Technological principle of vacuum precision casting in dalian

The process principle of vacuum precision casting is to put the investment shell mold in the sealing chamber, the sealing chamber drops, the sprue is immersed in liquid metal, and then start the vacuum pump to vacuum the sealing chamber, and the liquid is cast at the same time. After the castings in the shell of Dalian precision casting mold solidify, the vacuum state is relieved, and the residual metal liquid in the runner returns to the furnace, and the vacuum casting castings are obtained through sand cleaning. According to the difference of pressure difference established by vacuum casting process, vacuum precision casting can be divided into direct casting method and special vacuum method:

1、 Direct casting

Taking CLA method as an example, firstly, the mold shell made by common investment casting technology is placed in the sealing chamber, the sealing chamber descends, and the sprue is inserted with liquid metal. Start the vacuum pump to pump the seal chamber into vacuum and fill the mold with liquid metal at the same time. After the metal liquid in the mold shell solidifies, the sealing chamber is connected to the atmosphere to eliminate the vacuum, and the liquid metal that has not solidified in the runner flows back to the crucible. Then take out the mold shell and sand it to get the casting. In addition to the CLA method, there is also the tilting inversion method of vacuum precision casting, that is, after the mold filling is completed, the mold is inverted, and the remaining metal liquid in the sprue provides feeding for the solidification of the casting. This method is easy to realize continuous production and has high production efficiency.

2、 Special vacuum casting

This kind of vacuum precision casting method is mainly based on the casting process requirements or alloy types, and some special operations are added in the casting process. For example, to enhance the feeding capacity of vacuum precision casting. Vacuum the upper sealing chamber after completion; After the metal liquid fills the mold cavity, the lower seal chamber is then filled with compressed gas to increase the pressure difference between the upper and lower seal chambers, thus enhancing the feeding capacity of the metal liquid during the casting crystallization and solidification. There is also vacuum precision casting under the protection of inert gas. This method is mainly used to produce superalloys and easily oxidized alloys by vacuum melting and casting (also known as CLV method). This method is to melt the metal under vacuum, inject inert gas into the vacuum melting chamber and casting chamber at the same time, and keep them at the same pressure. Insert the shell runner or riser into the liquid metal, and then reduce the pressure of the casting chamber for casting. After holding for a certain time, the liquid metal in the sprue flows back to the crucible after pressure relief.

Working principle of vacuum suction casting for formed castings 1 - vacuum chamber; 2 - Pipeline; 3 - Solenoid valve; 4 - Throttle valve; 5 - Vacuum tank; 6 - Electric contact vacuum gauge; 7 - Vacuum pump; 8-liter liquid pipe; 9 - Liquid metal

Vacuum precision casting process features: (1) high yield, good casting quality, stable filling of molten metal, less oxidation slag inclusion and splash, reduced porosity, slag inclusion and other defects of castings, and improved yield. In addition, a lower pouring temperature can be used for pouring, which can refine the grains of castings and improve the mechanical properties. (2) Good filling performance. In investment casting, the back pressure in the mold cavity is small and the filling speed is adjustable, so the filling ability is strong, and the thin part of the casting can reach 0.3mm. (3) The utilization rate of molten metal and the yield rate of the process are improved. (4) Simplify process and reduce cost. (5) It is easy to realize mechanization and has high labor productivity. Compared with the common investment casting process, each module can assemble more wax molds, which can generally increase the output by 85%~135%.

Vacuum precision casting is applicable to investment mold, ceramic mold, shell mold, gypsum mold, graphite mold and sand mold casting. It can be used to produce complex thin-walled castings with an average wall thickness of less than 5mm, such as aluminum alloy, magnesium alloy, titanium alloy, stainless steel and high-temperature heat-resistant alloy, and castings with a single casting weight of less than 100kg.