Categories of standard injection mold bases
A standard mold frame for injection molding is the basic framework of the injection mold. It is assembled from standardized parts such as the fixed mold base, movable mold base, mold plate, guide pins, and guide sleeves. Its function is to support the mold cavity, ensure mold opening and closing accuracy, and transmit clamping force. Using a standard mold frame can significantly shorten mold design and manufacturing cycles, reduce production costs, and facilitate mold maintenance and part replacement, making it widely used in the injection molding industry. Standard mold frames for injection molding can be divided into various categories according to different classification standards. Understanding the structural characteristics and applicable scenarios of each type of mold frame is crucial to the rationality and cost-effectiveness of mold design.
Standard injection mold bases can be categorized by structure into three main types: two-platen, three-platen, and hot runner. The two-platen mold base is the most commonly used. It consists of a fixed platen and a movable platen, with the cavity directly defined on each platen and the gate located at the parting surface. It is suitable for parts with simple structures and a single parting surface, such as housings and covers. Its advantages include compactness, low cost, fast mold opening and closing speeds, and direct clamping force transmission through the platens, making it suitable for injection molding machines of all tonnages. The three-platen mold base adds a runner pusher plate to the two-platen structure, separating the gate from the part. This makes it suitable for multi-cavity molds with point-gating feed and is particularly well-suited for the high-volume production of small parts. Because the runner system is located separately between the runner pusher plate and the fixed platen, runner aggregate automatically falls off during mold opening, reducing manual cleaning. However, the three-platen mold base is taller, requiring a higher mold opening stroke on the injection molding machine, and its clamping force transmission efficiency is slightly lower than that of the two-platen mold base. The hot runner mold frame integrates a hot runner system on a two-plate or three-plate basis, and keeps the melt in the runner in a molten state through a heating device. It is suitable for large plastic parts or products with strict requirements on gate marks (such as transparent plastic parts). However, its manufacturing cost is high and maintenance is difficult. It is mainly used in high-precision, high-output production scenarios.
Based on the mold plate assembly, standard mold bases can be divided into large-gate mold bases, small-gate mold bases, and simplified mold bases. Large-gate mold bases feature a two-platen structure, with the mold platen assembly consisting of a fixed mold base plate + fixed mold plate + movable mold plate + movable mold base plate. Guide pins are typically mounted on the movable mold platen, while guide bushings are mounted on the fixed mold platen. This makes it suitable for molds with non-point gates, such as side gates and fan gates. The mold platen thickness can be flexibly selected based on the cavity depth. Common specifications include A-plate thicknesses of 50-200mm and B-plate thicknesses of 80-300mm, meeting the molding requirements of most plastic parts. Small-gate mold bases feature a three-platen structure, with the mold platen assembly supplemented by a runner pusher plate and a fixed mold backing plate. Guide pins are divided into small guide pins that guide the fixed mold platen and runner pusher plate, and large guide pins that guide the fixed mold platen and movable mold platen. This ensures that the runner pusher plate and fixed mold platen separate first during mold opening, automatically separating the runner slurry from the plastic part. Pin-gate mold bases require higher platen precision, with parallelism errors between the mold plates controlled within 0.02mm/m. These mold bases are suitable for mold structures such as point gates and latent gates. Simplified mold bases, based on standard structures, reduce some auxiliary components (such as omitting the fixed or movable mold pads). They are suitable for small-batch production or simple plastic parts. While they offer lower costs, they have lower rigidity and are not suitable for injection molding applications requiring high clamping forces.
Standard mold frames are categorized by the type of injection molding machine they are designed for: horizontal and vertical injection molding machines. Horizontal mold frames utilize horizontal mold opening and closing. The fixed mold base is bolted to the machine’s fixed platen, while the movable mold base is connected to the machine’s movable platen. The mold frame is arranged horizontally, making it suitable for the production of most small and medium-sized plastic parts. Guide posts are typically symmetrically located at the four corners of the platen to ensure stability during mold opening and closing. The platen’s length and width must match the machine’s tie rod spacing. Common sizes include 300×300mm, 400×400mm, and 500×500mm. Vertical mold frames utilize vertical mold opening and closing, with the fixed mold base located at the bottom and the movable mold base located at the top. Mold opening and closing are guided by columns, making them suitable for insert molding or the production of large plastic parts. Because the direction of clamping force in vertical injection molding machines aligns with gravity, the mold base’s movable platen requires reinforcement ribs to prevent deformation after long-term use. The platen is typically 20%-30% thicker than a horizontal mold base to improve overall rigidity. Furthermore, the guide post arrangement of a vertical mold base emphasizes symmetry to prevent gravity-induced platen tilt, which could affect part precision.
Standard mold bases for injection molding primarily fall into the Chinese (GB/T) standard, the International (ISO) standard, the Japanese (JIS) standard, and the European (DIN) standard. Chinese standard mold bases (such as GB/T 12556) specify mold base structure, dimensional series, and tolerance requirements. The mold base is typically made of 45 steel or S50C, with a hardness of HRC28-32 after quenching, making it suitable for most domestic injection molding companies. International standard mold bases (ISO 2862) differ from Chinese standards in dimensional series and precision levels, with stricter mold base parallelism requirements (≤0.015mm/m). These standards are suitable for export molds or the production needs of multinational companies. Japanese standard mold bases (such as JIS B 5003) are renowned for their high precision. The mold bases are made of S50C or S55C steel, and dimensional accuracy is ensured through precision grinding. The clearance between guide pins and bushings can be controlled to within 0.005-0.01mm, making them suitable for molding precision plastic parts such as electronic connectors. European standard mold bases (DIN 16742) emphasize modular design and support a variety of mold plate combinations, allowing for flexible adjustment of the mold base structure to meet part requirements. However, their manufacturing costs are relatively high, and they are primarily used in high-end mold applications. When selecting a standard mold base, consider the part’s precision requirements, production batch size, and budget, and choose the appropriate standard system.
