Steps in Investment Casting Process | Advantages and Disadvantages
Investment Casting Process
The investment casting process, which is commonly referred to as the “lost wax method”, originated in and around the fourth millennium B.C. It is evidenced through the architectural works found in the form of idols, pectorals and jewelry in remains of the ancient Egypt and Mesopotamia. The investment casting process initiates with the production of wax replicas or patterns of the required shape of castings. Each and every casting requires a pattern to be produced. Wax or polystyrene is made used as the injecting material. The assembly of large number of patterns are made and attached to a wax sprue centrally. Metallic dies are used to prepare the patterns. The pattern is immersed in refractory slurry which completely surrounds it and gets set at room temperature forming the mold.
The mold is further heated, so that the pattern melts and flows out, leaving the required cavity behind. After heating, the mold gets further hardened and molten metal is poured while it is still hot. After the casting gets solidified, the mold is broken and it is taken out.
Step Involved In Investment Casting :
The basic steps of the investment casting process are as shown in figure:
1. Preparing the heat-disposable wax, plastic or polystyrene patterns in a die.
2. Assembly of the prepared patterns onto a gating system
3. “Investing,” (covering) the pattern assembly with a refractory slurry which builds the shell.
4. Melting the pattern assembly (burning out the wax) by firing, for removing the traces of the pattern material
5. The metal in molten state is poured into the formed mold.
6. Once the metal solidifies, the shell is removed (knocked out).
7. Fettling (cutting off) of the pouring basin and gates followed by finishing operations to get the desired dimensional tolerances and finish.
|Step Of The Investment Casting Process|
Advantages of investment casting
1. Many Intricate forms with undercuts can be cast.
2. A very smooth surface is obtained with no parting line.
3. Dimensional accuracy is good.
4. Certain unmachinable parts can be cast to preplanned shape.
5. It may be used to replace die casting where short runs are involved.
6. Excellent surface finish
7.Almost any metal can be cast
Disadvantages of investment casting
1. This process is expensive, is usually limited to small casting, and presents some difficulties where cores are involved.
2. Holes cannot be smaller than 1/16 in. (1.6 mm) and should be no deeper than about 1.5 times the diameter.
3. investment castings require very long production cycle times versus other casting processes.
4. This process is practically infeasible for high volume manufacturing, due to its high cost and long cycle times.
5. Many of the advantages of the investment casting process can be achieved through other casting techniques if principles of thermal design and control are applied appropriately to existing processes that do not involve the shortcomings of investment castings.
6.It can be difficult to cast objects requiring cores.