Vacuum casting is one of the three main casting methods, which can be used to pull the material into the mold. Vacuum casting has many advantages, many of which make it very suitable for ferrous and nonferrous metals. This process usually includes drawing molten metal into the mold, which can reduce turbulence and prevent floating slag and other impurities from entering the final casting. Vacuum casting is usually associated with a common change in sand casting and can also be used with elastomers. Another name of workers ' vacuum casting is anti-gravity filling, because it usually involves pulling a material upward into the mold, rather than pouring from the top. Since the material is not poured or forced into by air pressure, there is usually little turbulence related to this method. This makes the gate mechanism simpler than other types of castings, which may reduce overall costs. A simple gate mechanism can also improve the efficiency of the method because fewer metals tend to solidify on it. This may lead to 50 % or more efficiency increase. The final quality of the workpiece may also be higher, as lower turbulence can lead to free float of the slag at the top of the container. Since the molten material is extracted from the bottom of the pool surface, the slag is usually left. Sand mold vacuum casting is a variant of forming plastic mold by vacuum, which is usually used with various metals. A thin plastic is usually placed on the mold, and then the sand is sucked into the mold by vacuum. Sand contacts the plastic sheath rather than the mold itself, but presents the shape of the mold. The molten metal will then contact with the sand. On this point, it will show the mold shape when the vacuum is removed.
Vacuum modeling is a physical modeling method, which combines vacuum technology with sand mold casting. The cavity surface and back surface of the sand mold are sealed by plastic film, and the negative pressure is generated by vacuum pump suction, resulting in the pressure difference between the inside and outside of the sand mold to make the sand mold firmly formed. After placing the sand core, closing the mold, casting, and waiting for the solidification of the casting, the negative pressure is lifted or the suction is stopped, and the sand mold will collapse to obtain the casting. According to the current application fields, it can be divided into vacuum sealing modeling (V method) and solid vacuum casting (FV method).
It’s advantages are:
Vacuum casting can be roughly divided into vacuum suction casting, vacuum low-pressure casting and vacuum differential pressure casting:
The mold is placed in a closed container, and the air in the mold is extracted, which causes a certain negative pressure in the mold and causes the metal liquid to inhale the mold cavity. When the internal runner of the casting is solidified, the negative pressure is removed, and the unsolidified metal liquid in the vertical runner flows back to the molten pool. Its advantage is that the filling ability of alloy liquid is improved, the minimum wall thickness of suction casting can reach 0.2 mm, the casting area is 300 mm², and the defects such as porosity and slag inclusion are reduced. It is suitable for producing thin and fine small precision castings, especially steel castings (including stainless steel).
Its advantages are:
The vacuum low-pressure casting method is to vacuum the casting mold in the process of pressure filling. After the filling, the pressure is kept to make the casting crystallize and solidify under constant pressure, and the casting is fully filled and contracted, so the casting structure is dense and the mechanical properties are improved. This method is mostly used for precision casting of Al, Mg alloy castings.
Its advantages are as follows :
Vacuum differential pressure casting mainly seals the resistance heat preservation furnace and the casting mold, and injects compressed air with high pressure, such as 500 kPa, into the sealing cover. At this time, because the pressure inside the casting mold and the crucible is equal, the metal liquid will not rise. Then, 50kPa pressure is added to the metal liquid surface, and the metal liquid will rise to fill the mold hole. Especially suitable for the production of complex thin-walled castings, but the equipment is large, troublesome operation, only when special requirements are applied.
Its advantages are as follows :
