There are two temperature indexes in die casting production. One is pouring temperature. The second is mold temperature. The influence of these two temperature indicators on die casting production is discussed below.
1. Pouring temperature
The pouring temperature refers to the temperature when the molten metal enters the cavity from the pressure chamber to fill. In production, the pouring temperature is controlled by controlling the temperature of the alloy liquid in the holding furnace.
For castings with different shapes and structures, the pouring temperature can be controlled at 630-730 ℃; For thin-walled complex parts, higher temperature can be used to improve the fluidity of liquid metal and obtain good molding; For thick-wall structural parts, lower temperature can be used to reduce solidification shrinkage. However, if the pouring temperature is too high, the amount of air absorption in the aluminum water will increase, which will easily lead to pinholes, shrinkage holes and surface bubbles at the thick wall of the casting; At the same time, the corrosion of the mold is accelerated, which makes the mold prematurely aged and cracked. The pouring temperature is too low and the fluidity is poor, which is easy to produce defects such as cold shut, flow lines and insufficient pouring; Low temperature aluminum is easy to produce composition deviation, which causes hard spots in the casting and makes it difficult to process. With the increase of pouring temperature, the mechanical properties of die-casting die decreased significantly.
2. Mold temperature
The mold temperature generally refers to the surface temperature of the mold, and its standard state should be about 1/3 of the pouring temperature of the alloy liquid. The mold temperature greatly affects the mechanical properties, dimensional accuracy and life of the die casting.
(1) Die temperature affects die casting die life
In the process of continuous die-casting production, the mold temperature will be cycled from high temperature to low temperature once per die-casting, and will be continuously heated and cooled, resulting in thermal stress in the mold due to temperature difference. When the die material is in a ductile state, the stress causes plastic deformation of the die; In the brittle state, the stress causes the mold to produce hot cracks and cracks. Periodic thermal stress causes thermal fatigue and cracking of the mold. If the mold temperature is too high, the mold is easy to deform.
(2) Effect of mold temperature on release agent
When the mold temperature is too high, the release agent volatilizes excessively at high temperature, which can not form a dense skin film and is easy to cause mold adhesion. If the mold temperature is too low, the film formed by the mold release agent contains nonvolatile water, which makes the mold release effect poor, and also causes casting porosity and cold shut defects.
(3) Die temperature affects the quality of die castings
When the mold temperature is lower than 130 ℃: because the mold temperature is too low, almost all castings have defects such as under-casting, cracking, cold shuts, flow lines, and the yield is almost zero.
When the mold temperature is between 130-150 ℃: because the mold temperature is close to the ideal temperature, the casting may be formed, but the quality is unstable. Most of the work shows flow pattern and cold insulation.
When the mold temperature is between 150-300 ℃: suitable casting stable area.
When the mold temperature is higher than 300 ℃: the casting temperature is too high, which is easy to produce defects such as surface bubbles, mold sticking, shrinkage and welding.
It can be seen that when the mold temperature exceeds 250 ℃, the mechanical properties will decline.
(4) Mold heat balance
Die temperature directly affects the quality and productivity of die castings. In order to improve the stability of die casting production, the heat absorption and heat dissipation of the die should be kept in balance.