Design of Die Casting Mold Heating System
The design of a die-casting mold heating system must be tailored to the mold structure, die-casting alloy type, and production process requirements to ensure rapid preheating and uniform temperature rise, providing a stable temperature environment for the die-casting process. Key design considerations include heating method selection, heating element placement, and temperature control. Common heating methods include resistance heating, induction heating, and hot oil heating. Resistance heating generates heat through heating rods and tubes installed inside the mold. Its simple structure, low cost, and easy control make it suitable for small and medium-sized molds and localized heating, making it the most widely used heating method. Induction heating utilizes electromagnetic induction to generate eddy currents within the mold, offering fast heating speed and high efficiency. It is suitable for preheating large molds as a whole, but the equipment cost is relatively high. Hot oil heating circulates high-temperature oil to heat the mold, achieving excellent temperature uniformity. It is suitable for precision die-casting molds requiring extremely high temperature uniformity, but the system is complex and has high maintenance costs. For example, small and medium-sized aluminum alloy die-casting molds often use resistance heating, with heating rods installed in the mold plate and insert to preheat the mold to 200-250°C.
The selection of heating elements depends on the heating power, mold material, and installation space. Commonly used elements for resistance heating include single-ended heating rods, flanged heating tubes, and heating plates. Single-ended heating rods are suitable for installation in confined spaces (such as inside inserts). They have a diameter of 6-16mm, a length of 50-300mm, a power density of 20-50W/cm², and are made of stainless steel (304 or 316). Their insulation resistance is greater than 100MΩ. Flange-type heating tubes are suitable for heating inside the mold. They have a diameter of 12-25mm, a length of 100-500mm, and are fixed to the side of the mold via a flange. They have a power of 500-2000W and are easy to install and replace. Heating plates are suitable for heating large areas and can be customized to suit the mold shape. They have a thickness of 2-5mm, a power density of 10-30W/cm², and can be attached to the outside of the mold or embedded in the mold groove. For example, four single-ended heating rods of φ12mm×200mm are installed in the fixed mold plate of the die-casting mold, with a power of 500W each and a total power of 2000W. The mold can be heated from room temperature to 200℃ within 30 minutes.
The placement of heating elements is crucial for ensuring uniform mold temperature. The principle of “even distribution and focused compensation” should be adhered to, and optimized based on the mold’s heat dissipation characteristics and cavity structure. Heating elements should be densely arranged in areas with rapid heat dissipation, such as the mold parting surface and cavity edges, to increase power density by 10%-20%. Heating elements can be more sparsely spaced within the cavity or within thicker inserts. The distance between heating elements and the cavity surface is typically 20-50mm. Too close can lead to localized overheating, while too far can result in low heating efficiency. For example, for molds with deep cavities, heating rods should be added to the inserts corresponding to the deep cavity bottom, 30mm from the cavity bottom, to compensate for heat loss in this area. Heating element placement should also avoid interference with cooling channels, ejector holes, and other areas. The distance between these areas should be greater than 15mm to prevent interference with cooling. Large molds require a zoned heating arrangement, dividing the mold into multiple heating zones (such as the fixed mold, movable mold, and side core pulls), each with independent control to ensure consistent temperature.
The temperature control and monitoring system is a crucial component of the heating system, requiring precise control (±5°C) and real-time monitoring of mold temperature. Thermocouples are typically used as temperature sensors, located near the cavity surface (5-10 mm from the surface) and near the heating elements, providing real-time feedback on mold temperature. The number of sensors is determined by mold size, with 2-4 sensors required for small molds and 6-12 for large molds to ensure comprehensive monitoring of temperature distribution. The temperature controller uses PID control to automatically adjust the power output of the heating elements based on sensor feedback to achieve constant temperature control. For example, the temperature control system for aluminum alloy die-casting molds uses K-type thermocouples installed near the fixed and moving mold cavities to transmit temperature signals to a PLC. The controller automatically switches the heating rods on and off based on the set temperature (200°C) to maintain a stable mold temperature within the range of 195-205°C. For zoned heating systems, multiple controllers are required to enable independent regulation of each zone.
The safety design of the heating system must consider electrical safety, thermal expansion, and ease of maintenance. The electrical wiring of the heating element must comply with safety standards and use high-temperature-resistant wire (above 200°C). Terminals must be located on the side of the mold away from high-temperature areas and fitted with protective covers to prevent electric shock and burns. A clearance of 0.5-1mm should be maintained between the mounting holes of the heating element and the mold to compensate for thermal expansion during heating and prevent damage to the heating element due to compression. For example, a 10mm diameter heating rod requires a mounting hole diameter of 10.5-11mm to ensure free expansion during heating. The heating system should be equipped with an overheating protection device that automatically cuts off power when the mold temperature exceeds a set upper limit (e.g., 350°C) to prevent overheating and damage. Furthermore, the heating element should be arranged for easy removal and replacement. For fragile heating rods, ample operating clearance should be reserved during mold design to reduce maintenance time. A well-designed heating system ensures a stable mold operating temperature during the die-casting process, improving die-casting quality and mold life.
