Injection molded conical positioning block
Injection molding conical locators are key components for ensuring mold clamping accuracy. They are widely used in injection molds requiring high precision, especially large molds, multi-cavity molds, and molds with complex lateral core-pulling mechanisms. Compared to traditional flat positioning or guide pin and guide sleeve positioning, conical locators achieve precise positioning through the use of conical surfaces. They can effectively compensate for gaps caused by mold temperature fluctuations and deformation due to stress, ensuring the relative position accuracy of the cavity and core, thereby improving the dimensional consistency and surface quality of the plastic part.
The structural design of injection molding tapered locators must meet the dual requirements of positioning accuracy and strength. Their core consists of a conical protrusion and a conical recess, typically mounted on the parting surfaces of the movable and fixed molds. The angle of the tapered surface is a critical design parameter. Too small an angle weakens the locator’s guiding function and can easily cause interference during mold closing. Too large an angle reduces positioning accuracy and fails to effectively eliminate backlash. Practice has shown that a tapered angle of 15° to 30° is commonly used, with 20° being the most widely used. This ensures smooth guidance during mold closing and allows for high-precision positioning through a tight fit of the tapered surface once the mold is in place. The height of the locator should be determined based on the size of the mold. Small molds typically have a locator height of 20-30mm, while large molds require 50-100mm to ensure sufficient contact area to withstand lateral forces during mold closing. In addition, the working surface of the conical positioning block needs to be precision ground, and the surface roughness is controlled below Ra0.8μm. The fitting clearance is usually set to 0.01-0.03mm to ensure positioning accuracy while avoiding wear caused by over-tight fit.
The installation location of injection molding conical locating blocks should be strategically arranged based on the mold structure and stress conditions to ensure uniform force distribution and comprehensive positioning. For rectangular molds, a set of conical locating blocks is typically installed at each of the four corners, creating a symmetrical distribution to ensure consistent positioning accuracy around the mold during mold closing. For circular molds, three to four sets of locating blocks can be evenly spaced around the circumference to avoid uneven force distribution caused by single-point positioning. In molds with lateral core pulling mechanisms, the locating blocks should be installed close to the core pulling mechanism to offset the lateral forces generated during core pulling and prevent relative positional shift between the cavity and core. For example, in automobile bumper molds, reinforced conical locating blocks are installed at the corresponding positions of the lateral core pulling mechanism to effectively control mold deformation during the core pulling process and maintain the positional accuracy of the side holes in the plastic part within 0.05mm. The locating blocks should be secured with bolts and locating pins to ensure accurate mounting on the mold. The flatness of the mounting surface should be within 0.02mm to prevent tilted mounting that could affect positioning.
The material selection and heat treatment process for injection molding tapered locating blocks directly impact their wear resistance and service life. Because locating blocks are subjected to repeated impact and friction during the mold closing process, high-strength and wear-resistant materials are required. Commonly used materials include alloy tool steel Cr12MoV and high-speed steel SKD61. After quenching and tempering, Cr12MoV achieves a hardness of 58-62 HRC, offering exceptional wear resistance and suitable for small and medium-sized molds. SKD61, with a hardness of 45-50 HRC, offers increased toughness and excellent impact resistance, making it suitable for large molds or applications with frequent mold closings. To further enhance surface wear resistance, the working surface of locating blocks is typically nitrided. The nitriding layer depth is 0.05-0.1mm, achieving a surface hardness of 800-1000 HV, significantly extending their service life. Material selection also considers machinability. Cr12MoV has poor cutting performance and requires specialized cutting tools. SKD61 offers relatively good machinability and is suitable for precision machining of complex shapes.
Injection molding cone locators require regular maintenance and inspection during use to ensure positioning accuracy. During mold closing, impurities or plastic debris on the locator surface can cause inaccurate positioning or even scratch the cone surface. Therefore, the locator surface should be cleaned before each production run to ensure it is free of foreign matter. Over time, the cone surface of the locator may wear, increasing the clearance and affecting positioning accuracy. Regularly inspect the cone surface using a coordinate measuring machine. If the wear exceeds 0.02mm, repair or replacement is required. Repair can be performed by grinding to remove the worn layer and restore cone surface accuracy, but the grinding depth should be limited to 0.1mm to avoid compromising the overall strength of the locator. For locators used in large molds, the tightening of the mounting bolts should also be checked to prevent loosening due to vibration, which could affect positioning. With proper maintenance and inspection, cone locators can achieve a service life of over 500,000 mold cycles, continuously providing high-precision positioning for the mold and ensuring consistent part quality.
