In die casting
processes, the requirements of temperature have a great influence on filling, forming and solidification processes, service lives of die casting molds and stable production. Therefore, the temperature should be paid enough attention to and controlled.
The pouring temperature of the alloy
The pouring temperature is usually indicated by the temperature of the molten metal in the holding crucible. When the temperature is too high, the large shrinkage will happen in the solidification process, resulting in the crack and the coarse grain of the die cast; when the temperature is too low, the defects such as the cold shut and the flow liner will appear on the surface of the die cast
. Therefore, the relatively low temperature should be adopted as the appropriate pouring temperature on the premise that the die casting mold can be filled. Factors such as injection pressure, die casting molds' temperatures and filling speeds should be taken into account when we determine pouring temperatures.
Practice has proved that the pouring temperature can be reduced in the case of high pressure, and die casting parts can be made when the alloy is sticky like porridge. However, aluminum alloys containing the high silicon content should not be processed by die casting
processes when aluminum alloys
are sticky like porridge. A great deal of silicon will precipitate, and precipitated silicon will exist in die casts by free states, which will worsen processing performance. In addition, the pouring temperature is also related to the wall thickness and the complexity of the die casting part.
The operating temperature of the die casting mold
Influences of die casting molds' too high or too low working temperatures on quality of die casts are similar to those of alloys' pouring temperatures in die casting
processes. The operating temperature can affect the service live of the die casting mold and the normal production. Therefore, temperatures of die casting molds should be controlled within a certain range in the manufacturing processes. The temperature range is actually the operating temperature of the die casting mold. Usually, in the continuous production process, if the molten metal's heat which is absorbed by the die casting mold is less than the heat that is radiated, the temperature will gradually increase. Air or circulating cooling liquid such as water or oil can be used for cooling the temperature. Die casting molds must be heated to a certain temperature in order to facilitate fillings and formation of molten metals, protections of die casting molds and easy coatings before die casting processes.
Filling time, holding pressure time and the time of keeping the die casting part is kept in the die casting mold
1. The filling time
Filling time refers to the time from molten metals starting getting into mold cavities to the time when mold cavities are filled. Filling time is related to factors such as overall dimensions, wall thicknesses of die casts, complexity of die casts’ shapes as well as temperatures of molten metals and die casting molds. When temperature differences between pouring temperatures and die casting molds' temperatures are small, or die casts have simple shapes and thick walls, the filling time can be longer; otherwise, the filling time should be shorter. The filling time is mainly controlled by adjusting the injection pressure, the injection speed or the size of the ingate, and it is generally from 0.0l to 0.2s.