Injection molding eight-shaped rocker secondary demoulding mechanism
During the injection molding process, complex products with deep cavities, undercuts, or thin walls often face difficulty removing them from the mold in a single demolding operation, potentially leading to deformation and damage. The figure-eight swing lever secondary demolding mechanism is a highly effective demolding solution. By utilizing the swing lever’s unique motion trajectory, it achieves two distinct stages of demolding, effectively resolving the demolding challenge for complex products and finding widespread application in precision injection molds.
The structure of the secondary demoulding mechanism of the figure eight rocker arm is relatively precise, and mainly includes the rocker arm, the push rod fixing plate, the push plate, the guide column, the limit block and other components. The rocker arm has an eight-shaped structure, and its two ends are respectively connected to the push rod fixing plate and the push plate by pins. Its movement trajectory is determined by the connection points at both ends and its own shape. A push rod that contacts the product is installed on the push rod fixing plate, and the push plate is connected to the mold cavity plate or core plate through the guide column to ensure the movement accuracy during the demoulding process. The limit block is used to limit the relative movement distance between the push plate and the push rod fixing plate to ensure the accuracy of the secondary demoulding stroke. The entire mechanism is driven by the ejection power of the injection molding machine. During the demoulding process, the rocker arm drives the push rod fixing plate and the push plate to produce two different ejection actions in succession through its own swing, thereby realizing the step-by-step demoulding of the product.
The mechanism’s operating principle is based on the unique motion characteristics of a figure-eight rocker. During the primary demolding phase, the injection molding machine’s ejector rod pushes the push plate forward. Driven by the push plate, the rocker begins to swing. Due to the design of the connection point between the rocker rod and the push rod retaining plate, the push rod retaining plate moves with the push plate, but at a relatively slow speed. The pusher initially lifts the product from the core, creating a gap between the product and the core, completing the first demolding. After the push plate has moved a certain distance, the rocker swings to a specific angle, entering the secondary demolding phase. At this point, the rocker’s force on the push rod retaining plate increases, accelerating the plate’s movement. The pusher further pushes the product out of the mold cavity, completely freeing it from the mold and completing the second demolding. The two demolding actions are connected by changing the angle of the rocker rod, ensuring a smooth and orderly process and avoiding damage to the product caused by a single, forceful demolding operation.
The key points in the design of the figure-eight rocker secondary demolding mechanism lie in the determination of the rocker’s parameters and the optimization of its motion trajectory. The length of the rocker and the angle of the figure-eight directly affect the stroke and speed of the two demolding operations. Generally speaking, the length of the rocker needs to be determined based on the mold’s installation space and the demolding stroke, while the angle needs to be calculated through motion simulation to ensure the coordination of the two demolding actions and avoid motion interference. At the same time, the connecting pins between the rocker and the push rod fixing plate and the push plate need to be made of high-strength materials and undergo wear-resistant treatment to withstand the friction and impact forces generated by repeated movement. The guide column and guide sleeve must have high matching accuracy to ensure that the push plate and the push rod fixing plate do not shift during movement, ensuring the stability of demolding. In addition, the position of the limit block must be set accurately to strictly control the stroke of the two demolding operations to prevent incomplete demolding or damage to the product due to excessive or insufficient stroke.
In practical applications, the figure-eight rocker secondary demolding mechanism offers significant advantages. For products with deep cavities, the contact area between the product and the core is large during the first demolding, resulting in strong friction and making it difficult to demold in one go. However, the secondary demolding mechanism reduces the contact area and friction during the first demolding, making the second demolding smoother. For products with undercuts, the secondary demolding mechanism can work in conjunction with the core-pulling mechanism to release the undercut constraint during the first demolding before performing the second demolding, thus preventing the product from being damaged by the undercut. Furthermore, the mechanism operates smoothly with minimal impact, effectively protecting thin-walled products from deformation during the demolding process and improving the product’s pass rate. Compared to other secondary demolding mechanisms, the figure-eight rocker has a simple and compact structure, occupies little mold space, and is easy to install and use in small precision molds. It also offers ease of maintenance and a long service life.
However, when using the figure-eight rocker secondary demolding mechanism, some issues must be noted. The mechanism requires high machining precision. The dimensional error of the rocker and the clearance of the pin will affect the coordination of the movement. Therefore, the tolerances must be strictly controlled during the machining process to ensure the precision of the fitting of each component. At the same time, the demolding stroke and speed should be reasonably designed according to the material properties and structural characteristics of the product. For materials with good toughness, the speed of the secondary demolding can be appropriately increased; for brittle materials, the demolding speed should be reduced to avoid product breakage. During the mold assembly process, it is necessary to ensure that the rocker swings flexibly and without sticking. Mold trial debugging should be carried out, and the position of the limit block and the ejection parameters of the injection molding machine should be adjusted to achieve the best secondary demolding effect. As the injection molding industry continues to increase its requirements for product quality and production efficiency, the figure-eight rocker secondary demolding mechanism will play an important role in the molding of more complex products, providing a more efficient solution for mold design.
