Mastering Temperature Control in Die Casting for Optimal Quality

There are two temperature indicators which will affect the die casting production. One is the pouring temperature and the second is the mold temperature. 

1. Pouring temperature

Pouring temperature refers to the temperature at which the liquid metal enters the mould cavity from the pressure chamber. It is controlled by the temperature of the alloy liquid in the holding furnace during the casting process.

The pouring temperature can be maintained at 630-730℃ for castings with different shapes and structures. Regarding the complex components with thin wall, we normally choose the higher temperature to improve the fluidity of the liquid metal and obtain good shaping effect; and and vice versa, lower temperatures will be applied for thick-walled parts to reduce solidification shrinkage.

However, if the casting temperature is too high, the suction volume of liquid aluminum water will increase, which will easily cause pinholes, shrinkage holes and bubbles on the surface. Also, the mold corrosion speed will be accelerated and result in mold premature aging and cracking.

While there will be other defects like cold isolation, flow lines, insufficient pouring if the casting temperature is too low. Aluminum is easy to generate composition deviation and cause that the hard points within the casting and difficult to machining under too low temperature. The higher pouring temperature, the lower mechanical properties of die casting mould obviously.

2. Mold temperature

The mold temperature generally refers to the surface temperature of the mold, and its standard measurement should be about 1/3 of the alloy liquid pouring temperature. The mold temperature greatly affects the mechanical properties, dimensional accuracy and the life of the die casting die.

(1)Mold temperature affects service life of casting die

In the continuous die casting process, the mould is constantly heated and cooled, therefore the thermal stress will be generated due to the internal temperature difference. When the die material is in the ductile state, the stress will cause the mould plastic deformation. In the brittle state, the stress leads to hot cracking of the mould. Periodic thermal stress results in thermal fatigue and cracking of the die. The mold is easy to be deformed if the mold temperature is too high.

(2) Mold temperature affects the effect of the release agent

The release agent will be unduly volatilized under high mold temperature, thereforre the dense skin film cannot be formed and cause sticky mold. While if the mold temperature is too low, the skin film formed by the demoulding agent contains non-volatile water and cause poor demoulding, also lead to the casting pores and cold insulation.

(3) Mold temperature affects the quality of die casting components

• When the mold temperature is lower than 130 degrees: nearly all the casting almost got undercasting, fracture, cold isolation, flow lines and other defects, the yield is almost zero due to the casting temperature is too low.
• When the mold temperature is between 130-150 degrees: Since the mold temperature is close to the ideal temperature, the casting may be formed, but the quality is not stable. Most of the castings have flow lines and cold isolation on the surface.
• When the mold temperature is between 150-300 degrees: it is suitable casting stability temperature range.
• When the mold temperature is higher than 300 degrees: It is easily to generate surface bubbles, sticking mold, shrinkage, welding and other defects when the casting temperature is too high.As a result, the mechanical properties decrease when the mold temperature exceeds 250℃.