Advantages of three types of Vacuum casting
Vacuum casting can use the process of ventilation casting mold, this process can rely on the air pressure to melt the metal into the casting mold, and then remove the air to form a vacuum. This casting method is generally used directly for small parts or jewelry with delicate details.
Vacuum casting is actually a physical modeling method. It can combine vacuum technology and sand mold casting. The cavity surface and back surface of the sand mold are sealed by a plastic film, and then a vacuum pump can be used to generate negative pressure to cause sand. The pressure difference between the inside and outside of the mold makes the mold sand tightly shaped. After placing the sand core, closing the mold, and casting, waiting for the casting to solidify, the negative pressure is released or the suction is stopped, and the mold sand will collapse to obtain the casting. According to the current application field, it can be generally divided into vacuum seal molding (V method) and solid vacuum casting (FV method). Its advantages are:
(1) Moderate vacuum, high compactness of casting cavity, and high quality.
(2) Vacuum casting generally needs to cooperate with the computer's mold flow analysis and simulation to predict the occurrence of casting defects. For the design of the mold making scheme, it can save time and improve related production efficiency.
Vacuum casting can be roughly divided into three types: vacuum suction casting, vacuum low pressure casting, and vacuum differential pressure casting:
That is, the casting mold is placed in a closed container, and then the air in the casting mold is drawn out, causing a certain negative pressure in the casting mold, causing the molten metal to be sucked into the cavity of the mold. When the inner runner of the casting is solidified, the negative pressure can be removed, so that the unsolidified molten metal in the vertical runner flows back into the molten pool. Its advantage is to improve the filling ability of the alloy liquid. The minimum wall thickness of the suction casting is generally up to 0.2mm, and the casting area is 300mm2, while reducing defects such as pores and slag inclusions. It is suitable for producing thin and fine small precision castings, especially steel castings.
2. Vacuum low pressure casting
Vacuum low-pressure casting method generally evacuates the mold during the pressure filling process. After the filling is completed, the pressure is maintained to make the casting crystallize and solidify under a constant pressure, and the casting is fully compensated, so the casting is dense and the mechanical properties are improved. This method is mostly used for precision casting of Al and Mg alloy castings.
3. Vacuum differential pressure casting
Vacuum differential pressure casting generally seals all the resistance holding furnace and the casting mold. Compressed air with a larger pressure such as 500kPa can be introduced into the sealing cover. At this time, because the pressure inside the casting mold and the crucible is equal, the metal liquid is not There will be a rise, so you can add 50kPa pressure to the liquid metal surface, and the liquid metal will rise to fill the mold cavity. It is especially suitable for the production of complex thin-wall castings, but the equipment is large and the operation is cumbersome. It is only used when there are special requirements.