Key Points in Injection Molding Ejection System Design

Injection Molding Ejection System Design and Layout not do a good job, which also a nightmare in the later production.

Injection Molding Ejection System Design

In the realm of plastic injection mold design, the ejection system plays a pivotal role in ensuring the seamless removal of molded products from the core. As seasoned mold designers with over 15 years of expertise at JST Mould Limited—a premier provider of high-quality molds—we leverage a variety of ejection mechanisms, including round ejector pins, flat ejectors, ejector sleeves, straight ejectors, angled lifters, push plates, push blocks, and secondary ejection systems. In this comprehensive guide, we'll delve into the essential design principles of ejection systems, optimized for precision, efficiency, and reliability. Whether you're an engineer seeking best practices or a manufacturer aiming to enhance production quality, these insights will help you achieve superior mold performance and reduce downtime.

01 Essential Design Principles for Ejection Systems Matching the Core sub-insert with Ejector Pins

For ejector pins with diameters under 2.5 mm, the effective engagement length should be limited to 10-15 mm, with the remaining portion designed as a clearance to prevent overheating or seizing due to excessive contact. For pins 2.5 mm and larger, extend the effective length to 15-30 mm, scaling appropriately with the pin size. This approach ensures optimal heat dissipation and longevity, critical for high-volume injection molding operations.

Selection Guidelines for Round Ejector Pins

Round ejector pins smaller than 2.5 mm in diameter typically incorporate a shoulder design and are crafted from SKH51 material, hardened to approximately HRC58 for enhanced durability. Larger pins (2.5 mm and above) often use a shoulderless configuration, made from SKD61 at HRC52 hardness. During design and operation, prioritize sufficient stroke allowance and clearance to facilitate smooth ejection, minimizing defects like flash or part distortion—key factors in maintaining product quality in competitive markets.

Positioning Methods for Ejector Pins

Accurate positioning of ejector pins is crucial, especially for those shaping directional features in the plastic part. Three common methods exist, selected based on your facility's standard practices. For the third method, if the shoulder height is 4 mm, use a 1.5 mm diameter locating pin; for heights exceeding 4 mm, increase to 2.5 mm. Refer to the accompanying diagram for visual clarification, which illustrates these principles to aid in precise implementation.

Layout Principles for Ejector Pins

Adhere to these proven layout strategies to optimize ejection efficiency:

(1) Opt for larger pin sizes whenever feasible, maintaining uniformity in specifications. Ensure a minimum distance of 0.5 mm from the pin to the rear mold edge, not exceeding 3.0 mm, to balance structural integrity and accessibility. Consult reference diagrams for tailored layouts that align with your specific mold requirements.

(2) Position ejector pins preferentially at the base of the product (e.g., Pin A), ideally 0.3 mm from the core edge, rather than at the top (e.g., Pin B). This configuration promotes even force distribution and reduces the risk of part deformation.

(3) Avoid placing ejector pins on sloped surfaces if possible; if unavoidable, incorporate anti-slip features to prevent misalignment during ejection.

(4) For rib ejection, two primary methods apply: Direct pin placement beneath the rib for dual ejection and venting functions, or adjacent pin placement with an optional venting insert at the rib base. These techniques enhance mold venting, crucial for defect-free parts in high-precision applications.

(5) Ejector sleeve designs for pillars vary by height. For pillars under 6 mm, combine a central insert with flanking pins. Taller pillars (over 6 mm) can use direct sleeve ejection. For deep ribs, prioritize flat ejectors, resorting to bottom-mounted round pins only as a last option.

Ejector Sleeve Design Considerations

When employing ejector sleeves, focus on these details for flawless performance: Verify the presence of a guiding chamfer (C-angle) in the central hole, which can be formed on either the ejector pin (via milling) or the sleeve (via EDM). Maintain a minimum sleeve wall thickness of 0.8 mm to ease machining. Secure the ejector pin to the base plate using either headless screws (for fewer pins) or an 8-12 mm thick pressure plate with M5/M6 screws. At JST Mould Limited, these standards ensure robust, low-maintenance molds that deliver consistent results for our global clients.

Push Plate and Push Block Designs

For internal part features unsuitable for standard ejector pins—particularly in deeper geometries—push plates offer an effective solution for full-perimeter ejection. If complete encirclement isn't feasible, push blocks serve as a versatile alternative. While similar in function, both require attention to:

(1) A 3-5 degree taper on the contact surface between the push plate and internal insert to minimize wear and extend mold life.

(2) A 0.3 mm gap between the push plate and the part's internal core to prevent core damage, safeguarding your investment in precision tooling.

Angled Lifter Mechanism Design

Angled lifters not only facilitate undercut release but also assist in product ejection, eliminating the need for additional pins in their operational zone. Select angles between 3° and 12° based on undercut geometry—consult the provided schematic for optimal choices. This multi-functional design streamlines mold complexity, reducing costs and cycle times, which is why it's a cornerstone in advanced injection molding strategies at JST Mould Limited.

By integrating these key points into your injection mold designs, you can achieve superior ejection reliability, minimize production defects, and enhance overall efficiency. As experts in custom mold manufacturing, JST Mould Limited is committed to delivering top-tier solutions tailored to your needs. Contact us today to discuss how our 15+ years of experience can elevate your projects. For more insights on injection molding best practices, explore our resources on topics like mold cooling systems, gating designs, and material selection.