Investment Casting

Investment casting can produce very intricate and complex forms such as: turbocharger impeller wheels, turbine blades, and aircraft components, etc. and produces a net shape (closest to the finished product). Investment casting is usually used to manufacture hard to machine parts that have complex and difficult to reach areas. This type of casting can be done on metals that can’t be machined or fabricated by other processes. Compared to other casting processes, investment casting is much more expensive.

Intricate patterns can be made on the piece of metal in investment casting as it will be a single component, not two parts that will be placed back together. Because of this, investment casting is ideal for making complicated shapes, as well as jewelry making.

In investment casting, the pattern and the mold that are used are both consumed and a fresh set has to be made for every new component. The pattern is made by injecting wax or another material into a master mold and the assembly is then placed in a flask or container.

When you perform investment casting you need to make a mold of the pattern, generally out of wax, so it can melt away. If you are casting several pieces, the patterns are attached to a central wax stick (sprue) to form an assembly. The assembly is then dipped into a liquid ceramic substance that coats the pattern and forms a type of thin film. The object is then dipped into very fine sand until the film of skin thickens and creates a shell. The shell dries and the wax is melted out from inside in an oven, which leaves a negative impression in the shell. The mold is then heated to approximately 1800 degrees F, to remove any wax residues. This also makes sure that the molten metal completely fills the mold. The mold is filled with molten metal by pouring it through the sprue. When the metal cools down and hardens the sprue and the patterns become one solid piece. The ceramic is knocked off of the cooled metal and sections are cut from the sprue with a friction saw.

The casting process can be run on a variety of metals such as aluminum, stellite, bronze alloys, hastealloys, tool steels, stainless steel, precious metals and other types of alloys, etc. The castings may vary in weight from just a few grams to many pounds. When you are performing investment casting you need to leave suitable shrinking allowances.

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