The quality and productivity of die casting depends on whether the heat balance control of die casting die is correct or not. Only by controlling and adjusting the heat balance of die casting die effectively can the process parameters of die casting be stable.
In die casting production, when the heat lost by the mold is greater than the heat transmitted to the mold from the alloy liquid, for example, when the large mold is used to die casting thin-walled parts or the mold with more slider structure, in order to achieve the heat balance of the mold, additional heat must be given to the mold; Additional heat can be increased by means of mold temperature control machine, an adjustable tubular electric heater placed on the mold, an adiabatic body placed outside the mold or the excess part of the casting including the setting of the overflow tank. On the contrary, the heat input of the mold is greater than the heat lost and output, and the mold temperature exceeds the specification, forced cooling must be used manually.
For each die-casting cycle, the die absorbs input heat from the alloy liquid and outputs heat to the outside through heat conduction. In general, only 5% of the total input heat is lost by radiation and natural convection, and the remaining 95% is completely output by heat conduction of the die. When the heat absorption and heat dissipation of the mold are equal in unit time, the equilibrium state can be reached. That is, the heat input to the mold must be equal to the sum of the heat output through natural loss and artificial cooling when the mold reaches thermal balance, so as to ensure that the heat input and output of the mold are consistent in every die casting cycle.
In practical production, there are many influence factors in the mold heat balance, including pouring temperature, mould preheating temperature, the capacity of the liquid alloy, mold size, pouring position and quantity of the overflow system, mold cooling condition, and the cycle time of operation, etc., so to do good mould thermal equilibrium, must through the adjustment of the die casting technology parameters, Such factors as injection specific pressure, punch speed, die retention and die release time and spraying can be realized.
The selection and adjustment of mold temperature should be based on the shape, size and structural characteristics of the casting, as well as the properties of the alloy, mold structure and pouring conditions and other aspects of the comprehensive consideration, the recommended die casting die temperature is as follows: zinc alloy 160-200℃, magnesium alloy 180-240℃, aluminum alloy 200-250℃, copper alloy 280-350℃.
With the continuous entry of domestic die casting into the international market, the demand for die casting quality is increasing day by day, and the demand for mold temperature control is also more urgent. In foreign large and medium-sized casting enterprise, has put pressure into the mold design, mold heat balance theory and the technical requirements for pressure casting preset temperature control point of each part, by controlling the cooling rate of the alloy liquid, adjust the die casting size and internal organizations to refine crystal, mechanical performance, can also realize sequential solidification of alloy liquid cooling Eliminate the loose cold separation and other defects of casting.
The present domestic only new large-scale die-casting enterprise and joint venture or wholly foreign owned enterprise of the workshop is equipped with temperature control device, the import of die casting machine auxiliary equipment are mostly with a die mold temperature machine, most of the die casting factory production site is generally not set mold temperature machine, some even die casting workshop without preheating into production, the stability and improve the quality of die castings caused great impact.
Effective control and adjustment of mold temperature can not only prolong the life of die casting die, but also ensure the good filling of alloy liquid mold and stable casting quality of the key process parameters. At present there are requirements for die casting quality, and without proper means of control of mould temperature die casting workshop, the basic requirements before production mould preheating, avoid alloy liquid chilling too fast, suddenly increase the mold temperature gradient and reduce the casting quality and premature failure mould, according to technical pro.cess of mould check and adjust the temperature of the key parts, Control the production rhythm, the pouring flow of alloy liquid and the adjustment of spraying
In practical production, there are many influence factors in the mold heat balance, including pouring temperature, mould preheating temperature, the capacity of the liquid alloy, mold size, pouring position and quantity of the overflow system, mold cooling condition, and the cycle time of operation, etc., so to do good mould thermal equilibrium, must through the adjustment of the die casting technology parameters, Such factors as injection specific pressure, punch speed, die retention and die release time and spraying can be realized.
