Many process parameters can affect the quality of lost foam castings. The process parameters ofmainly studied in this paper include liquid metal pouring temperature and negative pressure. As for other parameters that can be selected from the relevant empirical values, their influence on the simulation process of lost foam casting will not be considered in this subject.
(1) Pouring temperature
lost foam casting is different from. Generally, the pouring temperature of lost foam casting is higher than that of sand casting. This is due to the reaction between metal liquid and foam pattern in the process of lost foam casting, and the endothermic reaction, which will reduce the fluidity of molten metal, so the pouring temperature of lost foam casting is higher than that of sand casting. According to experience, the casting temperature of lost foam casting is generally higher than that of sand casting casting at 30~50 C, so that the temperature can be raised due to the endothermic reaction with the foam pattern.
|Pouring temperature (℃)
|Cast aluminum parts
|Cast copper parts
Because the pouring temperature has a very important impact on the quality of castings, defects such as insufficient pouring, cold shut and wrinkle will occur when the pouring temperature is too low, and sand sticking defects will occur when the liquid metal temperature is too high. Therefore, reasonable pouring temperature has an important influence on castings. Generally, the pouring temperature of gray cast iron is 1360 ℃ ~ 1450 ℃.
(2) Negative pressure
Negative compaction is essential in lost foam. It can not only compact the sand mold, but also facilitate the discharge of various gases in the mold. The structure of coating, foam pattern and casting material are all related to the holding time of negative pressure and the magnitude of negative pressure. For coatings with small coating thickness, generally less than 1mm and good air permeability, the selection range of negative pressure is generally 0.04 ~ 0.06mpa. The selection of negative pressure is also different for different casting materials. The selection range of negative pressure for aluminum castings is 0.02 ~ 0.03mpa. Generally, if the foam shape is complex and more, the holding time of negative pressure can be extended a little longer. For those with poor air permeability and large coating thickness, the holding time of negative pressure should also be extended.