The purpose of this introduction to metalcasting is to provide a brief history and overview of the casting process as well as a brief outline of commonly used casting techniques. This article provides new manufacturers with a better understanding of how metalcasting works and what steps are involved in producing cast products. It is hoped that the reader will come away from this article with a clear understanding of the opportunities presented by metalcasting, as well as an appreciation of its potential as a modern manufacturing technique.
What Is Metalcasting?
The word metalcasting refers to the process of forming a product or part from molten metal, using any type of mold to govern its final shape. On the other hand, a metal casting is a product or part formed using a metal casting process. We use the word casting interchangeably throughout this article as well as elsewhere on our website as either a synonym for the process of metalcasting or a synonym for the object itself.
General Steps of Metalcasting
1. Create the master pattern and corebox.The first step in metalcasting is to create an object with a similar shape to that of the desired product, known as a pattern. The pattern is a tool used to produce the mold, and should be slightly larger than the final product to account for shrinkage during solidification. A pattern is generally produced by CNC machining in metalcasting, while cores are produced by another type of tooling: coreboxes, as described in Step 2. It should be noted that casting methods that use reusable molds, such as permanent mold casting, generally do not require patterns or coreboxes to be produced. The mold and core are produced directly by the toolmaker in these cases.
2. Create the mold and core. A successful casting can only be produced by creating a mold cavity that contains and forms molten metal. In many cases, they are also required to produce a core that fits inside the mold, resulting in hollow cavities within the final product. The mold or core can be reusable, as in die casting or permanent molding, or it can be single-use, as in shell mold casting or greensand casting.
3. Melt the alloy. The next step is for the manufacturer to melt the metal. Many times the metal used is an alloy, or a combination of elements that provide optimal mechanical characteristics when combined. In its simplest form, melting involves placing alloy in a container containing a high melting point and heating it over a flame or burner. A contemporary melting method, such as induction melting, utilizes the physical properties of alloys to melt them and reach casting temperature more efficiently.
4. Pour the molten metal into the mold. In order to pour the molten metal into the mold cavity, the manufacturer must melt the alloy. The pouring process is normally supported by a ladle system, which allows operators to control the pouring speed either manually or automatically. Incorrect pouring techniques can lead to defects, as gases can become trapped within the mold, resulting in holes in the casting.
5. Allow the metal to solidify. The manufacturer must carefully create optimal conditions for the metal to solidify within the mold. Again, manufacturers must take into account shrinkage of the molten metal as it cools, as well as the release of gases that accumulate inside the mold as it pours.
6. Remove the casting from the mold. After the casting has cooled and solidified sufficiently, it must be removed from the mold by the manufacturer. In methods employing single-use molds, operators simply remove the mold from the casting. To avoid sticking, special coatings are often used on reusable molds, and casting removal features (such as ejector pins) must be incorporated into the molds.
7. Finish the casting. A majority of cast parts require finishing processes such as cleaning (removing excess material from the part); gate removal (removing pouring channels from the part); heat treatment (heating and cooling the castings in a controlled environment to enhance physical properties); and quality assurance inspections. The dimensional accuracy and aesthetic value of many products are improved by CNC machining processes as well.
