Pressure casting, in foundry industry because of its rapid development has become a booming industry department and the important market, the growing demand for high quality die casting, prompted the die casting industry in high-performance equipment, advanced technology method, the performance of die casting alloy improve, the progress of mould manufacturing technology, and other fields have a significant difference, but compared with advanced foreign technology, die casting, The overall gap is still not small, so technological innovation has become the driving force for the development of the die casting industry.
Improving the quality of die casting, adapting to the demand of domestic and foreign market, and constantly discussing the factors that the development of die casting technology lags behind the development of production have become a common concern in the current die casting industry. This paper makes a preliminary discussion on the influence of die casting die temperature control on the quality of die casting.
Influence of mold temperature control on die casting quality
1, 1 mold temperature control role
(1) The mold temperature control has an important influence on the temperature, fluidity, filling time, filling flow state, cooling rate, crystallization state and order, shrinkage stress of the alloy liquid flow.
(2) The die temperature is too high, the die casting is easy to shrink and form depression or surface bubbles; When the mold temperature is too low, the surface of the casting is condensed, and then the high-speed liquid flow breaks through to form the surface defects of the casting, and the shrinkage stress of the casting increases, resulting in cracks.
(3) Mold temperature control plays a significant role in prolonging mold life and improving production efficiency. Mould temperature gradient changes too much, the stress state formed and frequent stress alternating, will lead to premature cracking and deformation of the mould.
(4) Die temperature control has an impact on die casting and dimensional accuracy. When the mold temperature is controlled within a certain range, the shrinkage rate of the casting is relatively stable, and good dimensional accuracy, surface quality and mechanical properties of the casting can be obtained.
1.2 Main factors affecting mold temperature
(1) Pouring temperature, pouring amount, heat capacity, mold volume, casting structure and thermal conductivity of the alloy liquid.
(2) Mold pouring system and overflow tank design and layout, and adjust the degree of thermal balance state.
(3) The time of die casting cycle and holding time, the continuity of production rhythm, the faster the frequency, the higher the mold temperature.
(4) Mold lubrication and heating and cooling mode and medium.
Die casting die temperature machine application site
1.3 Influence of die temperature on die casting performance
(1) Influence on mechanical properties: Appropriately raising the mold temperature can improve the filling conditions and improve the mechanical properties of the casting. However, if the mold temperature is too high, the liquid cooling speed of the alloy will be reduced, the fine crystal layer on the casting will be reduced, and the grain size will be coarse, and the strength will be decreased. For aluminum alloy, when the mold temperature exceeds 250℃, the strength will be decreased. When the mold temperature is less than l 5 0℃, the value will gradually decrease.
For die casting magnesium alloy AM50, the influence of mold temperature on mechanical properties is studied when pouring temperature is 680℃ and injection velocity is 3.5 m/s. When the mold temperature is higher than 180℃, all the mechanical properties begin to decline, the mold temperature is too high, not only directly affects the cavity cooling ability, mechanical properties are reduced, but also makes the casting mold stick, demold difficult. If the die temperature is too low, the cooling rate will be too fast, resulting in the formation of a cold layer on the surface of the die casting, the surface organization is fine crystal zone, high hardness, strength and elongation decreased, which is mainly due to the die casting in the solidification period, due to the rapid solidification of the surface, so that the alloy liquid can not be fed caused by micro porosity and porosity.
(2) Impact on dimensional accuracy: The castings of the same alloy of the same brand pressed on the same die are measured on site, and their dimensional accuracy is not exactly the same. This is due to the influence of die casting process parameters, and the most important influencing factor is mold temperature. The experiment proves that the die temperature is high, especially after a period of continuous die casting, the die casting size is large, the shrinkage rate is small, on the contrary, the die temperature is low, the die casting size is small, the shrinkage rate is large.
The mold temperature is high or low, so that the balance of the mold temperature field can not be formed, resulting in the change of shrinkage rate, which is the main reason for the size fluctuation of the casting. Therefore, to ensure the dimensional accuracy of the die casting and the inherent quality of the casting, it is necessary to bring the calculation of heat balance into the category of mold design.