Today i will be discussing on the working principles Investment casting process. Previously an article was published on evaporative casting.
Steps of investment casting process
The first step of this process is to create a wax pattern; it is typically done by injecting wax into a metal tool or die. Due to the evolution of additive patterns manufacturing, it can also be printed. In art world, artist carve out pieces of pattern from wax block. Finally, in a situation where multiple casting is needed, a silicon tool is made from artist’s sculpture and wax is poured and injected to the resulting cavity.
Second step is the assembling of wax in a tree form; it is typically uneconomical to produce small parts one at a time. Assembling is carryout by attaching wax pattern to a part called “wax sprue”.
Sprue provides a mounting surface to assemble patterns into a single mold. It also provides a flow path for molten alloy into the void created by wax pattern. The wax between the pattern and sprue is called “gates”. Because it throttles the direction and flow of alloy into voids created by pattern.
Third step is building of shell. It is achieved by dipping wax tree into a ceramic shell. It eventually become the mold in which alloy will be poured into. After dipping the wax tree into a ceramic bath or slurry, fine sand or stucco is applied to the wet surface. This process is carried out twice or until a layer of ceramic mold is formed on the wax pattern. The layer must be capable of undergoing stresses of the casting process. Next stage is performed after the mold dries.
The next step is known as dewaxing or burnout. It is carried out before pouring the molten metal into the mold. helping in removing the wax pattern leaving the shape in the ceramic shell. It is typically achieved by using a stream-dewax autoclave to melt out the wax. Autoclave is a large industrial pressure cooker.
Another method is by using flash fire oven to melt and burn off the wax. These two dewaxing methods are used in most foundries because they offer advantage of choices; The autoclave method removes majority of wax, which can be reconditioned and reused. Whilst, flash fire burns off residual wax and cures the shell, prepare it for casting.
The final step is pouring the liquid metal. This is done after the ceramic mold or shell is preheated to a specific temperature. it helps to prevent the alloy from solidifying before the entire mold is filled. The metal is melted in a crucible cup by induction melting. Induction melting is a high frequency electric current, creating a magnetic field around the alloy and generating electric field inside the metal (eddy current). Eddy current heat the alloy due to the materials electrical resistance.
After the alloys is heated to specific temperature, it is poured into the ceramic mold, then the mold is allowed to cool.
- Heat Treatment of non ferrous metals
- Process of Heat treatment of ferrous metals
- The 3 Stages of Heat Treatment Process
- 4 Different Types of Metal Casting Process
And that is it for this article, working principles of investment casting. I hope you enjoy reading. Freely ask questions and don’t forget to share. Thank for reading!