Vacuum seal modelling technology formed from the 1970 years, by the year 1980 was born vacuum casting technology, the technology can be used in the production of shape is very complicated, thickness of very thin castings, castings without porosity and shrinkage phenomenon, which is more advanced and very promising technology, in the field of aviation, cooperate to use computer technology to support simulation, estimate the defects in casting production, can greatly save time, reduce the production cost, improve the production efficiency of the casting.
1， the vacuum molding
Vacuum molding is a kind of physical modeling method, which combines vacuum technology and sand mold casting, by plastic film will sand mold cavity surface and sealed on the back, with the aid of vacuum pump, vacuum pump commonly usedrotary vane vacuum pumps, water ring vacuum pump suction to produce negative pressure, caused by sand mould sand fastening with internal and external pressure forming, under the core, box, casting, casting solidification, remove or stop the smoke gas, negative pressure casting sand then to pieces.According to the present the main areas of application can be divided into the vacuum seal modelling method (V) and firm type vacuum casting method (FV).Of vacuum modelling research at home and abroad mainly focus on the following aspects.
2， the influence of the vacuum degree of cavity tight
In terms of modelling study found:
High vacuum and high compactness mold, casting quality is high.But when the vacuity is too high, the modelling material of compactness is big, the casting is easy to appear crack;Liquid metal and the coating layer is often smoked the acupuncture and adhering sand on the surface of the casting defects.
Vacuum through low, will reduce the mould compactness.At the same time also reduce the exhaust efficiency, the carburization and porosity caused by casting defects.
Research showed that the root cause of the collapse when molten iron filling, because the flow front air gap, internal and external vacuum fell sharply, at the same time the stress out of balance, causing dry sand to the air gap flow, lead to collapse.And mechanics formula is established.With the size of the vacuum casting, wall thickness and the weight of the casting alloy and molding materials category.In addition, as well as vacuum degree, swept volume is also a research focus.In different stages of the same mold, the swept volume, while pouring the swept volume is the largest.Election of water ring vacuum pump, vacuum degree is appropriate in 0.080 ~ 0.025 MPa.In general, the small or thin wall castings under 100 kg vacuum degree can be controlled in 0.050 ~ 0.025 MPa, thick wall or medium sized castings control in 0.060 ~ 0.045 MPa