Design of Injection Molded Inclined Guide Pillar and Inclined Guide Pillar Press Block
The injection molding inclined guide pin and inclined guide pin clamp are the core mechanisms that enable the slider to pull cores in the mold. They are widely used in the molding of plastic parts with side holes, undercuts, or complex curved surfaces. The inclined guide pin is usually fixed to the fixed mold, with its axis forming a certain angle with the mold opening and closing direction. When the mold is opened, the inclined guide pin cooperates with the guide hole on the slider to drive the slider to move perpendicular to the opening and closing direction, completing the core pulling action. The inclined guide pin clamp is used to press the slider during mold closing to prevent the injection pressure from pushing the slider open, ensuring the stability of the molding process. The rationality of the design of both is directly related to the smoothness of the core pulling action, the dimensional accuracy of the plastic part, and the service life of the mold. Therefore, they must be given full attention in mold design.
The angle and dimensions of the inclined guide pin must be determined in conjunction with the part’s structure and core-pulling distance. The guide pin’s tilt angle is a key parameter affecting core-pulling force and mold size. Too small an angle results in insufficient core-pulling distance, while too large an angle increases the bending force on the guide pin, making it susceptible to deformation or breakage. Typically, the tilt angle ranges from 15° to 25°, with a maximum of 30°. For parts with longer core-pulling distances, the requirement can be met by increasing the guide pin’s length or adopting a dual-guide pin configuration. The formula for calculating the guide pin’s length is L = (H + h)/sinα + D/tanα + (5-10) mm, where H is the core-pulling distance, h is the length of the guide pin within the slider, α is the tilt angle, and D is the guide pin’s diameter. An additional 5-10 mm is provided to ensure a sufficient fit. The diameter needs to be determined based on the core pulling force, which is generally selected according to the formula d=1.13√(F/(σb)), where F is the core pulling force and σb is the tensile strength of the inclined guide column material.
The material and heat treatment process of the inclined guide pin are crucial to its performance. Because the inclined guide pin must withstand bending and friction during operation, high-strength and wear-resistant materials are required. Commonly used alloy structural steels include 40Cr and Cr12. After quenching and tempering, 40Cr can reach a hardness of HRC28-32, offering excellent toughness and strength, making it suitable for general core pulling applications. After quenching and tempering, Cr12 can reach a hardness of HRC58-62, offering excellent wear resistance and suitable for molds with high core pulling frequencies and high loads. The surface treatment of the inclined guide pin is also crucial. Nitriding is typically used to enhance surface hardness and wear resistance. The nitriding layer depth is typically 0.1-0.3mm, achieving a surface hardness of over HV800, effectively reducing frictional losses with the slider guide hole. Furthermore, the clearance between the inclined guide pin and the guide hole must be appropriately controlled, typically within 0.02-0.05mm. Excessive clearance can lead to unstable slider movement, while too small a clearance can cause sticking due to poor lubrication.
The structural design of the inclined guide pin clamp must meet the requirements for clamping strength and guiding accuracy. The clamp’s primary function is to press the slider against the fixed or movable mold during mold closing, preventing the melt pressure during injection from dislodging the slider. Therefore, its contact surface must possess sufficient strength and wear resistance. Common clamp structures include integral and split types. Integral clamps are integrally machined with the mold plate, offering superior strength but increasing manufacturing costs. Split clamps are secured to the mold plate with screws, facilitating replacement and adjustment, and are more widely used. The angle of the contact surface between the clamp and the slider should align with the angle of the inclined guide pin to ensure uniform force distribution during mold closing. The contact surface should be ground to a surface roughness Ra of no greater than 0.8μm to reduce friction during mold closing. The thickness of the clamp should be calculated based on the pressure it will withstand, generally not less than 10mm. For large molds, the thickness can be increased or reinforced with ribs to prevent deformation under stress.
The coordinated design of the inclined guide pin and the pressure block is key to ensuring the smooth operation of the core-pulling mechanism. During the mold closing process, the inclined guide pin must be smoothly inserted into the guide hole of the slider, and the pressure block must precisely fit the inclined surface of the slider. The coordinated movement of the two directly affects the life of the core-pulling mechanism. During design, it is necessary to ensure that the axis of the inclined guide pin is parallel to the inclined surface of the pressure block, and the center distance error between the two does not exceed 0.02mm to avoid uneven force on the slider due to misalignment. When opening the mold, while the inclined guide pin drives the slider to pull the core, the pressure block and the slider gradually separate. At this time, it is necessary to ensure the synchronization of the core pulling action and the mold opening action to prevent interference. In addition, it is necessary to set a guide device between the slider and the template, such as a guide groove, guide pin, etc., to ensure the straightness of the slider movement and reduce the additional torque of the inclined guide pin. For large molds or molds with large core-pulling forces, the combined drive method of inclined guide pins and hydraulic cylinders can be used to improve the reliability of the core-pulling mechanism.
