Conical surface positioning of injection mold plate
Conical surface positioning of injection molding templates is a key technology for ensuring precise alignment between the movable and fixed molds during mold closing. The conical surface structure on the template achieves both radial and axial positioning, significantly improving mold closing accuracy and reducing problems such as cavity wear and part flash caused by positioning deviations. Compared with traditional guide pin and guide sleeve positioning, conical surface positioning offers advantages such as high positioning accuracy (the fit clearance can be controlled to 0.005-0.01mm), strong load capacity, and excellent resistance to off-center loads. It is particularly suitable for large molds (template dimensions ≥ 1000mm), precision molds (part dimensional tolerance ≤ ±0.02mm), and molds subject to significant lateral forces during the molding process (such as deep-cavity molds).
The structural design of the injection mold platen’s tapered positioning surface typically consists of a convex and concave tapered surface, located at corresponding positions on the movable and fixed mold plates, respectively. The taper of the convex and concave surfaces is strictly matched. Common tapers are 1:50, 1:100, or 3° and 5°. The choice of taper depends on the mold size and positioning accuracy requirements. For large molds, since the mold plate is prone to deformation under the clamping force, a smaller taper (such as 1:100) is often used to increase the positioning contact area and improve positioning stability. For small, precision molds, a larger taper (such as 5°) can be used to speed up positioning during clamping. The surface roughness of the tapered surface must be controlled below Ra0.4μm and must be hardened (hardness ≥HRC50) to improve wear resistance and deformation resistance. A transition radius (R1-R3mm) is provided at the base of the tapered surface to prevent stress concentration and cracking.
The working principle of conical surface positioning is based on the self-guiding and self-centering properties of conical surfaces. During the mold closing process, the convex conical surface gradually enters the concave conical surface. The contact between the conical surfaces generates a radial guiding force, automatically aligning the movable and fixed molds, eliminating positioning errors caused by initial installation errors and mold plate deformation. When the mold is closed, the conical surfaces are completely aligned. The axial preload generated at this time enhances the overall rigidity of the mold plate and reduces deformation of the mold cavity under injection pressure (typically within 0.01mm). For molds subject to lateral forces (such as those molding parts with undercuts), conical surface positioning can resist lateral forces through friction between the conical surfaces, preventing relative displacement between the movable and fixed molds and avoiding wear and flash on the cavity sidewalls. For example, in a deep-cavity mold with an injection pressure of 150MPa, using conical surface positioning can keep lateral displacement below 0.005mm, far less than the 0.02mm of guide pin and guide bushing positioning.
The layout of the injection mold’s conical surface positioning must be designed based on the mold’s structure and stress characteristics. Common layouts include four-corner symmetrical layout, central layout, and peripheral ring layout. The four-corner symmetrical layout is suitable for molds with rectangular molds. A set of conical surface positioning is set at each of the four corners of the mold, forming a symmetrical positioning system to ensure uniform stress on the mold. This layout is widely used in small and medium-sized molds. The central layout is suitable for circular molds or molds with greater central stress. A large conical surface positioning is set at the center of the mold to effectively resist injection pressure in the central area and reduce bending deformation of the mold. The peripheral ring layout is suitable for large disc-shaped molds (such as automobile instrument panel molds). A continuous annular cone is set around the perimeter of the mold to provide 360° positioning, ensuring that the mold maintains coaxiality (coaxiality error ≤ 0.01mm) during the mold closing and injection processes.
The machining accuracy and assembly quality of conical surface positioning are crucial to effective positioning, thus requiring strict control of the machining and assembly processes. Conical surface machining typically utilizes CNC grinding or form grinding processes to ensure that the angular tolerance of the cone surface is within ±5° and the circular runout of the cone surface is ≤0.005mm. The convex and concave cone surfaces must be machined and ground in pairs to ensure a contact area of at least 80%, with evenly distributed contact spots (≥25 spots per square centimeter). During assembly, the clearance between the cone surfaces must be controlled by adjusting shims or grinding the reference surface. For precision molds, the clearance should be controlled between 0.003-0.005mm to ensure precise positioning while avoiding mold closing difficulties caused by interference fits. Dust and oil should be cleaned regularly during use to prevent impurities from entering the mating surfaces and causing wear. The cone surface should also be inspected for wear. If wear exceeds 0.01mm, regrind or replace the mold plate to ensure consistent positioning accuracy. In addition, during the transportation and storage of the mold, the conical surface needs to be protected (such as applying anti-rust oil and installing a protective cover) to prevent damage from bumps.
