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In Focus: Ejector Pins

Injection moulding is a complex, multi-faceted process. It involves several different stages, including a design phase, the building of an aluminium tool and the subsequent moulding of plastic components.

Throughout these many stages, there are various elements which contribute to the success of the overall operation. These elements are often overlooked or taken for granted, but if care is not taken to ensure that each of these details has been thoroughly considered and planned for, the overall result may be significantly compromised.

In the first of our ‘In Focus’ series, we will be highlighting the importance of ejector pins to the injection moulding process.

Let’s look in more detail at what they are, and what they do…


Ejector Pins

Ejector pins are located within a mould cavity and are used to push the finished plastic component from the mould. This allows each piece to be released so that a steady flow of automation can continue.

Also known as knockout pins, ejector pins extend and contract in a repetitive motion to force the plastic from the mould. They are typically made from steel.


When the mould is opened, the pins extend into the mould cavity and force the plastic part out. They then retract, the mould closes and refills, and the process begins again.

Each set of ejector pins is customised to match the size, shape, and structure of the plastic component that they will have to eject. The location of the pins will depend upon these factors and must be given careful consideration during the design process.

Main Types of Ejector Pins

Through Hardened Pins: heat treated and durable. Often used in plastic injection moulding and can be used in temperatures up to 200 degrees.

Case Hardened Pins: also known as nitride pins. Harder than Through Hardened Pins and can be drilled or tapped. Can be used at temperatures exceeding 200 degrees.

Black or Oxidated Pins: for use at high temperatures, usually between 600-1000 degrees. Have a self-lubricating coating which is black. Often used in automotive production.

Value of Ejector Pins to the Injection Moulding Process

The introduction of ejector pins to the injection moulding process has been crucial for many reasons. They have become an integral element of the process of creating machined parts.

Key benefits:

  • Allow for automated operations
  • Enhanced production speed
  • Reduced project delivery times
  • Improved consistency in the design and quality of finished components
  • Reduced wastage


As with anything, there are certain considerations to make when employing the use of ejector pins in the injection moulding process.

Here are some of the potential issues which can be encountered:

Dents/Pin Marks

When the ejector pins push the component from the cavity, they can sometimes leave an imprint on the component itself. Upon closer inspection, the component may appear to be dented, or marked. These dents can make the product less durable, and can, in cases where the impact has been too forceful, result in the product failing to stand up to scrutiny and splitting during use.

The best ways to combat this are to ensure that the locations of the ejector pins are positioned to ensure that there is equal distribution of force when the plastic is ejected from the mould cavity.

Ejector pins should always be placed in a balanced manner in relation to one another to allow for consistent pressure to be applied across the surface area of the component.

They should also be located on the even, flat parts of the component, rather than on the edges of the component.

There will need to be an even distribution of force applied to the surface area of the component. If the ejector pins are located incorrectly, the plastic component will not be cleanly ejected from the tool, which will slow down the automation process.


Consultation with a customer is sometimes necessary to ensure that ejector pins are situated in the correct place. Care should be taken to ensure that the imprint of the pins does not inhibit or undermine the final use of the product. For instance, in some cases, customers may wish to weld on one side of the component. To do this, there cannot be any indentations or visible pin marks.

Damage to the Pin

Ejector Pins can be damaged due to the required amount of pressure that is required to eject the component from the mould cavity. If too much force is required, the pin can break.

This can result in increased timescales for the completion of projects, damaged components and higher levels of waste.

The easiest way to reduce breakage is to either employ more pins or to use pins with larger diameters.

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