Ejector Pins in Injection Molding: Functions and Design Guidelines

Table of Contents

There are specific parts of the injection molding machine that make you wonder what exactly is the value they add to the overall injection molding process. One such part is the ejector pins in injection molding.

PlasticsInjectionMoulder die
Plastic InjectionMould
Source: https://upload.wikimedia.org/wikipedia/commons/thumb/1/15/PlasticsInjectionMoulder-die.jpg/640px-PlasticsInjectionMoulder-die.jpg

Its name should be enough to give it away, but it is also essential to examine what role this ‘unsung hero’ plays in injection molding. 

When the injection molding is completed, the part formed must be pushed out of the mold cavity. This is what your ejector pin aims to achieve in the concluding stages of the injection molding process. 

Without wasting time, let’s further explore and outline the functions and design guidelines of this small but mighty instrument that completes the injection molding process. Shall we?

ejector pins in Injection molding
ejector pins in Injection molding
Source: https://upload.wikimedia.org/wikipedia/commons/thumb/3/32/Injection_molding_diagram.svg/640px-Injection_molding_diagram.svg.png

1. Understanding Ejector Pins in Injection Molding

1.1 Function and Purpose of Ejector Pins

The primary function of the ejector pin is to eject the molded part safely and easily in the mold’s cavity without damaging the part or causing deformity. Even so, how this would be done with precision and meticulousness becomes paramount. 

Once the molten thermoplastic is injected into the mold and the desired part is formed, cooling and solidification takes place. After this, the ejector pin swings into action. 

It applies a controlled force to eject the part from the mold cavity so there’s no distortion in the molded part ensuring perfect removal. Different types of ejector pins offer different functions but ultimately, similar goals. 

1.2 Types of Ejector Pins

Although their contributions may seem brief, ejector pins are very crucial to a successful injection molding process. However, they are available in different shapes and sizes and suited for different injection mold removal scenarios and functions. 

Firstly, we have straight pins that are the typical ejector pins used in most injection molding procedures. They are straightforward and resourceful and are used for simple ejections. 

Then there’s the blade pin, suitable for ejecting complex parts, enhancing this process basically because of its shape. Blade pins are shaped like a tiny spatula having a blade-like shape that is deployed when gently prodding out the part from the mold. 

And the last common type is sleeve pins. These pins are usually employed when ejecting difficult angled parts.

Cutting injection mold ejector Pins 2
Cutting injection mold ejector Pins
Source: https://www.youtube.com/watch?v=IhyoGptt8gA

2. Design Guidelines for Ejector Pins

2.1 Ejector Pin Placement and Quantity

For ejector pins, the nature of their functions requires that they are given adequate consideration in their design, especially their placements and quantity. 

Ejector pins’ main aim is to ensure no damage or fault comes to the part during ejection. And the purpose of proper placement of ejector pins is to allow it to seamlessly remove the part from the mold cavity. On that account, the intricacy of the part and potential undercuts that can influence ejection from the mold is critical to its placement. 

Likewise, the quantity of the ejector pins. There should be a balance in the number of ejector pins to be made. Why is this so you may ask? 

The thing is, excessive ejector pins will result in part deformation and distortion, while too few ejector pins can lead to stickiness on the mold cavity and difficulty removing the part from the mold walls. All this is determined also by how complex the design and geometries of the part itself are.

Another major influence of ejector pins’ placement and quantity is the appropriate application of draft angles. With the necessary draft angle in place in the mold, the ejector pins can effectively and efficiently function, aiding an easy ejection and keeping part and mold integrity.

Cutting injection mold ejector Pins 3
injection mold ejector Pins sizing
Source: https://www.youtube.com/watch?v=IhyoGptt8gA

2.2 Ejector Pin Size and Dimensions

The use of new and innovative technologies like 3D printing technology in manufacturing is a testament to the importance of accuracy and precision of dimension. These considerations are also critical for the injection molding process and mold features such as injector pins cannot be left out. 

However, for mold designers to efficiently determine the ejector pin’s dimensions and sizes they’ll have to evaluate critical parameters. These factors include the size of the part, its intricate dimensions, and specifications required by the mold. 

You do not want your ejector pins damaging the part manufactured or causing wear in the mold. This will only slow down production runs, and compromise the part produced. 

In addition, the material composition must be identified and understood by operators of both the injection molding and ejection process. Again, the thickness of the material is also essential because thicker parts demand stronger pins to apply sufficient force to the molded part ready for ejection. 

Too few thicker parts may become deformed while too much force will lead to distortions. Hence, the dimension of the ejector pin requires a sufficient length that can achieve the complete removal of the molded part from the mold cavity. 

Furthermore, an excess length can result in buckling which hurts the ejection process. The pressure to be exerted to eject the molded part also directly affects the ejector pins and it is for this reason designers should reach a balance between all these conditions. This effort on their part will help to attain proper ejection of injection molded parts. 

2.3 Surface Finishes and Coatings

Mold surfaces and ejection pins are primary contributors to faster wear and tear between both tools. 

With efficient surface finishes of ejection pins, there is often a significant reduction in the wear and tear leading to depreciation and damage to both tools. For this reason, specialized coating such as Diamond-Like Carbon (DLC) is used to create a frictionless surface for the ejector pins. 

Also, the application of nitride treatments makes for hardened surfaces that further protect the ejector pins. What this coating offers is enhanced surface finish, longevity, and durability. 

More importantly, applying these coatings will eliminate a special type of wear that results from adhesive elements sliding and colliding with each other. This abrasion is typically known as galling. 

Apart from protection against friction causing wear, coatings on ejector pins are necessary to protect the molded parts too. An adequately coated ejector pin ensures the compactness of the molded part shielding it from cosmetic defects. 

A perfect injection molding process is often a delight for manufacturers, especially one that features an evenly gliding ejector pin with no wear or friction, and a blemish-free molded part. Carefully considering these factors guarantees excellent injection molding with terrific precision and aesthetics previously only attributed to methods like high-quality CNC Machining

Cutting injection mold ejector Pins
Designing injection mold ejector Pins
Source: https://www.youtube.com/watch?v=IhyoGptt8gA

3.1 Sticking or Binding of Ejector Pins

As with any given manufacturing tool, ejector pins are likewise vulnerable to faults and damages that require repair. Although various reasons can lead to such occurrences. 

A typical example is the improper lubrication of the ejector pin. When this happens, friction and resistance is sure to occur when ejecting the molded component, further damaging the ejector pin. 

On top of that, a misalignment resulting from damage to the ejector pins or guiding systems will halt the movement of the ejector part. 

To further worsen the already damaged pins, ejection force is reduced due to worn-out or shortened ejector pins. All mentioned defects are major drawbacks that are likely to make production fall short of the expected turnaround times. 

Fortunately, there is a way out. 

The best way to troubleshoot these challenges and make necessary adjustments is to begin with proper lubrication of these ejector pins. This oiling process should be followed by a constant maintenance system set up to check lapses and faults in the ejector pins. 

Early detection permits quick troubleshooting measures in correcting defaults. The ejector pin aims to perform its duties efficiently and to attain that feat it must run like a well-oiled tool. Should binding and sticking continue, it may just be time to upgrade to a better-suited material for the ejector pins. 

3.2 Ejector Pin Marks or Blemishes on the Part

Often during injection molding, after cooling and solidification are completed, ejecting and checking the part for blemishes and ejector pin marks is the next process. However, there are cases where hideous marks are not easily sighted initially but they are usually noticed eventually. 

These marks can only be an effect of excessive force on the molded part or the wrong placement of the ejector pins. You do not want ejector pin marks and blemishes as it diminishes the part’s aesthetic appeal hence the removal of such flaws through post-production cleaning. 

Lessening blemishes and pin marks on the molded parts and avoiding repeated occurrences can be done by ensuring an even distribution of ejection force and pressure. Another way of achieving this is to ensure appropriate pin sizing. 

What’s more, incorporating draft angles within the mold cavity can assist in ejecting molded parts effectively without blemish. Another noteworthy method to eliminate these ejector pin marks and blemishes is also by applying sufficient coatings on the pin’s surface as it will assist the ejector pins to function within their capacity.

Don’t forget that reaching a balance where the distribution of ejector force throughout the part’s surface and keeping the molded part’s aesthetics intact is crucial when dealing with ejector pin marks and blemishes.

3.3 Ejector Pin Breakage or Wear

Ejector pin breakage and wear are inevitable considering the conditions of its input. Time and continuous usage are often responsible for speeding up these wear or breakage situations and there must be provisions made for replacement. 

Although if the wear and tear occur too frequently, then eyebrows will be raised as there may be underlying concerns and causes of such constant recurrence. One major cause of such is the use of the wrong pin material. 

Sourcing for a higher-grade material is usually sufficient to solve this dilemma. A stronger material is more durable, will last longer, and stand the test of time.  Materials such as heat-treated steel with durability and extra hardness might just do the trick. To further boost the lifespan of your ejector pin, understanding ejection force requirements is critical. You do not want an overloaded or undersized pin, the risk of it failing is almost always guaranteed. 

Furthermore, continuous lubrication as a good maintenance practice can avert ejector pin breakage and wear, thereby elongating its lifespan. But also know that it is essential to look out for completely damaged ejector pins to promptly replace them. 

In any case, if there is a continuous breakage after complying with all these preventive and corrective measures, then a redesign of the mold and ejection will be the next point of call.  Observing the process for necessary up-scaling of both design and high-quality mold manufacturing  for a sufficient ejection process should solve this challenge.

Cutting injection mold ejector Pins 5
Ejector Pins cutting tools
Source: https://www.youtube.com/watch?v=IhyoGptt8gA

4. Best Practices and Considerations

4.1 Material Selection for Ejector Pins in injector molding

With all that has been highlighted so far about sourcing the right materials to ensure durability and longevity of ejector pins, we still understand that this might sometimes be challenging. However, here are some pointers to make the material selection process easier for you. 

Notably most molding applications have material requirements and standards, and this will be a good place to begin the selection of the best material for the job. 

But regardless of the standards and specifications, ejector pins are most efficient when you consider materials with heat and corrosion-resistant qualities. In addition, ensure that the material possesses high hardness and likewise high wear resistance. 

4.2 Regular Maintenance and Lubrication

As earlier mentioned, a maintenance system must be in place to inspect, clean, and lubricate ejector pins. You will quickly notice signs of wear, damage, or misalignment by doing this and corrective measures executed promptly. 

Also, a major reason for maintenance is to examine ejector pins for residues or debris that should be cleaned out to eliminate any chance of sticking and binding occurring, and to minimize friction that leads to the depreciation of the ejector pins. 

A well-oiled ejector pin ascertains excellent performance while optimally utilizing the ejector pins in the injection molding process. 

4.3 Collaboration with Mold Designers and Toolmakers

In the high-quality mold manufacturing industry, seeking professional input and liaising with mold designers and toolmakers makes all the work easier. These liaisons often provide insights to aid the maximum efficiency of the ejector pin. 

They can instantly understand the part’s design and necessary ejection requirements. Additionally, swift instructions on ejector pin placement, sizing, and its alignment with the mold’s complexity and part complexities will be communicated. 

The combined effort of all stakeholders assists in optimizing ejector pin setup and ultimately the quality in part produced as the injection molding process is simplified, likely challenges are eliminated or reduced, and a cost-effective production is achieved. 


In a nutshell, ejector pins are crucial to injection molding processes. It is for that reason adequate consideration is given to the design and maintenance of the tools. However, a proper understanding of its types and functions enables the right selection of tools required. 

Nevertheless, strict compliance with guidelines such as pin placement, size, and surface finishes allows manufacturers to improve the ejection process and overall mold performance. 

Furthermore, injection mold professionals may encounter challenges, but the best way to deal with it would be by troubleshooting to identify common issues. These issues can include sticking, binding, and blemishes. 

Periodical lubrication and maintenance systems account for the smooth operation of the ejector pin as longevity and durability are improved. 

Ultimately, cooperative efforts from designers and toolmakers ensure the seamless integration of ejector pins to optimize injection molding for outstanding part production. 


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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