The quality and productivity of die casting parts largely depend on whether the thermal balance control of die casting molds is correct. Effective control and regulation of the thermal balance of the die casting molds is necessary for stable die casting process parameters.
In die casting production, when the heat output from the die casting mold is greater than the heat transmitted from the alloy liquid to the mold, for example, when a larger mold is used to cast thin-wall parts or a mold with more sliding structures, additional heat must be added to the mold to achieve thermal balance. Methods for increasing additional heat include the use of mold temperature control machines, adjustable tubular heaters placed on the mold, insulation outside the mold, or setting of excess parts of castings, including overflow grooves. Conversely, when the heat input to the mold is greater than the heat output, and the mold temperature exceeds the standard, artificial forced cooling must be used.
For each die casting cycle, the die casting mold absorbs input heat from the alloy liquid, and outputs heat through heat conduction to the outside world. Generally, only 5% of the total input heat is lost due to radiation and natural convection, and the remaining 95% is completely output by heat conduction of the mold. When the heat absorption and heat dissipation of the mold are equal in unit time, an equilibrium state can be reached, that is, to achieve thermal balance of the mold, the sum of the heat input to the mold and the heat output due to natural loss and artificial cooling must be equal, achieving consistent input and output heat in each die casting cycle.
In actual production, there are many factors that affect the thermal balance of the die casting mold, including pouring temperature, mold preheating temperature, alloy liquid capacity, mold volume, position and quantity of the casting and overflow system, mold cooling conditions, and operating cycle time. Therefore, to achieve good mold thermal balance, it is necessary to adjust the die casting process parameters, including the die casting ratio, punch speed, mold retention and release time, spraying, and other factors that influence and restrict each other.
The selection and adjustment of the temperature of the die casting mold should be based on the shape, size, and structural characteristics of the casting, as well as the properties of the alloy, mold structure, and casting conditions, and other comprehensive factors. The recommended working temperature for die casting molds is: zinc alloy 160-200℃, magnesium alloy 180-240℃, aluminum alloy 200-250℃, and copper alloy 280-350℃.
As die casting parts continue to enter the international market, the demand for mold temperature control has become more urgent as the quality requirements for die casting parts increase. In large and medium-sized die casting enterprises, the theory of mold thermal balance has been incorporated into the design and manufacture of die casting molds, and temperature control points have been pre-set for each part according to the technical requirements of die casting parts. By controlling the cooling speed of the alloy liquid and adjusting the size and internal structure of the die casting parts, the crystal is refined, enhancing mechanical properties, and achieving sequential solidification of the alloy liquid during cooling, eliminating defects such as looseness and cold shut-off of the castings.
Effectively controlling and regulating the temperature of the die casting mold is not only critical for extending the life of the mold but also for ensuring good alloy liquid filling, stable casting quality, and productivity. For die casting workshops that require high-quality die casting parts but lack corresponding mold temperature control measures, preheating the mold before production, avoiding the rapid cooling of the alloy liquid, sudden increase in mold temperature gradients, and reducing casting quality and premature damage to the mold must follow the process regulations to check and adjust the temperature of the critical parts of the mold, and control the production rhythm, alloy liquid flow rate, and spraying adjustments.