Demolding of the fixed mold driven by the movable mold
In traditional injection mold structures, an ejector mechanism is typically installed on the movable mold side to release the plastic part. However, demolding from the fixed mold is relatively special. Demolding from the fixed mold driven by the movable mold is an innovative demolding method suitable for parts with specific structures. When the plastic part has a complex shape, the clamping force on the movable mold is less than the adhesion force on the fixed mold, or the plastic part needs to remain on the fixed mold side, the traditional demolding method of the movable mold is difficult to achieve smooth demolding. In such cases, demolding from the movable mold to drive the fixed mold becomes an ideal option. This demolding method utilizes a linkage mechanism between the movable and fixed molds, allowing the movable mold to drive the fixed mold to eject the plastic part during the mold opening process. This breaks the limitations of traditional demolding and broadens the design concept of injection molds.
The key to ejecting the fixed mold from the movable mold lies in the design of the linkage mechanism, which must precisely transmit the movable mold’s motion to actuate the ejection components on the fixed mold. Common linkage mechanisms include tie rods, rocker arms, and rack and pinion types. The tie rod linkage utilizes a tie rod fixed to the movable mold and a slider on the fixed mold. During mold opening, the movable mold drives the tie rod, which in turn pushes the slider to activate the ejection components of the fixed mold, releasing the part. This simple structure and reliable operation make it suitable for small and medium-sized molds. The rocker arm linkage utilizes the lever action of the rocker arm to convert the linear motion of the movable mold into ejection motion of the ejection components of the fixed mold. This provides high transmission efficiency and can achieve a high ejection force, making it suitable for ejecting large parts from the fixed mold. The rack and pinion linkage transmits the movable mold’s motion to the fixed mold through the meshing of a gear and rack. This allows for more complex ejection actions with high precision, making it suitable for applications requiring precise ejection movements.
The ejection process from the fixed mold driven by the movable mold must follow a specific sequence of actions to ensure smooth and undamaged ejection of the plastic part. Initially, the movable and fixed molds begin to separate. At this point, the linkage mechanism has not yet been triggered, and the fixed mold remains closed. When the mold is opened to a certain distance, the linkage components on the movable mold contact the ejection mechanism on the fixed mold, driving the ejection components of the fixed mold to move, ejecting or loosening the plastic part from the fixed mold cavity. As the mold opening process continues, the plastic part gradually detaches from the fixed mold, ultimately being completely ejected by the linkage mechanism, achieving separation from the fixed mold. Throughout this process, controlling the sequence of actions is crucial. Triggering the ejection action too early or too late can damage the plastic part or result in ejection failure. Therefore, precise control of the mold opening distance and the ejection action is required through limit devices.
The fixed mold demolding method, driven by the movable mold, offers significant advantages in practical applications, particularly for the production of plastic parts with specific structural characteristics. For parts with complex outer surface patterns or undercuts, and strong adhesion to the fixed mold, this demolding method can prevent deformation or surface damage during demolding, thus ensuring product quality. For example, large plastic parts like automotive dashboards require high surface quality and strong adhesion to the fixed mold. Using the movable mold to drive the fixed mold demolding effectively protects surface patterns and improves product qualification rates. Furthermore, this demolding method simplifies the movable mold structure. When the plastic part needs to remain in the fixed mold, there’s no need for a complex ejection mechanism in the movable mold, reducing the difficulty of mold design and manufacturing while facilitating mold maintenance.
The design and application of fixed mold release driven by the movable mold require careful attention to numerous details to ensure its stability and reliability. The strength and wear resistance of the linkage mechanism are crucial. Because high forces must be transmitted during the mold opening process, components must be made of high-strength alloy steel and undergo appropriate heat treatment to increase their service life. The mechanism’s guidance and positioning must also be precise to avoid jamming or offsetting during movement, which could affect the demolding effect. Furthermore, the stress conditions of the plastic part must be fully considered, and simulation analysis must be used to determine the appropriate demolding force and ejection stroke to prevent damage to the part due to excessive force. With the advancement of mold technology, the fixed mold release method driven by the movable mold has been continuously optimized. Combined with computer-aided design and simulation technology, precise linkage mechanism design can be achieved, improving mold performance and production efficiency. This plays an increasingly important role in the production of precision injection molding and complex plastic parts.
