Question

Name a metal casting process that can be used to cast intricated jewellery products and describe major steps of the process with simple sketches

Answer 1

Investment casting

Investment casting is the best process for producing intricate details on jwellery on mass production.

“Investment” means “to cover completely” which refers to the coating of the refractory material around the wax pattern. This is a precision casting process. Using this we can make castings of high accuracy with intricate details.

There are mainly 6 steps in investment casting

1. Tooling

Tooling or pattern will be precision machined by CNC router. The casted shape is the replica of the pattern.

2. Wax Injection and Pattern Assembly

The wax pattern is obtained by injecting wax into the pattern. We will get a model with the same dimensions of desired products. Then, we will repeat the injection job for more wax patterns. Then assemble these wax patterns onto the sprue. Finally hang these pattern assemblies in the room temperature for drying.

3. Shell coating

In Shell coating, the pattern assembly will be dipped into a ceramic slurry and coated with a refractory material. Repeating this process several times until getting certain thickness and strength. Then, the ceramic shell is finished and then put it into atmospherically-controlled environment until be dried.

4. Dewax

Putting the shell in a steam autocalve and rapidly heated. So that the wax will be melt and run out through the gate and pouring up under high temperature.The ceramic shell molds must be fired to burn out the last traces of pattern material and to preheat the mold in preparation for casting.

That is why investment casting also called “lost wax casting”.

5. Casting or pouring

After dewax, we will melt the steel or aluminum ingots into liquid status. Then pour the liquid metal into the spruce. Then cool it under room temperature for a moment.

6. Shell removing

After Cooling,Break the ceramic shell and cut the individual investment castings from the sprue. Then remove the excess metal from casting body by grinding.

These are all the major steps. After these heat treatment and sand blasting is done.

Die Expendable pattern Expendable pattern assembly Shell moul. Casting