Composition of the core pulling mechanism on the bending pin side of the die casting mold
The bent-pin side core pulling mechanism for die casting molds is a mechanical core pulling device suitable for complex core pulling trajectories. It utilizes a curved or broken-line bent pin to drive a slider, enabling high core pulling force and the ability to pull at unusual angles within the confined mold space. The mechanism comprises a bent pin, slider, guide slot, positioning mechanism, wedging device, and reset mechanism, all working together to ensure a smooth and precise core pulling process. Compared to traditional inclined guide pin mechanisms, the bent-pin mechanism offers greater load capacity and more flexible core pulling trajectories, making it suitable for castings with deep cavities, intersecting side holes, or complex curved surfaces.
The bending pin is the core power transmission component of the mechanism. Its shape is typically a broken line or arc, and it consists of a fixed section, a working section, and a guide section. The fixed section is rigidly connected to the fixed mold, ensuring that the bending pin does not move during operation. The working section is the functional part of the bending pin, converting the mold opening force into a lateral core-pulling force by cooperating with the slider. The bending line angle or curvature radius must be designed according to the core-pulling trajectory. For example, if vertical core pulling is required before horizontal core pulling, the working section can be designed as a 90° broken line. The guide section, located at the head of the bending pin, is cylindrical or conical in shape and mates with the guide hole of the slider to provide guidance and positioning. The bending pin is typically made of Cr12MoV or H13 steel, with a quenching hardness of 55-60 HRC. The working section surface must be polished to Ra0.4μm to reduce friction and wear with the slider.
The slider is the component that mounts the core and performs core pulling. It consists of a slider body, a core holder, and a guide. The slider body is the main structure, with a guide hole inside that mates with the bending pin. The guide hole’s shape matches the working section of the bending pin (a broken line or arc), with a clearance of 0.02-0.05mm to ensure smooth movement of the bending pin. The core holder, used to mount the forming core, is connected to the slider body via bolts and locating pins. Positioning accuracy is controlled to 0.01-0.03mm, ensuring accurate relative positioning of the core and cavity. The guides, located on either side of the slider body, mate with the guide grooves. They are typically designed in a T- or dovetail shape, with a clearance of 0.01-0.03mm, ensuring smooth, non-binding slider movement. The slider is made of 45 steel or QT500-7, tempered to a hardness of 28-32 HRC. The guide surface can be inlaid with wear-resistant alloy plates (such as ZCuSn10Pb1) to improve wear resistance.
The guide groove is a guiding component that constrains the movement trajectory of the slider. It is fixed to the movable mold base plate or the movable mold plate, and its cross-sectional shape matches the slider guide portion (T-shaped or dovetail-shaped). The guide groove must be of sufficient length, usually 2-3 times the slider stroke, to ensure that the slider is effectively guided throughout the core pulling process. The parallelism error of the guide groove is controlled within 0.02mm/100mm, and the matching clearance with the slider must be uniform. This can be achieved by adjusting the gasket or scraping the guide groove surface. The guide groove material is HT300 or 45 steel, with a surface hardening hardness of 40-45HRC and a working surface roughness of Ra1.6μm or less. An oil groove can be opened at the bottom and grease can be added regularly to reduce friction. For large sliders, the guide groove can be equipped with cooling water channels to control the operating temperature and prevent thermal deformation from affecting the guiding accuracy.
The positioning device and wedging device are auxiliary components that ensure the reliability of the mechanism. The positioning device secures the slider after core pulling to prevent movement due to vibration or inertia. Commonly used methods include spring-ball positioning and stopper positioning. Positioning accuracy must be controlled within 0.05mm. The wedging device locks the slider during die closing to resist lateral pressure from the molten metal. It typically uses a wedge block structure with a bevel angle 2°-3° greater than the equivalent angle of the bending pin working section to ensure reliable locking. The wedge block is made of Cr12MoV with a quenching hardness of 55-60 HRC. The contact area with the slider should be no less than 60% of the slider’s pressure-bearing area.
The reset device is used to return the slider to the molding position during the mold closing process. Common ones include spring reset and bent pin forced reset. Spring reset is achieved by setting a compression spring between the slider and the guide groove. The spring pushes the slider to reset when the mold is closed. It is suitable for sliders with small strokes. The spring stiffness coefficient needs to be calculated and determined based on the slider weight and motion resistance. Bend pin forced reset uses the reverse movement of the bent pin during mold closing to drive the slider to reset. It is suitable for sliders with large strokes or heavy weights. It has high reset accuracy and does not require additional power. The reset device needs to ensure that the slider is reset into place. A limit block can be set at the reset end point of the slider . The contact gap between the limit block and the slider is no more than 0.02mm to ensure the accurate position of the core.
