As a very important step of PCB manufacturing, vacuum casting is one of the three main casting methods. And it can be used to pull the material into the mold. There are many advantages vacuum casting, 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.
In this passage we will lead you to the detailed information of vacuum casting and if you are curious about the topic, please follow us and read the content below for more professional knowledge.
What are the advantages of vacuum casting?
Moderate vacuum degree, high cavity tightness and high casting quality
Vacuum casting combined with computer simulation of mold flow analysis can predict the generation of casting defects. The design of modeling scheme can greatly save time and improve production efficiency.
Vacuum casting can be roughly divided into vacuum suction casting, vacuum low-pressure casting and vacuum differential pressure casting:
1.Vacuum suction 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:
Vacuum suction casting is conducive to the elimination of gas in the casting mold, inhibiting the generation of turbulent flow and gas entrapment, overcoming the disadvantages of low-pressure casting and differential pressure casting, and significantly improving the filling ability of metal liquid.
Due to the improvement of filling ability in vacuum suction casting, the casting temperature of metal liquid can be 20 ~ 30 °C lower than that of gravity casting.
Castable castings with large wall thickness difference, thin wall and high-quality requirements.
Stable filling effect can be obtained by selecting the appropriate change rate of vacuum degree and controlling the speed of metal liquid entering the cavity.
2.Vacuum low pressure casting
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 :
The existence of vacuum negative pressure can make the mold sand tight and increase the strength of the mold.
Appropriately increase the vacuum degree to shorten the filling time, not only the filling speed is accelerated but also stable.
Vacuum low pressure casting can accelerate the flow of aluminum alloy at low temperature, avoid the phenomenon of aluminum alloy suction caused by high temperature casting, and increase the pinhole defects of the casting.
The casting has good form-ability, which is conducive to the formation of clear outline, smooth surface castings and large thin-walled castings.
The casting has dense structure and high mechanical properties.
In general, no riser is needed, so that the yield of metal liquid is greatly improved, usually up to 90 %.
3. Vacuum differential pressure casting
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 :
Compared with the traditional gravity casting and vacuum suction casting, vacuum differential pressure casting has a good filling ability on the thin sheet sample of 1mm thickness.
The casting has relatively dense crystal structure and mechanical properties. Compared with vacuum suction casting and gravity casting, the strength performance of the casting increases by about 20 %–25 %, and the elongation increases by about 50 %.