The Metal Casting Process, Explained

Metal casting is a $44 billion industry that supports half a million jobs in the United States. Almost every metal object we use–from tools to machine parts–is created using a metal casting process.

While these products play a huge role in our everyday lives, most people do not understand the metal casting process and what it entails. Very basically, it involves pouring molten metal into a mold to form different shapes. It is then cooled and removed from the mold.

But producers must implement complex systems to make this happen. And using the appropriate methods is an integral part of producing a quality part.

Understanding the details of the metal casting process means you will have a better sense of what goes into making the parts produced from it. And this can be essential to you identifying the best parts for your business. The information below will tell you everything you need to know about the metal casting process and why it is important to your industry.

History of Metal Casting

Metal casting has been around for thousands of years. The first evidence of it dates back to approximately 4000 BCE. Gold, due to its softness and malleability, was one of the first metals used, but bronze soon took its place for constructing tools and weapons.

People used stone to make the first molds. But around 1300 BCE, the Shang Dynasty of China started using sand for casting. In 500 BCE, the people developed the first cast iron for farming purposes.

In 1645, the first American metal casting factory, or “foundry,” opened in Massachusetts. Today, computerized automation has revolutionized the speed and precision of cast metal production.

Metal Casting Basics

The casting process can use almost any type of metal, but some of the more common ones are iron, steel, aluminum, and bronze. Metal casting is an efficient and economical process, especially for industries that need large output of the same components.

The first step in the metal casting process is to construct a pattern or replica of the outside of the object you wish to make. Plaster, wood, plastic, or metal are common materials for this.

Next, metalworkers form material around the pattern to produce a mold. A frame, or “flask,” holds the mold in place. The pattern is then removed which leaves the cast in place.

Once formed, a furnace or torch melts the metal down. The liquified or “molten” metal is then poured into the mold and left to cool and solidify.

When the metal cools, workers remove molding. They then clean the final cast metal object and file, or “fettle,” its rough edges.

Metalworkers then remove the molds. If they are using permanent ones, they reuse them, while discarding expendable ones. They might collect products used in expendable molds, such as sand, and reuse them in the mold-making process.

Types of Metal Casting

One of the biggest advantages of casting over other types of metal production is that it can make complex shapes. Forming internal cavities is something that is achievable with casting that is not with other methods. Also, as long as you can produce a mold large enough to form an object, you can produce it (rather than assembling it out of many component parts).

Metal shrinks when cooling. Dimensional tolerance is the amount of shrinkage acceptable in the final product relative to the original designed size. The type of part you are marking and the precision with which you need to produce it is variables in what type of casting method you must use.

There are two main categories of metal casting. permanent, which reuses the mold, and expendable. The type of metal, the complexity of the design, and dimensional tolerance all play a part in determining the appropriate method.

Reusable Molds

As the name suggests, reusable or permanent molds are ones that workers recycle for use over and over again. Since you are not constructing a new mold each time, speed is one of the big advantages of the process, which can also translate to cost-savings.

Reusable molds are best suited to metals that have a low melting point, like zinc, aluminum, tin, copper, and magnesium. Whereas expendable casting is the preferred method for producing brass, iron, and steel.

Permanent molds are typically made of metal. They must have simple cores that can be withdrawn for reuse.

Semi-permanent molds use the same type of casting as permanent ones but implement a disposable core. This allows for more complex core shapes since they don’t need to be extracted and reused.

There are other variations, such as centrifugal casting, which entails pouring melted metal into a mold that is spinning on an axis. This pushes the metal onto the outer surfaces of the mold in an even layer. It also means impurities end up closer to the bore and can be more easily removed.

Die casting uses high pressure to force molten metal into a mold. The molds are generally made of highly heat-resistant steel and comprise two halves into which the liquefied metal is pressed.

Expendable Molds

An expendable mold is one that, after usage, is broken apart to remove the casting. They are generally made of sand, plaster, or ceramics, and are non-reusable.

It seems commonsensical that molds you can reuse are more economical than ones you throw away after a single-use. But this is not necessarily the case. Expandable molds are inexpensive to produce because they do not have to be as sturdy as permanent ones.

Sand casting is probably the most common method used in metal casting in general. The reason for this is that sand is inexpensive, pliable, and heat resistant. And, as mentioned above, it is one of the oldest processes.

Sand is easily packed around the pattern to create the mold. And sand cores are particularly popular since they can be easily shaken and removed from the finished product.

There are variations of sand casting, where the sand is mixed with a resin to create a “shell mold.” This method affords a closer dimensional tolerance than typical sand casting since the resin provides added support to the interior surfaces.

Although sand is the most popular component used in expandable molds, wax, foam, and other materials can be advantageous for producing certain products.

Find Quality Parts

Now that you have an idea of what the metal casting process entails, you can have a better understanding of what products are possible through this method of production. There is a lot to know about metal casting, and hopefully, this information will help you and your business in your search for the best metal parts available.

At Faircast, Inc., we can meet all of your metal casting needs. We make a wide variety of products, from farm and railroad equipment to elevator parts and products used in construction and industrial machinery. Contact our staff to see if we can provide parts that will help your business produce a better quality product.