Working principle of injection molding inclined ejector mechanism
The injection molding inclined ejector mechanism is a key mechanism in the mold for solving the problem of demoulding the inner undercut of the product. Its working principle is based on the synthesis and decomposition of mechanical motion. By converting the vertical motion of the ejection mechanism into the tilting motion of the inclined ejector, the core pulling of the inner undercut of the product is achieved. When the mold is closed, the top of the inclined ejector fits tightly with the inner undercut of the product and participates in the molding of the product. When the mold is opened, the ejector plate moves upward under the drive of the injection molding machine’s ejection device, driving the inclined ejector to move synchronously. Due to the inclination angle between the inclined ejector and the template, under the constraint of the guide device, the inclined ejector will shrink inward while moving upward, gradually disengaging from the undercut part of the product, completing the core pulling action. When the ejection is in place, the product is ejected from the core, and then under the action of the reset mechanism, the inclined ejector moves downward with the ejector plate, returning to the initial position, ready for the next injection molding.
The kinematic principle of the inclined ejector mechanism can be analyzed in detail through coordinate system transformation. Assuming the inclination angle of the inclined ejector is α (the angle with the vertical direction) and the vertical movement distance of the ejector plate is H, the horizontal core pulling distance S of the inclined ejector can be calculated using the formula S = H × tanα. For example, when the ejector plate rises to a height H of 50mm and the inclined ejector angle α is 15°, the horizontal core pulling distance S is approximately 13.4mm, which means that the inclined ejector mechanism can handle an inner undercut with a depth not exceeding 13.4mm. This principle determines that the core pulling capacity of the inclined ejector mechanism is closely related to the ejection height and inclination angle. During design, the inclination angle and ejection height must be reasonably selected according to the depth of the product undercut to ensure that the core pulling distance can completely break away from the undercut, while avoiding excessive force on the inclined ejector due to excessive angles.
Force analysis of the lifter mechanism is an important basis for ensuring its operational reliability. During the core pulling process, the lifter is primarily subjected to the clamping force from the product and the friction during movement. The combined force of these forces will cause the lifter to generate a bending moment. If the bending moment is too large, it will cause the lifter to deform or break. Therefore, the diameter and strength of the lifter must be calculated based on the clamping force of the product. The calculation of the clamping force is related to factors such as the product material, undercut area, and molding temperature. For example, for polyoxymethylene (POM) products, the clamping force is relatively large, and the diameter of the lifter must be appropriately increased. In addition, the friction between the lifter and the guide sleeve will affect the smoothness of the mechanism’s movement. It is necessary to reduce friction by properly selecting the fit clearance and lubrication method to ensure smooth movement of the lifter and avoid jamming or abnormal noise.
Guiding and positioning are the key guarantees for the realization of the working principle of the inclined ejector mechanism. The mechanism usually sets a guide slider at the bottom of the inclined ejector. The guide slider is embedded in the guide groove of the ejector plate and can slide in the horizontal direction. When the ejector plate moves vertically, the guide slider drives the inclined ejector to complete the horizontal contraction or expansion. At the same time, a guide hole or guide sleeve is set on the template to constrain the movement trajectory of the inclined ejector to ensure that its inclination angle remains stable. The guide sleeve and the inclined ejector are matched with a clearance fit with a clearance size of 0.01-0.03mm, which can not only ensure the free movement of the inclined ejector, but also effectively prevent it from offsetting when subjected to force. The material of the guide component is selected from bronze or alloy cast iron with good wear resistance to reduce friction and wear between the inclined ejector and the inclined ejector, thereby extending the service life of the mechanism.
The reset principle of the inclined ejector mechanism is opposite to the core pulling principle and is achieved by the action of the reset spring or the reset rod. After the product is taken out, the ejector device of the injection molding machine drives the ejector plate to move downward. Under the tension of the reset spring or the thrust of the reset rod, the inclined ejector moves in the opposite direction along the guide device and gradually returns to its initial position. During the reset process, it is necessary to ensure the fit accuracy between the inclined ejector and the mold cavity to avoid affecting the molding quality of the next product due to inadequate reset. To ensure reliable reset, a limit block can be set in the mechanism. When the inclined ejector is reset into place, the limit block contacts the template, restricting its continued movement and ensuring the consistency of the reset position each time. Through a deep understanding of the working principle of the inclined ejector mechanism, it is possible to better carry out mechanism design and parameter optimization, thereby improving the working efficiency of the mold and the quality of the product.
