Metal casting is a common process used for producing components by pouring molten metal into a mold. The metal will be cooled down and solidified into the shape of a mold.

Most often, casting is less expensive than machining the component out of a solid metal. The good news is that there are several metal casting methods that you can choose from.

Choosing the most efficient type of casting will likely depend on the metals being used, the complexity of the casting, and the size of the object. Before you start with the production, it’s worth learning about the terms and methods used in the facilities.

Casting Terminology

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Cope and drag

If you are using horizontal molding, the top portion of the mold is known as the cope, while the bottom part is known as the drag.

Casting mold

This is the cavity where the liquid metal will be poured into and cooled down to produce the component you desire based on its shape. Casting molds can either be simple or complicated.

The forms used for making molds of metal are like loaf pans. The molten metal will be simply poured down inside the mold and left to cool down. There are molds that are quite complicated and are based on specific patterns. The pattern will be engraved into a split mold.

On one side of the mold will be half of the pattern while on the other mold will be the other half of the pattern. Afterward, the halves will be stuck together with a clamp, then the mold will be filled with the liquid metal.

The mold is made up of two parts so that there will be a way of removing the pattern before it is filled in. Molds can also be created with a horizontal split.

Molding cores

If molds require holes or internal spaces, then a core should be created. The shape of these cores should be the same as the internal space. Usually, the cores are held together in place by expanding the casting.

The core prints are responsible for holding them in place. The core will be suspended just like a bridge between two rivers. The core will have empty spaces around it and it will be filled with metal. Once the final casting is made, the core will be taken out. As a result, the hole will remain as it once was.

If you have a very long core, then chaplets will be used to support it so that it will prop up. Typically, the metals used are the same as the final casting since they are placed in the space where the metal will be poured, and it will become part of the final casting.

Swing and ram

When it comes to vertical molding, the back half of the mold is known as the ram while the leading half is known as the swing.

Dimensional tolerance

When choosing casting methods, one of the most significant factors to consider is dimensional tolerance. Dimensional tolerance refers to the variation in size that is tolerable in the final product.

Once the product has cooled down, metal tends to shrink, and the amount will depend on the type of casting. If the client requires a precise size of the product, then a casting method that provides near-net casting must be used. In other words, the size of the product is very close to the right size once it is taken out of the mold.

Surface finishing

Surface finishing is another important aspect to think about. How rough, bumpy, or granular, do you want the surface of the casting to be? Keep in mind that what is tolerable for a cast iron pan might not always be tolerable for a wedding ring.

Typically, extra smooth metal surfaces can be made possible with machining, which can be an additional cost. If you want your product to have a smooth and shiny surface, then you should choose a casting method with a finer finish to help reduce machining costs.

What Are the Different Metal Casting Methods?

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Metal casting can be divided into two main categories — casting processes with expendable molds and casting processes with reusable molds. Expendable molds will be ruined during the casting process while reusable or permanent molds can create numerous items.

Although based on most people’s perspective, reusable molds are more cost-effective for huge production runs, however, this is not always true. Most steel and iron products are created from expendable casting processes.

Reusable molds are often used in low-temperature molding substances such as wax, chocolate, resins, etc. What makes metallurgy unique is its high temperatures which can put more strain on the mold.

Hence, it is not surprising that metals with a lower melting point such as copper, tin, magnesium, aluminum, or zinc, are often effective in reusable molding processes.

However, in some cases, even ferrous metals can be used in reusable molds. The choice of metal, the complexity of design, and requirements for surface finishing and dimensional tolerance can all influence whether to use reusable molds or not.

Reusable molds

Reusable molds can either be permanent molds, semi-permanent molds, slush casting, centrifugal casting, etc.

Permanent molds

Generally, permanent molds are made of metal, specifically those that have a higher melting point compared to the metal that will be poured in. Liquid metal will be poured in without using any external pressure. It is a must that permanent cores are simple so they can be easily taken out for reuse.

Most often, these molds are used in iron casting, and with lower-temperature alloys. Instead of assembly lines, turntables are the most typical industrial workflow.

Individual processes, such as placing the cores, coating the mold, closing the mold, opening the mold, pouring, and ejecting the casting, are accomplished as each mold goes through the next stations. Before the first casting is poured in, molds are preheated so that it does not crack because of the difference in temperature.

The only difference in semi-permanent molds is that the cores used are expendable sand cores. With sand cores, it is possible to create more complicated core shapes since they do not have to be intact once taken out from the final casting.

If the casting has an opening for removing cores, then they can simply be shaken out, which is like draining sand through an hourglass.

Expendable molds

When it comes to casting ferrous metals, expendable molds are the best choice. They are cost-effective since they do not need to be tough for the high temperatures. Some examples of expendable molds are sand casting, shell molding, etc.

Sand casting

One of the most typical methods used for metal casting is sand casting. This manufacturing process is not new. In fact, it has already existed at least three thousand years ago.

There was evidence that shows that clay casting was used during the Shang Dynasty. Up until now, this process is still so popular due to many reasons. Sand is pliable, abundant, cheap, and can take the heat.

Cores that are made from sand are easy to extract, you can simply shake them out. Gates and runners that are used for guiding metal into the mold cavity can either be created as part of the pattern or cut by hand by an expert molder.

The dimensional tolerance of sand cast products is not accurate, and the surface finish is often rough. Hence, sand casting is perfect for creating large, rugged objects for car engine parts, cast iron pans, or decorative fences.

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