Secondary demoulding mechanism of injection mold
The secondary demolding mechanism of an injection mold is a key device for solving the demolding challenges of complex plastic parts. When a part’s unique shape (such as a deep cavity, undercut, or boss) prevents smooth removal during primary demolding or is prone to deformation or damage during removal, the secondary demolding mechanism applies a step-by-step demolding force to ensure smooth part release. The design of the secondary demolding mechanism requires precise control of the sequence, stroke, and force of the two demolding operations to ensure uniform force distribution during demolding and prevent defects. It is widely used in the production of complex plastic parts in the automotive, electronics, and medical device industries.
The core of the secondary demolding mechanism is to achieve two orderly demolding actions. Its working principle is to trigger two demolding actions in sequence during the mold opening process through a transmission mechanism inside the mold. The first demolding action typically loosens the plastic part from the core or cavity, weakening the adhesion between the plastic part and the mold and preparing for the second demolding action. The second demolding action completely pushes the plastic part out of the mold, completing the demolding process. For example, for a box-shaped plastic part with a deep cavity, the first demolding action uses a push plate to lift the bottom of the plastic part 1-2 mm, breaking the vacuum adhesion between the plastic part and the cavity wall. The second demolding action then uses an ejector pin to completely eject the plastic part. The connection between the two demolding actions must be precise. The stroke of the first demolding action is usually controlled by a limit device (such as a limit pin or a pull rod). When the first demolding action reaches the preset stroke, the transmission mechanism triggers the second demolding action to ensure orderly operation and avoid interference.
There are various types of secondary demolding mechanisms, including spring-type, hydraulic cylinder-driven, inclined guide post-type, and rack-and-pinion types. Each type is suitable for different mold structures and part requirements. The spring-type secondary demolding mechanism has a simple structure, utilizing spring force to achieve the first demolding action. After the mold opens to a certain distance, a limiter restricts further spring extension, and a push rod then activates the second demolding action. This mechanism is suitable for parts with low demolding force and short stroke, offering low cost and easy maintenance. The hydraulic cylinder-driven secondary demolding mechanism uses a hydraulic system to control the two demolding actions. It offers high driving force and adjustable stroke, making it suitable for large and complex parts. It provides stable demolding force and high control accuracy, but its cost is relatively high. The inclined guide post-type secondary demolding mechanism utilizes the coordination of an inclined guide post and a slide to convert the linear motion of the mold opening into lateral motion of the slide, thereby triggering the second demolding action. This mechanism is reliable and suitable for small and medium-sized molds. The rack-and-pinion secondary demolding mechanism utilizes the meshing transmission of a gear and rack to achieve precise control of the two demolding actions, making it suitable for applications with strict timing requirements for the demolding actions.
The design of a secondary demolding mechanism requires consideration of multiple factors to ensure its reliability and practicality. First, the demolding force must be calculated. The force required for both demolding operations must be determined based on parameters such as the part’s material, structural dimensions, and contact area with the mold. This ensures that the driving force is sufficient but not excessive to avoid damage to the part or mold. Second, the stroke must be set. The stroke for the first demolding operation should be sufficient to loosen the part, typically 1-5 mm. The stroke for the second demolding operation should ensure that the part is completely released from the mold, typically equal to the part’s height or depth. Furthermore, the mechanism’s guidance and lubrication are crucial. Guides (such as guide pins and guide bushings) ensure precise and accurate demolding during both demolding operations, while the lubrication system reduces wear on moving parts and extends the mechanism’s service life. Furthermore, the mechanism’s installation space must be considered to ensure it can be arranged appropriately within the limited space within the mold without compromising other mold functions.
In practical applications, the secondary demolding mechanism requires careful commissioning and maintenance to ensure long-term stable operation. During the mold trial phase, the stroke and force of the two demolding operations must be optimized by adjusting the position of the stopper, the spring force, or the pressure of the hydraulic cylinder. The molded part must be observed during demolding to ensure it is free of deformation and damage. For example, if the initial demolding stroke is too large, the part may prematurely release from the core, causing wobbling; if the stroke is too small, the part may not be effectively loosened, making the secondary demolding process more difficult. During routine maintenance, the mechanism’s moving parts must be regularly inspected for wear and seizure, and damaged parts must be promptly replaced, impurities removed, and lubrication maintained. For hydraulically driven mechanisms, the hydraulic system’s oil quality and pressure must be regularly checked to prevent leaks. With technological advancements, secondary demolding mechanisms are becoming increasingly intelligent. Incorporating sensors and control systems, these mechanisms can monitor the force and stroke during the demolding process in real time, automatically adjusting parameters to further improve demolding stability and efficiency.
