Classification of die casting mold pouring system
There are various ways to classify the pouring system of a die-casting mold. According to the location of the introduction of the molten metal, the flow path and the structural form, it can be divided into multiple types. Different types of pouring systems are suitable for different casting structures and die-casting process requirements. Reasonable selection of the pouring system type can give full play to its role in guiding and controlling the flow of the molten metal, and improve the density and dimensional accuracy of the casting. Common classifications of die-casting mold pouring systems include: top pouring, bottom pouring, and side pouring according to the location of the gate; single-runner and multi-runner according to the number of runners; non-impact type and impact type according to whether the molten metal impacts the core; direct type, indirect type, etc. according to the connection method with the cavity. Each classification method reflects the adaptive relationship between the pouring system and the characteristics of the casting.
Classification by ingate location is the most common approach. Top-cast systems feature an ingate located at the top of the casting. Molten metal is injected from above the cavity, filling the cavity via a combination of gravity and pressure. This type of system offers advantages such as rapid filling speed and reduced accumulation of molten metal at the bottom of the cavity. It is suitable for tall cylindrical or box-shaped castings (such as motor housings and hydraulic cylinders). Top-cast ingates are typically wide (accounting for 30%-50% of the casting’s top circumference) and thin, creating a flat stream of molten metal that evenly covers the cavity cross-section. However, care must be taken to control the filling speed to prevent the molten metal from directly impacting the cavity wall from the top, which could cause air entrainment or splashing. An overflow trough can be provided at the bottom to absorb impact energy.
In a bottom-pouring system, the ingate is located at the bottom or lower portion of the casting. The molten metal slowly rises from the bottom of the mold cavity, gradually filling the entire cavity. This method effectively prevents air entrainment and oxidation and is suitable for thin-walled, complex-shaped castings (such as instrument housings and radiators). The bottom-pouring ingate has a relatively thick ingate (typically 1-3 mm) and a width determined by the dimensions of the casting’s base. This ensures a steady rise rate (typically 2-10 m/s) and avoids eddy currents caused by excessive velocity. To prevent the formation of air holes at the top of the cavity, venting and overflow channels are required to drain any accumulated air and cold metal. The disadvantage of the bottom-pouring system is the long flow path and significant pressure loss, requiring a high die-casting pressure (typically 50-80 MPa) to ensure full filling.
The side-injection gating system features an inner gate located on the side of the casting. It is suitable for symmetrical, wide flat or frame-shaped castings (such as automotive door panel frames and machine tool bases). The molten metal in the side-injection system flows from the side along the length of the cavity. Multiple inner gates can be used to achieve multi-point feeding, reducing filling time and temperature differences. The inner gate should be positioned away from important machining surfaces of the casting. Its width is typically 20%-40% of the length of the casting’s side, and its thickness is adjusted based on the casting’s wall thickness to ensure uniform diffusion of the molten metal during flow. The advantage of the side-injection method is its simple mold structure, which facilitates the installation of overflow and venting grooves. The disadvantage is that the molten metal exerts a greater impact force on the side cavity walls, requiring the mold to be strengthened at the corresponding locations to avoid wear or deformation of the cavity after long-term use.
Categorized by the number of runners, single-runner gating systems are suitable for single-cavity or small multi-cavity molds. Their main runner connects directly to the ingode through a single runner. This system features a simple structure, high pressure transmission efficiency, a short molten metal flow path, and minimal energy loss, making it suitable for small and medium-sized simple castings (such as gears and connectors). The cross-section of a single-runner runner is typically circular or trapezoidal, and its length generally does not exceed 100mm, ensuring that the molten metal maintains sufficient temperature and pressure before entering the cavity. Multi-runner gating systems are used in large multi-cavity molds or complex single-cavity molds. Multiple runners distribute the molten metal from the main runner to different ingodes. Each runner can be independently sized to accommodate the filling needs of different cavities. The design difficulty of a multi-runner system lies in ensuring balanced flow across each runner. Typically, a symmetrical arrangement is employed or pressure balance is achieved by adjusting cross-sectional dimensions (such as length and width) to avoid variations in casting quality due to uneven distribution.
Non-impact gating systems are categorized by whether the molten metal impacts the core. Non-impact gating systems feature an ingate positioned away from the core, allowing the molten metal to flow along the cavity wall. This makes them suitable for castings with slender cores or delicate structures (such as engine blocks and valve bodies), minimizing core deformation or breakage due to impact. Non-impact ingates are typically located to the side or diagonally above the core, with the molten metal flowing at a 30-60° angle to the core axis, creating a gentle flow pattern. Impact gating systems allow the molten metal to directly impact the core. This makes them suitable for castings with high core strength that require impact to eliminate air bubbles (such as thick-walled bearing housings). However, the impact velocity must be controlled (generally no more than 20 m/s), and the core surface must be hardened (such as nitriding to a hardness of ≥60 HRC) to improve wear resistance. The choice between these two types should be based on a comprehensive assessment of the core’s structural strength and the quality requirements of the casting, ensuring both adequate filling and protection of mold components.
