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Investment Casting

Investment CastingWhat, exactly, is “Investment Casting”?

Investment casting is an industrial process based on and also called lost-wax casting, one of the oldest known metal-forming techniques.From 5,000 years ago, when beeswax formed the pattern, to today’s high-technology waxes, refractory materials and specialist alloys, the castings allow the production of components with accuracy, repeatability, versatility and integrity in a variety of metals and high-performance alloys.

Investment casting is generally used for small castings, but has been used to produce steel castings of over 600 pounds and aluminum castings up to 60 pounds. It is generally more expensive per unit than die casting or sand casting, but has lower equipment costs. It can produce complicated shapes that would be difficult or impossible with die casting, yet like that process, it requires little surface finishing and only minor machining.

Investment casting is not a recent technology, having been used as early as 1,800 B.C. and beyond to produce beautiful bronze works of art. Yet this method of casting fine ferrous and non-ferrous components is even more useful today than in the ancient times. Why? Because it can still do so many things so much better than many alternatives.

The process involves a number of intricate steps resulting in components which feature considerable design flexibility and economy. The method competes to some degree with machining, forging, die casting and other processes, but is the only means which combines many of the benefits into one. It can, for example, produce a part which previously required several steps, several parts, and was not as strong nor as cost efficient as the investment casting. The net shapes made possible frequently require only minimal finishing.

Advantages

There are many reasons engineers and purchasing agents specify investment castings for their projects.
Here are just a few:

  • Cost Savings of Investment Casting
    • Reduce the cost of close-tolerance or fine finish parts.
    • Net shape eliminates or minimizes machining.
    • Multiple part assembly.
    • Lower tooling costs.
    • Saves on material waste.
  • Quality and Design Flexibility of Investing Casting
    • Design intricate configurations as one piece castings.
    • Infinite alloy choices, thin walls, internal cores, better finishes.
    • Upgrade properties, increase strength to weight ratio, achieve consistency.

The Investment Casting Process

The following steps are used in the production of investment castings,

Wax Injection

Investment Casting Wax Injection

The process of investment casting begins with production of a heat disposable pattern. This pattern is usually made by injecting molten wax or plastic into a metal die or mold.

Pattern Assembly

Investment Casting Pattern Assembly

The wax patterns are attached by the gate to a central wax runner system. The runner system is called a sprue. Patterns, runners, and pouring cup comprise the cluster or tree.

Shell Building

Investment Casting Shell Building

The shell building technique involves dipping the assembly into a ceramic slurry and then into a bed of extremely fine sand. After drying, the process is repeated. Up to some layers may be applied in this manner.

Dewax Operation

Investment Casting Dewax Operation

The completed shell is placed in a steam autoclave where the pattern melts and runs out through the gates and pouring cup.

Firing the Shell Mold – Preheat

Investment Casting Firing the Shell Mold – Preheat

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, usually in the range of 1600-2000 degrees Fahrenheit.

Casting

Investment Casting

The preheated shell is filled with molten metal by gravity pouring. As the metal cools, the parts, gates, sprue, and pouring cup become one solid casting.

Shell Removal – Knockout

Investment Casting Shell Removal – Knockout

After the metal solidifies and cools, the ceramic shell is then removed by vibratory methods or water blasting. Casting Removal – Cut Off Individual casting are removed from the cluster by friction sawing or by means of a cut off wheel.

Finishing Operation – Gate Grinding

Investment Casting Finishing Operation – Gate Grinding

Remaining gate protrusions are removed by belt grinding.

Completed Casting

Meenaakshe_Investment_Mold Completed Casting

The finished parts are now ready for heat treating and shipping to customer.