The inclined ejector mechanism of an injection mold is a crucial device for removing molded parts from undercuts or recesses. It is widely used in the molding of parts with complex structures such as internal bosses and grooves. When undercuts are present, traditional straight ejector mechanisms are unable to eject the part vertically, and forced ejection can cause deformation or damage. However, the inclined ejector mechanism uses diagonal motion to simultaneously eject the part and pull the core from the side during the demolding process, allowing the part to be smoothly removed from the mold. The design accuracy of the inclined ejector mechanism directly affects the dimensional accuracy and surface quality of the part, making it a critical component in complex mold design.
The basic components of the inclined ejector mechanism include the inclined ejector, the guide slider, the ejector plate, the inclined ejector seat and the reset device. The inclined ejector is the core component, one end of which is in contact with the inner side of the plastic part, and the other end is connected to the ejector plate through the guide slider. The rod body is usually designed to be rectangular or circular, and the surface needs to be precisely processed to reduce movement friction. The guide slider is installed on the ejector plate to provide guidance for the oblique movement of the inclined ejector, ensure the accuracy of the movement trajectory, and avoid the inclined ejector from offsetting or getting stuck during the movement. The up and down movement of the ejector plate is driven by the ejection mechanism of the injection molding machine, which drives the inclined ejector to realize the oblique ejection action. The inclined ejector seat is fixed to the movable mold base plate to limit the range of movement of the inclined ejector and prevent it from being damaged due to excessive movement. The reset device usually adopts a spring or a reset rod to push the inclined ejector back to the initial position during the mold closing process to ensure the accuracy of the next molding.
The operating principle of the inclined ejector mechanism is to achieve a combined lateral core pulling and ejection motion by converting the vertical motion of the ejector plate into the diagonal motion of the ejector rod. During the mold opening process, the ejector plate is pushed upward by the ejector mechanism. Because the ejector rod and the guide slide are aligned at a certain angle (typically 5°-15°), the vertical motion of the ejector plate is decomposed into the inclined motion of the ejector rod. As the ejector rod moves upward, it simultaneously moves outward, gradually disengaging the undercut on the inside of the plastic part. When the ejector plate reaches its maximum travel, the ejector rod completely disengages the undercut, and the part is ejected from the mold. During mold closing, the reset mechanism causes the ejector plate to move downward, while the ejector rod moves inward along the inclined direction and returns to its initial position, preparing for the next injection. This motion conversion mechanism cleverly solves the demolding challenge of internal undercuts, ensuring that the plastic part is not damaged during the demolding process.
The design of the lifter mechanism requires consideration of several key parameters to ensure reliable and stable operation. The tilt angle is one of the most important parameters. A too small angle will result in excessive lifter travel, increasing the overall mold height. A too large angle will increase the lateral force on the lifter, making it prone to bending, deformation, or binding. Generally, the tilt angle should be controlled between 5° and 12°. For lifters with higher strength requirements, the angle can be reduced appropriately. The lifter length should be calculated based on the height of the plastic part and the tilt angle. An excessively long lifter will lack rigidity and may cause vibration or deformation during movement, affecting demolding accuracy. A too short lifter will not meet the required demolding stroke. Furthermore, the contact area between the lifter and the plastic part should be moderate. A too small contact area will result in excessive localized force on the part, resulting in marks, while a too large contact area will increase demolding resistance. The clearance between the guide slider and the lifter must also be strictly controlled. A too small clearance will increase friction, while a too large clearance will affect guiding accuracy. The typical clearance is set between 0.01 and 0.03 mm.
The lifter mechanism requires careful commissioning and maintenance in practical applications to extend its service life and ensure part quality. During the mold tryout phase, the ejector plate’s ejection speed and stroke should be adjusted to ensure smooth lifter movement and any interference with the part or other mold components. If the lifter is experiencing any stalling, check the lubrication and clearance of the guide slider and make adjustments promptly. For slender lifters, internal reinforcement ribs or the use of high-strength alloys (such as SKD61) can be added to improve rigidity and wear resistance. During daily production, plastic debris and oil stains on the lifter and guide slider should be regularly cleaned to keep moving parts clean and lubricated to prevent impurity accumulation and resulting in motion problems. The reset mechanism should also be regularly inspected to ensure that the lifter accurately returns to its initial position after mold closing to prevent mold damage or part dimensional deviation due to inadequate reset. With the advancement of mold technology, lifter mechanisms are moving towards modularization and standardization. The use of standard components and modular structures reduces design complexity and improves mold versatility and interchangeability.
