Look around you, what do you see that is made of metal? If you are standing outside, it is likely that you are surrounded by cars, lamp posts, and maybe a park bench. The chances are good that everything you see that is made of metal was created using a process called casting.
In this article we will define what metal casting is and discuss the difference between aluminum casting and steel casting.
Metal Casting, What Is It?
Before we examine the difference between Aluminum Castings and steel casting it would be helpful to define what metal casting is and why it is important.
Metal casting is taking molten metal and pouring it into a mold where it is allowed to cool. One of the earliest methods of manipulating metal, it is used to make most of the metal objects we use today. A copper frog that was produced in Mesopotamia in 3200 BCE is the oldest known metal casting. Throughout early history, the metal casting process has been used to make weapons like swords. Today it is used to make lamp posts, car parts, and much more.
There are five steps to the casting process.
1. Pattern Making. Patterns or replicas of the exterior of the object are made. They are made of wood, plaster, plastic, or metal and made to meet precise measurements to ensure the pieces made fit together correctly.
2. Core Making. For castings that are hollow, a core is needed to keep the interior from becoming filled with metal. Cores can be made of sand or metal and are collapsible so they can be removed once the metal has hardened.
3. Molding. Molding is a multi-step process best defined through visualization. When it snows, kids will plop onto their backs and wave their arms and legs to make a snow angel. The impression left in the snow is a mold, and the body that made it is the core. In metal casting, the angel mold would be placed in a wooden frame called a flask. Molding sand is packed into the flack around the angel pattern, and once it is packed tight, the pattern can be removed, leaving a cast of the angel.
4. Melting and Pouring the Metal. Metal is melted at high temperature and then poured into the mold cavity where it is left to harden.
5. Cleaning. Once the metal has hardened, the object is removed from the mold. Once removed, the item will be cleaned or fettled to remove any materials from the mold and smooth any rough edges.
Aluminum and steel are two common metals used in casting. Both have their own advantages. Aluminum is less dense than steel, which makes it very lightweight. It is much easier to machine than steel. When a casting is removed from the mold, there are steps required to finish the part. That process is called machining.
A machinist will drill holes into a part, grind away rough parts, or thread portions as part of finishing the product. Steel can be machined, but it is much harder than aluminum, which makes it more time-consuming to machine. Aluminum is more castable than steel. The lower melting temperature of aluminum makes casting a more efficient process because it takes less energy to melt and maintain in a molten state. The lower temperature also makes aluminum more versatile for different methods of casting.
Steel casting has many advantages in industrial use. It possesses corrosion resistance that is superior to aluminum. Steel melts at a higher temperature than aluminum, which makes it perfect for high heat applications. Finally, steel is stronger than aluminum. Its strength makes it possible to use steel in several industrial applications like car manufacturing and construction.
Casting is a method of shaping metal that has been in use for centuries. Without it, many of the tools we use, cars we drive, and building we live and work in would not be possible. While any metal can be used in casting, there are distinct advantage to using steel or aluminum.
Cover photo credit: Ludomil Sawicki / Unsplash