Investment Casting
1. From sample or drawing, we use CAD to ease the tooling or pattern design.
2. Example of tooling for investment casting process: It is machined from Aluminum alloy with cavity shape as a negative of the part.
3. Special wax is injected into the cavity to make a pattern. The pattern is cooled in the tooling to stable form. The pattern is removed from the tooling.
4. The pattern is touched up, such as removing unnecessary flash, or mounting some wax pieces to form more complex part.
5. All finished pattern must be inspected according to requirement, guarantee that no any defective parts happen during following process.
6. The pattern (one or more) are attached to a central sprue. The sprue, gates and runners form the channels where metal will flow which is often called a "tree".
7. 7-1 to 7-3 The pattern tree is dipped into a ceramic slurry and then into an air fluidized bed of ceramic sand. This is repeated to form a thin self supporting ceramic "shell".
8. After controlled drying , the ceramic shell is heated in a steam autoclave to melt out the pattern wax.
9. The shell mold is then fired to strengthen it and burn out any remaining pattern material. Also the shell mold is preheated to protect the mold shock during pouring because of too much gradient temperature.
10. In the meantime, the molten metal is prepared by induction furnace. The spectrometer is used to confirm that the chemical composition is conformed to standard. The result will be recorded for future reference (in case necessary).
11. 11-1 to 11-3 The molten metal is poured into the preheated mold, producing a metal duplicate of the original pattern.
12. After the metal has solidified and cooled, the ceramic mold material is mechanically removed, leaving the tree of cast metal parts.
13. 13-1 to 13-4 The individual castings are cut from the tree. Feed gate stubs are ground off, and the castings are cleaned by shot blasting or sand blasting.
14. Quality Assurance:
14-1 Dimensional inspection
14-2 Hardness testing
14-3 Microscope for identify microstructure of the metal.