itself has pins attached to it that go through the rest of the mold and gently push the part upward when it is finished. The plate holds the pins together so that they lift at the same time. The ejector plate is pushed upward by the press ejector attached to the machine.

Injector retainer plate:

This plate is a relatively thin piece of metal that is mounted to the injector plate. The retainers for each injector pin are perforated and serve as their support.

Waterline:

The waterline is the internal passage between the plates that allows cold water to flow through to keep it cool. Depending on the type of plastic resin used, the waterline also helps cool the part faster for faster cycle runs. Not all molds require a waterline.

Carriers:

Carriers are a rare, but sometimes necessary addition to the mold making process. Sliders are used when injection molded products require special closures that cannot be achieved in the fixed design of the mold. Sliders can be moved manually each cycle or sometimes can be triggered when the mold is closed.

Sprue:

The sprue is the first part of the mold that the plastic resin hits after it comes out of the sprue bushing. This is usually the deeper imprint in the mold and directs the plastic to the runners.
Runner: The runner flows into each mold cavity and achieves uniform flow while using the least amount of resin possible.

Gates:

At the end of each runner, the plastic resin enters the cavity through a gate. There are many different types of gates, but the most popular are edge gates and tunnel gates.

Closure:

Closure prevents plastic from entering a selected area and is most often used when a part needs a hole or needs to be hollow.

Heated Cartridges:

Sometimes it is necessary to heat the mold rather than cool it to prevent the plastic from hardening too quickly. A heated cartridge is an electric steel rod inserted into the mold to keep it hot. Engineering grade thermoplastics require a mold temperature of over 200 ° F to help stabilize the plastic during cooling. This will also help prevent short shots.
 

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