What is an Injection Molding Press?

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By Jeremy Losek, Nov 17th, 2020

Also known as an injection molding machine, an injection molding press is a machine used in the manufacturing of plastic parts using the injection molding process. Injection molding machines are highly efficient and can produce thousands of parts from the same mold. It is the most common method for producing plastic injection molded products.

History of the Injection Molded Press

In 1868, during a search for a suitable alternative to ivory, John Wesley Hyatt discovered he could produce billiard balls by injecting hot celluloid into a mold. By 1872, Hyatt and his brother Isiah patented the initial injection molding machine. In 1946 the design was improved by James Hendry who built the first plastic injection molding press with a screw. The majority of plastic parts on the market today are produced by plastic injection molding machines that use a screw.

Parts of the Injection Molding Machine

The injection molding press consists of multiple parts that work in conjunction to produce a useable part. The hopper is where plastic resin in the form of pellets, flakes, or shavings, are fed into the machine. The barrel consists of an injection molding screw and heater bands. The plastic is melted inside the barrel’s chamber using heater bands and then injected into the mold cavity by the screw. The platens are made of steel and hold the two parts of the mold. The clamp opens and closes the mold.

How Does Injection Molding Work?

There are two main components of injection molding machines; the injection unit and the clamping unit. The process begins inside the injection unit. Plastic granules are added into a hopper and then gravity fed into the barrel. The heating bands surrounding the barrel melt the plastic. It is then forced into the clamping unit by the screw. Here it is injected into the mold cavity where it cools and hardens to the shape desired. Once the part solidifies, the mold opens and ejects the part.

Injection Molding Process Steps

Before the injection molding machine is used, a 3D CAD design is made by an engineer. This model is then provided to a mold manufacturer who will produce a mold using aluminum, steel, or alloy. Since all plastic shrinks when cooled, the mold design accounts for any shrinkage that will occur. This mold is then added to the injection molding press and the manufacturing process begins.

Vertical and Horizontal Molding Machines

The plastic injection molding press will either be vertical or horizontal. The most common type of plastic molding machine operates on a horizontal axis. The horizontal molding machine holds the mold horizontally. When the clamp opens, the part falls from the mold and drops into a bin. Vertical molding machines operate on a vertical axis and require less floor space than a horizontal machine. The vertical machine holds the mold flat so it does not drop the part when opened. Therefore, the part must be removed by hand or by a robot. The use of a vertical or horizontal injection molding machine depends largely on the complexities of the project. For example, vertical machines are particularly useful for insert molding.

To learn more about injection molding machines or to begin your injection molded project, please contact ICOMold at 419-867-3900 or email sales@icomold.com.

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