What is Vacuum Casting?

Vacuum casting is a process used for making precise prototypes and small batches of copies, widely used for previewing injection-molded products. The commonly used plastic materials for vacuum casting are PP and PA. The color selection and flexibility of strength of the formed parts are high, which is very suitable for product designers to customize product prototypes.

Vacuum casting, also known as vacuum-assisted casting, is an ideal process for producing precise prototypes and small batches of replicated products, making it highly valuable for previewing injection-molded products. Utilizing commonly used plastic materials such as PP and PA, vacuum casting enables product designers to customize prototypes with a wide range of color options and achieve a desirable balance between flexibility and strength in the formed parts.

Vacuum casting is generally divided into two forms: vacuum suction casting and vacuum pressure casting. The range of application materials for vacuum casting is also very wide, but there are many requirements for the material used in mold making.

Introduction of Vacuum Suction Casting

Vacuum suction casting is a casting method in which a casting mold runner (or a riser) is inserted into the molten metal, and then the casting mold is vacuumed to make the cavity of the casting mold negative pressure. Under the negative pressure, the molten metal rises along the runner (or riser), fills the casting mold, solidifies and forms a casting. The advantages of vacuum suction casting are as follows:

• Vacuum suction casting is beneficial for the exclusion of gas in the casting mold, and the suppression of turbulence and entrapment, overcoming the drawbacks of low-pressure casting and differential pressure casting, and significantly improving the filling capacity of the molten metal.

• Due to the improvement of filling capacity during vacuum suction casting, the pouring temperature of the molten metal can be 20-30℃ lower than that in gravity casting.

• Thick and thin-walled castings with high quality requirements can be cast.

• By selecting the appropriate vacuum degree change rate and controlling the speed at which the molten metal enters the mold cavity, a smooth filling effect can be obtained.
  

Introduction of Vacuum Low-pressure Casting

Vacuum low-pressure casting is a method of vacuuming the mold during pressurized filling, and after filling, pressure is maintained to allow the casting to crystallize and solidify under constant pressure. The casting is fully supplemented with shrinkage, so the casting structure is dense and the mechanical properties are improved. This method is mostly used for precision casting of Al and Mg alloy castings. The advantages are as follows:

As a leading vacuum casting supplier, our vacuum low-pressure casting method involves the application of pressure and vacuum during the filling and solidification process. This technique ensures a dense casting structure, improved mechanical properties, and effectively addresses shrinkage issues, making it highly suitable for precision casting of aluminum (Al) and magnesium (Mg) alloy castings. The advantages are as follows:

• The existence of vacuum negative pressure can compact the mold sand and increase the strength of the casting mold.

• By moderately increasing the vacuum degree, the filling time is shortened, and the filling speed is not only accelerated but also stable.
  

• Vacuum low-pressure casting can accelerate the flow of aluminum alloy at low temperatures, prevent the aluminum alloy from absorbing gas caused by high-temperature casting, and increase the pinhole defects of the casting.
  

• The casting has good formability, which is conducive to forming castings with clear contours, smooth surfaces, and large thin-walled castings.
  

• The casting structure is dense and the mechanical properties are high.
  

• Generally, no riser is needed, which greatly improves the yield of the molten metal product, usually up to 90%.
  

• The working environment is good, the equipment is simple, and it is conducive to mechanization and automation.
  

Introduction of Vacuum Differential Pressure Casting

Vacuum differential pressure casting mainly seals the resistance furnace and the casting mold, and introduces compressed air with a pressure of 500kPa into the sealing hood. At this time, because the pressure inside the casting mold is equal to that inside the crucible, the molten metal will not rise. Then, 50kPa pressure is added to the surface of the molten metal, and the molten metal will rise and fill the mold cavity. It is particularly suitable for the production of complex thin-walled castings, but the equipment is relatively large, and the operation is complicated and should only be used when there are special requirements. The advantages are as follows:

• Compared with traditional gravity casting and vacuum suction casting, vacuum differential pressure casting has demonstrated good filling capacity on a 1mm thin test piece.

• The casting has a relatively dense crystalline structure and mechanical properties. In terms of casting strength performance, it is about 20% to 25% higher than that of vacuum suction casting and gravity casting, and the elongation is about 50% higher.
  

• Vacuum pressure casting can effectively reduce the pores in die casting and increase the density of the casting by more than 1%.