Metal Liquid Forming Process – Investment Casting (Lost-Wax/Precision)

Investment casting is a special type of casting, also known as lost-wax casting. Because investment casting produces castings with high dimensional accuracy and good surface quality, it is also called precision casting. The process flow diagram of investment casting is as follows:

  ① Making Wax Models: The wax model material is generally made of 50% paraffin wax and 50% stearic acid. The wax paste at 45-48℃ is cooled and solidified, and the resulting mold shape is the wax model. Multiple wax models are usually welded together onto a wax rod to form a wax model assembly, allowing for the production of multiple castings at once. See a-d in the diagram above.

  ② Manufacturing the Shell: The assembled wax model assembly is placed in a coating made of water glass and quartz powder. After removal, its surface is coated with a layer of coating, and then a layer of finely granulated silica sand is sprinkled on the surface. It is then immersed in a saturated ammonium chloride aqueous solution for hardening treatment. Repeating these steps creates a hardened mold consisting of 4-10 layers of refractory material on the surface of the wax model, typically 5-7 mm thick. See diagram e above.

  ③ Dewaxing: Place the prepared mold shell in hot water (80-90℃). The wax model melts within the shell and flows out through its gating system, forming a hollow cavity mold shell. See diagram f above.

  ④ Pouring: Dry the mold shell in a baking furnace, remove it, and place it in dry sand. While the shell is still hot, immediately pour the molten alloy into it and wait for it to cool and solidify. See diagrams g-h above.

  ⑤ Shell Removal and Cleaning: Remove the shell manually or mechanically, cut off the risers and gating system, and clean the mold to obtain the individual casting. Investment casting characteristics: High dimensional accuracy, good surface quality, ability to produce castings with complex shapes, virtually unlimited alloy types, and suitability for both mass and small-batch production. However, its processes are complex, production cycles are long, and production costs are high. Investment casting is mainly used to produce turbine and gas engine blades, pump impellers, and parts for various vehicles (airplanes, automobiles, tractors, etc.) and machine tools. The Rolls-Royce Spirit of Ecstasy hood ornament is produced using investment casting.

 The effects of investment casting are as follows: