Breaking the mold is one of the overused idioms people use when describing some people. For example, when they made Robin Williams, they broke the mold. And, to be honest, there's a lot of truth to that concept.
However, breaking the mold isn't a very good idea in manufacturing.
With this terrible introduction out of the way, let's chat about foundry casting, shall we?
Foundry casting is a process that involves melting metal and pouring it into a mold, producing hollow pieces of metal known as castings. Foundry casting involves using sand molds to create the final product, also known as green sand casting or permanent mold casting.
There are various types of foundry casting, each with its own benefits and limitations. Understanding this process is crucial for understanding how you can create finished metal parts from your raw metal stock. Let's look at the different foundry casting processes, where foundry casting began, and where it's going.
What Is Foundry Casting?
Foundry casting is a method of casting molten metal into a mold, a process used to create castings. We might use these hollow metal pieces as structural components in machinery or as decorative pieces, such as ornamental flowers.
Pouring molten metal into a mold, typically sand creates a casting. The metal often includes additives, such as carbon, to strengthen it. When the metal hardens, it forms a cast in the same shape as the mold. Because the mold is sand, it's destroyed in the process, and the molten metal otherwise could not flow into the correct shape.
A Little History
When mankind explored other ways of making tools beyond sticks and stones, casting metal was among the earliest efforts. According to the Reliance Foundry Blog, the oldest known casting found by historians was a copper axe buried with a mummy from about 3300 B.C.
The foundry and furnace originated from Mesopotamia and regions of Iraq and Syria. Clay castings and hot fire pits worked to melt and shape copper, gold, and silver. These primitive foundries melted copper and could create more complex forms, but it wasn't until tin was introduced that metalworking significantly advanced. The addition of tin lowered the temperature at which the two metals melted and formed bronze—the first alloy.
After that, the process became refined through three Metal Ages:
The Copper Age
At the beginning of man's journey to the modern day. The initial casting process was conducted using copper which would have been poured into clay and beeswax to make household tools, jewelry, and weapons. Copper was the metal of choice due to its easy workability.
The Bronze Age
After discovering the benefits in durability that mixing metals presented, The Bronze Age began. Tin and copper would be mixed in a more complex casting process.
The Iron Age
In this age, by no surprise, iron was utilized. This was also the point in time when mass production started to become common for farm equipment and later on more technologically advanced weapons and more. Following this age would be none other than the industrial age in which casting would become even more widespread. Innovations in travel and everyday utensils would call for even greater production of metal castings.
For a detailed chronology, Metal Technologies produced this nine-page document (pdf) with an excellent summary of each important date.
Because foundry casting was simpler, it became the method of choice for mass production. Railroads, mining, and other industries produced large numbers of parts quickly and cheaply. The demand for foundry casting gradually declined after the Second World War but has grown again in recent years.
Why Is Foundry Casting Important?
Conan's father, in the movie Conan the Barbarian, explained the Riddle of Steel:
There are many examples of foundry casting's importance. Here are six:
- Diversity: Foundry casting creates various products, from small decorative pieces to large structural features. It can also produce various metals, including iron, steel, cast iron, aluminum, and brass.
- Efficient: Quickly creating castings is important if needing to produce large numbers of parts.
- Versatile: You can create a wide range of different shapes using foundry casting and various molds.
- Cost-effective: The equipment needed for foundry casting is cheap and produces a wide range of products, helping keep costs down.
- Environmentally friendly: The foundry casting process doesn't produce much waste.
- Safe: The equipment and materials used in foundry casting aren't hazardous.
Four Foundry Casting Metals
As said above, foundry casting is a versatile process using several metals. Here's a sampling of the different types.
Cast iron is one of the most commonly used metals in foundry casting, and it is a relatively inexpensive material that can be used to make a wide range of different parts. Cast iron is created by adding carbon to molten iron and pouring it into a sand mold, and the carbon causes the iron to form a solid mass when it cools down. Cast iron has a high tensile strength, which means it can be pulled apart with high force without breaking. Cast iron is not very ductile, which means it tends not to stretch when deformed, making cast iron useful for making structural parts, such as machine frames and gears.
Cast steel is a hard material used for making a wide range of different parts created by adding carbon to molten iron and pouring it into a sand mold.
Cast steel has high tensile strength and elasticity, making it suitable for many uses, strengthening parts, such as machinery gears, and stretching and deformation. Steel is also used to create decorative items that are heavier and stronger than would be possible with other metals, such as ornamental flowers.
Aluminum Foundry Casting
Many people associate foundry casting with cast iron and other heavy metals, but casting aluminum is another alternative. Aluminum foundry casting, however, is a common process of creating high-strength parts weighing just a few pounds.
Aluminum foundry casting has a high strength-to-weight ratio, which is hard to break but light. For example, an aluminum aircraft wing is strong enough to support the plane's weight but light enough that the plane is not too difficult to fly.
Brass And Bronze Foundry Casting
Brass and bronze are two different metals, often foundry cast. We widely use them in decorative items, jewelry, and architectural features, such as door knockers and light fixtures.
3D Printing in Manufacturing and Beyond
We have used 3D printing to create prototypes of products for decades. Still, it only recently became possible to create large parts using 3D printing, opening up new possibilities for using 3D printing in foundry casting.
Creating castings using a 3D model and printer creates a mold using the model, creating customized products that include details such as logos not possible using other methods. Castings created using 3D printing can be used similarly to other castings and used in architectural features and other decorative items. Using other methods, they also create large structural parts too heavy to produce.
A process as old and ubiquitous as casting will always find purpose in manufacturing. Despite the method's simplistic approach, it allows for diverse uses and, most importantly, evolves with new technology and material.