Vacuum casting is a process in which a naturally ventilated casting mold is applied. The molten metal material is injected into the mold by gas pressure and the gas is subsequently removed to create a vacuum. This type of casting is mainly used for small parts or jewelry that have delicate critical points.
Vacuum mold making is a kind of physics mold making method, which fuses vacuum technicality with sand mold casting, relying on plastic film to seal up the mold cavity surface and the reverse side of the sand mold, relying on the vacuum pump to pump vacuum to vacuum casting cause negative pressure, resulting in the pressure difference inside and outside the sand mold to tighten the mold sand into shape, after placing the sand core, locking the mold, casting, waiting for the casting to condense, eliminating the negative pressure or terminating the vacuum pumping, the mold sand will get the casting with the depression and tranquilization particles. According to the key aspects used at this stage can be divided into vacuum sealed mold making (V method) and solid vacuum casting (FV method). Its characteristics are:
(1) appropriate vacuum, mold cavity tightness increased, the casting quality is also high.
(2) Vacuum casting with each other with electronic computer simulation of mold flow analysis, can predict and analyze the casting shortcomings caused by the design plan for the mold making scheme, can significantly save time and effort, and improve productivity.
Vacuum casting can be roughly divided into vacuum suction casting, vacuum low voltage casting, vacuum gas pressure casting three:
1、Vacuum suction casting
The casting mold is placed in a closed glass container, and the gas is pumped out of the mold to cause a certain negative pressure in the mold, which causes the metal material to be sucked into the mold cavity. When the inner sprue of the casting is condensed, the negative pressure is removed and the uncondensed metal material flow in the vertical sprue is made to return to the fusion. Its characteristic is to enhance the working ability of aluminum alloy liquid filling, the minimum wall thickness of the casting can reach O.2mm, and the total area of the casting is 300mm2, and at the same time to reduce the shortcomings such as air hole and welding tumor. Suitable for the production of thin and detailed small and medium-sized high-precision castings, cast steel parts (including stainless steel plate) parts are particularly suitable. Its characteristics are:
(1) vacuum suction casting is beneficial to the removal of air in the mold, suppressing the vortex and roll gas caused by the low voltage casting and gas pressure casting shortcomings, so that the metal material liquid filling work capacity is significantly enhanced.
(2) Because of the enhancement of the working ability of filling in vacuum suction casting, the casting temperature of the metal material liquid can be 20~30℃ lower than that in action casting.
(3)Casting with large wall thickness distance, thick wall and high quality standard can be cast.
(4) By picking the appropriate vacuum degree elasticity coefficient and manipulating the rate of metal material liquid into the mold cavity, the actual effect of stable filling can be obtained.
2、Vacuum low voltage casting
Vacuum low voltage casting method is in the process of filling pressure filling mold vacuum, filling the mold after the test pressure so that the castings in a stable working pressure crystal condensation, castings get enough metal type casting, so the casting body high density, physical properties to enhance. This method is mostly used for high precision casting of Al and Mg aluminum alloy castings. Its characteristics are shown below:
(1) The vacuum negative pressure can make the mold sand to obtain the tightness and expand the compressive strength of the mold.
(2) Appropriate increase in vacuum level, so that the filling time is shortened, not only the filling rate is accelerated and stable.
(3)Vacuum low voltage casting can accelerate the flow of aluminum alloy profile at lower temperature and prevent the breathing condition of aluminum alloy profile caused by high temperature casting, which enlarges the disadvantage of pinhole of casting.
(4)Good casting formability is beneficial to produce castings with clear corridors and smooth surfaces and large and medium-sized thick-walled castings.
(5) Casting body high density, high physical properties.
(6)Generally, no riser is used in the case, so that the qualification rate of the metal material liquid is further improved, usually up to 90%.
(7) good office environment, simple machinery and equipment, conducive to mechanical automation and automation technology.
3、Vacuum gas pressure casting
Vacuum gas pressure casting, the key is the resistor holding furnace and casting mold all carry out sealed, in the sealed cover into the working pressure is relatively large such as 500kPa air compression, this time because the mold and crucible internal structure of the same working pressure, the metal material liquid is not easy to rise, and then fill in the metal material liquid level 50kPa working pressure, the metal material liquid will rise to fill the mold cavity. It is especially suitable for the production of complicated thick-walled castings, but the machine and equipment are huge and the actual operation is inconvenient, so it is used only when there are special requirements. Its characteristics are as follows:
(1) Compared with the traditional force casting and vacuum suction casting, vacuum gas pressure casting shows very good filling capacity on 1mm thick sheet specimens.
(2) The casting has a higher density of crystalline mechanism and physical properties, and the compressive strength characteristics of the casting are about 20% to 25% higher than vacuum suction casting and action casting, and the tensile strength is about 50% higher.
(3) Vacuum aluminum die-casting can effectively reduce the air outlet of die-castings and improve the relative density of castings by more than 1%.