The design of the slider and slider clamp is a key component of the mold’s lateral core pulling mechanism, directly impacting core pulling accuracy and mold life. As the moving component supporting the core or cavity, the slider must meet strength, guidance, and wear resistance requirements. It typically adopts either a monolithic or modular design. Monolithic sliders are machined from a single piece of steel, offering high strength and rigidity. They are suitable for applications with low core pulling forces (less than 50kN), such as lateral core pulling for small electrical plastic parts. The material used is Cr12MoV, which has been quenched (HRC50-55) to ensure surface hardness and wear resistance. Modular sliders, consisting of a slider body and core insert, facilitate replacement of vulnerable cores and are suitable for complex core pulling applications, such as the molding of lateral bosses in automotive bumpers. The slider body is constructed of quenched and tempered 45# steel (HB220-250), while the core insert is SKD61 (HRC48-52), ensuring overall strength while reducing the use of precious materials. The guide part of the slider needs to be precisely matched with the guide groove, and the matching clearance is controlled at 0.03-0.05mm. A T-slot or dovetail groove is set at the bottom of the slider to cooperate with the T-block or guide rail on the fixed template to ensure smooth movement without jamming.
The design of the slider clamp (also known as the wedge clamp) must fulfill two key functions: locking the slider during mold closing to prevent injection pressure from causing slider displacement; and ensuring that it does not interfere with the slider’s core pulling during mold opening. The wedge angle of the clamp is a key design consideration and is typically 2°-3° greater than the angle of the guide pin. For example, if the guide pin angle is 20°, the wedge angle of the clamp should be 22°. This ensures reliable locking while preventing rigid friction between the clamp and the slider during mold opening. The clamp’s locking surface must be ground to a surface roughness of Ra ≤ 0.8μm, with a minimum of 80% contact surface area with the slider to ensure uniform pressure transmission. The clamp is secured with bolts, with the bolt diameter determined based on the calculated locking force. For example, for a locking force of 100kN, M12 high-strength bolts (grade 8.8) are used, with bolt spacing between 1/3-1/2 the clamp length to ensure a secure hold. For large sliders, combined pressure blocks can be used, with 2-3 pressure blocks arranged along the length of the slider. Each pressure block bears part of the locking force. For example, for a slider with a length of 500mm, 3 pressure blocks are set with a spacing of 200mm to avoid deformation caused by excessive force on a single pressure block.
The matching precision design of the slider and the pressure block needs to be strictly controlled to ensure reliable locking and smooth movement. The locking surface of the slider and the wedge surface of the pressure block must be kept parallel, and the parallelism error must not exceed 0.02mm/m, otherwise it will lead to uneven distribution of locking force and excessive local stress causing deformation. When the slider is in the mold closing state, the contact depth between the pressure block and the slider must reach 1/2-2/3 of the pressure block height. For example, when the pressure block height is 30mm, the contact depth must be within the range of 15-20mm to ensure sufficient locking area. The core pulling direction of the slider must be consistent with the direction of the wedge surface of the pressure block, and the coaxiality error must not exceed 0.03mm to avoid additional torque that causes the slider to deflect. At the end of the slider’s movement stroke, a limit block must be set, and the gap between the limit block and the slider must be controlled at 0.1-0.2mm to prevent excessive movement of the slider and collision with the pressure block or other parts of the mold. For example, for a slider with a core pulling distance of 50mm, a 10mm thick limit block is set at the end of the stroke to ensure that the slider lightly contacts the limit block after it is in place, which not only ensures accurate positioning but also avoids rigid impact.
Lubrication and wear-resistant design of the slider and pressure block are crucial to extending the life of the mechanism. Effective lubrication and surface treatment measures are required for the moving contact surfaces. Lubrication grooves, 2-3mm wide and 0.5-1mm deep, arranged in a spiral or annular pattern, should be provided between the slider and the guide groove to store grease and reduce friction and wear. For example, annular grooves can be machined on either side of the T-slot at the bottom of the slider and refilled with molybdenum disulfide lithium grease every 1000 molds. The locking surface of the pressure block can be nitrided with a nitride layer thickness of 0.1-0.2mm and a hardness of HV800-1000 to improve surface wear resistance and prevent surface damage caused by long-term locking friction. The guide surface of the slider can be inlaid with bronze or graphite self-lubricating blocks. The bronze blocks should have an oil content of at least 15%, ensuring short-term operation without lubrication and suitable for applications where regular lubrication is difficult. For example, in high-temperature forming molds (such as PA66+GF30), the guide surface of the slider is inlaid with graphite bronze blocks, which can maintain good lubrication in an environment above 200°C, and the service life is extended by 2-3 times that of ordinary sliders.
The design of the slider and pressure block must consider the overall mold layout and installation space to ensure no interference with other components. The slider’s length and width should be determined based on the core size and core-pulling force. Typically, the slider’s length is 2-3 times the core-pulling dimension, and its width is 1.5-2 times the core width. For example, if the core’s pulling dimension is 100mm, the slider’s length should be 250mm to ensure sufficient support area. The pressure block should be installed away from the mold’s cooling channels, ejector pins, and other moving parts, maintaining a minimum distance of 10mm from the cooling channels to prevent cooling degradation or leakage. In a single-mold, multi-cavity mold, the sliders should be arranged symmetrically to avoid uneven loading caused by uneven forces. For example, in a four-cavity mold, the four sliders should be arranged symmetrically around the center, with the core-pulling force tolerance of each slider controlled within 5%. Furthermore, the slider and pressure block should be designed for ease of machining and assembly. For example, the slider’s T-slot is machined using wire-cut machining to IT7 precision, and the pressure block’s wedge surface is surface-grinded to ensure interchangeability and reduce mold maintenance costs.
