The most commonly used component in a mold ejection system is ejector pin, which includes ejector sleeves and flat ejector pins. Part size, draft angle, shape complexity, vertical wall height, and type of plastic being molded all help determine appropriate ejector pin type, location, and quantity. Due to its wide range of uses, ejector pin selection is often overlooked, however, there is no "one type of ejector pin fits all" solution, so a proper understanding of ejector pin selection strategies is important to avoid many problems in subsequent molding process, including poor ejection, bent ejector pins, broken ejector pins, product deformation, and more.

 

To help guide selection process among various available types, this article will review materials, treatment processes and coatings used to produce ejector pins, as well as best practices for using ejector pins.
Ejector Pin Basics
To achieve optimal performance, ejector pins must have certain basic characteristics, including good strength, toughness, and wear resistance. More application-specific characteristics include hot hardness (ability of a material to maintain hardness at high temperatures), as well as corrosion resistance and lubricity, which vary depending on type of molding application. Geometric accuracy is another basic requirement for ejector pin performance and life. Ejectors must be manufactured to tight tolerances and specifications. Roundness, straightness and a high-quality surface finish are all critical to their function - poor geometric accuracy can lead to premature flash or product scratching, for example. A combination of material, treatment process and coating determines whether an ejector pin is suitable for a particular application. However, enhancing one or more of these characteristics may require sacrificing other characteristics.
Material Advantages

 

Being familiar with materials used to manufacture ejector pins and their properties will help mold designers and mold manufacturers make better choices. Here are some of the most commonly used materials and their properties:
H13 Steel
H13 is a chromium-molybdenum hot work tool steel that combines excellent strength and toughness. It has the highest hot hardness and thermal shock resistance values of all commonly used materials, with a hardness value of 54 HRC (slightly lower than some other through-hardened steels). However, its lack of wear and corrosion resistance can be compensated by surface treatment. Due to its unique combination of required properties, H13 is probably one of the most widely used materials in ejector pin manufacturing worldwide.
Through-hardened cold-work tool steels
Ejectors, ejector plates and ejector tubes can also be made from O1, A2 and other high-carbon cold-work tool steels. These materials are through-hardened to around 60 HRC and have good wear resistance, making them suitable for molding general-purpose plastics and a variety of materials that do not require high mold temperatures.
Through-hardened high-temperature tool steels
M2 steel belongs to high-speed steel (HSS) category, has excellent strength and moderate toughness. Similar to H13, it has high hot hardness and thermal shock resistance. M2 steel is through-hardened to 64 HRC and has excellent wear resistance, another characteristic is ability to hold a sharp edge.
Stainless steel
When molding highly corrosive materials, stainless steel ejectors are a viable option. Depending on steel grade, through-hardening hardness values can reach 50-60 HRC. To achieve high hardness and wear resistance, martensitic stainless steels are usually used (note: their corrosion resistance is not the highest in stainless steel family). However, due to its combination of strength, toughness and hardness, it is more suitable as an ejector material.
Copper Alloys
Copper alloys are primarily used to make core pins. They can also be used to make ejector pins (including beryllium copper and beryllium-free copper alloys [medical applications]) in certain extreme conditions when rapid heat conduction is a priority. However, copper alloys have certain limitations due to their soft texture and low strength.
Ejector Pin Selection
Understanding characteristics and material types of ejector pins provides a good foundation for material selection in mold design. However, with many options available from suppliers today, there is still more to know and it can be confusing. Here is a classification of common ejector pin products, including their composition and benefits:
H13 Through-hardened Nitrided Ejector Pins
These ejector pins typically have a core hardness of 48-55 HRC and a surface hardness of 65-74 HRC. Ion nitriding is one of common surface treatment processes. This ejector pin has a wide range of applications and can be used in high and low temperature scenarios. Operating temperature approaches 1112°F (600℃), making it suitable for metal injection molding (MIM) and die casting molds. It is important to note that when machining nitrided ejector pins, micro-chipping should be avoided, grinding and electrical discharge machining (EDM) are preferred processes.
Fully hardened cold work tool steel ejector pins
These steel ejector pins have good wear resistance and are well suited for medium and low temperature mold applications. Ejectors without additional coatings or treatments are an economical choice, combining good performance and service life. It should be noted that ejectors made of this type of steel will begin to anneal or soften in high temperature environments.
High-hardness M2 steel ejector pins
These versatile ejector pins generally do not require additional coatings or treatments, but are high-performance, durable options for all types of resin molding. High hot hardness of steel allows it to be used in cold and hot molding scenarios, and its ability to maintain a sharp edge ensures that it can be formed without flash for a long time in high-precision molds (such as connector molds). Due to high strength of ejector pin, it can be made into smaller diameters or sizes, which is suitable for molding micro parts. Its hardness is consistent from core to the surface, and it can be used in conjunction with ejector tube as a core pin.
Plated (Armor or Chrome) H13 Ejector Pins
Chrome plating process increases surface hardness of H13 ejector pins to approximately 70 HRC. Extremely thin but dense coating provides excellent wear resistance, improved corrosion resistance, and a very low coefficient of friction (approximately 0.20-0.25), making pin durable. These properties make plated H13 ejector pins ideal for high-volume molds and cleanroom environments. Note that operating temperature of plated material may be lower than that of H13 core material, for example, operating temperature of some types of ejector pins is approximately 842°F (450℃), and plated material may not be suitable for PVC molding. Since plating process may vary from supplier to supplier, it is best to confirm whether these factors apply.
Black Nitrided H13 Ejector Pins
As a newer product type, black nitrided H13 ejector pins have a core hardness of 50 HRC and a surface hardness of approximately 70 HRC, in addition to improved wear and corrosion resistance. Nitriding process also improves fatigue life, allowing it to maintain high performance under harsh conditions. With an operating temperature approaching 600℃, they are suitable for die casting molds (especially where sticking is an issue) and metal injection molding (MIM). Enhanced anti-stick properties significantly extend ejector life and significantly reduce pinhole wear in mold or cavity. Finally, these ejector pins are durable and can run without lubrication, making them ideal for cleanroom environments such as molds for medical, food, and packaging products. Care should be taken during processing to avoid micro-cracking.
Diamond-Like Carbon Coated (DLC) Ejector Pins
Diamond-Like Carbon Coated (DLC) ejector pins are ideal for cleanroom and medical applications because they can run without lubrication. These ejector pins are typically made of cold-worked tool steel and are through-hardened to a hardness of approximately 60 HRC. Coating has excellent wear and anti-stick properties, a very low coefficient of friction (0.1-0.15), and can operate at temperatures as high as 350℃. In addition, surface hardness of DLC ejector pins is approximately 3000 HV, far exceeding any other ejector type discussed in this article. All of these characteristics make them a high-performance, high-durability choice.
Stainless Steel Ejector Pins
Stainless steel ejector pins are the best choice for molding highly corrosive materials such as PVC and are also well suited for medical and other cleanroom applications. Steel grade selection may vary from supplier to supplier, so other properties should be evaluated to help select right type for application at hand. If used in high temperature applications, confirm suitability with manufacturer as high temperatures may reduce corrosion resistance and hardness.
Additional Considerations for Ejector Pins
It is important to note that many common ejector pins have a deviation in diameter near head due to manufacturing process and are softer near head due to annealing. This is standard practice in industry, so these ejector pins are not suitable for use as short core pins. Standard core pins made of H13 are available in different hardness options and are sometimes used as ejector pins. They are not coated or nitrided in any way, so they can be machined, coated or nitrided later. However, tolerances of inch-sized core pins and ejector pins are different, so hole size must be adjusted to accommodate. Ejector pins with a lower hardness in the core are prone to coining, which may damage core or cavity pinhole. Through-hardened ejector pins can help alleviate this problem.
Proper design of a mold ejector system is critical to its productivity, service life, and performance, including molding speed and smooth, uninterrupted operation. Information provided in this article can serve as a reliable guide to help you make right ejector pin selection.