Investment Casting Review

Investment Casting Review

Investment casting ( lost-wax process ) is utilized when complex detail, undercuts or non-machinable features and accurate parts are required. Investment castings typically require significant lead time, are best suited for low volume production rates. Investment casting tends to cost more than other production type casting processes

The first step in investment casting is to create a die or form of the part to the desired specifications. This die is used to inject paraffin wax, which is used to create the complex shapes required of the manufactured component or part. The die is attached to a central wax sprue. Multiple dies may be attached to the same sprue. The sprue is a channel which distributes the molten wax into each of the dies or forms.

The wax assembly is now dipped into a ceramic slurry, to obtain the shell thickness desired. A layer of fine sand (Zircon) is added on top of each ceramic layer. This process will be repeated until the desired shell or casting form is created.

After the shell / casting form is created, the wax is removed. This is where the term " lost-wax process " comes from. This leaves an impression or casting form which will create the desired investment casting part, which will be filled with the desired metal or material. Before beginning the casting , however, the shells must be heated up in a furnace so they don't fail due to the differential temperature introduced poring in the molten metal or material.

Next, the casting metal or material is poured into the pre-heated ceramic shell. The casting material fills each part and feature of the investment casting shell. The individual cast parts will be removed after the mold cools and the shell is removed. The shell is typically removed by water-blasting, though alternate methods are available. What remains is the investment cast parts, however they are still attached to the sprue assembly and each other. The individual parts are removed by cold-break (dipping in liquid nitrogen and breaking the parts off with hammer and chisel) or with alternative manufacturing machine tools.

The rough cast parts are now separated from each other and the investments casting sprue. First the gate, or the place where the part was connected to the sprue, must be removed. The gate is ground or manufactured off to end item part specifications.

Investment casting yields exceedingly fine quality products made of all types of metals. It has special applications in fabricating very high-temperature metals, especially those which cannot be cast in metal or plaster molds and those which are difficult to machine or work.