Injection Mold Ejection Systems On Precision Products
Table of Contents
- Injection Mold Ejection Systems On Precision Products
- What is the ejection system of an injection mold ?
- an injection mold ejection system
- injection mold ejection system
- Key details of the ejection system
- Injection Mold Design and Ejection System
- selecting an injection mold ejection system
- Injection mold ejection system type
- The impact of injection mold ejection systems on the plastic product manufacturing process
- in conclusion
- Frequently Asked Questions
A reliable ejection system can eject finished products quickly, smoothly, and reliably. If the ejection system is poorly designed, residual parts in the mold during mass production can cause production delays and damage mold components . Furthermore, additional production costs will be incurred.
Experienced injection mold manufacturers can easily handle mold complexity and produce high-quality parts by utilizing appropriate ejection systems. These advantages can save you significant costs in the long run. When choosing the best ejection system, you need to consider factors such as the type of ejection system, its surface area, and the ejection location. This article delves into the impact of injection mold ejection systems on plastic product manufacturing by examining their working principles and design considerations.
What is the ejection system of an injection mold ?
In an injection molding system, the ejection system is the final step in the process, removing the product from the mold. High-quality steel and robust tools constitute the complete structure of the mold. Professional mold makers utilize these materials to remove solid parts from the mold. Injection molding systems are available in various shapes and sizes, depending on the product’s design, structure, and the properties of the plastic. Ejector pins, ejector blocks, stripper plates, and other components are some of the most common parts.
an injection mold ejection system
The ejection system mainly consists of the following parts:
| Ejector pin (push rod) | The component that directly contacts the plastic part and pushes it to be demolded must have its shape and layout designed reasonably according to the structure of the plastic part. |
| Top plate (push plate) | Used to push multiple ejector pins simultaneously to ensure uniform ejection. |
| Reset rod | Used to reset the ejection mechanism after ejection, so that the next injection can be performed. |
| Demolding pin | In cases of complex structures or lateral core pulling, it assists in demolding plastic parts. |
| Air-cushion device | Used for ejecting precision molds or easily deformable plastic parts, it utilizes air pressure for non-contact ejection. |
| Spring or hydraulic system | Used to control the ejection speed and reset action to ensure smooth ejection. |
injection mold ejection system
The working principle of the ejection system mainly relies on the ejection mechanism of the injection molding machine to provide power, push the ejection components in the mold, and make the plastic part detach from the mold cavity.
| Mold opening | After injection molding, the mold is separated, and the core and cavity are separated. |
| Ejection mechanism start | The ejector rod of the injection molding machine pushes the top plate or ejector pin forward. |
| Plastic part ejection | Ejector pins or push plates act on the plastic part to detach it from the cavity. |
| Ejection Reset | After the plastic part is removed, the reset device (spring or hydraulic system) resets the ejector pins, etc., in preparation for the next molding. |
Key details of the ejection system
Simply put, an ejection system is the machine “hand” that helps you safely remove the product after the plastic is finished.
| Components | It includes ejector pins (push rods), flat ejector pins, ejector sleeves (push tubes), ejector blocks, push plates, and reset rods, etc. |
| Workflow | Mold opens -> Ejection system activates (ejector pins move forward) -> Part falls off -> System resets -> Mold closes. |
| Design Principles | The ejection force should be uniform to avoid deformation or damage to the parts; the ejection point is usually set in a rigid place such as a rib or boss; try to avoid leaving ejection marks on the appearance and decorative surface. |
| Main purpose | To prevent product deformation, cracking, and breakage, and to ensure that the produced plastic products have a complete appearance and structure. |
Injection Mold Design and Ejection System
| Identify the top point | Choose a rigid, non-decorative surface as the point of force application. |
| Consider the inverted design | Use a support or angle pin if necessary. |
| Design draft angle | Generally, 1–2° is used to facilitate smooth demolding. |
| Calculate the top output force and stroke | Ensure sufficient but not excessive amounts to avoid damage to molds or parts. |
| Material matching | Adjust the ejection method according to the material’s hardness, viscosity, and shrinkage characteristics. |
| Combined with automation | Large-scale production can be combined with robotic arms or pneumatic assistance to improve efficiency and stability. |
| Reasonable calculation of jacking force | Appropriate ejection force needs to be calculated based on factors such as the material, shape, and wall thickness of the plastic part to prevent deformation or damage. |
| Reasonable distribution of ejection positions | Ejector pins should be evenly distributed to avoid stress concentration that could damage the plastic part, especially in areas with thin walls or complex structures. |
| Avoid leaving marks | For plastic parts with high surface finish requirements, large-area push plates, air ejectors, or multi-point ejection should be used to reduce ejector pin marks. |
| Prevent plastic parts from jamming | Auxiliary devices such as ejector pins and ejector pins are used to avoid jamming caused by shrinkage of plastic parts. |
| Control of ejection speed | Use springs or hydraulic buffer devices to prevent damage to the plastic parts caused by excessively rapid ejection. |
selecting an injection mold ejection system
selecting the optimal ejection system for an injection mold , size, location, and surface type should be considered. To gain a deeper understanding of this system, let’s examine each aspect closely.
Extruded area
Smaller features, bigger problems . Proper ejection depends on the size and geometry of the part. Unreliable ejection surfaces can lead to breakage, deformation, and longer molding cycles. It’s best to choose a larger ejection surface area. For plastic parts with smaller ejection features, smaller ejection sleeves are required. Due to their smaller size, these sleeves are more prone to wear and breakage. Thin-walled plastic parts require specialized thin-walled ejection sleeves. Injection molders should be aware of this. The shorter lifespan of such sleeves can increase production costs.
Top position
The smoother the better . The optimal ejector surface should be flat to facilitate the use of ejector pins and should be ground to the appropriate height. If the ejector surface is uneven, the ejector components may affect the geometry of the part. In some cases, curved parts may require redesign. Remember that plastic parts are easier to eject when the surface is parallel to the parting line. Injection mold manufacturers should avoid plastic part defects and ejector breakage due to over-ejection. However, excessive ejectors must be considered in relation to increased mold wear and costs. Furthermore, if ejectors are too densely packed, the mold walls will become thinner. Experienced mold manufacturers can optimize ejectors while maintaining mold performance. Adjusting the configuration of the ejection points can allow parts to eject quickly and smoothly. Mold manufacturers should take this into account.
Injection mold ejection system type
In injection molding, mold makers typically only use ejector pins (KO ejector pins). However, this is not the case for most injection-molded parts. Ejector pins, blades, sleeves, rods, stripper plates, and ejector pins are all common ejection methods. Each ejection method has its own advantages and disadvantages. You can choose from several methods to eject parts, and each method requires proper maintenance.
thimble
Ejector pins are the most commonly used ejection system in many mold-making companies. This system is one of the simplest and most cost-effective ejection methods. By default, ejector pins leave a circular ejection mark on the part. Larger ejector pin sizes are preferable because they experience higher pressure during molding. If ejector pins cannot be used due to space constraints, blade ejectors are a good alternative. Blade ejectors can eject thinner parts. Blade ejector pins have a larger surface area than traditional ejector pins and wear out faster. You can replace a blade ejector pin by inserting it into the mold.
How to design the appropriate ejector pin type for injection molds ?
Today, the market offers a wide variety of ejector pins, making it difficult for users to choose the right one. In most cases, selecting the wrong ejector pin will waste resources and reduce production output. The material and toughness of the ejector pin are important factors to consider. However, operating temperature is the focus of this section.
Operating temperature
Operating temperature affects the lifespan of ejector pins. If the operating temperature is too high, the lifespan of the ejector pin will be very short. Furthermore, ejector pins are designed to reduce operating temperature. Some ejector pins include hard ejector pins, H13 nitride ejector pins, and newer black ejector pins. These ejector pins are all useful, but each has its unique characteristics and applicable scenarios.
H13 Nitride Ejector Pin
Excessive temperature will shorten the lifespan of ejector pins. If the operating temperature exceeds 2000°C, H13 nitrided ejector pins are required. This is because these ejector pins have a surface hardness of HRC 65 to 70, resulting in a longer lifespan at high temperatures. These ejector pins are ideal for die casting.
Through-type hard pin
This ejector pin design provides the same rigidity as ejector pins with through-hole hard ejector pins. Due to this characteristic, the ejector pin has a longer service life at temperatures below 2000°C. It is only suitable for plastic injection molds.
Black thimble
If the operating temperature exceeds 6000°C, black ejector pins are required. These ejector pins have a black coating that allows them to withstand temperatures up to 10000°C. The black coating provides the ejector pins with additional self-lubricating properties, making them ideal for automotive injection molding. For extremely high temperatures, these ejector pins are perfect.
Advantages and disadvantages of thimbles
| advantage | shortcoming |
| Suitable for high temperature environments | It will leave a circular top mark on the surface. |
| Simple and easy to use | Not suitable for small surface areas. |
| Economical and efficient | |
| Suitable for automotive injection molding |
push rod sleeve
Evenly distributing material around the small circle is crucial. This will help you produce well-designed products. Since you need to eject small parts, an ejector sleeve should be used as the ejection system. An ejector sleeve consists of a hollow sleeve and a smaller, solid ejector pin inside. When the mold is not activated, the ejector pin typically extends beyond the sleeve. Once the ejection system is activated, the sleeve moves, pushing the part out of the mold. Ejection marks on the product reflect the shape of the sleeve. Check the fit between the outer side of the ejector pin and the inner side of the sleeve. This helps prevent plastic flash from entering the ejection system. Ejector sleeves can be used to eject bosses, recesses, and other parts. Ejector sleeves typically wear out faster than ejector pins, partly because they have two working surfaces, inner and outer. The wider protruding area of the sleeve allows for a more even distribution of ejection force, which is not possible with traditional ejector pins. This doubles the mold’s venting efficiency. Ejector sleeves in the mold aid in ejecting parts. The principle is to apply ejection force to a localized area of the part and work in conjunction with other ejection structures integrated into the mold. Ejector sleeves can also assist in partial ejection and even be used for repositioning or “closing” parts in multi-color injection molding. Later applications of ejector sleeves meet the requirements of multi-color injection molding, presenting significant challenges and unique characteristics.
Advantages and disadvantages of push rod sleeve
| advantage | shortcoming |
| The top force is evenly distributed. | The wear rate is faster than that of the ejector pin. |
| It will not leave any marks on the surface. | High difficulty in manufacturing and assembly |
| Best suited for multi-color injection molding | High cost |
| Prevent plastic flash |
Top rod stripper plate
Stripper plate ejection is best suited for large parts. This technology adds a stripper plate between the core plate and the cavity plate. The stripper plate contacts the cavity plate. The cavity plate and core plate remain separate to remove flash. Visible ejection marks are rarely seen on the part. The ejector plate and ejector pins work together in the mold ejection mechanism. The ejector pin injection molding process holds the ejector pin head in place. This prevents the product from falling out. The edge of the part is ejected from the stripper system. During maintenance, the stripper plate or stripper block must be kept level with the rest of the mold. Inspecting the part at the parting line can determine if maintenance is needed. A stripper plate is a plate used to remove the part from the core of an injection mold. This process occurs during manufacturing. By removing the core, space is made for the next injection in the mold. Ejection methods in injection molding require complete contact with the outer edge of the part. A stripper plate can be used if ejector pins or compressed air are insufficient to complete the ejection. Parts such as bottle caps, lids, and containers often require stripper plate ejection. For thin-walled parts, the ejection method requires complete contact with the outer edge to remove the part from the core. For parts with a wall thickness exceeding one millimeter, ejector pins and compressed air are often the only options. Even then, the part may not always eject as expected, and in some cases, it may even get stuck on the core. Regardless of how smoothly the ejection process goes, taller parts often require longer molding cycles. Using a stripper plate is a reliable way to ensure fast ejection of parts every time. Stripper plates can be used in both single-cavity and multi-cavity injection molds.
Advantages and disadvantages of stripper plate
| advantage | shortcoming |
| It is best suited for unloading cylindrical plastic parts, various shell-shaped plastic products, and thin-walled containers. | High manufacturing costs. |
| It has high, stable and uniform material discharge capacity. | The mold has a complex structure. |
| Plastic parts are not easily deformed. | |
| No traces of material stripping are left on the surface. | |
| The structure is simpler than that of a traditional stripper plate. Ejector sleeve. |
Eject block
Ejector blocks are suitable for plastic products where ejection marks are not permitted. Transparent plastic products are one example. These products require a high degree of surface smoothness. Ejector blocks can fully utilize the entire surface of the plastic product.
Key points of popping out blocks
Ejector blocks have higher hardness and lower surface roughness. The hardness difference between their material and the insert should be greater than HRC 5. Mold manufacturers recommend nitriding of ejector blocks, except for stainless steel. To ensure smooth sliding, there should be no flash in the ejector block’s clearance. Furthermore, its sliding surface should include a groove. This aids in lubrication of the sliding surface. The mating surface between the ejector block and the insert must be tapered, not straight. If the ejector block has a tapered structure, the ejection stroke is greater. The ejection height of plastic products is relatively low, but less than half the height of the ejector block. For large ejector blocks, more than two ejector pins must be used to achieve stable demolding. Some products are too thin to use ejector pins; some products are too heavy to use ejector blocks.
The impact of injection mold ejection systems on the plastic product manufacturing process
Incorrect ejection methods reduce mold uptime and shorten mold lifespan. Effective ejection strategies improve part quality and optimize both short-term and long-term mold costs. Ejection systems can also extend part production time. A well-designed mold ejection system is essentially balanced, stable, safe, and simple. Its layout balances force distribution, the ejection method matches the product structure, ejector pin specifications ensure strength, and stroke reset is safe and reliable, while also considering processing, maintenance, and production efficiency. By comprehensively considering product structure, material, appearance, and mass production feasibility during the design phase, smooth ejection, intact products, stable molds, and long-term efficient production can be achieved.
in conclusion
Ejection systems are a critical component of injection molding and plastic product manufacturing , and design professionals should not overlook them. In molded products, they help prevent ejector pin marks and other ejection defects. The key is having a high-performance, reliable ejection system. For any company, manufacturing-oriented design expertise is essential. They need knowledge of injection molding and a proven track record of excellence in ejection systems.
Elimold’s professional and experienced team of injection mold engineers can help you optimize your designs. You can visit their website and consult their expert team for manufacturing advice. The company also offers in-house production molds, injection molding, and precision CNC machining services. If you are looking for a company with extensive experience in ejection systems, Elimold is a trustworthy choice. Please contact our team if you have any questions or ideas .
Frequently Asked Questions
If the surface area is limited, what injection molding designs can be used?
In design cases with limited surface area, where there are no points on the part that allow for demolding from the mold, you can optimize the design by adding a boss as an ejector pad and replacing ejector pins with liquid silicone rubber parts. After cooling, the part can be manually ejected from the mold by the liquid silicone rubber.
What is the best material for the parts?
When selecting materials, it’s best to consider the function and performance your product should possess. In the long run, cheaper alternatives will fail. Therefore, it’s preferable to use high-performance materials that meet the needs of your product.