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03
2020
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Temperature control and its effects in die casting process
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There are two temperature indicators in die casting production. One is the pouring temperature. The other is the mold temperature. Below, we will discuss the impact of these two temperature indicators on die casting production.
1. Pouring Temperature
The pouring temperature refers to the temperature of the molten metal when it enters the cavity from the pressure chamber to fill it. In production, the pouring temperature is controlled by managing the temperature of the alloy liquid in the holding furnace.
For castings of different shapes and structures, the pouring temperature can be controlled between 630-730°C; for thin-walled complex parts, a higher temperature can be used to improve the fluidity of the molten metal and achieve good forming; for thick-walled structural parts, a lower temperature can be used to reduce solidification shrinkage. However, if the pouring temperature is too high, the amount of gas absorption in aluminum will increase, making it easy for defects like pinholes, shrinkage cavities, and surface bubbling to occur in thick-walled castings; at the same time, it accelerates mold corrosion, leading to premature aging and cracking of the mold. If the pouring temperature is too low, fluidity will be poor, easily resulting in defects such as cold shuts, flow marks, and insufficient pouring; excessively low temperatures can cause compositional deviations in aluminum, leading to hard spots in castings and difficulties in post-processing. As the pouring temperature increases, the mechanical properties of die-casting molds significantly decrease.
2. Mold Temperature
Mold temperature generally refers to the surface temperature of the mold. Its standard state should be about 1/3 of the alloy liquid pouring temperature. The mold temperature greatly affects the mechanical properties of die-cast parts, dimensional accuracy, and the lifespan of die-casting molds.
(1) Mold Temperature Affects Mold Lifespan
In continuous die-casting production, each time a casting is made, the mold temperature cycles from high to low once, being continuously heated and cooled. The internal mold experiences thermal stress due to temperature differences. When the mold material is in a ductile state, stress causes plastic deformation; when in a brittle state, stress leads to thermal cracks and fractures. Periodic thermal stress results in thermal fatigue of the mold, causing cracking. If the mold temperature is too high, it is prone to deformation.
(2) Mold Temperature Affects Release Agent Effectiveness
When the mold temperature is too high, release agents evaporate excessively at high temperatures and cannot form a dense film, leading to sticking issues. Conversely, if the mold temperature is too low, the film formed by the release agent contains unvaporized moisture, resulting in poor release effects and potential gas holes or cold shut defects in castings.
(3) Mold Temperature Affects Casting Quality
When the mold temperature is below 130 degrees: Due to excessively low casting temperatures, castings almost entirely exhibit underfilling, cracking, cold shuts, flow marks, and other defects, resulting in an almost zero yield.
When the mold temperature is between 130-150 degrees: As the casting temperature approaches ideal conditions, castings may form but with unstable quality. Most workpieces show flow marks and cold shuts.
When the mold temperature is between 150-300 degrees: This is an appropriate stable casting zone.
When the mold temperature exceeds 300 degrees: The casting temperatures are too high, easily leading to surface bubbles, sticking issues, shrinkage, welding defects, etc.
It can be seen that when mold temperatures exceed 250°C, mechanical properties decline.
(4) Mold Thermal Balance
Mold temperature directly affects casting quality and productivity. To improve stability in die-casting production, heat absorption and dissipation of molds should maintain thermal balance.
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